UK damp &
decay control

Notes and general principles.

Correct diagnosis of damp problems: the first and most important stage in any remedial treatment.

The eye of experience is the most useful instrument for the recording and diagnosis of damp and timber decay problems in buildings. When analysing damp and timber decay problems in buildings look for moisture penetration and movement from top to bottom and from outside to inside.

When analysing damp problems in buildings note must be made of moisture sources. Particular attention should be given to sources of concentrated moisture penetration such as roof drainage and ground drainage systems. Particular attention should also be given to defective drains, cavity ventilators, evaporative surfaces and structures. The course of moisture from to be plotted. Vapour movement should be checked together with air movement from warm to cold or from wet to dry areas.

Measurements of relative humidity are generally useful particularly with reference to dew point temperatures. The moisture content of air equilibrated timber is often a more useful indicator of chronic environmental problems. Generally, relative humidities over 70% in occupied buildings is likely to cause condensation if not vented to the exterior. Timber at equilibrium with 70% r.h. will have a moisture content of approx. 15%. Prolonged relative humidities of over 80% allow mould growth and will provide the conditions for microbial decay of materials.

Timber at equilibrium with 80% r.h. will have a moisture content of approx. 18%. Prolonged relative humidities of over 85% will result in bio deterioration. Timber at equilibrium with 85% r.h. will have a moisture content of approx. 20%.

Material moisture content rather than relative humidity is the most important factor to be measured in the analysis of damp and decay problems.

The significance of the percentage gravimetric moisture content varies between materials due to differences in their density and the extent to which water is bound hygroscopically. The significant factor is the partial water vapour pressure in the material or the available moisture. In building surveying, a convenient approximation to available moisture is the timber equivalent moisture content (EMC) which may be defined as the moisture content that would be found in a piece of timber that was allowed to come into equilibrium with the material in question.

As a rule of thumb for site investigations timber equivalent moisture content is approximately 10 times the gravimetric available moisture content of in-contact masonry. The most cost effective way of estimating timber equivalent moisture content on site is to use resistance-based moisture meters, but the readings from such meters are commonly misinterpreted and this often leads to inappropriate chemical damp-proofing being offered as a remedy fro risng dampness

The deep moisture content of a material is more important than the superficial moisture content. In order to estimate the deep moisture content of materials with a resistance-based moisture meter, deep probe electrodes are required

The readings from resistance-based moisture meters are commonly misinterpreted for the following reasons:-

1. The limits of superficially measured wet or dry readings are not appreciated.
2. Artificially high readings are taken due to conductive salts in the material.
3. Artificially high readings are taken in timbers due to previous chemical treatments.
4. Artificially high readings are recorded in composite materials, such as plywood, masonry containing carbon (e.g.Pulverised Fuel Ash PFA etc.), some surface printed finishes and metal foil!
Useful rules of thumb for assessing the significance of resistance-based moisture meters during site surveys are as follows:-

1. Readings of less than 20% timber moisture equivalent indicate that moisture is too dry for active fungal decay
2. Readings of less than 13% timber moisture equivalent indicate that timber is too dry for significant insect decay (except in the case of House longhorn and Powder post beetles)
3. The internal materials in an occupied building will usually have moisture contents of less than 12% timber equivalent moisture content
4. Roof timbers in an occupied building commonly have moisture contents of 16% or less
5. Roof timbers in an occupied or intermittently occupied building may have moisture contents varying between about 12% and 25% throughout a year, but these may not be significant. Experience has shown that an annual average of 14% results in ‘safe’ conditions.

Timber equivalent moisture contents of 30% (timber fibre saturation point) or greater are damp enough for wet rot decay or for dry rot germination to occur i.e. there must be available liquid water.

Surface capacitance meters are useful for initial survey of masonry or plaster structures, but readings are poorly correlated to gravimetric or available moisture contents.

Low surface capacitance readings are a useful negative finding, but high readings require further investigation.

Sampling and gravimetric analysis of materials is the only accurate and cost effective surveying technique for determining the true moisture content of building materials

The use of the oven drying technique, as described in BRE Digest 245, 1986 is the standard technique.

The formula for determining the percentage of gravimetric moisture content is:-
Ww - Wd x 100% divided by Ww - where Ww is the wet weight and Wd is the dry weight.

Hygroscopically bound moisture content is significant in most masonry and plaster due to water bound to salts. This is defined in BRE Digest 245 as the moisture bound to a material at equilibrium with air at relative humidity of 75% at 20°C. The formulae for the percentage of hygroscopic moisture content is:-

W75 - Wd x 100% divided by W75 - where W75 is the weight after equilibrium at 75% RH at 20oC

Moisture content is the most useful indicator of water available for deterioration and biodegradation processes. This is defined as the total gravimetric moisture content less the hygroscopic water. The ‘Speedy’ meter is of limited use because it can only determine total moisture content. However, the results are obtained on site and are relatively accurate. Slavish reliance on total moisture content as an indicator (e.g. the 5% threshold estimate given in BS 6576 1985) is usually a mistake and experience shows such values are frequently misinterpreted. The ‘Speedy’ does have the advantage of providing sub-surface readings that can be replicated through or over a structure, thereby illustrating moisture content gradients. This is perhaps its most useful function.

A sub-surface moisture gradient correctly taken using a Speedy meter or, preferably, the gravimetric method can point to the source of dampness. With experience and intelligence, surface electronic readings can sometime be used in the same way. However, in the case of ground water penetration this method is notoriously unreliable because of the influence of salts. In the case of rising dampness the source of moisture is the ground, and moisture contents will always decrease with height above ground. This will generally not be shown with surface reading electronic meters.

Condensation will often cause dampness that resembles rising dampness because heat rises leaving the base of walls preferentially cool. Air circulation at the base of walls is often very slow. Drying of condensate may be very slow. This results in a net increase in moisture content in the wall surfaces over time, however, the interior of the wall may be dry.

Condensation may occur at the internal surface of the wall or within the wall. When the surface of a wall is dampened by condensation which is not allowed to dry out the rate of condensation will increase because the wall will loose heat more rapidly. The ‘wet front’ advances into the wall. Over time, this often resembles rising dampness.

Water soluble salts translocated to the wall surface by water penetration and evaporation over time will affect electrical conductance. Calcium sulphate from the building material will be translocated and may appear at the surface as efflorescence. Salts from the moisture source way also be translocated. In the case of water from the ground nitrate and chloride salt combinations are commonly found. Salts become hygroscopic in relative dry air (30-50% r.h). Hygroscopic salts are often blamed for dampness but without formal assessment of available moisture (using the gravimetric method) such statements are meaningless. Hygroscopic moisture is not available to cause decay. Hygroscopic salts in plaster are therefore not a significant structural issue.

Never trust the man with a meter- You should never rely on the dampness and timber reports of a damp surveyor who relies solely on the use of moisture meters to diagnose rising as most damp surveyors are usually commission based salesmen looking for a sale and who have a default setting to say that there is rising damp and the only cure is to inject a chemical damp-proof course when we all know that the insertion of a chemical damp course is rarely effective and dampness can be controlled by much more environmentally friendly methods

This is an edited version of an articled entitled-Wall base damp: Is one horizontal damp-proof course sufficient dampness protection? written by Ralph Burkinshaw

Over the past 40 or more years, it has been common practice for some in the property industry to label nearly every patch of damp just above a ground floor skirting board as `rising damp`. That `diagnosis` has been made usually from visual evidence and moisture meter checks alone.

Standard treatment of `rising damp` has usually been the insertion of a chemical-injected damp-proof course (D.P.C.) together with the application of protective dense sand and cement render as a final defence to mask the dampness. This might well be termed `damming the damp`. This kind of remedy may not target the root cause of the dampness, but merely mask the symptoms and eventually the dampness may resurface. Money spent on chemical injection DPCs and the associated protective replastering in many cases might be more usefully spent on a remedy more targeted to the root cause.It could also be argued, however, that there are some occasions when such damming of the damp might be the only realistic alternative?for example, when a dry wall surface suitable for decoration is needed quickly. There is sometimes not the time or the resources to follow through a more thorough building examination and long-term cure. .

During the 1990s a number of surveyors and researchers strongly challenged quick-fix solutions to dampness problems, with one or two even claiming rising damp to be a myth. But the debate was to a certain extent groundless, as, to my knowledge, there was never a workable definition of `rising damp` until the following was published (Burkinshaw and Parrett, 2004):`Where moisture travels upwards through the pore structure, or via small fissures or cracks, or as water vapour, against the forces of gravity, typically up a wall or through a floor from a source below the ground.` .

Certainly, many low-level dampness problems have resulted from low-level water penetration or plumbing leaks. In such cases, dampness does indeed rise or soak upwards, but usually from around ground level. For the purpose of this paper, any dampness found at a low level in house walls is termed `wall base damp`.Whether or not such problems should be described as `rising damp` is not really the most important issue. When dampness is found, and it is causing a problem for the building or users of the building, more than anything else the cause needs to be found together with a solution to put the problem right. It is less of an issue whether the damp should be labelled `rising damp`, `penetrating damp` or any other `damp`, and there should be no automatic remedy for any cause of dampness. .

Most houses built since 1877 actually possess a horizontal damp-proof course and, if this is intact, dampness from below the ground only would be a real threat on a very wet site. Unsuitable changes in and around the building, however such as the raising of external ground levels and bridging existing damp-proof courses increase the risk of low level damp penetration, but it is the height of external ground in relation to vulnerable floor timbers or easily reachable plasters and decorations that is the key factor. Whatever the height of the horizontal physical DPC it would not prevent lateral damp penetration. Timber will now be less high up in relation to external ground level, floor ventilation will be compromised,routes for damp penetration through the wall base will be created via air vents and poorly maintained masonry and the floor oversite level or solum now will be lower compared to the external ground level, making it more likely to become a water collection zone. Water splashing and pooling from rain is free water in significant quantities and free water can soak and trickle into porous low-level masonry at will. In a traditional masonry house, dampness may be prevented from causing problems by subtle combinations of wall base detailing. The first line of defence may be the dual protection of a horizontal damp proof course and a vertical wall base plinth. This in effect creates protective L shaped damp protection. In addition to these two barriers, moisture may evaporate out on both sides of the wall base, i.e. within the floor void and externally. Wall base finishes and the amount of sub-floor ventilation will influence the amount of that evaporation. The way in which the wall base takes in and gives out moisture needs to be carefully balanced to keep damp at acceptable levels. .

Rainwater splashing and collecting at the intersection of a wall and the ground should not be allowed to soak too readily into the wall base around ground level, and an effective plinth (or perhaps dense low level masonry), coupled with good surface water drainage, is the key. .

The intersection of a wall base and the ground creates a ledge effect where lateral water penetration can be a problem. This effect can be seen at all heights of a building, e.g. just above a decorative cornice, near the top of an abutting boundary wall, or even where builders rubble is piled up against a wall. The way moisture may be managed by drainage, evaporation or barriers was well described and illustrated by Peter Bannister at the Aston University Conference on 3 November, 2004:Dampness and Decay in Buildings. The Whole Solution. .

The Building Research Establishment (BRE) has over the years largely ignored low-level lateral dampness penetration, choosing to emphasise the threat of dampness from the ground or dampness penetration into the building at a higher level, for example, on exposed south-west elevations or via poor detailing of openings, or poorly installed cavity fill insulation.Low-level dampness penetration at the wall base is usually only referred to in the context of frost damage, where less durable bricks could become wet below a DPC and be damaged by the expansion forces from freezing. In the authors view, the BRE usually over-emphasises and misconstrues bridging. It is always assumed that a huge store of water is ready and available waiting in ambush from a below-ground source to track, i.e. bridge, around a DPC via porous renders and plinths to cause damp havoc above it. It may be more likely that this moisture was mainly soaking into and collecting in masonry near ground level from the vast volume of water splashing, pooling and soaking into the wall base every time it rains. Again, in this case, the position of the horizontal DPC may be less of an issue. .

SUMMARY POINTS.

A physical horizontal wall DPC on its own may not provide adequate dampness protection to the wall base and adjacent timber floor members. .

A horizontal wall DPC controls movement of moisture from above and below. .

Installing multiple horizontal DPCs may still not prevent low-level lateral damp penetration.

A horizontal wall DPC controls upward movement of moisture that has penetrated the wall base between the ground and the DPC, as well as controlling or sometimes stopping moisture originating from below ground. It should not be forgotten that much of this localised below ground moisture can result from inadequate rainwater disposal arrangements around the building. Just consider the amount of rainfall per square metre over the whole site compared to the sheer concentration of rainfall load at the bottom of each downpipe. .

In traditional houses built with solid walls, a vertical DPC may be needed below the horizontal DPC. Traditionally, this has been by way of a cementitious plinth or sometimes vertical slatework or asphalt. .

Even simple damp problems can be a mystery and a challenge at the early stages of investigation on site until all the pieces of the jigsaw finally piece together. Once diagnosed, all the symptoms presented can seem as clear as day. .

Pro-active surveying is the order of the day. Always lift floorboards, take measurements, pour water, make observations and analyse findings. .

A methodical manner should be adopted on site. Explain what is planned and how it might help to drive the investigation. Most occupiers will allow the surveying to be taken further than previously thought possible. Stained wallpapers and salt-laden plaster is already defective and became defective months or years before a surveyor arrived on site to scrape or drill it. .

Dampness investigation is not just checking with a moisture meter just above the skirtings near the end of a building survey, it is integral to the survey from chimney pot down to foundations. Dampness is always cited as the commonest cause of building defects. .

Diagnosing dampness is time-consuming and sometimes invasive. But spending hundreds of pounds on further investigation of dampness may save thousands. Many homeowners, facing a nightmare damp scenario from flood, mould, rot, or salt-damaged plaster, now wish they had invested in a fuller investigation of dampness prior to purchase. .

Drawing a sectional sketch enables one to understand the construction technology of the wall-base, which will help diagnose the cause of the dampness and formulate a remedy. It is useful to compare the detailing as found with current building regulations or with examples of more traditional construction that has proved satisfactory over the years. .

Few chartered surveyors possess the resources in terms of time, equipment or expertise to carry out intensive laboratory-style investigation such as the sampling method offered in BRE Digest of 1986 on rising damp, so practical site investigation methods are needed. .

For more information about the accurate diagnosis and effective treatment of rising dampness from the ground or any damp that is perceived to be rising please contact UK DAMP & DECAY CONTROL on 0800 028 1903 or email enquiries@ukdamp.co.uk.

We also provide impartial, independent damp and timber reports for mortgage purposes which are accepted by all Banks & Building Societies.

DAMP IN OLD BUILDINGS

WHY BUILDINGS NEED TO ‘BREATHE’

Introduction

Living in an older building should be an enjoyable and satisfying experience. So why can it sometimes turn into a costly nightmare for some owners? Discovering your building is damp, has dry and wet rot or death watch beetle can be distressing for all owners. But solutions do not need to cost thousands of pounds or involve putting large quantities of original fabric into a skip.

In fact, many properties have suffered greater damage and loss of fabric through chemical damp-proofing and other remedial work than was caused by the original problem!

There are two important principles to be considered.

The historic building should be managed so damp and its associated problems do not occur or, are at least minimised to tolerable levels.

However, if your home does suffer from dampness and decay, you should solve the problem by tackling the causes and allowing time for fabric to dry out. This will help make sure any loss of the building’s original fabric is minimised.

The quality of older buildings is often self-evident as many survive relatively intact for periods of up to 500 years. Continuing to use appropriate materials and techniques provides the best protection and will ensure the building remains both a home and a good investment for many more years to come.

UNDERSTANDING YOUR BUILDING

Why do older buildings get damp and why do they seem to have experienced more widespread problems with damp and decay in the last 30 or so years?

In order to repair older buildings, it is important to understand their construction, as buildings constructed before the mid-19th century behave differently to modern buildings.

Whereas modern buildings rely on cavity wall construction to prevent moisture from penetrating the walls, older buildings generally rely on allowing moisture which has been absorbed by the fabric to evaporate from the surface. This is achieved with the use of ‘breathable’ lime-based mortars, renders and internal plasters.

The walls of timber frame and clay lump buildings were plastered both inside and out with a porous lime plaster. Solid brick and flint walls were laid in a lime mortar and plastered internally with a lime plaster. These porous walls can absorb moisture in damp conditions and release it through evaporation on dry days, allowing the building to ‘breathe’.

Floors were commonly of ventilated suspended timber floor construction or brick or clay pammets bedded on sand, allowing moisture in the ground to evaporate. As only small amounts of water vapour are involved, evaporation is invisible and does not result in wet walls and floors.

Changing the building by replacing a lime render with a sand and cement render or a timber floor with a concrete floor, the breathable qualities of an older building can be compromised, leading to problems of damp and decay.

Since the 1950s, many older building owners have tried to keep out the weather by using cement renders, waterproof coatings, oil-based masonry paints and waterproof sealants. Traditional porous floors were replaced with concrete floors with a damp-proof membrane.

This is standard practice in a new house, where the membrane is linked to a damp-proof course in the walls, but it will stop evaporation through the floor in an historic building, forcing any moisture to travel under the non- porous floor until it reaches the walls. If the moisture cannot escape through the walls because they have a cement render or a waterproof coating on them, it will accumulate in the wall, causing deterioration.

However, sealing the walls and floor to repel water does not take into account the amount of moisture generated inside a property through normal living – cooking, washing or drying clothes etc.,

As a result, well intentioned alterations actually increase the build-up of moisture in the walls by preventing the building from ‘breathing’. Once the fabric is damp, the environmental conditions exist where wet rot, dry rot and the death watch beetle can flourish.

The breathable fabric of older buildings naturally holds some moisture. Relying on a ‘damp-meter’ when trying to measure the level of damp in lime plaster, brickwork, clay lump or wattle and daub will inevitably lead to the ‘discovery of damp’. These meters are quite useful on timber, giving reasonable approximations of the moisture content in wood (which is what they were designed for).

However, they give readings which are way too high when used on bricks, plaster and wallpaper, giving the impression that a wall is damp when it is actually in a perfectly normal equilibrium state with its surroundings.

COMMON CAUSES OF DAMP

If you find a damp problem in your property, it can be due to a variety of causes.

Some are the result of poor or lack of maintenance whereas others may indicate a more serious problem. Sometimes there may be more than one cause so it is important to investigate all of the possible reasons for the damp. You should also remember that the damp area may be some distance from the cause of damp or be related to work done several months, or even years previously.

The most common causes of damp are described below:

Cement render, plaster, waterproof coatings and sealants prevent the structure from breathing and lead to a build-up of moisture within the walls when applied to the walls of older buildings. This then causes the walls to deteriorate.

A concrete floor inside a building to replace an older breathable floor means ground moisture is forced out to the walls, increasing the damp within the walls.

High ground levels can lead to damp penetration where external ground levels are allowed to build up until it is at the same level or higher than the internal floor. This allows water penetration directly into the wall.

Concrete paths laid around the outside of the building can prevent moisture from evaporating and channel ground water into the walls. If the inside wall has a breathable lime plaster on it, the moisture could escape into the room, maybe causing damp patches and flaking wall finishes at a low level if the wall is very damp. If the wall has an impermeable cement render both inside and out, the moisture will remain in the structure of the wall, causing gradual decay.

This type of damp is particularly damaging to timber frame properties as it can lead to the decay and failure of the sole plate (the timber which forms the base for the whole of the timber frame structure) and the studs forming the walls. Similarly, if clay lump walls become saturated, this will inevitably cause them to slump.

Lack of ventilation restricts the evaporation of moisture within the building and leads to condensation on the walls.

Penetrating damp is water coming through the walls and roof. There are several areas where water can find its way into a building. These include missing, leaking or blocked guttering or down-pipes, missing pointing, cracked or missing render, decayed joinery around windows and doors, missing or cracked roof slates and tiles and faulty flashing around chimneys. Staining on walls and ceilings can also indicate leaking plumbing.

Rising damp is moisture which is absorbed up the walls from the ground. Many causes of damp are mistakenly identified as rising dampness, but most reports of damp can be attributed to one or more of the above causes. True rising damp is relatively rare.

SIGNS OF DAMP

There are several signs to look for to spot a damp problem, depending on the cause of the damp problem; many signs of damp will be accompanied by a musty smell.

Low level staining or flaking paint along the inside face of ground floor walls could be a sign of a build-up of moisture in the walls caused by a hard or waterproof render, high outside ground levels or a non-porous floor. Cracking or movement of the structure at low level or in corners could also indicate decay of the sole plate causing the timber frame structure above to move.

Crumbling brickwork is a sign of damp bricks which are deteriorating. This can be caused by the use of unsuitable, hard and impermeable mortar which forces moisture in the wall to escape through the softer bricks. Bricks can also become damp due to leaking guttering or down-pipes which do not take the water away from the surface of the wall.

When they become damp, bricks are also susceptible to frost damage. This is where the face of the brick is pushed off when the moisture freezes and expands. The softer material behind then deteriorates and crumbles.

Black spot mould is caused by condensation and it appears in corners and behind furniture in poorly ventilated or unheated areas. It is usually a surface mould and does not cause any damage to the structure.

Staining can indicate penetrating damp or rising damp. Penetrating damp can appear in patches and in any location on a wall or ceiling, depending on the exact cause. A leaking gutter, for example, will lead to a high level damp patch, whereas faulty joinery will result in damp around the window opening.

Rising damp is only ever found on the ground floor walls. It is recognisable by a ‘tide mark’ along the length of the wall which rises to about 900mm (about window sill height).

Staining on ceilings can indicate a leaking roof or chimney flashing. It could also be due to a faulty water storage tank in the loft space.

Holes in timbers or fungal growths on them can indicate an infestation of wood-boring beetles or an outbreak of wet or dry rot. Wood boring beetles, such as death watch beetle, will attack damp wood.

It is hard for a beetle to work its way into a dry, sound, oak timber frame. If a house has death watch beetle, it has a damp problem. It is important to correctly identify this beetle as it can cause severe structural damage.

The holes left by the common furniture beetle, also known as woodworm, provide timber treatment firms with one of their main sources of income. Most of the holes seen in old buildings are no longer active and are not evidence of an active infestation. Look for fresh bore dust (saw dust) beneath the holes. If this is present you should be able to dig into the wood around the holes and find new grubs.

Dry rot fungus spores are found everywhere. To thrive, dry rot fungus needs wood to have a moisture content of between 20 and 40%. It will then spread by sending out strands through dry areas to reach other sources of moisture. Look for timber which has darkened in colour, white or grey strands on wood, fruiting bodies growing and a pattern of large, square cracks – known as ‘cuboidal cracking’ – in woodwork.

The affected timber will be light and will crumble between your fingers. Wet rot is caused by a number of fungi which occur in persistently damp wood.

Depending on the species, the strands vary in colour. Wet rot fungi are confined to the area of damp. Again, affected timber will change in colour, some becoming darker and some becoming much lighter, giving it a bleached appearance.

HOW TO SOLVE THE PROBLEM

Taking a little time to establish the real cause of the problem and carefully considering your response could save you thousands of pounds.

If you need expert advice, contact a conservation expert or look for an independent specialist consultant or surveyor to establish the cause and extent of the damp and decay.

. Replace hard cement render and plaster with lime render and plaster. It is preferable to replace the render and plaster entirely, but if money is limited, replacing them on the lower parts of the walls, near to the ground, will help alleviate the problem. In the case of timber frame buildings this method will allow the sole plate to dry out. Lime render and plaster should be decorated using lime wash on external walls and distemper internally.

Cement based renders and plasters should not be used on older buildings. Working with lime is not rocket science but it does require an understanding of how to use the material.

Waterproof coatings and sealants can be impossible to remove without damaging brickwork.

You should take advice from a professional paint removal firm to find out what the coating is made of and if it can be removed. If removal is not possible, some of the other methods of controlling damp may help. If the coating is applied onto render and this is causing damp problems, you should consider replacing the render.

Concrete floors should be replaced where possible and replaced with a breathable limecrete floor.

The level of the floor should be below the sole plate in timber frame buildings. Traditionally, suspended timber floors, bricks and pammets were used, although a modern product, such as Limecrete, laid without a damp-proof membrane, may be an acceptable replacement.

This will give a solid floor finish but with breathable qualities. If the whole floor cannot be replaced, then making a breathable channel around the edge of the room, to allow the base of the walls to breathe and keep dry, will help.

The channel should be filled with a breathable product such as Limecrete or covered with a narrow grate.

High external ground levels should be lowered so they are below the level of the floor inside the building, taking care not to undermine shallow foundations. A French drain around the outside walls will ensure that the base of the walls remains well drained and dry.

Ensure external paths are sloping away from the walls of the building to channel rainwater away.

Opening windows and heating a room will help prevent damp caused by inadequate ventilation. Windows which have been sealed shut or painted so they don’t open should be overhauled so they work properly. It may be possible to install an extract fan or air vent in severe cases or in areas which are difficult to ventilate.

Check the condition of the roof, chimneys, guttering, render, brickwork and joinery to establish the cause of penetrating damp. Remember to check for leaking plumbing. Carry out the necessary repairs, using matching traditional materials on listed buildings, and allow the fabric to dry out thoroughly before redecorating.

If you have a true case of rising damp, then lowering external ground levels, improving drainage around the building with French drains and laying breathable floors and walls will help to improve the situation. There are exceptional cases where these measures will not help solve the problem and a damp-proof course, if possible, may be the only option.

Injecting a chemical damp proof course into an older building seldom works and can actually make the problem worse. Water will be concentrated within the base of the wall below the level of the damp-proof course, causing its saturation and preventing it from drying out. This will then freeze, expand and thaw over winter, damaging the stability of the wall.

The thickness and solid construction of the walls of older buildings make it very difficult for a contractor to guarantee that the damp-proof course will be effective. To compensate for this, many contractors remove lime plaster and finish the injected walls with modern, waterproof plaster, which merely serves to disguise a continuing damp problem.

Why would waterproof plaster be needed if a damp-proof course is going to solve the problem? If the treatment is effective and the lime plaster surface is still in place, salts will appear on it as the wall dries out. These can be brushed off until the drying process is complete and act as a useful measure of the success of the damp-proof course. They also show up any recurring problems.

As chemical damp-proof courses often fail in older buildings, the waterproof cement plaster would stop any reoccurrence of damp appearing on the surface. Many contractors do not explain the process to the customer and prefer a cement render which will continue to hide the problem and damage the building. After several months have passed, it is common for the damp to reappear above the height of the cement render.

A physical damp-proof course may be acceptable in brickwork, including the plinth of timber frame buildings. This involves cutting out a line of pointing and inserting an impermeable layer, such as slate, to restrict moisture moving up the wall. Although not ideal, it is more effective than injecting chemicals into a solid wall and does not require the replacement of lime plaster with waterproof plaster.

The irregular nature of flint walls means that it is very difficult to insert any type of damp-proof course, as it is not possible to form a continuous barrier. Any gaps in the barrier will allow moisture through and the damp-proof course will fail. Drilling into a flint wall to inject a chemical damp-proof course will damage the wall and can also disturb its structural stability?

Beetle and fungal attacks on damp timbers are best cured by solving the damp problem which has created the conditions allowing them to thrive.

Solving the damp problem is the most important step you can take in ridding a building of death watch beetle. Chemical warfare may be appropriate in some cases but in isolation it will not eradicate the infestation. Changing the very particular environment required by death watch beetle is the most important strategy.

If you find an active woodworm infestation, treating the affected area should solve the problem. Spraying an entire house because of one or two out-breaks is unnecessary.

To tackle problems of wet and dry rot, cut off the source of damp and allow the timber to dry out. The fungi will become dormant and eventually die.

Building societies often ask for timber treatment and damp-proofing or a survey by a ‘specialist contractor’ as a condition of a mortgage. If this happens, you should consider calling in an independent consultant to see if such work is really necessary.

