PLGN 2.04 Condensation

The amount of water vapour that air can hold is limited. When this limit is reached the air is said to be saturated. The saturation point varies with temperature. Cool air can hold less water vapour than warm air. The water vapour held by air at a given temperature is expressed as a percentage of the amount that would saturate it at that temperature and is referred to as relative humidity (rh). If moist air is cooled and the amount of water vapour present remains the same rh will rise. When saturation point (100% rh) is reached condensation will occur. The temperature at which condensation occurs in given conditions is the dewpoint; eg 15°C is the dewpoint of air at 20°C in 80% rh. Most condensation in buildings is caused by warm moist air coming in contact with cooler surfaces. In domestic and non-industrial buildings condensation is usually light and intermittent although in some situations it may be sufficient to cause water runs and drips disfigure paintwork or promote mould growth. In houses condensation is most likely to occur in kitchens and bathrooms. The average family gives out 21 pints of water a day into the air of their home through washing and cooking. Even breathing contributes to the problem. Some forms of heating generate large volumes of moisture vapour paraffin stoves being the most notable.

Solution

Condensation is best prevented or controlled by providing good ventilation to remove moisture-laden air from buildings preferably from a point near the source of the moisture. Adequate levels of heating will increase the capacity of the air to hold moisture but have to be combined with good ventilation otherwise the problem will be aggravated. Thermal insulation also helps to reduce condensation. Special anti-condensation paints are available but these only hide the problem and will only provide short term relief. A paint treatment alone will not cure condensation problems. Conditions within the building must be improved. One of the most common effects of condensation is mould growth. Dulux Trade Mouldshield Fungicidal Eggshell and Dulux Trade Mouldshield Fungicidal Matt will help prevent disfiguring surface mould growth from recurring when applied to clean suitably prepared surfaces.