Airtightness protects the basic structure of the building

The airtightness of a building is a basic requirement that must in all cases be met.

Airtightness is a quality requirement and is the responsibility of professionals.

Leaks in the basic fabric of a building will result in heat loss, draughts and the risk of condensation in the outer walls and roof. The elements on the exterior are protected by the layer of airtightness from humidity generated by interior domestic processes (such as cooking, washing, showering and breathing).

Three-layer safety

Wood frame construction, which owing to its typical multi-tiered structure is open to diffusion, has three important layers that are important for thermal and moisture protection:

  • Windproof seal: It is located on the exterior before the thermal insulation and protects against the flow of outer air and thus against cooling and thermal loss.
  • Vapour seal: It is located on the interior in front of the insulation layer and protects the construction against the diffusion of water vapour, preventing condensation in the constructional element.
  • Airtight layer: It is also located on the interior before the insulation layer and protects the fabric of the building against inflaming room air and the associated risk of condensation. It also prevents draughts in the rooms.

The blower-door test provides certainty

The blower-door test is a standard recognised method for measuring airtightness and locating leaks. It should be executed when leaks can still be closed, before planking is fitted and floor fill put down.

Tip: The blower-door test is an effective way of ensuring that a house is assured of a good future and that it will retain its value. A convincing argument of quality – also when negotiating with the bank.


Peter Müller achieved what is possibly a record-breaking result of n50 = 0.23 in a blower-door test in a wood frame construction in Blegny in June 2010.