Usually it is just a waste of time and money and can sometimes fail to identify a problem which should be dealt with. A report from a qualified, independent specialist surveyor or conservation officer questioning the need for such work will normally be enough for the building society to withdraw this condition from a mortgage offer.

THE NEED FOR CONSENT

Some of the remedial works described above to solve or alleviate problems of damp in older buildings may need local authority approval, depending on the extent of the work.

You should contact the local authority’s conservation team for advice specific to your damp problem and to check if consent is needed.

CONCLUSION

Damp and decay in older buildings is a complex subject. It is because of this that so many mistakes, often well intentioned, have been and continue to be made. It also means incompetent or dishonest operators can easily deceive unwary owners and convince them that the only course of action is to have a chemical damp-proof course installed when ,in fact, this is the most ineffective and inappropriate treat for rising damp.

Timber treatment and damp-proof courses will not deal with the causes of the damp penetration. There may be cases where their localised use may be beneficial – but only as part of remedial works to remove the sources of damp from a building.

For advice and information of how to treat dampness and timber decay with resorting to using chemicals please call UK DAMP & DECAY CONTROL on 0800 028 1903

Rising Damp Assessments

Dampness is a problem which affects a very large number of properties, particularly those that were built more than 100 years ago. Some people are prepared to live with some degree of dampness, but not to the extent that it can cause problems with health & safety or the integrity of a building, and the effect on decor can be unsightly. But is the damp due to rising dampness or is it due to some other cause such as penetrating dampness or condensation?

If a damp problem is to be properly eradicated it is important that the source of the problem is properly identified. Affected areas need to be allowed to dry out thoroughly before remedial damp-proofing work is carried out. This is approach is recommended by the Property Care Association but rarely followed by their PCA members who opt for the quick-fix chemical damp-proofing method as this is the most profitable method of treatment.

If the source or cause of the problem is not treated, or the problem is incorrectly diagnosed, the original problem will continue to develop and unnecessary or incorrect repair work may cause added problems. Chemical damp-proofing treatments which are often recommended are usually inappropriate for traditionally constructed buildings and can mask dampness retained within the structure, only for such dampness to begin to show in future years.

When damp is found, particularly at low levels such as just above skirting boards, the immediate knee-jerk reaction is to call in a damp proofing company who are entrusted to diagnose the source of damp and recommend a suitable remedy. Most damp-proofing surveys rely on hand held moisture meters which are not calibrated for use on plaster or brickwork. Very rarely will you see a damp surveyor taking samples of plaster to test for chlorides and nitrates in the defective plaster before recommending the insertion of a new chemical damp-proof course and they will solemnly swear that dampness was present on the basis of flashing lights on a moisture meter.

The only time a damp-proofing company will allow their surveyors to take samples to find out the true moisture content is when there is a recall under guarantee and plaster samples are usually tested in Carbide Speedy meter which will usually show that there is no rising damp in the wall and therefore not covered by their guarantee.

Mortgage Valuers, especially with a more Responsible Lending Practice being implemented will now, more often than not, due to the requirements of lenders, request a specialist damp and timber report from a specialist damp-proofing and timber treatment company. Most damp-proofing and timber surveyors are commission based and their employers have a profit motive and there is a strong tendency to recommend chemical damp-proofing and water-proof plaster works for a problem that can be rectified quite simply by some simple repairs of external defects.

Most dampness tends to originate or be caused by other sources and often leads to induced rising damp which can be mis-diagnosed leading to inappropriate chemical damp-proofing treatments

Do not to forget the inherent nature of the materials used in old buildings, and how such buildings were constructed compared to modern construction detail. A building of modern cavity construction is specifically designed to stop moisture extending through to the internal surfaces. An old building of solid construction is constructed of porous materials that were not designed to prevent moisture into the building, but equally moisture within the structure was able to evaporate out. Any impermeable membrane incorporated into or on such a structure will tend to displace such moisture or prevent such moisture evaporation.

Traditionally, walls were constructed using lime mortars and lime plasters, which absorb moisture before slowly releasing it. Modern methods of repair now use cement, which does not have the moisture permeability of lime. A consequence is that moisture is either displaced or held within the structure. Basically, due to rainfall etc it is not possible to prevent moisture entering a wall, but modern methods including chemical damp-proof courses, use of cement etc, can prevent moisture in the wall from evaporating leading to further problems internally. For free ,independent advice about any possible damp problem please call us on 0800 028 1903

We have, for a considerable amount of time, been prepared to believe the claims of product manufacturers. I`m not a dentist but this toothpaste makes your gums stronger and your teeth whiter (because it contains an advanced anti bacterial system if you must ask).

The Dutch philosopher Baruch Spinoza, a contemporary of Descartes thought (unlike Descartes) that the very act of understanding information was believing it. Finding evidence to the contrary would enable a `mind change`, but until that time we believe everything. Whether or not we like the idea, the success of modern advertising techniques and more recent experimentation indicate Spinoza was correct. However this had been recognized some time. `Mundus vult decipi, ergo decipiator`, attributed to Petronius, a kind of first century roman Oscar Wilde, literally translates as `The world wants to be deceived, so deceive it`.

It would be unfair to suggest the various `urban building myth` (such as what wood borers and wood decay fungi can actually do) were somehow initiated by those companies that would ultimately profit from them. It would be fair to say those companies have no commercial interest in a considered scientific approach and actively propagate the myths. They often affect draconian and specious treatments, using the vehicle of a guarantee that their (predominantly) unnecessary work will be effective.

The `remedial guarantee` is a marketing tool, which proved so commercially appealing (allowing building owners, insurers and lenders to `pass the parcel` with liability) that it became endemic in the building industry. It goes without saying a builder has to ensure the quality of his work or a professional indemnify his advice, but a point had been reached where some mortgagers would only lend against a 400 year old timber framed property on condition the timbers were sprayed or injected with biocide, or lend against a rubble walled vernacular building on condition the walls were injected with a damp proof course.

Thankfully this is now changing, with some national building insurers such as the NHBC changing their policies to reflect the realities of existing and historic buildings.

The USP of damp-proofing firms will soon be diminished as their main insurance agent,Guarantee Protection Insurance, is going to halve the length of term of the guarantee from 20 years to 10 years, quite possibly as a result of the high failure rate of damp-proofing firms and therefore extra claims on the insurance. Article written by The Floyd Consultancy.



For details of chemical free, building maintenance methods of controlling dampness and timber decay please contact UK DAMP & DECAY CONTROL on 0800 028 1903

INTRODUCTION

There is a lot of discussion in the media and on the internet about rising dampness
What it is,misdiagnosis and whether rising damp even exists.

Rising dampness is simply water from the ground that enters a structure by capillary action ? The tendency of water to be drawn upwards in porous materials. Building materials are porous, therefore moisture from the ground can rise into the structure of a building, much as water is drawn into a piece of tissue paper or a sponge ,unless there is a barrier, such as a damp proof course, to prevent it from doing so.

The problem causes discoloured wall coverings, often with a characteristic tide-mark due to salts dissolved in the ground moisture evaporating out towards the top of the profile.

Due to the fact that there are many other causes of dampness in buildings, such as rainwater ingress and condensation,as well as the high cost of remedial work for rising damp , it is vital that investigations into a suspected case are undertaken by a trained and competent surveyor, such as one who holds the CSRT (Certificated Surveyor in Remedial Treatment) qualification.

CHARACTERISTICS OF RISING DAMPNESS

Rising dampness is characterised by a descending moisture gradient within a wall from floor level up to a height of about 1.5 metres,although on rare occasions an impermeable covering on the face of a wall at lower levels, may cause the damp to rise higher than this.

A good indicator that a damp problem is being caused by rising damp is the presence of a salt deposition line. Ground salts migrate in solution with the moisture and will be deposited at the point where the water evaporates from the wall.

Sulphate salts will produce efflorescence on a plaster surface, whereas chloride and nitrate salts are hygroscopic, that is they attract moisture from the atmosphere and are seldom visible, although they can cause a line of increased dampness on the wall. While harmless to health, such salts can be responsible for damage to plasterwork and other wall coverings. Salts will continue to evaporate out long after a rising damp problem has been resolved unless the wall is resurfaced with salt resistant plaster or render.

RISING DAMP DIAGNOSIS TECHNIQUES

There are three phases to any investigation and diagnosis of damp in a building:
1. Visual inspection
2. On site measurement of the extent and severity of the problem
3. Laboratory analysis of plaster samples

Visual Inspection
The first task when investigating a suspected case of rising damp is to carefully examine the property in order to fully understand the building, as well as the clients requirements and expectations.

When determining the presence of any moisture in the fabric of a building it must be understood that no method of diagnosis can differentiate between water from one source or another, so all potential causes of dampness ? including rainwater ingress and condensation ? must be taken into consideration.

A visual inspection will therefore involve a thorough check of the common causes of dampness, such as faulty guttering, rainwater downpipes and flashing, as well as damaged pointing, cracked rendering and raised external ground levels. Induced rising dampness can be caused by excess water accumulating around foundations, such as might be caused by leaking water pipes.

If faults are found by a surveyor, the client should be advised to remedy them, allowing a period of time to elapse before further checks are made.

Only when all construction defects have been identified or eliminated from the investigation and work carried out to rectify these defects causing induced rising dampness, should the effectiveness of the building`s damp proof course be assessed.

On Site Measurement
To support the findings of a visual inspection the surveyor will then begin the process of quantifying and developing a full understanding of the damp problem. There are two types of moisture meter commonly used by surveyors during site investigations.

Electric moisture meters are commonly available and used for on site testing and screening. The vast majority measure either the electrical resistance of the wall materials, or the capacitance in a sensor, both of which are influenced by moisture.

These meters are quick and easy to use, have the advantage of being small and portable, and are valuable tools if used properly. Being non-destructive they are particularly suitable for pre-purchase property surveys. However, there are limitations to their use which must be understood by the operator.

Readings from electric moisture meters can be influenced by many factors, such as salt contamination, material density and the conductivity of different wall coverings. Reasonably accurate measurement can only be achieved on timber. If used on plaster or masonry, readings can be inconsistent and are not truly quantitative and readings from different situations should not be compared.

For this reason isolated readings from electric meters are generally of little value. However, electric meters can be used to take a number of readings very quickly, so they are particularly useful in establishing a pattern of relative readings over a surface.

Electrical meters are not suitable for checking the efficacy of a new damp proof course in a building that has previously been suffering from rising damp, as the presence of remaining salts can produce high readings.

A calcium carbide meter, often known as a `Speedy` meter, can be used either on site, or as part of a laboratory-based analysis. Samples are obtained by drilling a hole in a wall and collecting some of the dust, a measured sample of which is placed within a pressurised container and mixed with calcium carbide. The calcium carbide reacts with any water present, producing acetylene gas, the volume produced determining the moisture content of the sample.

The calcium carbide meter is a very useful tool for assessing the exact moisture content of a sample, but training is necessary to in order to correctly interpret the results. The meter can only indicate the total volume of water in the sample tested and cannot differentiate between capillary and hygroscopic water.

Laboratory Analysis
In order to achieve precise quantitative results a laboratory analysis is vital. A variety of tests are available, giving more comprehensive results than on site testing. Analysis in a laboratory is also necessary to accurately determine the presence and concentration of ground salts.

Gravimetric, or oven-drying analysis is able to distinguish between moisture derived from the ground and that due to existence of hygroscopic salts. It involves removal of a drilled sample from the wall which is weighed and then left in a controlled environment at 20 degrees centigrade with a relative humidity of 75 percent to be allowed to reach its equilibrium weight before being weighed again. The sample is then oven-dried and reweighed. The difference in weights can be used to accurately determine the hygroscopic and capillary moisture content of the sample.

Although this test takes some time and will be more costly to undertake than on-site testing, it is the most accurate test currently available.

Moisture Profiling
Moisture profiling can be particularly useful when diagnosing rising damp. This involves taking a series of vertical samples in order to establish the distribution profile of salt and moisture within a structure. Although relatively expensive to carry out, the process can be useful in sensitive buildings, historic structures where there is doubt in the diagnosis, or as part of litigation.

Sampling
Due to the possible influence of hygroscopic salts, condensation and ambient humidity, the results of tests taken from surface plaster alone can be misleading. If doubt exists concerning a diagnosis or in case of dispute, in-depth drilling and sampling below and at intervals above the damp proof course line may be necessary, with moisture content being assessed using either an oven drying or calcium carbide method.

Whilst the use of insulated probes with an electrical meter can help to eliminate interference from surface contaminants, the readings obtained can only be compared relative to each other and must therefore be interpreted with caution.

If samples are to be removed from site for laboratory testing, they must be stored in airtight containers to prevent any loss or gain of moisture in transit. In addition, an accurate record of the exact location for each sample is essential for correct interpretation of the results.

If an active electro-osmosis damp proof course is present within the wall under investigation, this must be switched off before tests are undertaken, prevent erroneous results.

REMEDIAL ACTION ON DIAGNOSIS OF RISING DAMP
If the source of the dampness problem is identified as rising damp and it has been identified that this is due to the lack or failure of a damp proof barrier, a new damp proof course may be required. This can be in the form of a physical barrier, a chemically injected damp proof course, or in some circumstances electromagnetic system.

In most cases the deposition of ground salts will also necessitate the removal of areas of damp or salt-affected plasterwork. This will not in itself remove water and salt accumulation from the wall, which may continue to evaporate out over time. For this reason subsequent replastering must use materials resistant to the passage of residual moisture or salt in the drying wall. Gypsum-based plasters are not usually recommended where walls have been affected by dampness or salt contamination.

Further information on the diagnosis of rising dampness in masonry walls be seen in various Property Care Association guidance notes, BS6576 and BRE digest 245.

The Property Care Association has also produced a leaflet entitled `The use of moisture meters to establish the presence of rising damp` which states that the electrical method, i.e. moisture meters, does not provide a percentage reading of the moisture content and therefore does not give a direct reading of moisture content

Despite these guidelines and evidence that moisture meters are not accurate on plaster most Property Care Association (PCA) members rarely honour their holistic code of practice and will always just rely on the use of hand-held moisture meters to diagnose rising damp and will then routinely advise that chemical damp-proofing is required even when it is very seldom needed as most cases of perceived rising dampness can be prevented by repairing construction defects at fraction of the price. This is the course of action advised by the Property Care Association but we find that most damp-proofing surveyors of PCA members opt for the insertion of an unsuitable chemical damp-proof course. To save money and avoid expensive, unnecessary,messy and disruptive chemical damp-proofing never trust the findings of a damp surveyor who relies solely on the use of a moisture meter and internal observations only.

The majority of damp-proofing surveyors are really employed as salesmen and have a default setting to offer damp-proofing treatments.If you if you have any doubts about this you only have to look at the Property Care Association website where Timberwise, the UK’s second largest damp-proofing and timber treatment company, are advertising for Experienced Preservation Sales Surveyors. Prospective surveyors are required to have a sales background and have a passion for sales and be able to demonstrate enthusiasm in their role and sell the company’s sales and services.Not really independent survey when all their surveyors are encouraged to sell damp-proofing and timber treatment products

In most case we come across there is never any true rising damp caused by the breakdown of an existing damp-proof course as they seldom breakdown and chemical damp-proofing is never required. Even if there is no damp-course rising dampness can be controlled by installing ventilated drainage channels and encouraging evaporation from walls by applying breathable plasters such as lime mortar.

For more information about accurate , impartial, independent damp and timber surveys which include taking samples of damp plaster please contact UK DAMP & DECAY CONTROL ON 0800 028 1903

.

What is rising damp? This article explores the issues and recommends that surveys be taken more seriously

In 1999, the BBC2 programme Raising the Roof caused annoyance within the remedial industry by suggesting that rising damp did not exist, and that it was a concept invented by the industry in order to sell damp-proof courses. Damp problems, it suggested, were apparently always attributable to some other cause that could usually be remedied.

The British Wood Preserving and Damp-proofing Association ( now renamed as the Property Care Association-PCA) responded by pointing out that regulations dating as far back as 1875 required homes to be built with a damp-proof course, and that current Building Regulations require a damp-proof course in all new buildings and extensions. Legislation to combat a problem that does not exist?

Open pores
A major source of confusion may be the meaning of the term rising damp.The Building Research Establishment Digest 245 (`Rising damp in walls:diagnosis and treatment`) indicates that if a wall is constructed from a porous building material and stands in saturated soil, then water will tend to rise up within the structure by capillary action. The height it rises to will depend, to a large extent, on pore size and distribution - because small pores exert a stronger capillary attraction than large ones - and on the amount of surface evaporation.

If the soil is not saturated, then this capillary attraction will tend to be countered by the suction pressure exerted by the soil. This, it states, is approximately equivalent to the negative pressure exerted by a column of water extending from the base of the wall to the water table. If the water table rises, then the suction pressure decreases, and the moisture rises higher within the wall.

The presence, and extent, of rising damp, according to the BRE concept, will therefore depend on a range of parameters, which will include the pore structures of the wall and soil, and the height of the water table. Rising damp may be a problem in fine-pored Georgian brickwork on clay soil with a high water table, but it should not, for example, affect masonry with courser pores on open textured sandy soil. If damp appears at the base of a wall in the second situation then it is likely to be caused by a drainage problem. Drainage problems may cause damp to rise in a wall, but this is not `rising damp`.

Probing issues
Unfortunately, many people believe that any water at the base of a wall indicates rising damp, and that any old building will be prone to rising damp unless a dpc is installed. The problem is not assisted by the incautious use of moisture meters by persons anxious to sell damp-proof courses. It should, however, now be apparent that groundwater does not automatically cause a problem with `unprotected` walls.

The British Standard Code of Practice for the installation of chemical damp-proof courses (BS 6576: 1985) states in section 3.1 that it is essential to `confirm whether the property has rising damp, or has suffered rising damp`, before installing a dpc.

Section 3.2.2 of the same document states that surface measurements alone cannot confirm the presence of rising damp, although they can, when moisture meters are correctly used, confirm the presence of dampness. This is perhaps an oversimplification because a series of meter readings taken up a wall may suggest a rising damp profile, but they cannot show the severity of the problem.

A major difficulty is that `moisture meters` are actually measuring the electrical properties of the material tested, and any salts that have been mobilised or carried into the test area by water movement strongly influence these electrical properties. Salts may produce high meter readings in a wall that is virtually dry.

One certainty is that wandering around a room prodding the wall at intervals with a meter probe will not diagnose rising damp, but this is the method usually employed by surveyors. It may, however, indicate areas that require closer investigation.

Have salt will travel BS 6576 refers the reader to BRE Digest 245 for proof of rising damp or quantitative measurements, and the method described in that digest will demonstrate the extent of any dampness that may be present, and its likely source. The method is based on the fact that soil contains salts that will be carried into the building material by any water travelling up through the upper soil layer (rising damp). These salts, predominantly chlorides and nitrates, will tend to accumulate in a band at the highest zone within the wall that the moisture reaches.

If their presence is demonstrated as a common phenomenon around the walls, then there is rising damp. If a salt profile is only found adjacent to a downpipe, then there is probably a long-term fault in the drain. If there are no soil salts in an old wall, then any moisture that is present has not travelled far through the soil, and may have come from faulty rainwater goods or surface run-off.

The term `soil salts` is used because water movement may mobilise large amounts of salts from the building materials. Brickwork, for example, may be coated in blown plaster and sodium sulphate crystals, but this does not mean there is rising damp.Most of the sulphate probably came from the clay from which the bricks were made.

The method used to detect the presence of rising damp must therefore assess the moisture content of the wall, detect the presence of salts, and differentiate between salts that have come from the ground and salts that have come from the wall.

The analysis requires samples to be taken in columns up the wall.
Sampling at 250mm intervals with a normal masonry bit is convenient, and to a height of 1.5m with a control taken at 2m. The first 10mm of dust from each hole is discarded or analysed separately so that surface effects do not confound the results.

Samples are then placed into tightly lidded pots for laboratory analysis.
The initial moisture content (MC) assessment is made by weighing the sample and heating it in an oven until it is dry. Digest 245 recommends that this is done for about an hour at 100 degrees C, but this temperature will drive off water of crystallisation from any hydrated salts that may be present and may give erroneous results. It should certainly never be used if plaster is to be tested. It is preferable to leave samples overnight at a temperature of 40 degrees C.

Slippery when wet The samples are then reweighed so that the original moisture content is established from percentage weight loss, and stored for a few days at a humidity of 75 per cent. Some labs prefer to place the samples straight into the controlled humidity chamber after the initial weighing and then obtain one dry weight at the end of the procedure.

The point of the constant humidity chamber is that chlorides and nitrates from ground water will absorb moisture from the atmosphere, but 75 per cent relative humidity (RH) is not high enough to affect the sodium sulphate. It is also easy to obtain 75 per cent RH by storing the samples over a saturated solution of common salt, but substantial errors may occur if there is insufficient salt solution or the solution is not fully saturated. In both cases the humidity will be too high and water absorption by any sulphate present may confound the results. If the samples are now reweighed, then hygroscopic moisture contents (HMC) are obtained and these provide a measure of salt contamination from ground water - rising damp.

It is considered that a dry reading in mortar or soft brick will be less than about three per cent moisture. Digest 245 recommends a HMC threshold of five per cent before remedial treatment is contemplated.

Rising damp need not be the only reason for installing a damp-proof course. If water is being funnelled into a wall from a neighbour's concrete yard, for example, then lowering ground levels or constructing a dry area may not be an option. The important factor is that the situation has been properly investigated so that an appropriate solution can be found.What is rising damp? This article explores the issues and recommends that surveys be taken more seriously

In 1999, the BBC2 programme Raising the Roof caused annoyance within the remedial industry by suggesting that rising damp did not exist, and that it was a concept invented by the industry in order to sell damp-proof courses. Damp problems, it suggested, were apparently always attributable to some other cause that could usually be remedied.

The British Wood Preserving and Damp-proofing Association responded by pointing out that regulations dating as far back as 1875 required homes to be built with a damp-proof course, and that current Building Regulations require a dpc in all new buildings and extensions. Legislation to combat a problem that does not exist?

Open pores
A major source of confusion may be the meaning of the term rising damp.The Building Research Establishment Digest 245 (`Rising damp in walls:diagnosis and treatment`) indicates that if a wall is constructed from a porous building material and stands in saturated soil, then water will tend to rise up within the structure by capillary action. The height it rises to will depend, to a large extent, on pore size and distribution - because small pores exert a stronger capillary attraction than large ones - and on the amount of surface evaporation.

If the soil is not saturated, then this capillary attraction will tend to be countered by the suction pressure exerted by the soil. This, it states, is approximately equivalent to the negative pressure exerted by a column of water extending from the base of the wall to the water table. If the water table rises, then the suction pressure decreases, and the moisture rises higher within the wall.

The presence, and extent, of rising damp, according to the BRE concept, will therefore depend on a range of parameters, which will include the pore structures of the wall and soil, and the height of the water table. Rising damp may be a problem in fine-pored Georgian brickwork on clay soil with a high water table, but it should not, for example, affect masonry with courser pores on open textured sandy soil. If damp appears at the base of a wall in the second situation then it is likely to be caused by a drainage problem. Drainage problems may cause damp to rise in a wall, but this is not `rising damp`.

Probing issues
Unfortunately, many people believe that any water at the base of a wall indicates rising damp, and that any old building will be prone to rising damp unless a dpc is installed. The problem is not assisted by the incautious use of moisture meters by persons anxious to sell damp-proof courses. It should, however, now be apparent that groundwater does not automatically cause a problem with `unprotected` walls.

The British Standard Code of Practice for the installation of chemical damp-proof courses (BS 6576: 1985) states in section 3.1 that it is essential to `confirm whether the property has rising damp, or has suffered rising damp`, before installing a dpc.

Section 3.2.2 of the same document states that surface measurements alone cannot confirm the presence of rising damp, although they can, when moisture meters are correctly used, confirm the presence of dampness. This is perhaps an oversimplification because a series of meter readings taken up a wall may suggest a rising damp profile, but they cannot show the severity of the problem.

A major difficulty is that `moisture meters` are actually measuring the electrical properties of the material tested, and any salts that have been mobilised or carried into the test area by water movement strongly influence these electrical properties. Salts may produce high meter readings in a wall that is virtually dry.

One certainty is that wandering around a room prodding the wall at intervals with a meter probe will not diagnose rising damp, but this is the method usually employed by surveyors. It may, however, indicate areas that require closer investigation.

Have salt will travel BS 6576 refers the reader to BRE Digest 245 for proof of rising damp or quantitative measurements, and the method described in that digest will demonstrate the extent of any dampness that may be present, and its likely source. The method is based on the fact that soil contains salts that will be carried into the building material by any water travelling up through the upper soil layer (rising damp). These salts, predominantly chlorides and nitrates, will tend to accumulate in a band at the highest zone within the wall that the moisture reaches.

If their presence is demonstrated as a common phenomenon around the walls, then there is rising damp. If a salt profile is only found adjacent to a downpipe, then there is probably a long-term fault in the drain. If there are no soil salts in an old wall, then any moisture that is present has not travelled far through the soil, and may have come from faulty rainwater goods or surface run-off.

The term `soil salts` is used because water movement may mobilise large amounts of salts from the building materials. Brickwork, for example, may be coated in blown plaster and sodium sulphate crystals, but this does not mean there is rising damp.Most of the sulphate probably came from the clay from which the bricks were made.

The method used to detect the presence of rising damp must therefore assess the moisture content of the wall, detect the presence of salts, and differentiate between salts that have come from the ground and salts that have come from the wall.

The analysis requires samples to be taken in columns up the wall.
Sampling at 250mm intervals with a normal masonry bit is convenient, and to a height of 1.5m with a control taken at 2m. The first 10mm of dust from each hole is discarded or analysed separately so that surface effects do not confound the results.

Samples are then placed into tightly lidded pots for laboratory analysis.
The initial moisture content (MC) assessment is made by weighing the sample and heating it in an oven until it is dry. Digest 245 recommends that this is done for about an hour at 100 degrees C, but this temperature will drive off water of crystallisation from any hydrated salts that may be present and may give erroneous results. It should certainly never be used if plaster is to be tested. It is preferable to leave samples overnight at a temperature of 40 degrees C.

Slippery when wet The samples are then reweighed so that the original moisture content is established from percentage weight loss, and stored for a few days at a humidity of 75 per cent. Some labs prefer to place the samples straight into the controlled humidity chamber after the initial weighing and then obtain one dry weight at the end of the procedure.

The point of the constant humidity chamber is that chlorides and nitrates from ground water will absorb moisture from the atmosphere, but 75 per cent relative humidity (RH) is not high enough to affect the sodium sulphate. It is also easy to obtain 75 per cent RH by storing the samples over a saturated solution of common salt, but substantial errors may occur if there is insufficient salt solution or the solution is not fully saturated. In both cases the humidity will be too high and water absorption by any sulphate present may confound the results. If the samples are now reweighed, then hygroscopic moisture contents (HMC) are obtained and these provide a measure of salt contamination from ground water - rising damp.

It is considered that a dry reading in mortar or soft brick will be less than about three per cent moisture. Digest 245 recommends a HMC threshold of five per cent before remedial treatment is contemplated.

Rising damp need not be the only reason for installing a damp-proof course. If water is being funnelled into a wall from a neighbour`s concrete yard, for example, then lowering ground levels or constructing a dry area may not be an option. The important factor is that the situation has been properly investigated so that an appropriate solution can be found.

