There is always some moisture in the air, even though we cannot see it. When that moisture is allowed to accumulate in a dwelling, the atmosphere becomes saturated and condensation occurs which can eventually result in damage to the structure of the building and its contents. This leads to expensive repairs and maintenance plus associated discomfort to the occupants. The point at which moist air may begin to cause deterioration is 70% Relative Humidity (RH).

The British Isles has a naturally humid environment. A humidity map will show the regions that are regularly at, or in excess, of 70% RH. An estimated 4.5 million British homes suffer from the damaging effects of condensation.

Therefore we need to take extra measures in the UK to prevent the expensive consequences of condensation such as rotting window frames, peeling wallpaper, mould growth, damp and eventually, rotting of the building fabric itself.

Condensation is aggravated by a reduction in natural ventilation. This is common in today's sealed and insulated buildings which incorporate replacement windows, draught proofing and fitted carpets, etc.

If moist air is unable to escape, it will condense on cooler surfaces and migrate to colder parts of the dwelling. Problems often start in the kitchen or bathroom, where cooking, washing, drying clothes, showers and bathing generate excess moisture.

Not only does moist air cause problems to the fabric of the building but also to air quality and health. People who suffer from asthma or any other bronchial problems can have their condition aggravated by a moist environment.

The microscopic droppings of the house dust mite can cause asthma, rhinitis, bronchial and other allergic problems. Constant wholehouse ventilation can reduce the relative humidity to below 70%, which inhibits the ideal living and breeding conditions of the house dust mite.