Allergy Plus

Common Irritants

Condensation is the process whereby water vapour in the atmosphere is returned to its original liquid state. In the atmosphere, condensation may appear as clouds, fog, mist, dew or frost, depending upon the physical conditions of the atmosphere. Condensation is not a matter of one particular temperature but of a difference between two. Condensation of water vapour occurs when the temperature of air is lowered to its dew point.

The risk of condensation therefore depends upon how moist the air is and how cold the surfaces of rooms are. Both of these depend to some extent on how a building is used. In a room with a cold outside wall, the temperature of which falls below the dew point temperature, it is quite normal for condensation to occur predominantly on the lower parts of the external walls and may be confused with rising damp.

Condensation occurs usually in winter, because the building structure is cold and because windows are opened less and the moist air cannot escape.

Condensation which you can see occurs often for short periods in bathrooms and kitchens because of the steamy atmosphere, and quite frequently for long periods in unheated bedrooms; also sometimes in cupboards or corners of rooms where ventilation and movement of air are restricted. Besides condensation on visible surfaces, damage can occur to materials, which are out of sight, for example from condensation in roofs.