Article written by Brian Ridout for Architects Journal. October 2001

The term rising damp is often used when referring to problems, or potential problems with houses, but if you own a period property there are certain issues you need to take into account

You have probably heard of the expression `Rising Damp`. Some of you may even remember Leonard Rossiter in the TV Sitcom? Here however, I am referring to that phenomenon of damp staining and failed plaster at low level, seen mainly on the external walls of properties built before 1900.

But what is rising damp? And does it actually exist? Now even to ask that latter question is controversial as there is a whole industry out there making its living providing reports and carrying out `remedial works` to cure rising damp and even offering 20 to 30 year guarantees.

Rising damp is the name given to dampness manifesting itself in the lower parts of external walls. Tide marks may be present internally and sometimes `salts` are visible on the internal plasterwork which causes damage to the extent that the plasterwork fails.

In the later part of the 20th Century, the generally accepted treatment was to inject a silicone damp-proof course into the walls and hack off all the plaster up to 1 - 1.5 metres and re-plaster with sand and cement render often incorporating a water proofer. This can cost anything from £5,000 - £10,000 for a three bedroom terrace or semi and causes lots of other consequential disturbance.

Is this necessary? Probably not and it was mainly the water proofer that held back the damp. Injecting silicone into bricks or their mortar is problematical. Injecting it into porous stonework, such as limestone or sandstone simply doesn`t work. Solid walls are not actually `solid` being usually two skins of stone with rubble infill and you can`t inject rubble infill.

The Society for the Protection of Ancient Buildings (SPAB) talk of `breathing buildings` and this is one of the mainstays of their philosophy of a period or listed building with no damp proof course.

Rising damp will only occur in a wall where there is no damp proof course (d.p.c.). This is a layer of something that is impermeable to water, sometimes under pressure. Traditionally, from about the 1880s onwards, slate was laid in two layers just above ground level. Sometimes it was two courses of very hard dense engineering brickwork. Later mastic asphalt was used and later still lead cored bitumen and latterly in the 20th century to the current day a variety of polymers. The other innovation was to incorporate open cavities but pre-1880s these are not generally present.

So why are we concerned about Rising Damp? It usually comes to mind after you have put in an offer on a house and the building society or bank surveyor has said to get your mortgage you will need to `cure the rising damp` and then insists on you getting a `damp specialist` to report and undertake works.

So you have a solid walled house with damp walls why? Rising damp? It`s a possibility. However look first for other causes such as:-

* High ground levels, i.e. above the inner ground floor level. It is generally accepted that the outside ground level should be about 15cm below the inner floor level. However this is not always possible, especially when you don`t own the adjoining land.

* Another very common cause of dampness at low level is leaking gutters or overflows and the inherent splash back resulting from this. If you have thatch and no gutters then ensure that the ground is not hard paving around the building to reduce this splash back.

* Defective render, poor or inappropriate pointing, poor brickwork or stonework can also be a cause of internal damp.

* Depending on the internal pore size of the bricks or stones, liquid water may rise up through the individual bricks or stones mainly by capillary action. Once the water reaches the point where it can evaporate faster than it can rise up, it rises no further. In a traditionally built property, this transpiration is called `breathing` and is the natural result of no damp proof course in solid walls. All such walls will be slightly damp at low level. It is not a fault, it is how they were built and how they work.

Action to take for rising damp

* If the property has not already been `modernised`with cement render internally then replace any defective plaster with a breathable lime based plaster and apply a vapour permeable paint.

Note: It is very important not to use modern acrylic vinyl emulsion or other vinyl paints and preferably no wallpaper.

* Deal with all the external housekeeping issues. If the house has cement based pointing consider removing and replacing it with lime based mortar. Be very careful to not damage the bricks or stones in the process and never ever use disc cutters or mechanical means.

* If it is really bad or you have high ground levels outside, then use a hydraulic lime plaster that breathes but doesn`t allow liquid water to come through.

In conclusion..

Traditionally built properties are fundamentally different from modern buildings and require a holistic approach to the diagnosis of damp problems and their solutions. Initially, make sure you consult with a suitably qualified building surveyor to identify the cause of your damp issues and then employ a company experienced with the use of traditional materials to carry out remedial works.

Article written by Martin Hall , a conservation accredited Chartered Building Surveyor , Hall & Ensom Surveyors

These controversial damp-proofing systems are much derided as having no effect on controlling rising dampness but they could have some benefit in removing dampness from walls as long as they get enough air flowing through the tubes or air chambers fitted in the walls. However their actual effect may be limited by the strength and direction of the wind and will only work satisfactorily if the wind is blowing strong enough and in the right direction for sustained periods.

Until recently only two companies were offering this sort of damp-proofing system, one of which is Schrijver Damp-proofing and the other until recently Holland Dampproofing but lately they seem to have been replaced by a new company offering a similar brick insert called DR Damp. The most heavily advertised system is Schrijver Damp-proofing who often take out full page adverts in papers such as The Independent which may or may not add to their green credentials. Their claim is that the Schrijver System is a green alternative to chemical damp-proofing and that there will be no need for any internal plastering works.

There is still a lot of debate about the effectiveness of chemical damp-proofing but there is no evidence to indicate that either the Schrijver System or the DrDamp Damp Proof System are the complete answer. There is not very much technical information about how the systems work on either Schrijver System or DrDamp websites and neither of these systems do not have any third party accreditation or certification from the British Board of Agrement to confirm that these systems are effective as the claims made regarding controlling dampness.

According to Schrijver their form of damp-proofing is a humidity regulating system which consists of a stone element (and in the case of a cavity wall a tube is also used to channel the moisture). The whole system is fixed in a specially prepared niche in the outside wall. Through an opening in the element, dry air can flow into the system from the outside environment.

The idea of the Schrijver damp-proofing system is to reduce humidity in the air and exterior walls to control damp. Schrijver use phrases such as `the clean, green way to a drier indoor climate`, `successfully installed`, `humidity regulating`, `combating the effects of rising damp` and `damp control`. They tend to avoid using more conventional phrases expected when carrying out treatments to stop dampness such as `treating rising damp`, `successfully cured`, `damp treatment`, `damp proofing` or `damp cure`.

The Schrijver website says `The system comes with a life-time guarantee. We also offer a 12 month money back guarantee.` But the guarantee is for a `dry indoor climate` as assessed by Schrijver and not for the successful alleviation of rising dampness from a wall.

The solution according to DrDamp is the use of their `innovative method, which is completely natural and does not use harmful chemicals like other traditional damp proofing methods. By using specially designed bricks fitted into the outside wall, air is allowed to flow into the air chambers of the system and out again. On its way through the inside of the wall, this airflow causes moisture to evaporate, therefore drying out the wall.`

The only research undertaken about the effectiveness of the Schrijver System/DrDamp Damp Proof System was carried out a few years ago by the Independent Dutch Laboratory, TNO (Organisation for Applied Scientific Research) which states that the performance of these damp-proofing systems is governed by external environmental factors such as wind speed, wind direction, temperature and relative humidity.What it is really saying is that for these systems to work effectively then the wind has to be blowing in the right direction at a fairly high speed to have much effect on removing dampness from walls. These conditions are unlikely to occur for any extended time and the performance is further hindered by the fact that wind speed drops at ground level and therefore quite strong gusts of wind would be required for the units to perform effectively or as claimed by both Schrijver System/DrDamp

In the UK wind usually comes in one direction at a time ( it might be different in Holland) and therefore if all the external walls of a detached house had Schrijver System/DrDamp Damp Proof System installed then it is likely that only one elevation wall would be subject to wind at any given time meaning that the units in the wind free walls will unlikely to be as effective as claimed by Schrijver or DrDamp.

The mass marketing of both these damp-proofing systems does seem to work as I have seen several houses in towns and cities all over the country which have had this sort of damp-proofing work undertaken.I am not sure whether consumers understand the effectiveness or limitations of these damp-proofing systems or are they just gullible and taken in by slick sales talk which may be proffered by the surveyors of both DrDamp and Schrijver Damp-proofing but Giovanni Massari, in his book `Damp Buildings Old and New ` refers to Knapen`s Atmospheric Siphon and similar damp-proofing systems as `Appealing to the lazy-minded with the suggestive power of simple, predigested solutions that do not cause one the trouble of having to think for oneself `

Schrijver System/ DrDamp both claim that internal re-plastering will not be necessary and this is true if there is no rising damp present but then damp-proofing treatment would not be required anyway. However if there is rising dampness from the ground it the wall then the water travelling up the wall naturally by capillary action will have drawn soluble salts such as nitrates, chlorides and sulphates from the ground. These salts will contaminate wall plaster as the moisture migrates through the plaster as part of normal evaporation internally and as the salts are hygroscopic they will continue to attract moisture into the plaster and the wall will appear wet even though it may be dry behind the plaster. This is a similar process to what happens to normal household salt if a salt cellar is left in a humid kitchen then the salt will soon become soaked, lumpy and useless.

The only way of preventing any future dampness due to salt contamination is to remove the affected plaster and replace it with a render containing a salt inhibitor to prevent salts from passing from the wall into the plaster which would then be deposited on the wall surface. A better plastering system would be to incorporate some form of thermal insulation by applying a combined damp-proofing/insulating plaster such as Walltransform or dry-lining the walls with a water-proof membrane such as Platon and then overboarding this with a thermal plasterboard. Both of these plastering systems will prevent the passage of moisture and salts onto any internal wall finish and also lower u-values to around 0.3 and reduce heat loss and ultimately pay for themselves in the former of lower energy bills.

The YouTube video of installation of the Schrijver System shows the damp-proofing units being installed at a height of approximately 350mm which is much higher than that recommended for the installation of any retro-fit damp-proof course and even if these damp-proofing inserts work as effectively as claimed by Schrijver/ DrDamp,if there is dampness in the ground it will rise to the height of the units before evaporating externally.This will still cause some dampness in the plaster, and possible timber decay and wet rot in skirting boards , at ground level and these may need to be replaced in the normal way associated with normal remedial damp-proofing works. .

Most rising damp occurs as a result of water from saturated ground passing into the below ground masonry walls which then become saturated themselves and as the walls usually have finer pores than the ground water will rise up the wall due to capillary forces. If there is no damp-proof course or a defective one then dampness can rise up to a height of more than 1.2m but the height of the dampness is controlled by a balance between evaporation from the wall and upward capillary forces. .

The most effective way of controlling rising damp is to remove the moisture source to prevent the base of the wall become wet and this can be achieved either by installing a French Drain or excavating the ground to create a vented channel covered with paving slabs/York stone or similar allowing moisture to evaporate from the base of the wall before it can affect skirtings and plaster at ground level. To further improve this method extra air bricks should be installed to ventilate sub-floor areas as the extra air flow under the floor will purge excess water vapour from the floor void, reducing humidity levels in the floor void and the possibility of condensation occurring on exposed masonry leading to ?rising damp? internally. Another benefit of improving the sub-floor ventilation is that the moisture content of sub-floor timbers such as joists and wall-plates etc would also be reduced and this would and lessen the risk of fungal decay or woodworm infestation making chemical timber treatments hard to justify.

We believe this form of damp control is much more effective, and also much cheaper, than the Schrijver System/DrDamp Damp Proof System or any other form of siphon tube damp-proofing and also any chemical damp-proofing.The current cost of the Schrijver System/DrDamp Damp Proof System is around £120.00 per linear metre which is around five times the cost of the installation of a chemical damp-proof course. If you need any further advice on which form of damp-proofing system is best for your house then please call us on 0800 028 1903 or email enquiries@ukdamp.co.uk.

For a more detailed report about the effectiveness and advantages or otherwise of the Schrijver System/DrDamp Damp Proof System in controlling risng dampness from the ground please contact us and we will send a pdf copy to you.

More information about the perceived success of the Schrijver System can be found at www.schrijverdamp.weebly.com which is written by previous customers of the Schrijver System form of damp-proofing

Dampness in buildings can cause the early failure of the components of the structure; encourage insect or fungal growth and the development of moulds, many of which may be injurious to health.

No building is dry because all air will contain moisture. What is important is to maintain the level of moisture within a building at acceptable levels.

The interpretation of dampness from the moisture content

The moisture content is the amount of water in a material divided by the weight of the material. This means that a heavy material will have a lower percentage moisture content than a light material if they were both to contain the same amount of water.

For example, 5% in mortar is fairly dry, in brick it is damp and in plaster it is wet. A plaster would be regarded as being wet if there were to be a moisture content of over one percent. For a brick, dampness would be identified if the reading was above three percent and for timber over 20% moisture content.

It will be reasonable to say that dampness occurs where a material is wetter than air dry. Air Dry means in equilibrium with a typical atmosphere with a relative humidity of between 40% and 65%.

The agents of decay in building materials, moulds, decay fungi, mites have a biological origin. They are able to develop where the relative humidity is between 75% and 85%. (Timber in such air conditions would have a moisture content of between 17% and 20%). Above 85% relative humidity, however, these agents of disaster will develop much more quickly. It is therefore possible to say that damp occurs where building materials are in equilibrium with a relative humidity in excess of 85%. Such a statement must recognise that some materials may be damper than the supporting relative humidity of the air and be discharging water into the surrounding atmosphere. This may occur where there is water penetration taking place as a result of defects in the construction.

Rising Damp

Rising dampness is the rising of water within the vertical structure of the building. Claims that rising dampness exists are frequently exaggerated; it is present in only 10% of the buildings that have been examined where dampness was assumed to have been a problem.

Common causes of dampness in walls include:
- damp material being placed against the wall (ground levels being too high)
- plumbing leaks (especially central heating pipes bedded in floor screeds)
- defective gutters and downpipes
- poor window or door junctions with the wall (especially on south west elevations in exposed locations)
- overzealous watering of plants - leaks in roofs (particularly to bay windows )
the replacement of a timber floor with a concrete slab
Condensation

Condensation will occur when the water suspended in the air is deposited upon a surface whose temperature is below the dew point. It requires cool or cold surfaces, moist air and low air movement. Increasing the moisture in the air (bathing, boiling clothes or cooking) will increase the probability of moisture forming on surfaces. Mould growth will occur on organic matter (leather, natural clothing fabrics, dirty surfaces). This mould can be removed temporarily by the application of bleach. It will return unless the symptoms are treated. Condensation will be worse in the winter (when the outside air is cold) and less of a problem in the summer (when windows tend to be open more often).

Reduce condensation damage by:
- increasing air circulation in rooms - do not place furniture or beds against walls
- open room windows for at least an hour a day
- use extract fans in kitchens and bathrooms for at least an hour a day
- Control the moisture content of the air by closing bathroom and kitchen doors when bathing, showering or cooking.
Vent all clothes dryers to the outside, dry clothes with the windows open and the door shut.

The use of gas and paraffin heaters, both of which emit a lot of water, will make matters worse. As well as the health risk to the occupants these conditions may result in damage to the building.

Mould growth is common in buildings which have condensation problems. In order to avoid mould the relative humidity should be kept below 70%. The risk of mould growth and condensation can be reduced by improving thermal insulation, increasing heating, increasing ventilation and by reducing the moisture content of the air.

New buildings tend to be damp. A lot of water is used in construction and a new building may take two or three years to dry out. Expect the levels of condensation to decrease within the first 3 months or seek guidance as to the possibility of a defect.

Professor Malcolm Hollis is an experienced Chartered Surveyor and Building Pathologist whose work has taken him around the United Kingdom, as well as Europe, Asia and North America. He has reported on buildings from Beijing to Boston, Beirut to Berlin and Bolton to Belize. He has given expert evidence before most of the English Courts, as well as courts in Guernsey, Holland and Belgium and acts as a Single Joint Expert.

He is retained by Insurance Companies, Solicitors, Major industrialists, High Street retailers, and Local authorities and Government Departments.

Dampness refers to the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure. A high proportion of damp problems in buildings are caused by either condensation, rain penetration or rising damp, although other causes such as pipe leakage should not be overlooked. The issue of damp within traditional buildings is often misunderstood and solutions can be wrongly advised and become expensive and ultimately damage the building.

Understanding how a building is constructed is key when dealing with the repair and maintenance of traditional buildings especially in relation to damp. Unlike modern construction methods which rely on cavity walls and impervious barriers to protect from damp, a traditionally built structure relies on its ability to `breathe` allowing the evaporation of moisture to occur naturally from its surface

By changing the materials of the building, for example by replacing a lime render with a cement render, the special breathable qualities of a traditionally constructed building can be damaged, causing an increase in the build-up of moisture in the walls which inevitably leads to damp and decay.

Traditional properties should be managed so damp and its associated problems do not occur or are at least minimised to a tolerable level. The problem should be tackled by identifying and rectifying the causes and allowing time for the fabric to dry out.

Signs of Damp
There are many visual signs of damp to look out for, they can be accompanied by a musty smell. Low level staining or flaking paint along the inside face of ground floor walls could be a sign of built up moisture in walls caused by impervious finishes (cement is the most common example), high ground levels externally and a non-porous floor.
Cracking or movement of the structure at low level or in corners could indicate the decay of the sole plate causing the timber structure above to move.
Crumbling stone or brickwork is a sign of damp bricks/stone deterioration. This could be due to broken guttering or downpipes or unsuitable cement pointing that forces the water and salts through the softer masonry face. When these materials become damp they are susceptible to frost damage, this is where the face of the brick or stone is blown off due to the water expanded and freezing.
Black spot mould is caused by condensation and appears in poorly ventilated or unheated areas. It is usually a surface mould and will not cause damage to the building structure but can cause health issues.
Staining can be an indication of penetrating or rising damp. Penetrating damp, usually caused by rain, can be seen as patches on any location on the wall or ceiling. Whereas rising damp is the slow movement of moisture through the walls from the ground and is usually isolated to the ground floor wall and is recognisable by a `tide mark` . Staining on ceilings can indicate a leaking roof or a faulty water storage unit.
Holes in timber or fungal growths can indicate an infestation of wood-boring beetles or an outbreak of wet or dry rot. To solve the problem of beetle and fungal attack the source of damp must be stopped and the timbers allowed to dry out.

Common Causes of Damp
If there is damp in your property, it may be due to a variety of issues including failure of materials or inappropriate interventions. It is imperative that all possible reasons for the damp ingress are fully investigated as there could be more than one source. It should be noted that the damp area may be a distance from the cause or could be related to work carried out several months or even years beforehand as many problems can go unnoticed for some time.

Inappropriate materials and repairs
When repairs are carried out care should always be taken to use appropriate traditional building materials as modern alternatives are not always suitable. Their inappropriate use often has an adverse effect by inhibiting moisture movement and dispersal and often exacerbate the problem. Poor quality work can also create or contribute to damp problems. Water penetration through walls and chimneys can occur as a result of poor re-pointing, or through inadequately installed lead coverings at roof junctions, especially on exposed elevations. The situation is often made worse by the use of non-porous surface coatings such as cement render and masonry paint. Here, moisture can be absorbed through fine cracks in the coating, but cannot then evaporate back out through the waterproof surface and is held within the wall as a result. Aside from creating possible structural issues and inappropriate internal conditions, the large scale saturation of walls leads to reduced thermal performance and consequential effects on heating bills.

Inspect and repair roof coverings and flashings
Defective roof coverings and flashings are an obvious area for water to penetrate. Where regular inspection of roofs is not carried out a small crack, dislodged tile, slate or lead flashing can go undetected for some time. This creates excellent conditions for rot to flourish leading to progressive decay of structural timber and decorative finishes. It is therefore important to check that all coverings are sound and that flashings are in place.

Inspect render and pointing
Many traditional buildings were originally coated with a breathable lime render and have subsequently been re-rendered with cement, which is inflexible and impervious. Due to natural movement within the structure it can frequently crack allowing moisture to penetrate behind the render where it cannot evaporate back out and as a consequence moisture is held within the wall or released internally causing damp patches and flaking wall finishes. If a wall has an impermeable cement plaster both inside and out, the moisture will remain in the wall structure causing it to gradually decay. It may become necessary to remove this render and replace it with a lime based one that is both flexible and porous and will allow any excess moisture to evaporate. Lime mortar render and pointing over time may become eroded and allow water ingress into the masonry. It may have also been replaced by a cement render which may crack, allowing water to penetrate the masonry where it is unable to evaporate out. The replacement of badly eroded pointing and if possible the replacement of cement render with lime should help reduce damp. However it should be noted that removal of any cement mortar may significantly damage masonry and therefore should be considered carefully.

Repair and maintain rainwater goods
Many problems regarding water penetration can be traced back to inadequate drainage; correctly functioning rainwater goods is vital. Failure can lead to large volumes of water pouring directly onto walls, spreading outwards as it filters through the structure. This sort of failure is most visible during or just after rain, where soaked sections of wall can easily be spotted. The porous nature of traditional construction means that walls can quickly become saturated and transport the water some distance from the original source. Rainwater goods should be repaired if damaged and downpipes cleared of debris and vegetation, the fall of a gutter should also be directed away from the building.

Poor ventilation
The need for greater thermal comfort in our homes has lead to an increased number of insulation techniques. It is often the case that as well as installing sealed windows, airflow is restricted throughout the building by closing traditional ventilation grilles, this causes stagnant air to build up creating conditions suitable for damp and decay to set in. Blocked chimneys, enclosed floor voids, airspaces behind skirtings and panelling all contribute to this and should not be encouraged. Woodbeetle infestation, dry rot and wet rot outbreaks all occur due to increased moisture levels. It is essential that proper levels of ventilation are kept in order to ensure that excessive water moisture in the air is removed efficiently.

Condensation
Damp, resulting from condensation occurs when warm air inside a building condenses on a cooler surface. This is mainly caused through lack of ventilation or short intense heating cycles that do not allow the walls to fully warm up. Excessive condensation frequently results in severe mould growth and decay.

Solid Floors
Replacing a traditional breathable floor with concrete or other solid floors will exacerbate any damp problems. This type of flooring prevents moisture evaporating through the floor forcing the excess moisture into the walls. This stops the building acting and working as it was designed to do.

Cellars
Cellars are often the area within a building that suffers from excessive damp due to their positioning underground. Tanking a cellar is not recommended as this prevents water moisture from entering the room and instead retains the water in the walls which can cause severe problems in the long term. The most sympathetic way of dealing with damp in cellars is to use a generic cavity drain membrane system. This attaches a waterproof membrane to the walls of the cellar, preventing water from entering the room itself, and then drains the water effectively away. This allows the building to continue to breathe and is a reversible system.

Correct drainage and ground levels
High ground levels can lead to damp as water can penetrate directly into the wall when the ground level outside the house is allowed to build up until it is the same level or higher than the internal floor. The immediate external ground level should be lowered so it is below the internal floor to stop water penetrating. Impervious paths laid against or around the building can prevent water from evaporating and can channel the water into the walls. Creating a drainage channel on the outside of the building can help reduce the ground water level. Generally this can be achieved by digging a shallow channel around the building and laying land drains within, these drains will then transport the collected water to a more suitable location away from the external walls. This channel is then backfilled with gravel and is usually known as a French Drain.

Rising damp
Many causes of damp are mistakenly identified as rising damp, but most reports of damp can be attributed to one or more of the causes previously described. Rising damp is quite rare, it is caused by moisture rising up from the ground by capillary action. This could be due to excess water lying on the ground, cracked or leaking pipes or defective ground or surface drainage.

Problems can appear in floors and the base of walls, the visual evidence of rising damp is a band of discolouration or surface damage running around internal walls, usually about 500mm to 1m above ground level. The band described is caused by salts from the soil being drawn into the wall with the rising moisture and crystallising as the moisture evaporates into the room. This expansion of the salt can break the materials surface causing it to crumble. The nature of the salt can also cause more moisture to be drawn in from the air, adding to the problem.

Damp Proof Course
Before embarking on the insertion of a damp proof course (DPC), it is essential that all of the above have been investigated and addressed as far as possible and the building given time to dry out.

It is unlikely that your traditionally constructed building will require a damp proof course, membrane or injection. Furthermore it is also probable that as these will have to be inserted after the building has been constructed they will not work to their expected levels as there is no guarantee that they will permeate through the entire wall. Any such insertion can actually make the problem worse.

Injecting a chemical DPC seldom works as water will be concentrated within the base of the wall below the level of the DPC, causing saturation and preventing it from drying out. This will then freeze, expand and thaw over the winter, damaging the stability of the wall.

The thickness and solid construction of walls in traditional buildings make it very difficult for a contractor to guarantee that a DPC will be effective. To compensate many contractors remove lime plaster and finish the injected walls with a modern waterproof plaster, this merely disguises the continuing damp problem and after several months, it is common to see the damp reappear above the height of the new waterproof render.

The irregular nature of flint walls, walls constructed in random rubble or those which have a rubble core, mean it is difficult to insert any form of DPC as it is not possible to form a continuous barrier. Any gaps will allow moisture through and the DPC will fail. Drilling into the wall and injecting a chemical DPC will damage the wall and can also damage the structural integrity as well as being visually detrimental to the character of a building. It is not advised to use this process on a cob wall or the plinth below a cob wall as this type of material relies on a certain level of moisture for its structural integrity.

Timber framed structures are less likely to suffer from rising damp than masonry structures. However the timber sole plate (the bottom timber) may suffer from damp which has risen up through the masonry below. If the sole plate becomes saturated the infill panels around it may also suffer from damp.

Dry Lining
Where none of the previously mentioned actions have been successful in preventing damp it may be possible to consider the utilisation of dry lining. Dry lining is the application of plasterboard to surfaces such as timber, masonry or metal. This can be carried out using stud framing clad with polythene sheet and plaster board, however the cavity created must be properly ventilated or there is a real danger of outbreaks of wet or dry rot occurring.

It should be noted that the application of dry lining only masks the signs of damp and is not a solution to fix the cause.

Summary: Causes of Damp
Leaking gutters and overflowing downpipes can quickly saturate a wall. Look for staining and damp patches, especially after rain to identify where the problem lies. If there is a parapet gutter on the property, check for staining around the overflow.
Failure of below ground drainage can gradually saturate the ground beneath a property.
Once rain water is taken off the roof, it should be piped away from the building, either to the main drain or to a soak away placed well clear of the building. Check that the gutters and downpipes are of sufficient size for the roof. Check for blockages where the downpipe enters the ground, especially if it leads into an open gully, and that the subsequent drain is clear.
Ensure that ground levels outside have not risen, compromising the original design intent and causing dampness in the walls and any adjacent timbers.
Maintaining a steady level of heating inside a building (15-20 degrees C) allows the walls to warm up sufficiently to prevent condensation on hidden surfaces. If the building has been uninhabited, or unheated, for a period more moisture will be held in the fabric and this needs some warmth to drive it off.
Chimneys and flues should not be blocked off if fires are not in use. A ventilated chimney cap should be used and the hearth left open to allow a through flow of air.
Ground level vent grilles should be clear of all ground level finishes and internally free of any applied insulation. Do not block or remove vents. The area below floor joists should also be kept clear and the ground level outside set significantly below this level.
Check the pointing on skews, copes, chimneys and other upper level masonry. These exposed elements are vulnerable to water penetration.
A traditionally laid roof would not have had felt or roofing papers as part of the original construction. The inclusion of this material in later repair or replacement work may cause damp and could require the addition of concealed vents at eaves, ridge or gable ends in order to keep the levels of moisture in the roof space under control.
Inappropriate materials used as external or internal finishes restrict the breathability of the building. Traditional external finishes such as lime render, distemper or limewash allow moisture to pass through the structure unlike modern equivalents, such as damp resistant paint which will tend to hold moisture in the building.
Many modern internal paints are not sufficiently permeable to allow the dispersal of moisture from a plastered wall and their use should be treated with caution. Dry lining or framing out with plasterboard should only be considered as a last resort, as this could create areas with restricted airflows.
Concrete floors should be replaced with a breathable floor where possible. Suspended timber floors, bricks and pammets (floor tiles) were traditionally used and should be looked to as replacements however, modern products such as limecrete laid without a damp proof membrane may also be an acceptable replacement. If the whole floor cannot be replaced, then making a breathable channel around the edge of the room, to allow the base of the wall to breath and keep dry, will help. The channel should be filled with a breathable product such as limecrete or covered with a narrow grate.

