The phenomenon of surface condensation on double-glazed units occurs in three forms:
- On the external face (face 1)
- On the inner surfaces 2 and 3 of the double-glazed unit
- On the internal face or face 4.
Condensation forms very differently depending on whether it is inside or outside the building, due to the thermal bridge effect around the cavity.
Surface condensation on the internal face always starts in the corners, mainly due to the additional cooling caused by the thermal bridge. “Warm-edge” spacerbars, made of insulating material, reduce the risk of condensation at the corners.
Surface condensation on the external face rarely occurs in the corners, given that the edges of the external glass heat up adjacent to the thermal bridge. The coldest point on the external face of the glazing is generally in the centre, where there is the least heat loss.