Dew point is the temperature at which water vapour in the air begins to condense, forming condensate. In the context of construction, this means a place in a partition (e.g. in a wall or roof) where conditions are conducive to condensation. This happens if the water vapour penetrating from inside the building encounters a surface with a temperature equal to or below the dew point.
The occurrence of a dew point inside a partition can cause: moisture in insulation materials, a decrease in their thermal efficiency, mould growth and structural damage. It is therefore important in the design of the envelope that the layers are arranged appropriately. So that the dew point is as close as possible to the outside of the envelope and condensation does not occur within the moisture-sensitive materials.
Correctly estimating the dew point helps to select a suitable layering system: vapour barrierthermal insulation and diffusion-open layers. In modern construction, thermal and moisture calculations are used to prevent condensation problems.