Conclusion
Damp and decay in traditional buildings can be a complex problem for this reason mistakes, although made with the best intentions, can easily be made. The source of the damp needs to be identified clearly and the affected areas allowed to thoroughly dry out. If the source is not treated or incorrectly diagnosed, the original problem will continue to develop and unnecessary or incorrect remedial actions can cause added problems.

Treatments suggested for modern construction may not be appropriate for traditionally constructed buildings and it is always advisable to contact an experienced professional when dealing with this issue.

For advice on how to treat damp in a traditional building please contact UK DAMP & DECAY CONTROL on 0800 028 1903

Damp can damage much more than a buildings appearance. It may lead to the deterioration of plaster and masonry, promote timber decay and create unhealthy conditions for occupants. Unfortunately, inappropriate treatments for damp commonly cause greater harm to old buildings than centuries of degradation. Over-reliance on electrical moisture meters frequently leads to unnecessary expense and damage through the retrospective installation in walls of horizontal damp proof barriers (damp proof courses or DPCs). Equally the harm done by modern solutions that aim to seal old walls rather than improve their ability to breathe is underestimated. An appreciation of how the basic construction of old buildings differs from that of new ones will help you avoid such misguided remedies.

Breathability

Old buildings must be allowed to breathe. Whereas modern buildings rely on keeping water out with a system of barriers, buildings that pre-date the mid-19th century are usually constructed of absorbent materials that allow any moisture that enters to evaporate back out.

Because most old buildings were constructed with solid walls without DPCs and originally had no roofing felt, rain or below ground moisture could both enter. This did not, however, mean dampness was inevitable. Before central heating was commonplace, heat from open fires drew in large quantities of air through loosely fitting windows and doors. This high rate of ventilation would have quickly evaporated moisture from permeable internal surfaces while the wind dried out any damp roof timbers or permeable external wall surfaces. An equilibrium was therefore established whereby the moisture being absorbed was equal to that evaporating. When upgrading an old building, you must maintain this equilibrium for the building to work as intended and remain dry.

Causes of Dampness

The main risks arise from:

Air moisture condensation: Energy-saving measures that reduce ventilation in old buildings such as double-glazing increase relative humidity. Humidity is also raised by modern lifestyles that generate large quantities of water vapour, from bathing, cooking and washing. Condensation will occur on any surface below the dew point (i.e. temperature at which saturated air releases surplus moisture vapour). Interstitial condensation within the pores of materials reduces thermal insulation and further increases the risk of condensation.

Penetrating damp: Roofs, chimneys, parapets and other exposed parts of a building are most susceptible to rain penetration, especially where access for maintenance is difficult. Junctions in roofs are potential trouble spots, with water exploiting defective lead flashings, mortar fillets, ridges or hips. Concentrated and prolonged wetting of walls and external joinery arises from poorly maintained rainwater fittings, and leaks from parapet and valley gutters can cause significant damage to structural roof timbers. Hairline cracks in pointing and render invariably admit moisture where cement mortar has been used for repair, rather than lime.

Internal spillage: This results from overflowing baths or showers, burst pipes, the gradual breakdown of pipe joints, leaks from washing machines or dishwashers and accidental damage.

Below ground damp: This may be rising damp, which is neither as widespread as commonly thought nor a total myth, as sometimes now claimed. Floors become damp where the evaporation of moisture from below is inhibited by vinyl sheet, rubber-backed carpets or other impervious coverings. New concrete floors or impervious coverings also drive excess moisture into the bases of nearby walls (including chimney stacks), where it rises by capillary action. DPCs were not compulsory in walls prior to 1875 but this is only likely to become a problem where breathability is compromised. In addition to rising damp, below ground moisture can result in problems where ground levels around your building rise unduly.

Tips for Diagnosing Damp

Roofs and Rainwater Fittings

Inspect your roof during wet and windy weather to decide if a damp ceiling patch is due to roof leakage and/or condensation. Debris on the ground (broken slates, tiles and so on) or daylight seen inside lofts indicate possible roof problems.

Defective rainwater fittings may be most obvious during heavy rain, but stains on walls and plant growth provide further clues. Don't forget to check gulleys at ground level.

Condensation is diagnosed from diffuse areas of damp, beads of water droplets on hard shiny surfaces and mould growth on internal finishes. It is intermittent, like penetrating damp, but unrelated to wet weather.

Penetrating damp typically shows up as well-defined patches after heavy rain on south and west-facing walls. Anticipate moisture ingress through hairline cracks in unsuitable hard, modern cement pointing or rendering.

Below ground moisture causing rising damp can extend up to 900mm above floor level, sometimes with a classic tidemark on finishes. Salts appear as white deposits but mould growth is rare.

Plumbing

Unusually high water bills (if metered) or a constantly refilling tank may suggest leakage.

DPCs and Alternative Systems Compared

Retrospective DPCs:

Physical:

Inserted by cutting in or during rebuilding.
Can cure rising damp but this drastic method is usually inappropriate.
Drawbacks: possible major structural problems; potential damage to historic finishes internally;
Unsuitable for randomly coursed walls; access difficulties; deterioration sometimes of masonry below DPC where moisture is concentrated.

Chemical:

Walls impregnated with chemical solution through holes at bottom to create waterproof barrier.
Widely used today but not always appropriate for old buildings.
Drawbacks: drilling holes inadvisable in flint, granite, etc; hard to form proper barrier in rubble walls with voids; holes unsightly; deterioration sometimes of masonry below DPC where moisture concentrated.
Cost: typically £195/m (including replastering).

Ceramic tubes:

Holes drilled to receive porous siphons approximately 50mm in diameter that absorb damp and evaporate it from each tube.
Sound in theory but problems may occur in practice.
Drawbacks: salt accumulation in tubes may increase moisture; air-flow sometimes inadequate; tubes commonly set in hard cement mortar; unsightly.
Cost: typically £125/m.

Electro-osmosis:

Electrical potential aimed at reducing capillary rise using electrodes bedded in wall.
Cheap but dearth of evidence that electro-osmosis is effective and system rarely used today.
Drawbacks: adjustment of current needed to match variations in damp along a wall usually impractical.

Other

An Austrian product presently under trial in the UK claims to inhibit the passage of water up a wall by inducing a local magnetic field. Achieved non-invasively with unit plugged into mains, typically in loft.

Likely cost: £3,000/unit (one unit covers an average-sized house).

Investigating Damp

Scientific analysis can be an essential aid for accurately diagnosing a damp problem but the importance of your sight, feel and smell should not be undervalued. Tests include the use of electrical resistance and capacitance meters, on-site moisture testers, hygrometers and salt analysis. Bear in mind though, that care must be taken when interpreting results. A frequent mistake is to diagnose rising damp purely on the basis of high electrical moisture meter readings. Elevated readings may indicate the presence of salts from past dampness or, if there are no salts, an on-going condensation or possible penetrating damp problem. Continued monitoring is often needed to establish the true cause of a damp problem.

Surveyors have a legal duty to follow a trail of suspicion. Regrettably, many still simply note the occurrence of high meter readings and pass on all responsibility for further investigation to remedial treatment contractors. These contractors have a vested commercial interest, encouraging over-specification. Should a mortgage company insist on work you believe is misguided, challenge this and consider obtaining a written report from an independent surveyor or architect.

Remedial Measures

Effective remedial measures depend on accurate diagnosis, but applying staged remedies can also be part of understanding the cause of a damp problem. Before deciding on more extensive work, the first remedy may involve nothing more than basic maintenance such as clearing a blocked rainwater gulley. Remedies will either cure dampness by addressing the cause (for example, improving drainage) or will manage it by treating the symptoms (changing washing or cooking habits, for instance).

Be sceptical of written guarantees, which are often loaded with get-out clauses and may have no insurance backing. The right approach from your contractor coupled with good workmanship is your best guarantee.

Controlling Air Moisture Condensation

Condensation can be treated by reducing air humidity or keeping surfaces above dew point temperature. Humidity is reduced by cutting the amount of moisture available or increasing ventilation by opening windows, etc. Tumble dryers should be vented to the outside if not of the condenser type, and clothes drying indoors is best avoided.

Temperatures are maintained above dew point with suitable heating. The permanent use of dehumidifiers is a poor substitute for efficient heating and adequate ventilation. Condensation in chimney flues can be eliminated with proper linings. Redundant flues that have been sealed should be fitted with ventilation grilles or re-opened. Lofts should be well insulated and ventilated but make sure insulation does not restrict ventilation at the eaves.

Controlling Penetrating Damp

Reinstate dislodged and missing slates and tiles before damage occurs to roof timbers or plaster ceilings. SPAB, the Society for the Protection of Ancient Buildings, recommend that renovators avoid spray-on roof foams for the underside of roofs, or external bitumen coatings although other experts disagree. SPABs view is that they prevent proper inspection, hinder the re-use of slates or tiles and, by reducing ventilation, increase the risk of decay. Brush moss off roofs since it can block gutters and retain moisture, which may damage certain roof coverings in frosty weather. Also, clear gutters and rainwater pipes regularly, particularly if your building is surrounded by trees or perched on by pigeons. Parapet and valley gutters need to be cleared of snow to prevent melt-water rising above them and causing damp internally.

Re-point deeply eroded mortar joints in walls. Whilst cement is fine for modern buildings, it is important to use a lime:sand mix (preferably without cement) for most buildings pre-dating about 1900. Localised re-pointing is generally all that is required. Daub, lime mortar or oakum (ships caulking) are useful for closing gaps that may develop around the edges of panel infillings in timber-framed buildings. Where rain penetrates an exposed south- or west-facing wall, limewash, lime render and slate or tile hanging are traditional solutions although these cannot be employed without changing the external appearance of the wall. Sometimes installation of a ventilated dry lining system internally is appropriate. The use of colourless water-repellent treatments or plastic-based paints on old masonry is strongly inadvisable.

Controlling Below Ground Damp The best solution to rising damp may well be to take measures that help your building breathe. Replacing hard cement render or pointing using a more suitable lime-based mortar often improves a damp wall and enables rising damp to dry out. Conversely, the application of waterproof renders and bituminous coatings tends to create or exacerbate damp problems. Where a floor has a modern damp-proof membrane (horizontal barrier or DPM) that is displacing moisture to the bottoms of walls, it may be sensible to replace this completely with a breathable construction or to at least provide a breathing zone for evaporation around the perimeter of the room. When underfloor heating is being installed, there are many situations where DPM-insertion can be avoided by employing materials such as lime concrete and expanded clay insulation.

Reducing or removing the source of moisture may also help alleviate rising damp. French drains can be an effective and relatively inexpensive answer but it is preferable not to site them directly against walls and rodding points must be provided. Otherwise, blockages can effectively convert them into a sump and increase dampness. Consider also the structural and archaeological implications.

Although retrofit DPCs can sometimes be appropriate, with an old building always consider first whether rising damp is actually too minor to matter and, if it is significant, whether more sympathetic ways exist of dealing with it. Where any timber is at risk of decay, for example, you might be able to simply isolate it. Similarly, the eradication of any contributing moisture from other sources such as rainsplash off closely abutting patios could obviate the need for more extensive remedial treatment.

Damp can be particularly troublesome in cellars but increased ventilation (including opening up redundant flues), re-pointing and lowering the water table locally can be effective. Failing this, it may be worth considering a dry lining system. Tanking (applying waterproof linings to walls and floors) is not recommended in old buildings.

Internal Finishes

To minimise the risk of future problems, lime plaster should usually be used for any replastering rather than the anti-sulphate or renovating plasters favoured by many treatment companies. Decoration with paints such as limewash and soft distemper, where possible, will maximise breathability. Old items of joinery removed during work should be carefully repaired and reinstated, not automatically replaced.

For further information on how to deal with dampness in the most environmentally friendly way please contact UK Damp & Decay Control on 0800 028 1903

How to prevent condensation dampness in rented accommodation and whose fault is it?

During the winter months from November to March ,often known as the condensation season ,many tenants report dampness to Landlords or agent which turns out in fact to be condensation. This happens when warm air comes into contact with a cold surface and moisture in the air turns into droplets of water.

If your home has condensation, you may find a black mould growing on the inside face of external walls, in the corners of rooms, on window frames and behind wardrobes and other furniture.

Condensation is probably one the main reasons why a full deposit is not returned to a tenant at the end of the tenancy period. This is because it is the responsibility of the tenant to take all reasonable steps to adequately ventilate as well as heat the house.

If any appreciable condensation develops, the tenant is normally expected to wipe down and clean the affected surfaces from time to time to prevent the growth of mould and any other associated damage that can caused to the window frames, floor, walls and ceilings.

You can reduce the risk of condensation dampness by doing the following:

1. Open a window when you are cooking and keep lids on saucepans.
2. Leave the bathroom window open after a bath or shower to clear steam.
3. Keep the bathroom door shut when you are having a bath or shower.
4. Do not block air vents of air bricks.
5. Open windows in all your rooms for a few minutes each day to let some fresh air circulate.
6. Leave some background heating on all day in cold weather.
7. Do not cover radiators or storage heaters with damp clothing.

Further Facts About Condensation (extracted from BS 5250 (1975)

Condensation dampness has become of the most common causes of dampness within buildings. A Report of the Building Research Establishment estimates that one and a half million homes in the UK are badly affected by condensation.

Condensation occurs when moist air is cooled that it no longer has the capacity to hold water in vapour form. Typically this can be seen to occur at cold surfaces such as window panes as mist or cold water pipes as droplets of water.

A brief summary of the terminology: The amount of water vapour (or moisture) which can be held by air, (the humidity) depends on the air temperature. The warmer the air the more water (or moisture) it can hold. Cold air at 0 C is unable to hold any moisture. The temperature at which the air cannot hold any more moisture is described as the dew point. The dew point is the point at which condensation occurs (water or moisture that was in the air has condensed to liquid on a surface that was or at below dew point). As the air temperature increases the dew point temperature will be determined by the amount of moisture in the air.

The relative humidity is the amount of moisture in the air relative to how much moisture the air can hold at that temperature. So, at any given temperature, increasing the moisture in the air will increase the dew point temperature. As the humidity increases the relative humidity increases and the risk increases that relative humidity will reach 100%. Dew point temperature occurs when relative humidity reaches 100 % (and vice versa). The inter-related nature of temperature humidity relative humidity and dew point can be seen from examination of a ?psychrometric chart?.

The amount of moisture within the air in a building varies continuously. Certain lifestyle activities generate moisture and these will increase the amount of moisture in the air. Examples of these are cooking, drying clothes, bathing and even breathing. Such activities need not always produce a condensation problem. The moisture can be dispersed out through an open window or extractor fan, or it may condense on a nearby window pane and be easily wiped away.

It is to where the moist air goes and the temperature of the places it goes that will determine whether a condensation problem is produced.

When the air is heated throughout the property the air is capable of holding moisture as vapour to the extent that can be seen from the psychrometric chart. Most properties are not heated to the same temperature all the way through all the time. For example, it is not unusual to hear living room to a higher temperature than a bedroom. This means that the air in the living room can hold more water vapour than the air in the bedroom.

Typically moisture generated in a kitchen and bathroom might be allowed to escape through the whole house. This might typically result in some local visible condensation in the kitchen and bathroom, no signs of a problem in the living room but some damp patches and mould growth on the external wall of a back bedroom. Unless a study is made of the varying temperatures and humidities within a property it can be difficult to predict whether the property is likely to be affected by a condensation problem.

The factors that cause the problem, vary all the time. It is certainly true that the tendency in recent years to draught proof houses and insulate to conserve energy has reduced the amount of air (and therefore airborne moisture) escaping to the outside. This has had the effect of increasing the overall humidity levels.

The reduction in ventilation and increase in humidity can also encourage the growth of mould fungi. These are often the first visible sign that a problem is present. Relative humidity does not require to be as high as 100 % for mould growth to occur. Mould growth can occur when the relative humidity is around 70 %. This often happens in a part of the property that is less well heated and where the ventilation is reduced. For example, a cupboard or wardrobe on the external wall of a back bedroom.

Although there may not be a visible wetness due to condensation. The temperature in this location may not be as consistently high as that throughout the house, and as a result the relative humidity can be locally increased to above 70 % at certain times of the day. That can be sufficient to support mould growth.

It is fairly easy to spot a condensation problem when there is visible evidence of moisture on a window or cold water pipe. Fungal growth (usually moulds) can occur before the problem is visible in that way.

The conditions, which produce condensation and related problems of mould growth depend also to greater extent on the temperature and humidity of the air outside the building. It is not uncommon therefore for a house to be affected by condensation or mould growth only at certain times of the year. In such cases it would be unlikely that altering the ventilation alone would be sufficient to reduce or eliminate the problem.

A successful strategy for combating condensation will usually depend on a number of factors. Since these will be most likely to produce a successful result.

Four Essential Elements Need To Be Considered

(1) Reduce humidity
(2) Improve air circulation
(3) Improve insulation
(4) Improve overall background heating

There are a number of ways of dealing with each factor and the most appropriate will depend on the individual property. It is generally true that more than one factor will require modification.

It makes good sense to start with the simplest and least expensive option which typically might be the installation of extractor fans in kitchen and bathroom, the places where most of the airborne moisture is generated.

A monitoring period should be allowed after each course of action is taken so that the contribution of each factor can be evaluated.

For more information or advice about condensation dampness please call UK Damp & Decay Control on 0800 028 1903

From time to time we are sent information about the latest wonder cure for rising damp and the article below is for a product that will apparently banish rising damp for up to 80 years and is taken from the Aquapol website :-

Rising damp, a worldwide phenomenon, is a major cause of decay to masonry materials such as stone, brick and mortar. Even when mild it can cause unsightly crumbling of exterior masonry and staining of internal finishes. When severe it is a potential health hazard to building occupants due to high humidity levels and the growth of moulds. When coupled with high salt concentrations, severe damp can cause extensive fretting and crumbling of the lower parts of walls, requiring difficult and expensive repairs.

What is Rising Damp?

Rising damp occurs where a damp proof course (DPC), a moisture barrier, is broken or missing and so water molecules creep up the capillary system within the brick and stonework of the building. The moisture rises in the wall to the limit of capillary action or until it evaporates from the wall surface. This is called the `Evaporation Zone`. When the soils contain appreciable amounts of soluble salts, these are drawn (in solution) into the network of pores in the wall. These salts however cannot evaporate with the moisture. Consequently, the salts build up just beneath the wall or plaster surface where they grow as minute crystals. The crystal growth and as a result their physical forces are sufficient to rupture the masonry, causing fretting and crumbling, even of very strong materials. This combination of salts and rising damp causes substantial damage to the building stock. It is of particular concern in older buildings, many of which were constructed before the problem was well understood.

A new technology that ends rising damp problems
Mainly chemical treatments and other `cures` are broadly advertised as solutions for damp problems in buildings. They have however a limited application and the biological effects are questionable. But there is good news indeed. A new technology and in actual fact a revolutionary solution to rising damp is making its way through the European continent, despite the fact that many do not fully understand how it really works. But actual measurable success and high sales figures speak for the system.

Aquapol is the brainchild of Austrian engineer Wilhelm Mohorn who received the highest award of his country for successful research and invention, the Kaplan Medal in 1995. The name Aquapol comes from `aqua`, the Latin word for water, and `pol`, shortened from polarisation. Aquapol reverses the polarity of the water molecules in the capillary system of the walls and causes the damp to flow downwards, leading, over a period of month or years, to dehydration. The patented Aquapol system does not contain any parts that can be worn and it has the huge advantage that it does not get in touch with masonry itself, avoiding building works. It demoistens most economically and maintains the dried condition for 80 to 100 years in the most environmentally friendly manner.

Now 36,000 Installations throughout Europe
Aquapol has been installed over 36,000 times in properties throughout Europe since 1985. Some of the more illustrious buildings are the Hungarian Parliament in Budapest; the Joseph Haydn Museum in Austria; the Greek Oriental Church in Vienna, the Schlatt Castle in Germany and other important buildings and in private homes and properties in the UK.

The Aquapol system does not need any electricity or batteries, thus no cables are necessary. The energy supply, which is needed to create a polarisation of the water molecules, is based on long lost discoveries made by the Croatian scientific genius, Nikola Tesla (1856-1943) about the properties of water and naturally occurring energy fields within the earth and air. Tesla was an inventor, physicist, mechanical engineer, and electrical engineer of profound genius. He is often regarded as one of the greatest scientists in the history of technology. In addition, Tesla is recognized among the most innovative engineers of the late 19th century and early 20th century. His patents and theoretical work form the basis of modern alternating current electric power (AC) systems, including the AC motor. After his demonstration of wireless communication in 1893 and after being the victor in the `War of Currents`, he was widely respected as America?s greatest electrical engineer.

Based on Tesla?s first discoveries of the so-called `Space Energy`, which according to him exists everywhere, Austrian engineer Wilhelm Mohorn developed the very special Aquapol device. It is composed of a Receiver Unit, a Polarisation Unit and a Transmitter Unit. By transforming the received space energy into a stable clockwise rotating energy form of a specific wavelength and shape (polarisation effect), the water molecule is now directed into the ground where it came from.

Positive biological effects for a better living
Scientific studies carried out by Professor K. A. Lotz, a leading German scientist in the area of building biology, proved astonishing positive effects of the Aquapol system. Interviews with people who had an Aquapol device installation in their room, revealed the following biological effects: better sleep and well being a better room climate even in geologically disturbed houses. A natural earth field is influenced in its intensity by a watercourse or other geological factors. A watercourse acts like a lens on the earth field and amplifies this in its intensity. The Aquapol system is capable of suppressing this intensity and creates a proportionate (homogeneous), natural and biologically positive radius of action.

Ask for a radiation check in your sleeping area
The service that Aquapol offers includes a free damp analysis and the preparation of a comprehensive report and damp eradication plan with details of work and costs. The dehydration is then achieved by the installation of a specific Aquapol device, which must be located in exactly the right spot according to a series of different measurements and salt tests from samples taken from different areas of the walls in the building.

Aquapol receives the Grand Prix Award for Monument Conservation in Poland 2006
`The fact that the Polish Jury for Monument Conservation on the 11th Trade Fair (Conservation 2006) has awarded our technology with the Grand Prix for their clean and eco friendly drying of rising damp proves once again that the Aquapol system, especially for listed buildings, is the best suitable way. ` Explained engineer Wilhelm Mohorn, the Austrian inventor of the Aquapol Method. Mohorn alludes on the demand; local conservationists have on a system that works without any intrusions into walls and without any electricity.

The Jury of the Trade Fair in Torun/Poland based their decision for Aquapol on the reason that the method approaches both the problem of rising damp as an integral method and it has been proven to be extremely efficient.

Among experts the renowned Grand Prix is awarded annually to chosen conservation organisations. The trade location Torun speaks for itself, the UNESCO has listed the Gothic old town centre as World Cultural Heritage.
`The AQUAPOL system is the solution for the preservation of British heritage, historic buildings and old houses in the United Kingdom, which suffer from rising damp problems, ` said Volker Kubillus, Managing Director of AQUAPOL UK Ltd.

No electricity, no batteries, no chemicals, no drilling or cutting into walls, zero maintenance, 3 year money back guarantee, 20 years warranty on the Aquapol device. There are other similar systems being touted such as ProSYSTEM- Capillary Rising Damp Sanation System- which is also utilises electromagnetic forces and also Home-Dry which is a German based firm offering another wonder cure for rising damp. It is very doubtful that any of these damp-proofing systems work and if you need independent, impartial advice about the diagnosis and control of rising damp contact UK DAMP & DECAY CONTROL on 0800 028 1903

Damp in UK houses is a relatively common occurrence. Essentially there are three forms of damp:

? penetrating damp ? from external rain sources;
? rising damp ? moisture drawn up from ground sources
? condensation.

Of these, condensation has the greatest potential for misdiagnosis, and subsequent inappropriate and ineffective remedial work. More significantly, condensation dampness has the greatest potential impact on human health, so an understanding of it is vital.

What is condensation?

All air contains varying amounts of water vapour. The warmer the air temperature, the greater the amount of water vapour the air can hold. Condensation occurs because the moisture in the air can no longer be held as a vapour and returns to its liquid form. This occurs when warm moist air comes into contact with either cooler air, or more importantly, a cooler surface. ?Dew point? describes the temperature when air containing a given quantity of moisture vapour will condense onto that surface.

While condensation is obvious when it occurs on impermeable surfaces ? most commonly window glass, cold-water pipes and ceramic tiles, etc ? it will, however, form on any surface which is at or lower than dew point. The evidence of it occurring on more absorbent surfaces, such as paint, plaster or wallpaper, etc, becomes obvious when disruption, damage, and particularly mould growth occurs on that surface.

Mould growth is a typical sign of chronic condensation and occurs as spores, present in the air all the time; they find water (condensate) and organic material (dirt and grease) that support their life cycle. Mould is a significant health risk to asthmatics, those with other respiratory conditions, the very young and the elderly. The high humidity levels associated with condensation also enables house dust mites to flourish. The droppings from these microscopic creatures and mould spores can cause allergic reactions which are also linked to the onset of asthma.

So for those concerned with condensation in buildings, the quantity of water vapour in the air and the temperature of surfaces within buildings are two key issues.

Sources of moisture

Water vapour in the air is generated by a range of human-related activities. A typical daily moisture level produced in a three-bedroomed family house is approximately 10kg. This large quantity of moisture can come from a range of sources, for example:

Activity Kg moisture A family asleep 1.5-2.0 A family?s typical daytime activities 2.5-3.5 Cooking 2.0-3.5 Washing and bathing 1.0-1.5 Washing clothes 0.4-0.6 Drying clothes 3.0-5.0 Animals, such as dogs, also produce large quantities of moisture into the atmosphere.

Heating appliances can also produce significant quantities of moisture. In the case of solid and gas-fired heat sources, most of this moisture is removed via flues. However some appliances, such as portable gas bottle heaters, produce large quantities of moisture which are not removed from the habitable space, while electrical radiant fires produce no moisture at all.

Increasing numbers of appliances that produce significant quantities of moisture are being used in dwellings. By far the worst culprits are tumble dryers ? particularly if not appropriately vented - though dishwashers and washing machines also both produce moisture.

In addition to these sources, any incidents of rising damp or damp penetration will contribute further to the quantity of moisture in the house.

Where does condensation occur?
It should be obvious that any cool surfaces within a dwelling are at risk of condensation; single glazing, cold-water pipes and WC cisterns are obvious examples. Areas in the house that produce large quantities of moisture, such as the kitchen and the bathroom, are frequently subject to condensation. Both are spaces where building regulations insist on the provision of ventilation, partly in order to reduce the air humidity.

However condensation does not always occur where the source of moisture is created. For example, though substantial amounts of moisture vapour can be created in kitchens, the additional heat produced in this space will raise the surface temperature of the structure and elements, thus reducing the likelihood of condensation occurring directly. Additionally, moisture vapour exerts extra pressure on the air. This makes the moisture-laden air travel further and thus condensation can occur a long way from the source of moisture production, once that air encounters a surface at or lower than dew point.

This effect can be quite insidious. For example, in the UK it is typical to lay thermal insulation at ceiling level in the upper storey of houses. Where warm moisture-laden air rises through the dwelling, it will diffuse slowly through the ceiling and insulation. If the insulation is doing its job, then there will be a significant reduction in the temperature of the air on the cool side of the insulation within the roof void; i.e. dew point will rapidly be attained. Condensation within insulated roof voids is very common if there is insufficient ventilation of the loft to evaporate it. Building regulations again insist on high levels of ventilation in roof voids. A build-up of moisture on the roof timbers enables the lifecycle of various fungi and insects which will use the timber as a food source with potentially calamitous and expensive results.

