Condensation dampness in a building usually occurs when warm air comes into contact with a cold surface. The air is cooled below its saturation point causing its excess water vapour to change into liquid water. The condensed water usually appears as water droplets or water film on non-absorbent surfaces such as windows or tiles. This form of condensation is described as surface condensation.
Condensation in houses is mainly a winter problem particularly where warm moist air is generated in living areas and then penetrated to colder parts of the building. Water vapour is produced in relatively large quantities from a large number of activities. Condensation will also occur under suspended timber floors where the temperature of humid air in the floor space is lowered by cold air moving in through ventilators and water is then condensed on the underside of the timber floor, this will often induce timber decay of the wooden floor.
In houses condensation is related to modern living standards, economic pressure and changing building design. The main cause of condensation is naturally the generation of moist warm air by domestic activities. Moist air can come from cooking, bathing, washing and drying clothes as well as paraffin heaters and flueless gas heaters - up to 17 litres of water can be produced daily in some homes (BRE Digest 297- Surface Condensation & Mould Growth in Traditionally Built Dwellings). In certain areas such as bathrooms and kitchens the moist, warm air can spread to cooler parts of the house to condense on cold surfaces.
The effect of moisture generation is further aggravated by the way houses are ventilated - it is theoretically possible to avoid condensation by adequate ventilation. Up to about the late 1960s there was natural ventilation in many homes because of the lack of double-glazing, poorly fitting windows and doors, open fireplaces. Present attitudes have eliminated natural ventilation by the use of double-glazing, draught excluders, fitted carpets (preventing air movement up through suspended wooden floor boards) and the removal of open fireplaces with the introduction of central heating systems. To put it simply buildings have being effectively sealed and provided ideal conditions for condensation to occur.
Many houses remain unoccupied and unheated throughout the greater part of the day allowing the fabric of the building to cool down, The moisture producing activities are then concentrated into a relatively short period. This sudden increase in warm air can produce condensation as the air comes into contact with the relatively cold structure which is still warming up. Rising gas and electric bills often force many occupiers to under use heating systems, not heat unused rooms and seal all draughts and reduce ventilation as described previously.
Mould growth will appear on any damp surfaces such as plaster, wall-paper and timber and is associated with condensation problems in many buildings. It is unacceptable because of appearance (unsightly growths of various colours - greens, yellows, pinks, black, grey or white).
The main requirement for the development and growth of moulds is a source of moisture although food, oxygen and a suitable temperature are also important. It is available water which is critical to mould development. Moulds can be regarded as high hydrophilic fungi (tolerating high water availability) although individual species have their own optimum requirements for moisture. In most situations where surface condensation occurs and the relative humidity of the internal atmosphere exceed 70% mould growth will be established.
There have been approximately 100 species of fungi detected in dwelling houses. The species most commonly encountered were penicillium, cladosporium, rhizopus, and mucor.
Condensation dampness is an increasingly serious problem in dwelling houses and offices. It affects over 50% of buildings in the UK. Accompanying condensation dampness there is an increase in the presence of mould growth and many of the household pollutants. Positive Input Ventilation units (Dampbuster) along with our Passive Ventilation Units (Mouldbuster) are a cost effective and guaranteed way to control condensation and black spot mould problems.
Positive Input Ventilation units (Drimaster-for houses and Flatmaster for flats)

The DRIMASTER provides whole home ventilation using the Positive Input Ventilation principle. This form of ventilation is becoming increasingly recognised as the "best value" approach to ventilating a home. Essentially, the concept is to introduce air to the home at a continuous low rate, encouraging movement of air from inside to outside. A single unit situated in the loft space will normally be sufficient to continuously dilute, displace and replace the old contaminated air in the home with drier, tempered (by utilising otherwise unused heat in the loft space) and filtered air. The result is a significant contribution towards providing a healthy, condensation dampness free, energy efficient home. With only one electrical connection and no trickle vents normally required, the installation costs for this type of damp proofing system are generally less than for a conventional set of extract fans with trickle vents – and the entire home benefits from the ventilation provided.
Good quality loft mounted units normally incorporate a heat recovery function to introduce more heat into the home when the loft is warm during the winter months. Heat recovery functions are normally either "Fixed Temperature Heat Recovery" which adjust the flow rate of the unit to suit the loft temperature; or "Intelligent Heat Recovery" which adjusts the flow rate to suit the loft temperature and the way the home is heated. The latter type is particularly good in terms of energy efficiency. These systems are highly effective but do require proper application and installation for optimum performance. Units incorporating low watt motor technology (Low Energy Positive Input Ventilation Units) can provide a significant net energy gain to the home. These units are therefore very energy efficient, even when compared to natural ventilation systems such as Passive Stack Ventilation.

