Dew Point - Damp in Buildings

Damp in Buildings

The temperature drops from the air surface inside the building to the air surface outside the building, say from 20 degrees to zero on a cold day. Somewhere along that gradient (location dependent on humidity) is the Dew Point, where water condenses from vapour to liquid. If the air-to-air gradient runs through clothes in a wardrobe (or on the back of a door), then the Dew Point may occur in the clothes, which get wet. The air-to-air gradient needs to be restricted to the building fabric, with the Dew Point occurring preferably in the cavity, where the condensed liquid water then simply drains away to the base of the wall and then to the outside. People should be very careful not to let their clothes rest against an outside wall, for the clothes can get damp from "interstitial condensation".

Another factor is restricted air circulation behind furniture, which can lead to condensation and mildew appearing on the internal wall.

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