In poorly insulated houses where the surface temperatures of the principal structure (i.e. external walls, ground floors and upper-storey ceilings) are low, then condensation can occur at any or all of these points. For example, in traditional solid masonry construction, the insulation qualities of these walls are low. Consequently they will lose heat quite quickly when compared with modern well-insulated cavity wall construction, where surface temperatures will be relatively high. Certainly heat produced within such a structure will be retained far longer than in the former example, again reducing the risk of condensation.

Detached, semi-detached houses and extensions, where walls are more exposed to the cold and cooling winds, if not appropriately insulated, will be colder than other surfaces in buildings.

Even where houses are generally well insulated, there can be discontinuity in the insulation. These ?cold bridges?, typically found around window and door openings and at the edges of insulated structures, such as ground floors and upper-storey ceilings, cause a localised drop in temperature and hence the potential for condensation. Where this occurs, the associated dampness is frequently misdiagnosed as either penetrating or rising damp.

?Increasing numbers of appliances that produce significant quantities of moisture are being used in dwellings. By far the worst culprits are tumble driers ? particularly if not appropriately vented ? though dishwashers and washing machines also produce moisture?

Areas where there is restricted air circulation, for example behind cupboards and wardrobes (particularly those on external walls), are also more likely to suffer condensation.

Finally, elements of a building that are subject to rising or penetrating damp will be cooler. This is because this moisture fills the pores of the structure, significantly reducing their thermal insulation qualities. If these walls are cooler, then they too will be more likely to suffer from condensation, in addition to the aforementioned defects. This often leads to confusion in diagnosis and inappropriate and ineffective remedies.

Is condensation an old problem?
Yes. However modern lifestyles and approaches to construction have exacerbated both the risk and the effect of condensation. Almost all pre-1960?s houses had chimneys and these provided substantial ventilation by drawing air through the dwelling which in itself helped to remove moisture vapour and evaporate any condensate. The fact that the cool air drawn into the building by burning solid fuels was heated, balanced the potential risk of this process causing condensation. While structures were far more permeable to uncontrolled ventilation, i.e. through ill-fitting/poorly sealed windows, this cool air infiltration was again balanced by the more continuous heating regime adopted in the past.

In contrast, nowadays heating is far more intermittent through the day; buildings have become increasingly sealed to avoid uncontrolled draughts. ? Indeed the current and future building regulations are increasingly concerned with creating tight, sealed homes with mechanical ventilation and heat recovery in order to improve energy efficiency. Additionally expectations of high levels of thermal comfort and a myriad of moisture-producing domestic appliances exacerbate the potential for condensation.

How can I spot condensation?
Practically, diagnosis of condensation cannot be just visual. Measurement of temperature, humidity, ventilation, and consideration of insulation qualities and heating patterns need to be undertaken.

Typical signs of condensation to look out for are:
? Mould growth on wall surfaces, around external wall openings and in areas of low air circulation or poor ventilation;
? Misty wall surfaces;
? Water staining and streaking running down walls, particularly in bathrooms and kitchens;
? Patches of damp with no obvious edges.

Are there any solutions?
A combination of factors will help reduce the incidence and effect of condensation:
? Reducing and controlling the production of moisture;
? Increasing targeted and controlled ventilation;
? Improving thermal insulation;
? Improved management of the space heating.

EXTENSIVE EXPOSURE
Dry rot and death watch beetle are often heralded as the most destructive pests in our histonc buildings, but neither causes so much damage as the misguided determination to pursue all evidence of decay ruthlessly to its furthest extent. Fears of extensive concealed damage frequently result in over-zealous exposure work and in some instances the expense of reinstatement can ultimately be so extortionate that finishes may never be replaced. Major recommendations for minor problems not only divert limited resources away from more important conservation repairs, but the combination of investigation and treatment is commonly more destructive than the problem they are supposed to eradicate.

Opinions range from a belief that all timber buried into external walls is bound to be decayed, to convictions that all old timber must be exposed and treated simply because it never has been. Extraordinarily destructive measures are taken to expose timber in order to treat it as a precaution against problems which have never occurred. Conversely, principal structural elements in the vicinity of serious decay may inadvertently not be investigated because the presence of concealed timber is not anticipated.

So how can all the risks be assessed without wholesale stripping out? There is no standard solution, but a pool of techniques is available and with experience these techniques can be adapted to investigate most situations.

CONCEALED CAVITIES
It may seem insulting to suggest lifting floor boards or removing access panels, but unfortunately I so frequently see such totally inappropriate exposure work that the opportunity clearly needs to be recommended. All too often a hole is smashed through a damp stained ceiling to avoid awkward, dirty roof space access or where a floorboard could have been lifted above. To lift individual boards rather than to break up the floor is often a skilled task and contractors employed for investigation works should be selected with the same sensitivity as for conservation repairs. It is important to recognise where metal tongued or secret nailed boards cannot be lifted and re-laid without damage, and where alternative investigation techniques may be less destructive.

Fibre-optic borescopes provide an invaluable means of inspecting concealed voids. Several versions are available for building surveys providing a range of light power, portability and flexibility. In principal, light from a powerful bulb is transmitted via a bundle of optic fibres to a scope with precision optical lenses.The principal choices of equipment are between rigid or flexible borescopes and battery or mains power. In practice the difficulty of maintaining a sense of orientation through a flexible scope complicates the interpretation of any observations. The penalty for the most brilliant mains-powered light intensity is a relatively large cumbersome unit. However, this is preferred to the undoubtedly more portable battery equipment because their convenience comes at the expense of light quality and it can be rather difficult to distinguish between cobwebs and fungal growth in the weaker yellowish hue produced.

A small access hole is required, approximately 12 mm diameter. Where available it may be possible to utilise existing holes (old service pipe holes or damage board edges). New inspection holes may be discreetly sited and either plugged after use or retained for future routine inspection. In practice, even with the most powerful instrument, the field of view is deceptively short and the range of vision tends to be no more than 1 metre. Inspection holes are therefore located where they are expected to reveal the most information, in suspected areas of worst decay, or to achieve the clearest view of the structure. Whilst it may not be possible to view all details clearly, it is usually possible to see sufficient clues to determine whether or not decay is suspected, and would necessitate further investigation.

Identification of concealed decay is particularly a problem behind valuable wall panelling, and dust analysis can provide many clues to detect the presence of bio-deterioration. Samples of accumulated dust and debris dislodged from panels and their fixing timbers are collected from beneath the skirtings. The sampled material will typically comprise dust, sand, mortar and plaster granules. The presence of decayed wood or insect fragments and distinctive bun-shaped death watch beetle frass can be detected by examination with the naked eye. Magnification using a hand lens (X 10) is necessary to distinguish the smaller lemon shaped frass produced by woodworm. More powerful microscopic examination is used to identify other domestic insect pests which may be attacking other organic materials and may indicate associated environmental problems.

SURFACE OR SERIOUS
Substantially sound timber is often unnecessarily discarded because its surface was decayed when probed with a trusty penknife. However, the sapwood of timber is generally rather susceptible to decay and beneath the superficial outer damage its greater proportion of more durable heartwood often remains sound and structurally adequate. Tapping the timber to detect decay may also be misleading as the hollow sound produced by concealed decay may not be distinguished from loosely fixed timber.

Until recently the usual method of checking such an initial diagnosis would be to drill with a standard auger bit and to judge whether the timber felt sound, soft, or decayed. The Sibert decay- detecting drill is a comparatively recent innovation which supersedes this subjective testing.. There are infinite applications including testing the integrity of beam bearings, detecting concealed decay in plates where only one face is accessible, checking the condition of mortice/tenon joints and assessing the depth of fire damage charring. It is possible to test moulded timbers without damaging their decorative surface, probe through floor boards or panelling into the underlying structure, or through very soft lime plaster into concealed lintels. Where timbers are buried behind denser materials (perhaps underfloor screeds or behind a single skin of brick) the Sibert can be used with an 8mm pilot hole and a sleeved extension probe.

ACTIVE OR ANCIENT
Dead fungus does not disappear and old beetle flight holes remain permanently visible after the beetles have left the wood. Unfortunately, it is not uncommon for old inactive damage to be rediscovered and often destructive exposure and expensive treatments are repeated to combat evidence of historic fungal decay or insect infestation. In order to avoid extensive futile works, it is essential to establish the level of current activity and continuing decay potential.

All timber decay organisms have a requirement for elevated moisture levels. Moisture meters are therefore fundamental to every survey kit and if used with intelligence they can be a useful tool. However, their limitations should be recognised and unconditional faith in their diagnosis of dampness is misplaced. It is commonly, though erroneously, upheld that decay is inevitable above 20% timber moisture content and moisture meters often highlight a scale of risk with warning lights illuminating at this legendary 20% threshold. In practice wood -boring beetle infestations may tolerate less and fungi generally require significantly more water.

The most widely used meters are based on the electrical resistance of timber. However our recent research has demonstrated that the electrical resistance properties of timber change with age. In consequence it is possible to have modern replacement and historic original timber adjacent and to derive two entirely conflicting moisture-content results. Extreme caution must also be applied where timbers are damp stained (the situation where a moisture meter is most likely to be used) because the presence of salts will erratically change the electric air resistance of the timber producing erroneous readings.

Most moisture meters cannot give a percentage moisture reading in materials other than timber and should not be used to measure wall moisture levels. The standard procedure is to collect mortar samples with a slow speed drill and to calculate their absolute moisture content from weight loss after controlled oven drying. The main disadvantage with this method is that mortar, masonry and brick are inherently variable materials and results may not be directly comparable, particularly where further readings are required, for example to monitor the progress of long-term drying.

Wooden dowel sensors are a simple, cheap and consistent alternative to overcome these disadvantages. Timber dowels are inserted into pre-drilled holes and allowed to equilibrate with the structure for 3-4 weeks. The equilibrium moisture content of the dowels is calculated by the oven/balance method and represents the wetting potential of the wall.

These dowels serve a dual purpose as bait rods to detect concealed fungal activity. In the presence of active dry rot Ramin dowels are readily attacked within four weeks. It must be noted that decay will reduce the density of the wood and proportionally increase its percentage moisture content. For long term monitoring the sensors need to be regularly replaced and redundant sensors should always be removed.

Variations on these themes of moisture measurement have been developed into permanent monitoring systems designed to provide early warning if leaks recur in vulnerable areas. As part of essential building maintenance the manually interrogated or fully automated sensors provide greater security against future decay than paper guarantees which are nullified by water ingress.

Evaluating the level of wood-boring beetle activity can be rather subjective unless there are large numbers of adult beetles present. Other visual clues may be inconclusive. Our recent research has demonstrated that death watch beetle do re-use existing emergence holes, so the absence of fresh holes may not eliminate the possibility of activity. Old frass is readily dislodged from damaged timber by vibration and heaps of pellets may not therefore provide confirmation of current activity. However, damage caused by insect infestations progresses at a relatively slow rate and monitoring is the best approach to determine whether a population is thriving or declining before proceeding with expensive, and often ineffective treatments.

Elevated timber moisture levels required to sustain wood-boring beetle infestations may be attributable to ambient conditions. Single relative humidity readings are of limited use as the environment is likely to fluctuate through daily or seasonal cycles which are most effectively evaluated by a period of continuous data logging. Estimates of beetle population levels may, if practical, be made by regular beetle counts, but often cleaning regimes remove the evidence, or fresh beetles cannot be distinguished amongst years of accumulated debris. Alternatively the number of emergence holes used in a flight season can be quantified by pasting tissue paper over flat surfaces, or by filling existing holes with beeswax. The latter technique is particularly useful for monitoring carved, moulded timbers.

DETAILED DIAGNOSIS
Correct diagnosis of the cause, nature and extent of decay is essential to minimise destructive intervention and maximise conservation of historic fabric, with the added incentive of reducing costs. There are many techniques available, using complex technology and simple robust equipment where appropriate. In experienced hands, all are useful tools to assist with problem analysis, but these form only a part of a thorough independent survey applying scientific knowledge of the performance of decay organisms within the limitations of the built environment.

This article was written by Chris Cullen and was published in the Institute of Historic Building Conservation magazine Context

Introduction

Preservation of historical buildings is a hot topic, and getting hotter if predictions about global warming and climate change impact upon the built environment in the way we think they will. Invasions of exotic insect species and extreme population fluctuations of indigenous species are widely reported around the world. Timber pests are no exception, and we have already seen termites establish themselves in Southwest England and observed an increase in the prevalence of the house longhorn beetle, Hylotrupes bajulus.This may be partly due to climate change, but it is also probably related to changes in lifestyle. Central heating systems are now present in most historical buildings. And coupled with reduced ventilation, it can lead to condensation and warmer, more humid environments inside buildings, creating a more conducive environment for timber pests.

It is also feared that another European timber pest, the death-watch beetle (Xestobium rufovillosum), is on the increase, which is a particular worry for architectural conservationists as the beetle has a preference for ancient oak timber found in cathedrals, palaces and stately homes (Belmain et al., 1998). Historically, beginning with attempts to treat the roof timbers of Westminster Hall at the beginning of the 20th century, surface treatment with chemicals has been employed as the treatment method of choice.Surface treatment has proved, however, of very limited effect in controlling the death-watch beetle in such historic buildings. As a result, between 1993 and 1997 the European Commission funded the international collaborative research project Woodcare, led by English Heritage, to understand the interaction between beetle behaviour, timber and fungus with a view to understand why surface treatments so often fail, and to evolve alternative environmentally acceptable treatment methods (Ridout, 1999).

This short article outlines the problems involved in the effective control of death-watch beetle and some of the research which has been carried out to discover why it is so problematical and to develop better methods of control.

The death-watch beetle
Life cycle
For many years it had been thought that the life cycle of the death-watch beetle was a maximum of 5?7 years (Fisher, 1940), and that the adult beetle laid its eggs on or close to the surface of the wood. The hatched larvae then burrow into the timber and continue to feed on the wood until they have grown sufficiently to pupate. The adult emerges during the spring, mates and renews the cycle. It is now established that the life cycle depends on the suitability of conditions, and that the larval stage may vary from one year in ideal conditions to 12 years or more, if conditions are not favourable. Deathwatch beetle larvae develop more rapidly when there is a high relative humidity and the presence of fungal decay in the timber. Whereas the short-lived adult does not directly feed on timber, the larva causes considerable damage as it digests its way through the wood, creating structural and aesthetic damage to our buildings. New research has shown that the adults do not necessarily need to emerge from the timber and can mate in cavities within the timber. Furthermore, newly mated adult females have been shown to re-enter existing flight-holes and lay their eggs deep in the timber, rather than on or near the surface. These observations have highlighted why existing treatments are often ineffective.

Tapping
The death-watch beetle has been living in our buildings for centuries and was first noted for the tapping sound the adult makes. When people usually died at home in ancient Europe, the death vigil, or death watch, would have allowed this tapping noise to be clearly audible when the house was quiet, the noise emanating from the structure of the house. The tapping noise subsequently became associated with bad omens, implying that when the tapping noise was heard a loved one would soon die. We now know the tapping is a form of communication employed for finding mates,through research conducted by Martin Birch and colleagues at Oxford University (Goulson et al., 1994; Birch and Keenlyside, 1991).

Environmental conditions
In many cases of active infestation, the environmental conditions allowing the beetle larvae to survive are only just met, so that the life cycle is continuing, but at a very slow rate; and structural damage occurs at a proportionally slow rate. However, a relatively small change to the environment can cause the attack to die out, or conversely, to become more active.

Moisture
At present it is thought that a moisture content of 14% is the lower limit for a flourishing colony of death-watch beetles, and if the moisture content drops below 12%, the larvae will die. It, therefore, ought to be a simple matter of ensuring that the moisture content is below this level, and the infestation would cease to be a problem. Unfortunately, even in a fairly well ventilated roof space, the normal moisture content of structural timber averages 14?15%, and in many buildings in which this beetle is a problem (such as irregularly heated churches), condensation coupled with poor ventilation can significantly increase this moisture level. As temperatures within buildings can wildly fluctuate between summer and winter, causing subsequent changes in moisture content, it is likely that the beetle larvae can tolerate periodic drops in moisture below their optimal requirements. In the long term, therefore, every effort should be concentrated on ensuring that the environmental conditions are adjusted, first to slow down, and ultimately to kill off, the beetle attack. The improved, drier environment must then be maintained year after year. Even if these improvements can be achieved, it may still be necessary, over the short term, to introduce chemical control where the beetle is particularly active. It is of course essential that moisture levels in surrounding masonry are measured and reduced as necessary. If this is not practicable, the timber should be isolated from the damp masonry as much as possible.

Fungal decay
For the death-watch beetle to flourish, timber is usually required to have been previously modified by fungal decay (often by the oak rot fungus Donkioporia expansa), making the timber more easily digested. The vast majority of structural oak used in historic buildings was converted and assembled green, when the moisture content was still very high, and it is likely that some timbers used had already suffered minor fungal attack before felling. In larger section timbers, the moisture content would have remained high enough to sustain fungal attack for many years, and so a suitable environment for long term death-watch beetle infestation was present in the building from the outset. Many have argued that the death-watch beetle larvae, themselves, were introduced into the buildings within the timber used for construction. Lack of maintenance over the ensuing years inevitably allowed periods of water ingress, setting up new fungal attacks, and consequent fresh food sources for the infestation. Our Irish collaborators based at University College, Dublin have studied the chemistry of Donkioporia expansa which has helped us understand the complex relationship between the death-watch beetle, timber, and fungus. Research has shown that the death-watch beetle uses fungally-produced compounds to ?home in? on suitable areas of timber for infestation.

Chemical control
Since the advent of chemical pesticides, they have been increasingly used in timber pest control. Various nasty chemical concoctions were developed from the beginning of the 20th century and applied as blanket treatments whenever pest problems were identified in buildings. For example, a formulation developed by Harold Maxwell Lefroy of Imperial College, London, consisting of 50 percent tetrachloroethane, 40 percent trichloroethylene, 6 percent cedarwood oil, 2 percent solvent soap and 2 percent paraffin wax, was used for the treatment of the roof timbers of Westminster Hall in central London in the 1920s. In many countries, lindane and dieldran continue to be used for timber treatment. However, toxicity concerns are resulting in their replacement with safer pyrethroid alternatives such as permethrin.

The situation of blanket chemical treatments has become institutionalised through the property market and insurance company requirements for timber treatment certificates. However, more recently, several forces have been at work which call into question the use of pesticides, especially with regard to the death-watch beetle. There is an increasingly widespread concern about the safety of pesticides, with consumers in many countries demanding reduced usage in agriculture and in urban environments. This is affecting the alternatives available to the timber preservation industry. More importantly, with the death-watch beetle there are many reported incidents of poor efficacy of pesticide treatments, most notably in Westminster Hall . The Hall experienced massive death-watch beetle damage after the Second World War initiated by ingress of rain water through bomb holes in the roof, and despite repeated pesticide treatments over a number of years, the Hall continued to have high infestations for decades until the timbers slowly dried out. The death-watch beetle is particularly ill-suited for control by pesticides for a number of reasons related to its biology and habitat. Perhaps one of the most difficult problems is related to pesticide application. The larvae of the death-watch beetle feed on hardwoods such as oak, often deep within large timbers hewn from entire trees. Because of the size of the timbers and the inaccessibility of the pest, even pesticide injected into affected timber under pressure often fails to reach its target. Other forms of pesticide delivery such as fumigating fogs or liquid and paste treatments on the surface of the timber are even worse at reaching larvae deep within it. Of course the adult deathwatch beetles must eventually emerge from the timber to mate and lay eggs. However, killing the adult is also no easy task. Adults usually emerge simultaneously in the spring within a fairly narrow window of time, and our research has shown that their contact with the treated surface is limited by their behaviour in seeking out cracks and crevices and their preferences for dark areas (Belmain et al., 2000). Poor treatment success is further compounded by the fact that the larvae can take upwards of 10 years to complete their development (Fisher, 1940), implying that surface treatments with pesticides would have to be either very long lasting or repeatedly applied to the timber over a number of years to have any impact upon pest populations.

Monitoring
Better prospects for timber pest control are now becoming a reality. Research within the Woodcare project has aimed at discovering potential solutions to control the death-watch beetle and preserve cultural landmarks such as cathedrals and palaces from continuing damage. The first step in designing an integrated approach to pest control is to ensure that there are effective monitoring tools to detect pest populations. The most common and perhaps most obvious method usually employed to identify actively infested timber has been the presence of insect emergence holes. However, most timbers in historical buildings are riddled with insect holes, and distinguishing between currently active and historical infestation is difficult. Our research has shown that holes and the presence of frass or wood dust around the holes do not necessarily indicate an active infestation and that death-watch beetles can also emerge out of pre-existing holes leaving no new tell-tale signs (Ridout, in press). Monitoring for pest infestation can be more effectively done using light traps and sticky traps , which we have found to give a good indication of active infestation (Belmain et al., 1999). Another new monitoring tool is being developed by our collaborators in The Netherlands (TNO Building and Construction Research) using ultrasonic sensors. When these small sensors are placed on the surface of the wood, they can detect the sounds the insects make when eating the wood, thereby pinpointing areas of a building that are infested. This will allow the pest control operator to focus pesticide applications on specific areas, increasing efficacy and cost effectiveness, as well as to monitor the success rate after treatment.

Integrated control

Effective monitoring and targeted application of pesticides is, however, only part of the new integrated approach being developed for timber pests.

Biological control
Biological control, now widely used in agriculture, can also work in buildings. Predators of the death-watch beetle such as spiders and a small blue beetle, Korynetes caeruleus , are naturally found in buildings. The predatory beetle is particularly interesting because it seeks out its prey inside the timber providing a means of controlling pest larvae deep inside timbers where pesticides do not normally reach. Biological control alone is unlikely to rid our buildings of pests, but if pest managers promote conditions which protect predators, such as more targeted pesticide applications, predators can help keep pest populations in check. Studies we have conducted in infested churches have shown that changes in the spider population follow changes in their prey population of death-watch beetles. However, it remains to be seen whether proprietors of historical buildings can overcome their arachnophobia to control the death-watch beetle.

Heat sterilisation

Heat sterilisation is currently receiving a lot of attention. It is claimed that a temperature of 52?55 degrees C maintained for 30?60 minutes will kill all wood-boring insects. Given that live death-watch beetle larvae have been found in the middle of large, recently fire-damaged timbers, the duration of treatment would need to be much longer than one hour if this temperature is to be achieved throughout a 300 ? 250mm oak member, for example. The potential effects on delicate finishes, oak panelling and other fragile fabric of such a temperature for a prolonged period are likely to be considerable.

Light traps
Traps which use an appropriate wavelength which attracts beetles during the emergence season (late-March to late July) can be effective in controlling beetles. The simplest and least expensive form of such traps is the Beetle Screen which utilises replaceable sticky sheets of paper, and is hung in a roof space where a population of death-watch beetles is suspected. The limitation of these traps is that they rely upon the ability of the death-watch beetle adults to fly towards the light and become trapped. Our research has shown that ambient temperatures must exceed 19 degrees C in order for adult beetles to readily fly. As such temperatures can not be guaranteed during a British spring, it may be necessary to artificially increase the temperature within the infested area using space heaters which would help ensure that the maximum number of beetles are caught.

Outlook
Further efforts are being made to develop traps which are so attractive to the death-watch beetle that newly emergent adults go to their death before they have had the chance to mate and lay eggs, breaking the infestation cycle. No one has yet discovered sex pheromones produced by the deathwatch beetle, but both males and females are attracted to a range of compounds found in its preferred food, i.e. timber. It is hoped that, eventually, traps laced with the right compounds will provide yet another tool for the integrated management of timber pests.Through our research, several essential facts about the death-watch beetle are now better understood. This information can be used to develop cost-effective and environmentally sustainable control strategies for historical buildings with timber pest problems. The main hurdle now faced is one of putting theory into practice. For IPM in buildings to work, the pest control industry requires better education so that pest control operators can recognise active infestations through monitoring and implement targeted treatments. The general public should understand that a few insects inside their buildings does not necessarily mean the building is structurally undermined, but if neglected, could result in severe problems. The cornerstone of IPM in buildings will rely upon good building management. A healthy building is a sound and dry building, and good health means fewer pest problems.

This article was written by Steven Belmain, Monique Simmonds and Brian Ridout and was published in Pesticide Outlook December 2000

An informed article written by Graham Coleman which explains how rising damp occurs and tries to dispel the theory proffered by some writers that rising damp does not exist .

People reading this piece will probably be aware there have been numerous articles in both the press and some professional journals regarding the actual existence of rising damp. Indeed, there has even been a small published book stating that rising damp is a myth. We are even told that the term `rising damp` originated in the 1960s but unfortunately for that author it appeared long before - the term was used in the British Medical Association Journal of the 1870`s. So what is the truth? What is the objective evidence for rising damp?

For a start, it is not a simple UK phenomenon as some publications would imply. Serious peer reviewed papers have appeared in scientific building and technical journals for many years in those parts of the world where rising damp has proved to be a problem. This includes not only the UK, but Belgium, Italy and especially Australia where it is referred to as `salt damp`. It occurs where any masonry is sufficiently permeable to take up water from the ground. Given this fact it is unlikely that Governments and Technical Institutes in these parts of the world would spend time and money on something that was considered to be a `myth`- unless one believes in international conspiracy theories!

We can define rising damp as water rising up through masonry - the water originating from the ground. The water rises via interconnecting pores within the wall by a process we refer to as `capillarity` - in other words permeable masonry acts somewhat like a wick. However, the wick idea is not quite that simple.

In order for water to rise the pores up through wall must be interconnecting. If the capillaries are sufficiently fine and interconnecting then water has the potential to rise. Pores in masonry are reported to be as small as 0.001 mm in diameter, but on average are around 0.01 mm. Pores of this latter size give a theoretical height of rise of 1.5 m. However, processes such as evaporation and pore continuity will in part control this.

Even now it is still not that simple. Think of the capillaries within the wall as a `suction` agent, and similarly think of the ground as the same. If the suction of the wall is greater than the suction of the ground then water will rise if the capillaries are of a suitable size and sufficiently continuous. If, however, the suction of the ground is greater than the wall then water will not rise even if the pores within the wall are continuous. Put quite simply it explains why not all walls without the benefit of the damp proof course will have rising damp. There are simply a number of factors which need to be present for water to rise. Hence, many properties without physical damp proof courses will not have, and probably never will have rising damp. So simply taking an old Victorian wall and standing it in water to see if rising damp occurs as one individual has done proves precisely nothing whatsoever if the water doesn`t rise, and as such it is not a basis on which to `prove` that rising damp is a myth as this individual has indicated.

We have defined the rising damp above. Where it occurs water rises up through the system of interconnecting pores to a given height depending on pore structure, evaporation and other factors: this process is continuous and will take place over many years.

Ground water contains soluble materials, a proportion of which are soluble salts; these are usually presents in lower parts per million and at this level they are of no significance. A proportion of the salts are soluble chlorides and nitrates neither of which exist in building materials at any significant level, usually less than 0.01% so effectively we may consider the materials to be free from such salts.

As water rises from the ground into the wall these dissolved salts are carried in the rising water. As the rising water continues to rise and evaporate these salts are left behind, and over many years significant levels become deposited within the wall and finishes. The majority of the salts are deposited towards the maximum height of rise of water where they form a distinct concentration known as the `salt band`. Since these salts are, for practical purposes, absent from bricks, mortar, stone, plaster, etc, it is their presence and distribution that is the key to the diagnosis of rising damp. Whilst there are a few occasions where such salts can arise from other sources, by far the most common occurrence of these salts in walls is water rising from the ground. In examining a wall therefore suspected to be affected by long term rising damp one will readily find these salts but only up to the height of the rising damp - above the height of rise these salts will effectively be absent. So looking for the presence and distribution of these salts, especially in relation to the presence and distribution of water ingress, is essential for a definitive diagnosis, and it is this fact that the supporters of the `myth` conveniently ignore.

