The air and wind tight building envelope explained.

 

The air and wind tight building envelope can be compared with clothing. In cold and damp weather several layers of clothes prove their value ("onion principle").

On the skin you wear functional
material to carry sweat away from the skin. This corresponds to the airtight building envelope formed by the base plaster on the masonry and the vapour control layer in the roof. It is required by Part L of the Building Regulation from July 2008 (IRL, UK) and § 6 of the German energy saving regulation (EnEV) and can be easily tested by a blower-door test.

A woolly sweater protects from cold
(insulation).   But in cold, windy weather this sweater is not sufficient; you additionally need a windtight jacket (facade membrane or breathable membrane). When this jacket is open, cold wind and moist air enter the sweater and you feel cold. If it is, however, closed, which corresponds to the windtight building envelope, wind and weather are kept out and the body remains comfortably warm. This layer is formed by the roofing tiles and the permanently sealed breathable membranes.

More than one third of the warm air escapes through leaking areas in the building envelope. Consequently an air and windtight layer is the most reliable protection againstenergy and heating cost loss! Regular, controlled ventilation or a ventilation system provide for healthy indoor air.

In addition, the air and
windtight building envelope fulfils further important functions:

The insulation is protected from damage by mould, which would lead to expensive renovation work and health hazards!

It prevents draught and increases the living comfort!

You can do without toxic wood preservatives and keep the construction free from vermin!

It locks out odours, noise and summer heat!

It increases the value of your building!