Air gap analysis
Pathology of humidity. Clad walls - Case study

We often speak of a ventilated air space as the potential solution to a pathology whose cause lies in the condensation of water vapour. This stems implicitly from the common belief that wet linen lying outside dries faster in windy conditions.

A distinction is made between unventilated and ventilated air gaps. The following are considered :

• unventilated, air gaps, either without contact with the outside (see § ), or air gaps where the surface area of the openings bringing them into contact with the outside is less than 500 mm² per linear metre (ml) of facade;

• The surface area of the openings that bring them into contact with the outside is between 500 and 1,500 mm² per ml of facade (corresponding to a horizontal slot 5 cm long by 1 to 3 cm high).

In a chimney, the circulation (draught) of gases depends either...