To reiterate the fact - the salts and their distribution are the key to diagnosis together, of course, with whether or not water is still entering the wall. Moisture and salt `profiling` will readily identify the presence of rising damp in relation to any other form of dampness. Condensation, surface or interstitial, never introduces ground water salts into the wall neither does rain penetration. In the case of condensation in the UK there is a `condensation season` and this is broadly between October and April. If there is dampness outside of this period it is probably not condensation. Furthermore, unlike rising damp, condensation is very frequently intermittent and if so it may not remain sufficiently long to cause any visual problem. If it is long term then it is clearly readily evident. It is unlikely therefore that condensation will be misdiagnosed as rising damp especially considering that surface condensation literally forms on surfaces and will penetrate permeable surfaces only a few millimetres if the condensation is severe. Effectively condensation is highly unlikely to occur during the warmer months of the year

Another misconception is the classic `mains water leak` where the rising damp is supposed to be caused by such a problem with the water soaking the ground. Basically, if the wall has sufficient suction water will rise from the ground whether there is a leak or not. Indeed, the most common source of water in the ground is rainwater where it clearly wets up the upper surfaces of the ground, i.e. where the walls are in contact with the soil.

Physical damp proof courses were introduced into `Building Regulations` in the 1870s in relation to public health although some properties were built with such damp-proof courses prior to this time. However, it took a number of years before all properties were built incorporating physical damp proof courses.

So how common is rising damp? It is very unlikely, but not absolute, that properties with physical damp proof courses will have rising damp unless it becomes bridged or seriously defective, the former usually being readily identified. Of the properties that do not have a damp proof course some may have rising damp, others may not: not having a damp proof course is not synonymous with having rising damp.

Building Research Establishment positively identified rising damp to a greater or lesser extent in around 80% of the properties they investigated in Cardiff several years ago. These results together with other data suggest that rising damp is probably not that uncommon in United Kingdom (it is sufficiently common in Denmark, Belgium, Italy and Australia for the Institutes to research and report on the problem, especially in relation to their historic buildings). However it appears likely that severe rising damp is sufficient to cause significant decorative spoiling, staining, blowing of plaster and timber decay

So does rising damp exist? - A resounding yes! Can it be readily diagnosed? - yes, it has very distinct features not present in other forms of dampness, but it may take laboratory facilities for a positive identification. Is rising damp a myth? - no, and certainly not in Europe and Australia.

By: G R Coleman B.Sc.(Hons). M.S.B., C.Biol., M.I.W.Sc., F.Inst.S.S.E..

Notes and general principles.
Correct diagnosis of damp problems: the first and most important stage in any remedial treatment.

The eye of experience is the most useful instrument for the recording and diagnosis of damp and timber decay problems in buildings. When analysing damp and timber decay problems in buildings look for moisture penetration and movement from top to bottom and from outside to inside.

When analysing damp problems in buildings note must be made of moisture sources. Particular attention should be given to sources of concentrated moisture penetration such as roof drainage and ground drainage systems. Particular attention should also be given to defective drains, cavity ventilators, evaporative surfaces and structures. The course of moisture from to be plotted. Vapour movement should be checked together with air movement from warm to cold or from wet to dry areas.

Measurements of relative humidity are generally useful particularly with reference to dew point temperatures. The moisture content of air equilibrated timber is often a more useful indicator of chronic environmental problems. Generally, relative humidities over 70% in occupied buildings is likely to cause condensation if not vented to the exterior. Timber at equilibrium with 70% r.h. will have a moisture content of approx. 15%. Prolonged relative humidities of over 80% allow mould growth and will provide the conditions for microbial decay of materials.

Timber at equilibrium with 80% r.h. will have a moisture content of approx. 18%. Prolonged relative humidities of over 85% will result in bio deterioration. Timber at equilibrium with 85% r.h. will have a moisture content of approx. 20%.

Material moisture content rather than relative humidity is the most important factor to be measured in the analysis of damp and decay problems.

The significance of the percentage gravimetric moisture content varies between materials due to differences in their density and the extent to which water is bound hygroscopically. The significant factor is the partial water vapour pressure in the material or the available moisture. In building surveying, a convenient approximation to available moisture is the timber equivalent moisture content (EMC) which may be defined as the moisture content that would be found in a piece of timber that was allowed to come into equilibrium with the material in question

As a rule of thumb for site investigations timber equivalent moisture content is approximately 10 times the gravimetric available moisture content of in-contact masonry. The most cost effective way of estimating timber equivalent moisture content on site is to use resistance-based moisture meters, but the readings from such meters are commonly misinterpreted

The deep moisture content of a material is more important than the superficial moisture content. In order to estimate the deep moisture content of materials with a resistance-based moisture meter, deep probe electrodes are required

The readings from resistance-based moisture meters are commonly misinterpreted for the following reasons:-

1. The limits of superficially measured wet or dry readings are not appreciated.
2. Artificially high readings are taken due to conductive salts in the material.
3. Artificially high readings are taken in timbers due to previous chemical treatments.
4. Artificially high readings are recorded in composite materials, such as plywood, masonry containing carbon (e.g. PFA etc.), some surface printed finishes and metal foil!

Useful rules of thumb for assessing the significance of resistance-based moisture meters during site surveys are as follows:-

1. Readings of less than 20% timber moisture equivalent indicate that moisture is too dry for active fungal decay
2. Readings of less than 13% timber moisture equivalent indicate that timber is too dry for significant insect decay (except in the case of House longhorn and Powder post beetles)
3. The internal materials in an occupied building will usually have moisture contents of less than 12% timber equivalent moisture content
4. Roof timbers in an occupied building commonly have moisture contents of 16% or less
5. Roof timbers in an occupied or intermittently occupied building may have moisture contents varying between about 12% and 25% throughout a year, but these may not be significant. Experience has shown that an annual average of 14% results in ?safe? conditions.

Timber equivalent moisture contents of 30% (timber fibre saturation point) or greater are damp enough for wet rot decay or for dry rot germination to occur i.e. there must be available liquid water.

Surface capacitance meters are useful for initial survey of masonry or plaster structures, but readings are poorly correlated to gravimetric or available moisture contents.

Low surface capacitance readings are a useful negative finding, but high readings require further investigation.

Sampling and gravimetric analysis of materials is the only accurate and cost effective surveying technique for determining the true moisture content of building materials

The use of the oven drying technique, as described in BRE Digest 245, 1986 is the standard technique.
The formula for determining the percentage of gravimetric moisture content is:-

Ww - Wd x 100% - Ww - where Ww is the wet weight and Wd is the dry weight.

Hygroscopically bound moisture content is significant in most masonry and plaster due to water bound to salts. This is defined in BRE Digest 245 as the moisture bound to a material at equilibrium with air at relative humidity of 75% at 20?C. The formulae for the percentage of hygroscopic moisture content is:-

W75 - Wd x 100% - W75 - where W75 is the weight after equilibrium at 75% RH at 20oC

Moisture content is the most useful indicator of water available for deterioration and biodegradation processes. This is defined as the total gravimetric moisture content less the hygroscopic water. The `Speedy` meter is of limited use because it can only determine total moisture content. However, the results are obtained on site and are relatively accurate. Slavish reliance on total moisture content as an indicator (e.g. the 5% threshold estimate given in BS 6576 1985) is usually a mistake and experience shows such values are frequently misinterpreted. The `Speedy` does have the advantage of providing sub-surface readings that can be replicated through or over a structure, thereby illustrating moisture content gradients. This is perhaps its most useful function.

A sub-surface moisture gradient correctly taken using a Speedy meter or, preferably, the gravimetric method can point to the source of dampness. With experience and intelligence, surface electronic readings can sometime be used in the same way. However, in the case of ground water penetration this method is notoriously unreliable because of the influence of salts. In the case of rising dampness the source of moisture is the ground, and moisture contents will always decrease with height above ground. This will generally not be shown with surface reading electronic meters.

Condensation will often cause dampness that resembles rising dampness because heat rises leaving the base of walls preferentially cool. Air circulation at the base of walls is often very slow. Drying of condensate may be very slow. This results in a net increase in moisture content in the wall surfaces over time, however, the interior of the wall may be dry.

Condensation may occur at the internal surface of the wall or within the wall. When the surface of a wall is dampened by condensation which is not allowed to dry out the rate of condensation will increase because the wall will loose heat more rapidly. The `wet front` advances into the wall. Over time, this often resembles rising dampness.

Water soluble salts translocated to the wall surface by water penetration and evaporation over time will affect electrical conductance. Calcium sulphate from the building material will be translocated and may appear at the surface as efflorescence. Salts from the moisture source way also be translocated. In the case of water from the ground nitrate and chloride salt combinations are commonly found. Salts become hygroscopic in relative dry air (30-50% r.h). Hygroscopic salts are often blamed for dampness but without formal assessment of available moisture (using the gravimetric method) such statements are meaningless. Hygroscopic moisture is not available to cause decay. Hygroscopic salts in plaster are therefore not a significant structural issue.

Article written by Peter Bannister of Hutton & Rostron.

Stephen Boniface, former chairman of the construction arm of the Royal Institution of Chartered Surveyors (RICS), has told the institute?s 40,000 members that `true rising damp` is a myth and chemically injected damp-proof courses (DPC) are `a complete waste of money` In response, the RICS has put the term `rising damp` in inverted commas in its latest factsheet ? according to Boniface, as a `non-subtle hint` to its members.

`The most likely causes of damp are moisture penetration and, most commonly, condensation,` said Boniface in an interview with NBS Learning Channels .

In response, Elaine Blackett-Ord, chair of the Register of Architects Accredited in Building Conservation, has also spoken out against rising damp, saying it was as rare as `rocking-horse shit`.

Blackett-Ord said:`This self-perpetuating industry is believed to be worth over ?200 million per year.`

`Not only are chemically injected DPCs a waste of time, they are ineffective and grossly expensive. [Installing] damaging impermeable cement based internal renders?serve simply to conceal the problem in the wall behind. For most historic buildings this is extremely damaging and irreversible.`

Jeff Howell, a qualified bricklayer and author of The Rising Damp Myth (2008) said trials in the laboratory confirm the falsehood.

`If you build a brick pillar and stand it in a tray of water, the bricks in the water will get wet, but the water doesn?t rise by capillary action,` said Howell. `Cement-based and most lime-based mortars will not allow water to go through.`

However not everyone is convinced. Terry Brown, of GMW Architects, said: `It?s right to question the diagnostic skills of commercial damp proofing firms, but to state categorically there is no such thing as rising damp undermines a whole litany of rules of brickwork detailing I?ve adhered to all my professional life.`

`Of course there is no reason why inherited conventional wisdom shouldn?t be challenged. [But] the challenge has to be scientific and not anecdotal.`

RISING DAMP by U. A. Fanthorpe

A river can sometimes be diverted but is a very hard thing to lose altogether.
(Paper to the Auctioneers` Institute, 1907)

At our feet they lie low,
The little fervent underground
Rivers of London

Effra, Graveney, Flacon, Quaggy,
Wandle, Walbrook, Tyburn, Fleet

Whose names are disfigured,
Frayed, effaced.

There are the Magogs that chewed the clay
To the basin that London nestles in.
These are the currents that chiselled the city,
That washed the clothes and turned the mills,
Where children drank and salmon swam
And wells were holy.

They have gone under.
Boxed, like the magician`s assistant.
Buried alive in earth.
Forgotten, like the dead.

They return spectrally after heavy rain,
Confounding suburban gardens. They inflitrate
Chronic bronchitis statistics. A silken
Slur haunts dwellings by shrouded
Watercourses, and is taken
For the footing of the dead.

Being of our world, they will return
Westbourne, caged at Sloane Square,
Will jack from his box,
Will deluge cellars, detonate manholes,
Plant effluent on our faces,
Sink the city.

Effra, Graveney, Falcon, Quaggy,
Wandle, Walbrook, Tyburn, Fleet

It is the other rivers that lie
Lower, that touch us only in dreams
That never surface. We feel their tug
As a dowser`s rod bends to the surface below

Phlegethon, Acheron, Lethe, Styx.

The recommendation of ?Further Investigation? is frequently made by Surveyors and Valuers following surveys of domestic properties, often for mortgage valuation purposes. Unfortunately, the result of this recommendation is often to deliver the client into the hands of surveyors from remedial treatment companies, who usually have a sales commission incentive to specify as much remedial work as they can. The diagnostic evidence used to justify the various forms of remedial treatment is usually inadequate and much of the work carried out is, therefore, unnecessary.

Introduction to the Remedial Treatment Industry - Timber Treatment, Damp-Proofing and the 20-year Guarantee
The remedial treatment industry came into being in the UK in the period following the Second World War. At this time a number of companies established themselves to offer chemical pre-treatment of timber for use in the building industry, using preservation chemicals and techniques developed during the war. By the early 1950s, the industry had progressed to in-situ chemical treatment of timbers in buildings. The two major players at this stage were Protim and Rentokil, who both moved to embrace damp-proofing technology, within days of each other, in 1963. The gradual development of chemical injection technology, and the availability of a cheap, portable electric injection pump, brought a growing number of building contractors into the business in the late 1960s and early 70s.

There are currently estimated to be between 1700 and 2000 contractors offering remedial timber treatment and chemical damp-proofing in the UK, with an estimated turnover of between ?200 million and ?300 million. Around 200 companies, with some 300 branches, are members of the British Wood Preserving and Damp-Proofing Association (BWPDA), now incorporated into the Property Care Association (PCA).

The concept of the 20-year guarantee first arose, in respect of remedial timber treatments, in 1956, at the insistence of the building societies. This would appear to be a peculiarly British practice, brought about largely by the Caveat Emptor clause of the British legal process. In other European countries the buyer can demand rectification of hidden faults up to two years after purchasing a house. In Britain a guarantee is required. The 20-year length of such guarantees dates from that period, when 20 years was the usual mortgage term. The length of the guarantee was largely meaningless in 1956, however, since no company had anything like that length of experience in remedial timber treatment. When remedial damp-proofing was introduced in Britain in 1963, similarly 20-year guarantees were issued, although neither of the two companies concerned, Protim or Rentokil, had any length of experience in the field, and their respective damp-proofing systems - Protims Knapen tube and Rentokils Electro-osmosis - were unproven, and later discredited. The founder of Protim has expressed the opinion that, aided by the provision of local authority improvement grants, the whole success of the remedial treatment industry is due to the 20-year guarantee demanded by the building societies.

Prior to this period, problems with dampness and timber infestation were approached by attention to construction practice, ie. ventilation, isolation of vulnerable floor timbers from contact with masonry, use of porous lime plasters etc. A very real danger with the quick-fix chemical treatment approach is that it encourages householders and builders to think that poor construction practice can be rectified by chemical treatment. This is almost certainly not the case; timbers will only become affected by insect or fungal attack if they are damp; if you have damp timber and you drench it with chemicals then you end up with damp timber drenched with chemicals. In addition, timber treatment chemicals are toxic, and there are well-documented hazards associated with their use. Surveyors would be well advised to acquaint themselves with the potential dangers of timber treatment chemicals in case their recommendation should result in litigation.

Moisture Measurement in Masonry - the Myth of Rising Damp
The measurement of moisture content by electrical conductance methods has been widely used in various industrial processes, primarily those involving wood products and the storage of foodstuffs, particularly grain. Electrical conductance has also been widely used for the moisture measurements of soils, sand and aggregates. The earliest surviving documentation of the method dates from the 1930s, with much research material being published during the 1940s, 50s and 60s.

Nonetheless, before 1955 there does not seem to have been a portable moisture meter available specifically for use in buildings. In 1954 Protim, suppliers of chemicals for the pre-treatment of building timber, first became involved with the in situ treatment of timbers in buildings. In order to ascertain the presence and extent of dampness in the timbers one of the partners, Gerald Gobert, constructed a conductance meter using parts obtained from an RAF surplus shop. Some forty years later his brother, Ernest, told me that they always knew, from experience and visual inspection, when there was a dampness problem in a building being surveyed - the prime purpose of the meter was to impress the client, or local authority Sanitary Inspector, with the scientific nature of their equipment. This was the first Protimeter. In 1957 Protimeter Ltd was formed as separate company to manufacture and sell the meters.

Protimeter Ltd also began manufacturing meters for the measurement of moisture in agriculture and industry, but the current turnover in building surveying instruments alone is of the order of ?600k - ?750k p.a., representing several thousands of instruments being sold annually.

Since the 1970s, there has been a lively debate concerning the accuracy or otherwise of electrical conductance meters in the diagnosis of dampness problems in buildings, the main protagonists being Protimeter Ltd and the Building Research Establishment. Early BRS/BRE publications on dampness do not refer to the use of electrical moisture meters. However by 1975 it was being stated in BRE publications that ... the use of electrical conductivity meters in survey work does not allow for the correct diagnosis of rising damp, and that the only reliable way to measure moisture in a wall is by weighing and drying drilled samples. These sentiments found their way into the seminal Digest 245, in which it is stated.

The electrical meters commonly used by surveyors are responsive to both the amount of moisture present and to the salt concentration and are incapable of distinguishing between the two. Such meters quite commonly give high readings on the walls of old properties where some accumulation of salts inevitably occurs on internal surfaces. This does not mean, however, that the property necessarily has a dampness problem; high readings can be obtained from a wall where the concentration of salts is high, even if the wall is virtually dry.

A major source of confusion in the use of electrical conductance meters concerns their use on plaster and masonry materials, rather than timber. The meters are calibrated for use on timber, a material which does exhibit a certain direct proportionality between its moisture content and its electrical conductance. Timber, moreover, does not exist in buildings in a dry state - it has a certain cellular moisture content, ranging between approximately 5% and 25% depending upon species, use and environmental conditions. It is known that fungal decay does not occur in timber at a moisture content lower than 16% to 18%, measured by weight, so it was a fairly logical step to draw attention to this fact by accentuating this level of reading on the Protimeter dial, which is marked percentage moisture content. The problem arises when the Protimeter is used by a surveyor to test for dampness on the surface of a wall; the electrical conductance of the wall may well vary according to its moisture content, but the readings on the meter dial are not indicative of percentage moisture content, nor do they allow for the fact that they may be caused by surface condensation or the presence of salts.

Notwithstanding, the fact is that Protimeters are used by Chartered Surveyors and Remedial Treatment Surveyors almost exclusively in the diagnosis of dampness problems in buildings. Invariably the practice is to use the meter to test an internal wall surface - paint, plaster or wallpaper - and to interpret any reading near ground level as evidence of rising damp. The diagnosis of rising damp requires a much more detailed study, which Surveyors usually feel is beyond their remit. Unfortunately, the specialists whose services are subsequently called in are themselves no more knowledgeable, and are, moreover, concerned to gain commission by selling chemical damp-proofing.

Chemical damp-proofing
Chemical damp-proofing itself has an uncertain pedigree. Although it is theoretically possible to achieve a water-repellent barrier by the pressure injection of some of the variety of fluids on the market, research has shown that it may take injection times of up to 21 minutes per hole to achieve a satisfactory result. In that case it could take up to three weeks to pressure-inject a single house. In practice, the job is normally undertaken in a few hours.

Conclusion
Many Surveyors and Valuers assume that the subjects of moisture measurement and chemical damp-proofing are thoroughly researched and proven. In fact, these are both very inexact sciences, and the current dominance of electrical conductance-type moisture meters, and chemical injection damp-proofing, owe more to the marketing efforts of the damp-proofing companies than to independent scientific research.

There is no certainly no independent research that shows that large numbers of British houses are affected by ground water rising up into the walls by capillary action. Rising Damp is a myth.

For more information about impartial and independent damp surveys together with environmentally , chemical free, cost-effective solutions to rising damp please contact UK Damp & Decay Control on 0800 028 1903 or email enquiries@ukdamp.co.uk

Moisture meters are used frequently in surveys of buildings without professionals being specifically trained as to their capabilities or their limitations. It is therefore important to understand the limitations of the standard electric moisture meter to avoid misdiagnosis of rising damp:

The moisture meter is intended and calibrated for use on timbers, not masonry.
The percentage moisture meter readings in materials other than timber are not very meaningful
The temperature and relative humidity at the time of the inspection will strongly influence readings, and these can be highly variable.
The moisture meter cannot differentiate between moisture originating from capillary action, either rising or penetrating dampness, or from the presence of salts.
The readings are limited to surface readings.
The readings can easily be misinterpreted, as they can be affected by the presence of salts and/or past damp-proofing treatments.

Damp-proofing surveyors should exercise extreme care, particularly when interpreting meter readings on non-wood materials. An over reliance upon the results can lead to misdiagnosis and unnecessary damp-proofing work ;for this reason the interpretation of the readings needs to be based upon an understanding of the limitations of the equipment and of what is actually being measured. It is unwise to recommended damp-proofing treatment where the assessment has relied solely upon the results of a moisture meter; it should only be used as a tool to aid diagnosis, not as the sole arbiter that is unfortunately become.

The moisture meter can however be used to provide information and aid diagnosis in a positive manner that builds up a picture of the problems being investigated. For example:

Where no, or low, readings of dampness are found this can be a positive indication that the fabric is dry
Where high readings are found this indicates a problem that requires further in-depth investigation.
The moisture meter is calibrated to measure the wood moisture equivalent. This can be used to confirm the dampness of masonry by measuring the moisture content of timber in contact with the walls. This provides a more accurate picture of the level of dampness compared with relying solely on the moisture readings of masonry.
Plotting the moisture profile and distribution across the whole of a wall or areas identified as being at risk in a building will assist in identifying the potential sources of dampness and any timbers at risk of decay.

For more information regarding accurate, impartial and independent damp surveys please contact UK Damp & Decay Control on 0800 028 1903

Dry rot is the decay of wood caused by the fungus Serpula lacrymans, the effects of which in buildings can be truly dramatic. Diagnosis of dry rot in a building, like the diagnosis of cancer in a patient, has the ability to strike terror into the heart of the recipient of this dire news. However, all wood-rotting fungi require both food (wood or other cellulosic material) and water, and the dry rot fungus is no exception; deprived of either, it cannot survive.

Much of the mythology surrounding dry rot is founded on the ability of its strands to penetrate through non-wood building materials, to transport water to otherwise dry areas and for the fungus to manufacture its own water. In reality, the delicate hyphae are the primary colonisers and the ability to conduct water is limited and can be negated by good ventilation. The process of wood decay itself produces water but in this respect dry rot is no different from any other wood-rotting fungus and, likewise, its ability to produce moisture in this manner can be negated by ventilation. Decay will cease if the moisture content of the wood is reduced to below about 20 per cent, and many extinct outbreaks of dry rot are discovered in buildings where the fungus has died out as a result of this happening, probably following maintenance which has eliminated a water source.

CONTROL STRATEGIES

Because of the total dependency of dry rot on moisture, the primary control strategy must be based on environmental considerations aiming to restore and maintain dry conditions. However, in many cases drying will take a long time, often measured in years, especially where some types of historic buildings are affected. Therefore, secondary measures will often be required to prevent further damage by the fungus before it is effectively arrested by the drying.

PRIMARY CONTROL MEASURES

A detailed survey should be carried out to identify and locate sources of moisture ingress. Particular attention should be paid to roofs and rainwater systems with emphasis on gutters and downpipes, parapet roofs and roof coverings. Rain penetration can also be through renderings and flashings or around windows and doors. Rising dampness through missing, bridged or otherwise defective damp-proof courses must be rectified. Any plumbing should also be inspected for leaks.

Rapid drying should be encouraged through the provision of heating and ventilation which may also require specific building work to prevent moisture ingress and transfer, and to encourage aeration. Dehumidifiers can remove moisture from the air but their effectiveness in aiding drying of walls depends on the rate of evaporation from the wall surfaces.

OTHER MEASURES
Assessing the outbreak
It is necessary to determine how far the dry rot has spread. All woodwork in the vicinity of any outbreaks should be inspected carefully to assess the extent of decay and the current moisture content of the timber. Extensive removal of plaster is necessary only if it is suspected that timber is embedded in the walls and is at risk.

Removing affected timber
Removal of all timber affected by dry rot is destructive but necessary in principle. Retaining affected timber presents problems for the structural integrity of the building and falling debris can be a hazard to occupants and others if decay continues. Timber already below 20 per cent moisture content presents little risk of further decay but, at higher moisture contents, the level of risk depends upon the speed with which drying can be induced and the ease of monitoring the reducing moisture content. Higher risks may be acceptable where timbers are of historic value or where their removal cannot be achieved without damage to important historic fabric - for example, where they support a fine plaster ceiling. In such cases the retention of some timbers may be essential or at least highly desirable.

If the wood can be removed, it can be sterilised in a kiln. The temperature throughout the wood must be maintained at just over 40?C for 15 minutes. Care is needed to prevent splitting and distortion and this method provides no protection to the wood after reinstatement.

Special building measures are necessary if timber is to be retained, including isolation from damp masonry.

Wood preservative treatments
Liquid preservatives can be applied to the surface of sound timbers left in situ to help prevent new infections developing during the drying process. However, they should not be used or regarded as an alternative to physical methods of protection.

If timber infected with dry rot has to be retained for special reasons and decay cannot be arrested in the short term by drying, preservative treatments that penetrate throughout the affected part of the timber can be used. For example:

? application of a preservative paste
? repeated addition of liquid preservative to sloping holes drilled into the wood or by pressure injection
? insertion of borate rods or tablets (these are only effective if the wood is wet).
Treatment of hardwoods must include an insecticide if there is a risk of infestation by death watch beetle.

All new timber used in repairs should be pre-treated with a wood preservative. Detailed guidance on the treatment required for various timber components is given in the British Standard BS 5268: Part 5, which deals specifically with structural timber, and BS 5589 which covers a wider range of uses. Guidance is also given on the use of naturally durable timbers (see also Digest 429 published by the Building Research Establishment Ltd).

MASONRY TREATMENTS

Although strands can grow through and across masonry, the dry rot fungus derives no nourishment from it. The concept of killing the fungus within masonry by wide-spread irrigation with a fungicide traditionally has provided a comfort factor, but it has to be questioned in each case whether this procedure can be justified. First, it is usually difficult to achieve a thorough treatment and, secondly, the treatments introduce large quantities of water which then need to be removed, increasing the risk of salt efflorescence and damage to the masonry, as well as prolonging the time it takes to dry the structure.

The most important role of chemical treatments of the masonry is to prevent the fungus from obtaining access to a fresh food supply in the form of timber in adjacent areas, or replacement timbers being introduced into the area. For this purpose, localised chemical treatments of the masonry can create a useful barrier between the fungus in the wall and the wood.

Examples of such treatments are:
? surface application of fungicidal fluid (which also helps prevent fruit-body formation during the drying phase)
? use of fungicidal renderings
? insertion of preservative plugs or pastes
? localised irrigation treatments.

Whilst these localised treatments play a role in the overall control strategy, they must not be regarded as a substitute for getting the building dry.

Heat sterilisation of masonry walls and timber in situ
In the past, the use of heat to sterilise walls was condemned because it was too difficult to apply effectively and provided no residual protection. In the search for chemical-free control measures, sterilisation with hot air is now increasingly being used, particularly in Denmark. However, the process needs to be carefully controlled so as to prevent damage to the building as well as to ensure that the necessary temperature has been achieved deep in the affected area.