Drimaster diagram of air circulation

All DRIMASTER low energy input ventilation units are supplied and fitted with a 60 day, no quibble, money back guarantee and also comes with a 5 years parts & labour warranty. An average sized 3/4 bedroom property, without extension, can be fully installed, including all electrical connections for a flat fee of £750.00.
We also supply Drimaster units for self installation and prices are:
Drimaster- £280.00
Drimaster 2000- £3255.00
Drimaster Heat- £350.00
All prices include V.A.T and delivery
The benefits of installing a Drimaster PIV unit are great and some of the advantages are listed below:-

  • First, it means that a significant proportion of external pollutants are prevented from entering the home.
  • Secondly, the use of the otherwise unused heat in the roof results in the ventilation unit providing a significant net energy gain to the home.
  • Thirdly, there is no better way to ventilate a home than from the inside out via a single, centrally located, supply air diffuser.

The installation of a low energy positive input ventilation unit will ensure the air in your home is completely replaced with better quality air around 20 times a day. This is the recommended rate to maintain good air quality. The old air exits through the thousands of air leakage points found in all homes. Indeed, positive input ventilation will even help to suppress unwanted infiltration (draughts).
The end result of installing a DRIMASTER PIV unit is improved indoor air quality and an environment in which condensation dampness cannot exist.
To arrange free no obligation feasibility survey then please call 0800 029 1903 or e-mail  .



The Flatmaster operates in a similar way to the Drimaster but is designed for homes without lofts. Input air is directed across the ceiling (usually in your hallway). This uses a scientific principle called the Coanda effect, which has the impact of mixing with the wasted warmer air that has risen above head height in your home. It therefore increases the efficiency of your heating system. We can also supply and fix heat exchange units if preferred.
The unit will cure and/or prevent the problems associated with condensation dampness in your home, providing a healthier living environment for all occupants. The unit will prevent mould growth on walls, ceilings, furniture, clothes and curtains. The unit also eradicates the musty smells evident in homes with severe condensation problems. (When using your air conditioning in the summer, fresh air will circulate the house and help to prevent dry throats and congestion).
The price for this unit supplied and fitted is £1,050.00 which includes all making good and localised re-decorating.
For a free, no obligation feasibility survey please call 0800 028 1903 or e-mail
Passive Ventilation Units

In some instances where cost is a concern and only individual rooms require to be treated we can recommend the ‘Passyfier Vent’ which has no running costs, has minimal heat loss and is scientifically proven to reduce condensation dampness.
The Passyfier combines a through-the-wall ‘warm’ telescopic sleeve with a slab of mineral wool inside, which is impervious to the exodus of moisture vapour whilst an internal louvered vent and an external cover simultaneously preventing cold draughts.
A typical house may need for or five Passyfier units and they operate by taking advantage of the differential partial moisture vapour pressure that is normally higher inside an occupied building than on the outside. This pressure is completely independent of that in the air, for example, a typically cold misty British winter’s day may have an outside temperature of 5 oC and humidity at 100% while the inside temperature is usually around 20oC. Keeping the inside relative humidity to 70% generates a difference between inside and outside moisture vapour pressure of 8 millibars which is ample to alleviate condensation. All this is achieved with little or no heat loss and the Passyfier will significantly reduce condensation dampness, steamy windows and unsightly, unhealthy mould growth.
Building Regulations require background ventilation for habitable rooms require a vent opening with a total area of not less than 8,000mm2 and that these openings should be controllable, secure and located so to as avoid draughts. Passyfier vents surpass all of these requirements and are the ideal way of controlling high humidity levels, condensation dampness of unsightly mould growth.
The Passyfier operates continuously without noise 24 hours per day and can extract up to 2.3 litres (roughly one and a quarter gallons- which is ten pints) of water per day even at low pressures.
The diffusion rate of a Passyfier vents are slower compared with mechanical extract fans and they are not designed to cope with high amounts of water vapour produced in a short time ( i.e. in kitchens and bathrooms) and we recommend that if your kitchen or bathroom is suffering from condensation dampness that extract fans are fitted.
If the Relative Humidity of a room is around 70%, above which condensation dampness will occur at 20oC, each kg of air would hold 0.0104kg of water. Local Authorities recommend a maximum velocity of 0.9m/sec through vents, this is to avoid complaints about perceived draughts from occupants, and this would remove 0.023m 3 of water vapour per day. The average speed of air flow through a Passyfier vent is around a tenth of the maximum speed allowable but it is still able to remove 2.3 litres of water vapour per day and this greatly reduces the possibility of condensation and unsightly mould growth from occurring.


The average price for supplying and fitting of a passive dehumidifier is £350.00 or we can supply units which are easily fitted by a competent builder for £60.00. If you need more information on the supply and installation of our passive dehumidifiers then please call 0800 028 1903 or e-mail