Avoiding condensation

Press, 15 June 1983, Page 27

Avoiding condensation

Most houses seem to suffer in one way or another from condensation during the winter months. Channels fitted at the bottom of windows to collect the water and drain it to the outside do not prevent the problem, only remove a portion of its consequences. Any house which suffers from excessive condensation will also have problems with mildew, damp furnishings, and even saturated wall and ceiling linings. Condensation can be controlled, though, once its causes are understood. Condensation results from excessive airborne moisture, accumulated from the steam produced by cooking, showers, baths — and the home’s occupants. Each day an adult will give off about a litre of water, so a few adults with their children and pets will produce copious amounts of moisture with the potential to saturate the indoor air.

Most families like to keep their houses warm and have gone to the expense of insulating ceilings and, perhaps, walls and floors, so the indoor air is warm and can easily hold a large amount of moisture.

While the air temperature remains warm, and provided the humidity does not reach "dew point,” no ill effects will be noticed, unless a cooling factor is at hand. In a warm room where moist air comes into contact with cold outside temperatures through a singlepane window, the air in contact with the glass will cool and give off moisture. As the air cools, it falls, displacing warm air. This creates draughts across the floor and starts a thermocycle that forces more warm air to come in contact with the window.

This is why condensation at the bottom of the window is always more severe than at the top. As the air gets colder it falls, and the lower the temperature, the more moisture is released.

To prevent condensation, the problem has to be

tackled in three ways — with ventilation, temperature control and window insulation. No matter how well windows are insulated — and how hot a room is and can remain — unless ventilation occurs, humidity levels will rise well above what is healthy, and condensation will occur. To avoid a dank environment, the air within a house should be changed daily. The replacement of damp air with drier air requires some air movement. This is demonstrated by the fact that even when a bedroom window is left open on a cold, frosty night, condensation still occurs. But not on a windy night.

Frosts are associated with still air. In some cases it will be necessary to induce air flow by means of extractor fans, or opening windows or doors at the other end of the house.

Thermal drapes are reasonably successful in preventing heat loss, but they use the cavity between the drape and the window as the insulator, thus creating

a cold area which can cause excessive condensation.

Besides this, they have no thermal effect during daylight hours, when they are drawn back.

To be effective against condensation, window insulation. has to be in the form of a sealed, doubleglazing system which can offer insulation at all times.

Large areas of window glass need insulation, as in cold weather they may otherwise become the main

factor contributing to condensation.

With double-glazed windows, down-draughts can be virtually eliminated, so even temperatures can be maintained, and humidity can rise considerably without condensation occurring.

When walls, ceilings, floors and windows are all insulated, it is reasonably easy to maintain a comfortable temperature at little cost.