MONITORING

The importance of monitoring the conditions in buildings cannot be over-emphasised. Dry rot develops very slowly, so early detection and curing of moisture ingress will prevent decay occurring in the longer term. Routine monitoring can be as simple as regular visual inspection to check the integrity of the building fabric against ingress of moisture, and taking measurements of moisture content of vulnerable timbers with a hand-held probe. However, sophisticated permanent monitoring systems are now increasingly used involving computer-based equipment linked to probes permanently installed in timbers or other parts of the building fabric. Specific sensors can also be installed in rainwater goods to indicate overflows.

Dry rot is potentially a cause of seriously damaging decay for timber in historic buildings, but it does not have to be devastating or outrageously expensive to cure if caught in time. A careful diagnostic approach is required to identify and cure dampness, to treat in a very selective and targeted way and to re-instate with appropriately pre-treated or naturally durable replacement timber. Installation of monitoring systems to facilitate routine maintenance checks can enable massive economies compared with destructive re-build approaches and will provide greater assurance for the future.

Recommended Reading
Building Research Establishment (BRE) Information Paper IP 19/88 House inspection for dampness British Standards Institution
BS 4072, Wood preservation by means of water-borne copper/chrome/arsenic compositions, 1987 (revised version to be published shortly) BS 5268 Code of practice for the structural use of timber Part 5: 1997 Preservative treatments for constructional timber
BS 5589 Code of practice for preservation of timber, 1989

BRE Digests
163 Drying out buildings
299 Dry rot: its recognition and control
304 Preventing decay in external joinery
307 Identifying damage by wood-boring insects
321 Timber for joinery
327 Insecticidal treatments against wood-boring insects
345 Wet rots: recognition and control
364 Design of timber floors to prevent decay
371 Remedial wood preservatives: use them safely
378 Wood preservatives: application methods
429 Timbers: their natural durability and resistance to preservative treatment

BRE Timberlab Papers
Dry Rot - Causes and Remedies, TP No: 44-1971 (Reprinted 1981)

Books
DH Jennings and AF Bravery (eds), Serpula Lacrymans: Fundamental Biology and Control Strategies, John Wiley & Sons Ltd, Chichester, 1991
For further information contact BRE, Garston, Watford WD2 7JR
Tel 01923 664000 Fax 01923 664010 E-mail GrantC@bre.co.uk

Overview
In spite of the recent media hype over the presence of mould in residences and the workplace, there is virtually no scientific or medical data that supports the level of fear and concern generated by misleading and sensationalized news reports.

All houses, offices, and workplaces have mould. All houses and workplaces contain the dreaded ?toxic black mould? (a nonsensical term invented by the news media). Virtually every human, in virtually every location on earth inhales hundreds to hundreds of thousands of mould spores and mould fragments on a daily basis. And yet, contrary to common belief, there is currently no evidence that the presence of these moulds and the exposures to the same poses the threat to the health of members of the general public as suggested by irresponsible journalists, and dramatic news reports largely devoid of objective facts.

Ignoring for a moment that virtually all ?mould tests? and all ?mould samples? are completely invalid, and uninterpretable and cannot be used for decision making, indoor moulds almost always get the initial blame for complaints about indoor air quality. However, in the Summer of 2011, the US Department of Labor, OSHA published the guidelines ?Indoor Air Quality in Commercial and Institutional Buildings?, wherein OSHA referenced the Indoor Air Quality Investigation protocol in its Technical Manual and points out that all microbial contaminants combined (including viruses, fungi, mould, bacteria, nematodes, amoeba, pollen, dander, and mites) were found to be the primary sources of indoor air quality problems only 5% of the time. The unwarranted fear is propagated by a variety of ?mould remediators? and ?mould inspectors? who usually have no legitimate knowledge in mould or mycology but prey off the public?s fear and perform nonsensical and invalid mould ?testing.?

In July of 2009, the World Health Organization (WHO) published its position paper 2on indoor moulds and Indoor Air Quality. Contrary to what many people in the mould remediation business want to believe, the WHO guidelines reinforced the findings of the 2004 Institute of Medicine mould study group. In that study, the IOM stated there was insufficient evidence to find a causal association between the presence of moulds and any of the claimed adverse health effects. That is, after reviewing the global scientific and medical literature, the IOM could not find sufficient evidence to support the argument that the normal presence of mould in residences and workplaces caused any adverse health effects.

These findings are consistent with other notable organizations, such as the ?Health Alert? published by University Health Publishing and John Hopkins Medicine who state: 3

Popular reports about the health effects of muold are likely to include the term ?toxic mold.? But that term can be misleading, the experts say. They point out that only certain muold spores produce toxins, and only under certain circumstances. Just because a particular mould can produce toxins doesn?t mean it will. Even if the mould is producing toxins, a person must breathe in a sufficient dose to be affected. It is highly unlikely that you could inhale enough mould in your home or office to receive a toxic dose.

The WHO and the IOM, however, both concluded there was an association between damp living spaces and some adverse health effects. The unfounded assumption by those unfamiliar with the studies presume that mould was responsible for the association, however, this is not the case. Although it is well established that there exists an ?association? between damp in buildings and a slight increase in observed adverse health effects, it is also well established that no one has been able to conclusively demonstrate that the association is exclusively due to the presence of mould. WHO and the IOM note that dust mites, Bacteria, termites, protozoans, endotoxins, VOCs, formaldehyde, pesticides, viral survival and generally poor ventilation are similarly associated with damp, and these factors, too, are considered to be part of the etiological backdrop. As such, in the remediation of water damage, the stress is placed on correcting ?damp? and not on removing mould.

The common misconception is that when water damage occurs, and/or mould is found to be present, it is imperative to find and remove the mould. However, this position is promoted mostly by companies who make a living from removing mould (including ?hidden? mould), and therefore, the more mould they remove, the more money they make! Otherwise, there is no compelling reason to do any remediation beyond correcting the water damage, and (as part of that correction), address any remaining visible mould. The notion that ?hidden mould? presents a significant threat to human health or the quality of indoor air, is a myth. All studies performed to date have demonstrated that mould hidden in walls, do not adversely impact the air quality in the occupied space.

Indeed, leaving mould contaminated surfaces inside a property following a remediation is not only unavoidable, it actually constitutes part of the decision making process incorporated in such texts as the so-called ?Green Book? 4 and the WHO study, wherein WHO states:

The main challenge of field investigations is to decide which contaminated materials should be removed and which can be left in building assemblies with a reasonably low risk of indoor climate problems.

Far too many homeowners and property managers spend needless thousands of dollars of wasted financial resources unnecessarily tracking down and eliminating mould under the misconception that such removal is standard practice and is necessary to ensure good indoor air quality. In general, the removal of mould is considered to be acceptable when it is limited to that which is visible and/or known to be present and constitutes a problem due to aesthetic considerations. In general: 5

However, removal based on the mere fact of its presence, or based on nonspecific symptoms that are not related to muold exposure, is often not appropriate.

Similarly, other notable researchers have also concluded the same: : 6

?it is reasonable to infer that small amounts of mould enclosed in walls, floors, or ceilings will not have a large impact on the indoor air quality.

Studies and investigations performed by this author (Connell), consistent with other researchers, have not observed a correlation between mould hidden in walls and a degradation of indoor air quality or a correlation between mould hidden in walls and an increase in spore counts in occupied spaces.

Finally, we have encountered several poorly trained remediators and ?mould consultants? who claim they need to find the hidden mould to pass the ?final clearance sampling tests? following a mould remediation project. However, in short, there is no such thing as ?clearance testing? for moulds. No such tests, as commonly conducted, are scientifically valid, and none stand up to scientific scrutiny. The ?Green-Book? for example, addresses ?final clearance sampling? thusly:

18.5.2 Current mould remediation guidelines support the concept that project success depends on verification primarily through inspection that visible mould growth and associated debris and dust were appropriately removed. 7, 8, 9

The AIHA publication continues with:

The primary objective of mould remediation, based on based on guidelines published between 199310and 200411, 12 is to remove visible mould growth and return material surfaces to a satisfactory condition.

And the section concludes with:

A difficulty associated with using air sampling as the primary means of achieving final clearance is the absence of numerical guidelines for airborne fungi and for bioaerosols in general. 13, 14, 15 IOM16,concluded that, although there is an association between respiratory health effects and dampness, the exact causal agents of irritation and respiratory disease are obscure. Thus, from a health effects viewpoint it remains uncertain whether the EHS investigator should sample during final clearance for total spores, culturable spores, hyphal fragments, specific allergens, glucans, endotoxins, or other agents.

Dry rot is a destructive fungus whose history and name has left a legacy of confusion. Many still consider any brown, cuboidally cracked decay to be dry rot, and the inference from the name that dry rot needs less water than wet rots has had disastrous consequences for a number of buildings and the finances of their owners.

Dry rot is essentially a very efficient brown rot decay fungus with quite specific environmental requirements, but it has a reputation as a house-destroying superorganism. Much of the exaggeration and confusion concerning dry rot stems from the rather poor use of common names used to describe building fungi.

There are four terms in which building decay fungi are often described:

? Dry rot. In the UK this is a common name applied to one species of fungus only:Serpula lacrymans. It is sometimes applied to Meruliporia incrassata in North America.

? Wet rot. This is a catch-all term for every species of fungus that is not Serpula lacrymans.

? Brown rot. This term describes the mode of action of the fungus. In this respect, the term has some scientific relevance. Brown rots decay timber leaving the wood brown.

? White rot. In contrast, white rot fungi leave decayed wood white.

Dry rot (S. lacrymans) is a brown rot. Wet rots may use either mode of decay.

It is unfortunate the use of the terms dry and wet rot are so ingrained in the literature of building decay fungi as they are poor and misleading descriptors of these organisms. A brief overview of the history of building decay fungi in the UK reveals how we arrived at this unfortunate situation.

The origin of Serpula lacrymans in the British Isles remains obscure. The fungus does not occur outside of buildings over most of its range across the temperate regions of the world with the exception of a few colonies from the Himalayas, East Asia and the Czech Republic. Recent research has shown that two sub-groups of of the fungus exist, a wild type predominantly found in North America at high altitudes, and a more aggressive variety possibly of Asian origin.

It seems logical to suppose that dry rot reached these shores in infected timbers from Europe and the lack of genetic variation in the variety seems to support this. We know that the fungus attacked softwood on ships, and we also know that fungus had frequently to be scraped off cargoes of softwood when they were landed. Many cargoes of timber from the New World and from Europe had been largely destroyed in the ships holds before they reached port.

In 1759 shipbuilders along the Thames were asked to give an opinion on the comparative durability of English and French ships. They concluded that the English ship of war should long outlast the French. By the beginning of the nineteenth century, however, the situation had reversed. Matters came to a head in 1810 when the second HMS Queen Charlotte was launched at Deptford. Close examination revealed that all her upper-works (ends of the most of the beams, carlings, and ledges, the joinings of the planks etc.) were infected with the dry rot. The situation was investigated by A. Bowden of the Navy Office who published his conclusions in 1815 under the title -A Treatise on the Dry-Rot.

Two main forms of timber decay were recognized in Bowdens day, and these were common or wet rot and a relatively new phenomenon they called dry rot. We still use the same terms but our meaning is rather different, and it is important that we understand this difference.

In the eighteenth and early nineteenth centuries wet or common rot was seen as a form of decay which progressed inwards from the surface of the timber and was caused by the actions of wind, heat and water. The damage was thought to be chemical or mechanical. The resulting modified timber was considered particularly suitable as a substrate for fungus.

The connection between the dry rot and water was not made for a long time because the decay was seen as progressing from the inside of the timber outwards. The concept of water being absorbed and held within timber resulted in fungal decay was not grasped until later.

It is clear that what the earliest investigators termed ?dry rot? was in fact brown rot, and common or wet rot was white rot. The application of two different names is understandable when we consider that the two forms of decay do not look alike, and progress in a different fashion. The term was used because the damage was thought to be caused by internal ?fermentations? rather than water. It is also important to note that the term ?dry rot? was used for all brown rots, and would therefore have encompassed a wide variety of fungi which we would now consider to be wet rots (e.g. cellar rot).

The fact that fungi caused the decay rather than just living on it was not firmly established until work by the German botanist Robert Hartig was published in 1878, although the suggestion had been made as early as 1803. Considerable research into decay fungi ensued, not all of which was relevant to practical building situations. The conclusions reached, however, stay with us and have been woven into the mythology of dry rot.

Gradually throughout the nineteenth century the term became restricted to fungi which produced substantial mycelium, and even during the first half of the twentieth century there was a tendency to include the mine fungus Antrodia (Fibroporia) vaillantii as a dry rot. Eventually, however, the name referred to only one fungus Serpula lacrymans, and this became known as the ?true dry rot?. All other decay fungi (brown and white rots) were lumped together as wet rots. The ?true? prefix was gradually dropped towards the end of the twentieth century, although some literature still cites it as such.

The term ?dry rot? has come a long way from describing the fermentations of sap in eighteenth century ships? timbers. Work undertaken by the Forest Products Research Laboratory for the production of a British Standard in 1963 perceived the difference between wet rots and (?true?) dry rot was that the strands of dry rot had the ability to grow through walls and over inert surfaces. In contrast, the strands of wet rots (those that produced them) did not. Dry rot could therefore spread through the building where conditions allowed, whilst wet rot decay remained localised.

This is not the case: many species of wet rot will grow over or through walls. However, the separation of S. lacrymans from other building decay fungi and from other brown rot fungi has resulted in its inadvertent and quite unfounded status as a unique organism capable of quite the most biologically impossible feats. Coupled with a commercial treatment industry that is only too happy to pander to this unabashed scare-mongering in order to sell fungicide it has come to be feared by homeowners up and down the country.

Water damage in buildings and the prospect of timber decay

Should timber decay be expected without question, and what can be done to minimise the risk?

The following popular, but quite erroneous, wisdom has arisen from investigators? unquestioning but misinformed belief that the fungus has a name that accurately describes its biology, namely that:

? Dry rot produces enough water from the wood it is decaying to sustain it, so that the fungus continues to spread and cause damage even if the source of moisture that caused it is removed.

? Dry rot strands conduct water to make dry timber wet enough to attack.

? Buildings dry through a moisture zone where there is a risk of dry rot developing.

All of these ideas are nonsense, but widely believed and the consequence has been massive destruction. The treatment of dry rot has usually caused far more damage to our building heritage than the fungus. There are several archival cases where stately homes have been demolished due to financially prohibitive dry rot treatment quotations.

There is no doubt that dry rot, growing in a damp and neglected building, can cause considerable damage, but it will still be restricted by the local environment. A dry rot spore needs to land on timber with high moisture content (in excess of 28%) in order to germinate. Once growing, it will not spread to the dry parts of the house, a fact recently described by a German researcher, Tobias Huckfeldt, who also found its growth rate to be comparable to that of other building fungi. The fungus needs a substantial amount of fresh water to grow and thrive. Without that, it poses no threat to a building. Such potential sources of water should be considered before any suspended floor deemed insufficiently ventilated has the walls supporting it riddled with airbricks (with more loss of the building fabric).

?Dry rot? as a term to describe Serpula lacrymans is an unfortunate and inaccurate legacy of 200-year-old observations misapplied to an organism that does not warrant the infamy it has achieved.

The aims of this information sheet are to encourage the prevention and control of timber decay in old buildings by appropriate repair and regular maintenance by providing a step by step approach to timber defects. Many old buildings have been subjected to unnecessary, damaging chemical timber treatments. The most common reasons for this are:

The misdiagnosis of insect infestation and fungal decay.
The misunderstanding of the significance and structural implications of decay resulting in drastic remedies being used to deal with minor or extinct problems.
The carrying out of inappropriate or excessive treatments by timber and damp specialists as a condition of a mortgage.
The pressure to obtain instant and single solutions with guarantee backing ( as required as a condition of a mortgage)
Some remedial treatment companies having a tendency to recommend works in which they have a financial interest.
Some remedial treatment companies specifying more work than is necessary to minimise the risk of claims on guarantees.

The Step by step approach to avoiding unnecessary treatment

Step 1- Commission and inspection by someone with appropriate specialist knowledge.
Decisions about what, if any, timber treatment is appropriate should be informed ones, based on a careful inspection of the building. The assessment needs to be made by someone who understands the type of construction likely to be encountered, the timbers used in the construction, and the types of timber decay organisms that can attack the timbers.

Step 2- Careful assessment of the problem
This should include the following :
Detailed inspection of the timber defects-looking for signs of problems; probing accessible timbers to test their resistance; sounding timbers with a hammer for hollowness; testing with a moisture meter. The moisture meter is only a tool to aid diagnosis- its readings need to be interpreted by a person who understands the limitations of this equipment and what it is actually measuring- and must not be relied solely upon when deciding treatment. Identification of the causes and types of decay-dry timber is not vulnerable to attack by fungi or insects; they can only cause serious damage when there is damp. The first stage is to identify and eliminate the source of dampness otherwise the decay problem will continue.
The surveyor must understand the relationship between timber type, conditions within the building and decay organisms:-
The extent of damage and its structural significance.
The activity of the decay-decay that appears serious may be an extinct outbreak.
Is there a need for maintenance and/or further investigation? The more information available on the type and extent of the problem, makes possible the correct repairs and treatments. Thus the extra time and money of further investigation/monitoring is usually outweighed by the gains in avoiding necessary treatment.

Step 3- Implementing the repairs
Once the extent of damage and decay has been ascertained, appropriate repairs can be initiated. Achieved by :
Eliminating the sources of dampness
Controlled drying of the fabric.
Repairs to reinstate the structural strength of the timbers and the construction.
Providing support features-ventilation/isolation of the timbers.
Monitoring.

Step 4- Is timber treatment really necessary?
A sound basis to start from is the Health and Safety Executives recommendation that ? we must always seek to solve timber problems by construction methods (such as repair and replacement) where economically viable, before considering the use of chemical treatments.
The understanding of the building gained in Step 2 provides the information fro making a positive, well-informed decision on the most appropriate action for the building; whether the problems identified can be resolved by traditional construction methods of repair or whether chemical timber treatments are really necessary.

Any chemical treatment must be justified, targeted and applied in accordance with controlling regulations and legislation (Control of Substances Hazardous to Health 1988 (COSHH), Health and Safety at Work Act 1974, Control of Pesticide 1986, Wildlife and Countryside Act 1981)

Step 5- Implement regular and appropriate maintenance- the key to preventing future problems with timber decay.

If there is any doubt or concern about the advice or recommendations made regarding the repair or treatment of an old building, seek independent specialist advice or contact the SPAB.

Article originally published in the RICS Building Conservation Journal (No. 13 Winter 1995).

In the following article Richard Oxley expresses his concern over the increasing levels of uncontrolled and unnecessary remedial damp and timber treatments that a large proportion of historic buildings are subjected to. He identifies the problems and attempts to provide some solutions.

Introduction
Two examples of uncontrolled and unnecessary remedial damp and timber treatment are reviewed below together with some of the issues they raise. It is hoped that within the limitations of this article that I can convey the seriousness of this problem together with some of the items that I strongly believe need to be addressed.

Examples
The examples provided are both Grade II listed and typical of many historic buildings, in that they are of a vernacular construction; they are vulnerable to the impact of uncontrolled and unnecessary remedial treatment; and they do not have access to any significant resources, either in the terms of expertise or financial support, to be able to implement appropriate and sympathetic repairs. For example, English Heritage grant aid is aimed at the important Grade I and 11* listed buildings. These are the buildings which, in most cases, are already well protected and controlled and also have access to funding. The lack of resources available to the majority of listed buildings, combined with other external pressures and influences (such as the demands of the purchasers/owners for instant solutions; the requirements of mortgage lenders; the vested financial interest of the remedial contractors) leads to a significant loss of historic fabric. Uncontrolled and unnecessary remedial treatment can be shown in the examples below, and have played a prominent role in causing irreversible damage to historic buildings.

Example 1
A report from a remedial damp and timber contractor was provided on a late 17th century timber framed Grade II listed cottage. The causes of dampness to the building were positively identified by the contractor as defective rain water goods and high external ground levels. The contractor, however, stated that rising damp appears to be due to the apparent absence of an effective damp?proof course. As a consequence the provision of an injection damp?proof course and the removal of the existing floor were carried out.

A chemical damp?proof course was injected into the timber sill beam which was a complete waste of time, effort and money. To add insult to injury the contractors recommendations included providing an internal barrier of sand/cement render ... to those areas at least up to the level of the newly installed damp ?proof course. This would result in a sand and cement render abutting the injected timber sill beam, consequently trapping moisture and leading to the accelerated deterioration and failure of a principal structural component.

The contractor recommended the replacement of the existing floor with a modern concrete floor incorporating a damp?proof membrane. This would actually lead to exacerbating the problems of dampness within the building. The provision of this modern floor would remove a means where moisture could currently escape through evaporation. The consequence of this is that moisture will seek to be released via the walls, the hydrostatic pressure and capillary action causing a new damp problem. The historic fabric suffered severe irreversible disruption to facilitate the provision of the concrete floor.

In this case there is sufficient evidence to indicate that the inspecting remedial surveyor/contractor did not even have a basic understanding of the constructional nature of the building in question. As a result, standard treatment and practices have been carried out to a non?standard building. The dampness could have been eliminated through other methods, such as reducing external ground levels and repairing rain water goods. In combination with a lack of appropriate knowledge there would also appear to be evidence of implementing the standard remedial works (eg injection damp?proof course and re?plastering) ? as the contractor had the available in?house skills and materials to make this cost effective and assist in his achieving any financial targets. It can therefore be argued that the lack of knowledge and the vested financial interest of the contractor have resulted in works to a listed building which cannot be fully justified, are totally inappropriate, and have caused a vast amount of irreversible damage.

- Example 2
Prior to the sale of a Grade II thatched timber framed building the vendor commissioned a report from a remedial damp and timber contractor. The contractor stated that a survey for rising dampness and a timber inspection of accessible timbers had been carried out. A subsequent inspection by a chartered surveyor for mortgage purposes revealed that in this case the causes of dampness had not been positively identified by the contractor, such as poor detailing between the thatch and chimney stack resulting in water penetration at both ground and first floor levels. In addition the contractor gave no warning about the potential for rot to exist or develop behind timber panelling ? even though the levels of dampness identified by the contractor justified the provision of a chemical injection damp?proof course, into what is mainly a single skin timber framed building. The contractors recommendations were based solely on tests with a moisture meter and no tests were taken for the presence of salts. This did not stop re?plastering being recommended due to dampness from hygroscopic salts which absorb atmospheric moisture.

As mentioned, the brief inspection for mortgage purposes revealed the failure of the contractor to identify severe rot to a timber wall plate and rafters, caused by the poor detailing at the junction of the stack and thatch covering. This is a serious omission by the contractor due to the structural nature of the timbers involved. The contractors inspection and resulting recommendations show a blatant disregard for the recommendations of the Health and Safety Executive in their guide: Remedial Timber Treatment in Buildings. This guide clearly recommends that any inspection should identify the location of the sources of moisture; ingress of moisture into buildings is the main cause of damp timber and therefore fun gal attack. The surveyor must examine the whole building rather than just those parts obviously affected by damp.

In this case the cause of the damp penetration was identified by the mortgage valuation surveyor. This lead to an investigation of the areas at risk internally which showed that the mortgage valuation surveyor had followed the trail. Even within the limitations of a mortgage valuation this serious fault was positively identified, whereas it had been completely missed by the remedial contractor who had reputably inspected all accessible timbers.

This re?emphasises the recommendations made by the Health and Safety Executive in their guide; serious timber problems can be caused by more subtle failures in the building fabric, detailed survey must only be carried out by a qualified surveyor who has had appropriate and professional training in identifying building faults. There is no definition of a qualified surveyor within the guide but it can be assumed that a chartered surveyor would meet this requirement. At the very least it should be ensured that the inspecting remedial contractor has the Certified Surveyors in Remedial Treatment (CSRT) qualification, and, where possible, a knowledge of the physical and philosophical demands and requirements of historic buildings.

In this example, timber treatment was recommended by the contractor as a precautionary measure. The contractor did not identify and report any active infestation, only that there was evidence of previous common furniture beetle infestation. No justification for the recommended treatment was provided, thereby clearly ignoring the guidance of the Health and Safety Executive; The single most important question that must be asked by a surveyor is, is there any need to use wood preservatives to control and stop timber decay? It is evident that the potential health and safety considerations of the occupiers/users of this building have been overruled by the short term commercial gains that can be made by the contractor following the practice of treatment.

As a result of the findings of the mortgage valuation surveyor, a subsequent inspection and report from another contractor was obtained. The results of which caused great concern because exactly the same errors and mistakes were made by the second contractor. Reiterating that many remedial damp and timber contractors are not geared up to propose appropriate remedial repairs and treatments to vernacular historic buildings.

These two examples, which from my experience are not isolated cases, illustrate that great care must be taken when relying or commenting upon reports and estimates from a remedial damp and timber contractor. It is essential to ensure that the recommendations made by the contractor are appropriate to the building in question. There is a tendency for surveyors to accept the recommendations made by the contractor as being automatically appropriate and justified. The examples clearly show that this is not always the case. It is important for surveyors to appreciate that their reputation as a property professional will diminish if there is a continued reliance in contractors who have a vested financial interest in their own recommendations. If chartered surveyors adopted this approach it would be considered unacceptable from an ethical point of view by the RICS yet this is accepted as standard practice for the remedial treatment of damp and timber decay in buildings.

Practice should be reviewed with the long term interests of historic buildings and the reputations of both the surveying profession and the remedial damp and timber treatment industry in mind.

The Effectiveness of Existing Controls
Remedial damp and timber treatment in historic buildings is mainly controlled on a discretionary basis. Whether listed building consent is required for remedial treatment is subject to variable levels of interpretation by different Local Authorities and their Conservation Officers. The political will of the individual Authority and the resources available to the Conservation Officer (in respect of available time and finance) may well influence whether or not listed building consent is actually required for such remedial treatment or not. As a result, a significant amount of treatment is carried out on an inconsistent, uncontrolled and unjustified basis. This results in a substantial amount of unnecessary damage to a significant number of historic buildings. For this very reason there is a strong argument for listed building consent being made a mandatory requirement where such remedial treatment is thought necessary. This would result in an increased level of consistency, control and justification over and above that which currently exists

On a strict interpretation of the guidance provided by PPG15 listed building consent should be required in the majority of cases where remedial treatment is proposed. There are sufficient examples to illustrate that there is a substantial amount of work undertaken during remedial repairs that would affect the character of listed buildings. If only the guidance contained within Annex C (C.3) of PPG15 was followed when remedial damp and timber treatment was being carried out then a significant amount of reversible damage would be avoided:

Alterations should be based on a proper understanding of the structure. Some listed buildings may suffer from structural defects arising from their age, methods of construction or past use, but they can still give adequate service provided they are not subject to major disturbance. Repairs should usually be low?key, re?instating or strengthening the structure where appropriate; such repairs may sometimes require listed building consent.

Conversely PPGI5, the principal guidance document concerning the protection of historic buildings, does not positively recognise the issue of uncontrolled and unnecessary damp and timber treatment. Annex C of PPG 15 addresses in great detail the external and internal constructional elements and how alterations to listed buildings should be approached. There is no mention whatsoever of remedial damp and timber treatment, arguably one of the most common as well as intrusive and destructive forces that can be inflicted upon historic buildings. This omission shows a complete disregard and a lack of recognition of a serious reoccurring problem.

The first example illustrated that inappropriate and uncontrolled treatment can lead to the structural integrity of the building being put at risk. This example is not an isolated case and as such this issue needs to be urgently addressed in a practical manner, so that the continued uncontrolled and unnecessary loss of historic fabric can be abated.

However, it seems highly unlikely that this issue will be adequately addressed as the current Government is attempting to introduce more democratic and relaxed controls within the imminent Green Paper. The buildin2s that are most likely to suffer from the implementation of such a proposal are those already susceptible and vulnerable to uncontrolled and unnecessary repairs and treatment, eg Grade II listed buildings of a vernacular construction; in fact there is a strong argument for tighter controls over the most basic of repairs such as re?pointing, the application of non?permeable paints and treatments, and re?rendering, in addition to remedial damp and timber treatment. In fact, it is these every day repairs and maintenance works that are contributing to the accelerated deterioration of the fabric of these buildings, probably at a faster rate than most of these buildings have suffered in their previous and long history. For this reason alone there is some justification for imposing stricter controls upon listed buildings as the current system is obviously failing the buildings that require the most protection.

Funds need to be made available to counter the lack of resources and also enable controls to be enforced. This could be achieved by allocating a pool of funds which could be made available from the Heritage Lottery Fund. Funds could be directed at the buildings that are currently the most susceptible to such uncontrolled and unnecessary treatment. Just a relatively small amount of money will enable Conservation Officers to exert greater control over the repair, maintenance and modernisation of these buildings and also provide owners with an increased incentive to repair their buildings in an appropriate and sympathetic manner. Thereby substantially reducing the vast amounts of historic fabric which are currently being lost through this uncontrolled practice.

The actual level of physical disturbance can be shown to be ineffectively controlled. This can be illustrated to best effect by using the chemical damp proof course, and the hard cement replastering that usually follows, as an example. The provision of a chemical injection damp proof course does not require any approval or consent and can be implemented at the whim of the contractor, who as we have seen may well have a vested interest In carrying Out the works. This makes the control of such work to historic buildings through the planning legislation (The Planning (Listed Buildings and Conservation Areas) Act 1990) even more important thereby vindicating the stricter control of damp and timber treatment by requiring such works to obtain listed building consent.

There is definite legislative control on the type of chemicals that can be used and how these chemicals can be used (Control of Pesticides Regulations 1986 (CPOR), the Health and Safety at Work etc. Act 1974, The Control of Substances Hazardous to Health Regulations 1988, the Wildlife and Countryside Act 1981. the Water Act 1989 and the Environmental Protection Act 1990). However, there is no express control that would actually reduce the levels of uncontrolled and unnecessary remedial treatment. The Health and Safety Executive guide provides enough ambiguity for the remedial contractor to justify treatment, as the guide recommends that wood preservatives should not be used unless it is judged necessary to halt an attack now or in the future The second example illustrated that the contractor made little or no effort to determine whether the infestation was active, yet the contractor still recommended treatment. From my experience it is not rare for the contractor to recommend treatment without having ever determined whether the infestation was actually active or not. This is in conflict with the Health and Safety Executive guidance; The surveyor must attempt to establish whether the attacks are extinct ? and if they are, treatment is not necessary.

Unless the contractor is conservation and/or environmentally minded then it is highly likely that treatment will be justified on the basis that it will be required in the future. Commercial gain will take precedent over the correct use and general principle of the guidance, which is for treatment to be implemented only where necessary. This is a problem that will be difficult to address within the confines of current practices and procedures. Therefore remedial contractors must be given every encouragement to be included within the field of conservation so that historic buildings can benefit from their participation and receive appropriate treatment where necessary. But remedial contractors must, however, show a clear and full understanding of the needs and requirements of historic buildings for their involvement to be justified.

Can the problem of uncontrolled and unnecessary treatment be addressed?
The obvious solution is for this problem to be resolved through the provision of increased resources, in the form of expertise and finance. But in these times of reduced budgets and strict control over financial expenditure it is highly unlikely that the necessary resources will be made available to enable the protection of these buildings to be improved. There needs to be an appreciation that unless this issue is effectively addressed the less important historic buildings that provide a back drop to our national heritage will continue to be at great risk. Without these buildings the more important Grade I and 11* properties will loose their historical background and context, which in turn would reduce our understanding of these buildings over time. For this reason alone there is an urgent need for a change in priorities so that the majority of historic buildings are given an effective means of protection. Recent research has lead to the development of sophisticated investigative, remedial and monitoring techniques and the development of an environmental approach to damp and timber defects. Currently the majority of historic buildings do not have the benefit of these techniques and these are the very buildings that are crying out for such remedies. The main reason for this is that a number of these techniques and methods are beyond the resources of these buildings and their owners, either in terms of availability, practicability, cost, expertise and/or funding. There is also room to improve the promotion to these products and techniques so that they can be recommended and/or used by the investigating surveyors and contractors.

On this basis there is a good argument for further research to be carried out to determine whether these methods can be adopted and/or developed so that they maybe easily implemented in an inexpensive manner utilising readily available expertise and materials. For any treatment to be to the benefit of the majority of historic buildings it has to take into consideration that the vast majority of these buildings are residentially occupied. There is therefore a need for these techniques to be developed so that they can be applied under these circumstances.

The majority of historic buildings will not benefit from improved practices until surveyors improve the level of their knowledge and implement their recommendations accordingly. It is not sufficient to identify that a property is suffering from damp and timber defects and then recommend that a report is obtained from a specialist contractor; this normally results in the whole process of uncontrolled and unnecessary treatment being instigated. There is a need to break this cycle if we are to avoid the continued loss of the historic fabric. However, current practices and procedures limit how a surveyor can report upon damp and timber defects, especially within the confines of an inspection and report for mortgage purposes. There is a need for more readily available alternatives to enable a surveyor to recommend that an independent specialist in historic buildings and/or damp and timber defects can be instructed to report upon the property. This would be in keeping with the mandatory recommendations of the Appraisal and Valuation Manual (the new Red Book) at Annex A to Practice Statement 9 which states at 3.10 that;

Where the Valuer decides to report a necessity for works to be carried out to a property as a condition of any advance and the Valuer identifies the property as being: ... of architectural or historic interest, or listed as such; or... in a conservation area.., the Valuer should advise that a person with appropriate specialist knowledge be asked to give advice as to the appropriate works unless, exceptionally, the Valuer believes he/she is competent to give advice which if adopted would not be detrimental to the propertys architectural or historical integrity, its future structural condition or conservation of the building fabric.

A significant number of historic buildings, being residential, will therefore be subject to a mortgage loan. The complex influences and pressures placed upon historic buildings by the mortgage process mean that it is essential that the correct persons are instructed to inspect and report on these buildings. This means that lenders and surveyors have to make every effort for the recommendations of the Appraisal and Valuation Manual to be followed. If this could be successfully achieved it would be a significant step towards substantially reducing the level of uncontrolled and unnecessary remedial treatment suffered by historic buildings. This is currently the aim of the Building Conservation Skills Panel Working Party which is looking at the relationship between mortgage valuations and historic buildings.

Summary
The basic philosophical principles that should be applied to historic buildings of maximum retention of early fabric, minimum intervention and maximum reversibility can not be adhered to when uncontrolled remedial damp and timber treatment is carried out. If this dichotomy persists and is not addressed a substantial amount of historic fabric will continue to be lost for no other reason than inertia and commercial gain.

On the basis of the arguments and examples put forward in this article there is an urgent need to; 1-formally illustrate that current processes and methods are acting to the detriment of historic buildings;
2-determine whether damp and timber defects can be resolved in a practical manner that can be put into everyday use;
3- identify what influences uncontrolled and unnecessary remedial treatment and how these influences can be addressed, and;
4- assess the implications of chemical treatment upon historic buildings both technically and environmentally.

Damp rises, penetrates, or results from condensation or leaking services. Rising damp is the most commonly misdiagnosed and remedial solutions for it are often inappropriate.

The term ?damp? is broad and the problems associated with damp in buildings can manifest themselves in various ways according to the source of moisture. damp can be a very emotive issue for property owners as the results can be both damaging to the fabric and decoration of the building, and may create an unhealthy environment for the occupant. The problem could also lower the value of the property.

When the term damp is applied to a building it suggests the presence of an unacceptable level of moisture within the building fabric. The source of moisture ingress associated with dampness falls into four broad categories, rising damp, penetrating damp, condensation and leaking services. Of the four sources of damp, it is rising damp that is most commonly misdiagnosed and for which inappropriate remedial solutions are recommended within historic buildings.

When faced with damp in a historic building, the first step generally taken by owners and, surprisingly, some historic building professionals is to call in one of the many local damp specialists. Such companies are often referred to as remedial firms or, perhaps more ironically in some cases, preservation firms.

Much of the remedial industry?s concerns installing remedial damp-proof courses and waterproofing (tanking) basements and other subterranean structures. Many operatives within the industry legitimately receive a sales commission on materials or contracts.

The problem for us conservation professionals is that the advice given by such firms is often inappropriate for historic buildings. However, the possibility of offering a more appropriate solution often requires a robust independent diagnosis. Commissioning such a diagnosis generally proves to be financially unattractive to the property owner and beyond the means of the conservation professional. It may be possible to compel a property owner to commission a second opinion from a consultant capable of working with historic buildings in cases where the building is listed and the remedial work would require listed building consent.

Rising damp is caused by moisture rising up from the ground by capillary action through interconnecting pores within the material. Problems can appear in floors and the base of walls up to about 1.5m above ground level. The visual evidence of rising damp is a band of discolouration or surface damage running around internal walls, usually about 500mm to 1m above ground level. The band, often called the evaporation zone, is caused by soluble salts migrating up from the soil with the rising moisture concentrate (on or within the surface of the substrate) and crystallising as the moisture evaporates. The expansion of the microscopic crystals within the material?s surface pores breaks the surface, causing it to become friable. The hygroscopic nature of the concentration of salts can also continue to draw moisture from the air, depending on the humidity within the building. due to this phenomenon the evaporation zone may appear damp and slimy to the touch even if damp is no longer rising damp.

The soil beneath the building must also be damp for at least part of the year if rising damp is to occur. Such ground conditions can be due to prevailing hydrology, such as marshy ground. However, in most cases involving historic buildings it is likely that the presence of moisture will be due to building failures or later interventions. Such factors may include raised external ground level or the failure of external drainage. Later interventions can generally be addressed and moisture ingress reduced to an acceptable level without installing a remedial damp-proof course and causing the associated damage.

It should be possible to approach all damp problems, including rising damp, through the following sequence:

1. assess visual evidence of dampness affecting the external and internal fabric of the building.
2. assess possible sources of moisture ingress associated with the pattern of visual evidence.
3. Carry out an accurate test of moisture levels within the affected areas to establish whether the dampness is current or past. Additional tests for soluble salts may be required in cases where rising damp is thought to be an issue.
4. Implement repairs or other appropriate interventions to control moisture ingress.
5. Implement appropriate measures to dry the building fabric, and monitor the drying process.
6. Carry out reinstatement works or cosmetic repairs. Most remedial firms will carry out a free survey of the problem and issue a report. Such reports can range from a fairly detailed assessment of the problem to, more often, little more than a quote for the work. Remedial firms and building surveyors will generally cover steps 1 and 2 to varying levels of thoroughness in order to make their assessment. Few will include step 3, other than to take a few measurements using an electrical resistance meter.

It is generally accepted that electrical resistance meters (also called moisture meters) are accurate when testing timber. But, despite reassurances from manufacturers, there is some debate as to their accuracy in masonry. Readings can be corrupted by the presence of salts within the masonry and may falsely suggest the masonry is damp. Most such meters are designed to measure surface moisture. Some are also designed to measure moisture at depth within masonry, using radio frequency. It is also possible to extrapolate a moisture reading from a measurement of relative humidity by inserting a thermal hygrometer into a predrilled hole in the masonry. Such methods may provide an indicative moisture reading but they cannot diagnose rising damp.

The moisture content of masonry can be tested accurately by removing a masonry sample for analysis. Samples are generally removed by drilling into the masonry from inside the building (the diameter would not generally exceed 15mm) and collecting the emerging dust. This can be tested on site using the ?speedy carbide? method or off site in a laboratory using the ?oven-balance? method. The speedy carbide method involves mixing a measured dust sample with calcium carbide in a sealed flask. The reaction produces acetylene gas. The more moisture is in the sample, the more gas is produced. Levels are measured by a pressure gauge on the flask. This method is useful for instant on-site moisture testing, but the results can not be analysed later to indicate the source of the moisture.

The most accurate test for moisture content in masonry and the presence of rising damp is the laboratory oven-balance method, as described by Building Research Establishment Digest 245. The process relies on a series of samples taken in a sequence up the wall at several positions around the building. The dust samples are sealed into vials and delivered to a laboratory. Moisture loss is calculated by accurately weighing and drying the samples. The level of hygroscopic nitrates and chlorides present can be calculated by submitting the samples to a relative humidity of 75 per cent. an accurate pattern of moisture and hygroscopic salt distribution can be plotted to show the distribution of damp within the walls and the presence of any rising damp.

Both the sampling methods above are to some extent destructive and there may be situations where such tests would be inappropriate. However, the damage caused by the sample extraction would rarely outweigh the potential damage caused by inappropriate remedial treatment.

Some remedial firms may use a carbide meter on request. Some will also use test strips to establish the presence of different salts. Such tests may add weight to a contractor?s diagnosis, especially if there is no visible evidence of later interventions leading to moisture ingress. Other than paid independent damp consultants, very few specialists would entertain the use of the oven-balance method as described in BRE digest, due to the time and costs involved.

The solution to a damp problem will depend on the correct diagnosis of the source of the moisture. If any evidence of dampness is observed at low level within a building, it is likely that in most cases contractors will specify the installation of an injected damp-proof course, especially where no damp-course is visible.

Installing a remedial damp-proof course will generally involve drilling and injecting a chemical preparation along the external base of the affected wall. The chemical is designed to spread out within the masonry, inhibiting moisture from rising. This process does not entirely eliminate rising moisture, so the internal plasterwork is generally replaced up to one metre around each room. a fairly impermeable render is used, providing a dry finish for re-plastering or decoration. This procedure will also conveniently mask any failure of the injected damp proof course.

It is also likely that the installation of a damp-proof membrane (dpm) across the floor may be specified. This would inevitably involve excavating the floor surface and installing a dpm usually in the form of a plastic sheet. a new floor surface would then be formed over the membrane.

Notwithstanding damage which may be present due to genuine damp problems, the damage and loss of original fabric caused by these procedures can be significant, such as the drilling of external holes, loss of original plaster, and excavation of floor coverings. The work may also destroy archaeological features such as wall paintings and earlier floor coverings. as moisture will take the line of least resistance, the introduction of impervious materials can push the problem to another part of the building if the cause of the problem is not properly addressed. There are unlikely to be many occasions where a remedial damp proof course would be considered by conservation professionals to be appropriate in a historic building.

In the past, mortgage lenders often insisted on a damp-proof course (with a guarantee) being installed if an existing damp course had not been identified in the building survey. However, the relative cost of most remedial work is increasingly insignificant in relation to the equity in the property, and most mortgage lenders do not now insist on such work. The absence of a paper guarantee may put off buyers in some cases.

Various electrical remedial damp systems, using a process called electro-osmosis to remove the moisture, have been marketed over the years. Such systems tend to be less invasive, the minimum requirement being the installation of an electrical control unit. Electro-osmotic systems require the installation of a conducting electrode in the form of a wire circuit buried within the base of the wall and running around the perimeter of the building. Most practitioners are highly sceptical about the performance of such technology. although firms are constantly marketing new forms of electrical remedial damp systems, they are not generally considered to be fully proven.

Atmospheric siphons have been in and out of favour for many years now. Most popularly marketed as ?dalton tubes?, the technology is currently being marketed as a Dutch solution to rising damp. The procedure involves inserting a series of vents around the base of external walls to encourage moisture to evaporate from within the wall before rising further. The vents themselves tend to form the basis of the marketed product. They can take various forms, from cast-iron triangular tubes to circular ceramic designs. The ends of the tubes remain visible around the base of the external walls, causing visual detriment, and installing them causes physical damage. apart from the associated damage, the scientific theory behind the technology has apparently been discredited, not least by Giovanni and Ippolito Massari in the ICCROM publication Damp Buildings: old and new. Such solutions are not considered appropriate for use in historic buildings.

Later interventions affecting the performance of historic buildings are commonly responsible for damp problems around the base of buildings. Where possible these should be tackled before further remedial work is considered. damp masonry could take many months to dry following the elimination of the source of moisture.

Common later interventions include:
? external ground level raised above internal floor level
? raised flowerbeds built against external walls
? undrained hard surfaces built up against the base of walls
? trees and shrubs growing against buildings, encouraging moisture to dwell against the wall of the building and damaging subterranean drainage systems
? inappropriately designed rainwater drainage systems, such as down pipes that discharge at the base of the building
? inappropriate cementitious render or pointing encouraging a build-up of moisture within the fabric by directing rainwater into the building or discouraging evaporation.

The concept of the French drain is to intercept and reduce moisture around the base of external walls. The installation of a French drain involves excavation of a trench (commonly 600mm deep x 400mm wide) around the perimeter of the building to take a continuous, perforated land drainage pipe. The trench is normally positioned against the building or in a convenient position close to the perimeter. It is backfilled with a suitable gravel to allow free drainage and encourage evaporation of moisture from the trench or the base of the wall.

Conservation professionals generally favour French drains as a method of tackling damp at the base of historic buildings due to the minimal impact on the building?s fabric. However, there may be important archaeological and structural considerations to be considered in a particular case. Ian Hulme?s guidance note (an IHBC technical sub-committee paper) on French drains is available through the IHBC website.

Conservation professionals, faced with a scenario where rising damp has been offered as a cause but suspicious of or disagreeing with a proposed remedial solution, may want to investigate and negotiate. But they will remember that any standard remedial works can be highly destructive, can simply mask the problem and ultimately fail to address the cause of the moisture ingress.

If the building were listed, most standard remedial solutions would require listed building consent. In such cases an assessment by an independent consultant can be stipulated. Such an assessment would ideally involve tests using BRE digest 245. However, sourcing an independent assessment may not be straightforward.

The cost of an assessment by an independent damp consultant is often prohibitive for average-sized domestic properties due to travel and laboratory expenses. The choice of independent consultants offering specialist damp analysis for historic buildings is also extremely limited and the quality of service can be variable.

If you feel confident enough, it may be worth attempting a visual assessment of the situation yourself in the hope that there may be clear evidence of later interventions relating to areas of damp damage internally. Clearly, you may not be in a position where your professional indemnity enables you to dispute the judgement of another professional. Nevertheless, you may be able to persuade the client or building owner that it may be prudent to address the more obvious causes of moisture ingress before embarking on more damaging, and potentially more costly, procedures.

It is more than likely that the source of moisture affecting the base of the walls will be due to later interventions. Even if this is not the case and the presence of rising damp is proven, the use of a French drain represents a possible alternative solution.

The latest wonder damp-proofing product from Europe involving a magic box being fitted to a wall has arrived in the UK but instead of Germany this time it is coming from France and the explanation of how rising damp occurs in walls is as follows which was taken directly from the Mur-tronic website

WHAT IS RISING DAMP?

Because of its physical and geological characteristics, the Earth, which rotates and is covered by north-south magnetic ?force-lines?, generates a considerable amount of radiation. This radiation includes the presence of electromagnetic fields that give rise to electrical charges in water molecules and in the capillaries of the materials used to build walls.

The charges are very weak, but combined with the electric charges resulting from the circulation of water in the capillary system (zeta potential), over a period of time cause rising damp in walls. The result is more or less evident depending on the type of material, its porosity, mineral salt content, etc. To understand what happens in the capillary system of materials, which comprises bipolar molecules of water, and capillaries, you need to know that the system behaves like a cylindrical electrical condenser. Different concentrations of charges are observed depending on the level of the layers of water molecules and capillaries. These charges from the electromagnetic fields attract water to the drier capillaries at a higher level, until a balance is reached and a tide-mark of dampness forms.

The solution to rising damp is the installation of one their Mur-Tronic units which neutralises the effect of the natural electromagnetic fields by creating a natural counter-field with an opposite phase, which cancels out the cause of rising damp .It consists of sending very weak electromagnetic signals to the capillary system, thereby constantly modifying the polarity of the layers separating the charges in the capillaries. The surface tension of water and the angle of the meniscus in the capillaries is changed.

This principle makes it possible to neutralise the links between the H2O and salt ions and to lower the surface tension of the water which is high because of hydrogen bridges. This result is achieved using very little energy, contrary to the principle of electro-osmosis, which requires a greater input of energy.

The movement of water towards the top of the wall is halted i.e. the osmotic pressure is thus destroyed and the walls dry out, even in very damp environments. It is easy to see that the process does not merely mask the effects of the rising damp, as is often the case with the chemical and other methods used over the past decades, but deals with the cause, i.e. the electrical characteristics of the soil and the chemical components of the walls.

SIMPLE AS THAT!

The sole UK distributor and installer of this unique but yet unproven damp-proofing system is Advanced Geo Humidity Solutions from Sidcup, Kent who offer a 10 year guarantee against the recurrence of rising damp but are only able to offer their free damp diagnosis service within a five mile radius of Sidcup.

The Mur-Tronic form of damp-proofing appears to be very similar to the system offered by a German company called Drymat who say their magic box system will strengthen the reverse polarity of the flow direction thanks to the additional wall electrodes and a soil earth electrode. Water and salts contained therein migrate in this manner perceptibly faster and more effectively.

We have not come across either of these forms of damp-proofing and would like to hear from any householder who has had either the Mur-Tronic or Drymat damp-control systems fitted and whether they have been effective or not.

Clare McVey investigates damp diagnoses that leave consumers paying for unnecessary work

After viewing more than 20 properties, Denise Dawes felt she had finally found her dream Cotswolds cottage ? until she was told she would need to spend more than ?7,000 to fix a damp patch.

Dawes, 51, was buying a ?120,000 Victorian cottage that had been completely renovated by the previous owners, so she had not been expecting large-scale works.

?The mortgage company asked me to get a damp survey done by a member of the British Wood Preserving and Damp-Proofing Association (BWPDA),? she says. ?This chap showed me all the red lights flashing on his damp meter. I was horrified as we really wanted this cottage, so I decided to seek a second opinion.?

The vendors had had damp-proofing done, and a different surveyor confirmed that channels were already in place and that moisture being detected was caused by condensation and the recent plaster drying out.

Dawes?s house purchase is going through, but thousands of buyers each year are not so lucky. Damp ? and the fear of it ? plagues the housing market. Vendors are persuaded to drop their price, buyers back out, and homeowners fork out for expensive works. Despite the prevalence of the problem, however, consumers are still being ripped off.

Damp undeniably causes real damage. Chris Mahony, of the Royal Institution of Chartered Surveyors (RICS), says: ?Damp can lead to rot in timbers, corrosion of metal fixings and mould growth. What is important is for the surveyor to correctly identify the cause. Rising dampness occurs much less frequently than one might think.?

Other common causes include condensation, plumbing leaks, the localised failure of the damp-proof course and water penetration caused by blocked gutters.

?Small localised areas are unlikely to affect the integrity of the building, but if dampness has started to cause timbers to rot, prompt remedial action will be needed,? says Mahony.

Even a full structural survey has its limits, however; Mahony warns that patches of damp may be lurking behind furniture or covered by paint.

So how do you know if you have a genuine damp problem? Surveyors often advise buyers to get specialist companies in to conduct damp surveys, but many firms offer ?free? surveys and then recoup the cost by recommending extensive works.

Trevor Kent, a former president of the National Association of Estate Agents, says: ?Surveyors are reducing their exposure by saying that houses must be checked by independent so-called specialists to absolve themselves of responsibility. But the surveyors are the trained experts. The woodworm and damp people often have no training at all.?

Kent cites one client advised by his surveyor to get a specialist damp report. The buyer asked three firms for their opinion; each one found damp in a different wall.

Another common problem is that guarantees offered for damp work ?are not worth the paper they?re written on?, says Anthony Kerrigan, of Kerrigan?s Property Services in Doncaster. ?I don?t think we have ever had a situation where a surveyor has found damp and we?ve been able to claim on a guarantee. They?ve either gone out of business or claim the problems are related to an area they didn?t treat.?

Although guarantees offered by members of the BWPDA, the leading trade body, are backed by insurance if the company goes out of business, only 10% of firms operating in this area are members. In any case, even BWPDA companies may employ their surveyors on a commission basis, meaning that they have an incentive to ?find? work.

Chris Coggins, director of the BWPDA, says the body encourages members to charge for their professional services. ?The so-called free survey was introduced as a marketing ploy and has not served the industry or the public well.

?We would take disciplinary action against a member found to be fraudulently recommending work, knowing it was unnecessary.? But, he says, ?there may be more than one way to deal with the problem?.

Paul Taylor of UK Damp & Decay Control spent years installing chemical damp-proof courses before realising, he says, that he could offer customers simpler and more cost-effective solutions.

?Much of this work is unnecessary as rising damp is often assumed to be the problem, when it may instead be condensation or penetrating damp, which can usually be remedied at a fraction of the cost of chemical works.?

Steve Playle, a Surrey trading standards officer, advises: ?Don?t assume the companies with the biggest ads are necessarily the best. The bigger companies tend to subcontract which means they have less control over the work. If you think you?ve been ripped off, notify trading standards. If we have a few complaints about the same company we will investigate.?

The Rated Column in the News of The World focuses on damp and has lots of good advice about how to prevent dampness in the house.

It also has a small sub-column headed Cancer of Buildings relating to Dry Rot stating that the fungus can spread through a house in a manner similar to cancer and that the only course of treatment is to spray houses with chemicals and remove affected sections of wood and stone.

Most of these chemical treatments are not really required as dry rot can be controlled by removing the source of moisture and as dry rot is essentially a plant it will die out naturally without the need for mass use of fungicides to irrigate walls.

Other chemical free forms of dry rot eradication involve heat treatment of whole or part of buildings which successfully kills any fungus and beetle infestation or sacrificing the blood of two doves on affected sections of houses to kill fretting leprosy of the house as described in The Old Testament (Leviticus Chapter 14 verses 33-53).

But really common sense is all that is required in the treatment of any dry rot. Cut off the source of moisture, cut out any decayed timber and affected sections of plaster, promote rapid drying and then re-instate timber and plaster. No chemical treatments required.

Often dry rot stems from penetrating dampness due to a gutter or plumbing leaks but the most common cause that we find when carrying out damp surveys is where the original damp-proof course has been bridged and air bricks providing sub-floor ventilation have been blocked.

We have currently been on one such project in Tudor Hill, Sutton Coldfield, Birmingham B73. These are well built houses and normally would not have a problem with dampness or dry rot but the damp course had been bridged by a blocking paving drive and this had partially covered the air bricks and water flowing down the slope of the drive was being diverted into the sub-floor area through the air bricks. This resulted in a build up of moisture under the floor which lead to dampness and then dry rot in the floor timbers. We had to remove the entire lounge floor and replace it with new timbers after we had sterilised the affected area with a combination of heat treatment and organic preservatives. The work cost over 10,000 pounds but this could have been avoided if the contractors who installed the paving had created a drainage channel at the base of the wall and not blocked off the air bricks.

While on the job I took my dogs for a walk in Sutton Park and then a bit of phsychogeography around the local area including Driffold, Wylde Green,Maney etc. Most of the houses in the area are semi-detached or detached properties built around 1930-40 and all have a combination of a physical damp-proof course and a band of blue engineering bricks at the base of external walls to prevent rising dampness. However roughly twenty percent of the houses had their damp-course bridged and air bricks blocked by block paving drives so I expect thet we will be getting a few more calls in this area of Birmingham in the next couple of years as the damp and rot sets into these houses.

For more advice on the correct diagnosis and treatment of dry rot then please call us on 0800 028 1903 or e-mail enquiries at ukdamp.co.uk (anti-spam so please replace at with @ )