Skip links

Airtightness in a passive house

Why airtightness in a passive house is important ?

The airtightness in a passive house but also in every building is as important as its thermal insulation. This is indeed one of the key principle of the passive standard. 

A building is subject to a combination of air infiltration and air exfiltration. While the first phenomenon leads to an increase of heating requirements, the second one can damage the building components. Indeed, the moist warm air that escapes from the inside, condenses in contact with a colder surface. 

The main responsible for air leaks are the followings:

  • the connections
  • the ventilation system
  • the heating/cooling system
  • openings in the exterior envelope (doors, windows, chimneys).

A good airtightness has many advantages:

  • air quality
  • avoids pollutants (e. g. Radon)
  • avoids humidity
  • low heat loss due to infiltration
  • good acoustic insulation
  • prerequisites for CMV to work properly
  • best comfort
  • avoid the deterioration of the constructive elements

Rules for airtightness:

  • a continuous layer generally on the “warm” side
  • cover surfaces as wide as possible
  • merge the different airtight layers
  • avoid penetrations of the airtightness layer

Only some materials can be used for the airtight layer, such as membranes, OSB, plasterwork and concrete.

A space of 1 mm in the waterproofing layer is equivalent to 360g of water per day per meter (exfiltration of moist and hot air), hence the importance of the airtightness layer.

How to test airtightness with the Blower Door Test ? 

The most commonly used method to test the airtightness of a building is the Blower Door Test (BDT). It consists of:

  • Installing a cover on a building opening in which a fan is integrated that will allow the building to be pressurized/depressurized (50 Pa).
  • Measuring the rate of air passing through the envelope. All other openings to the outside must be closed and the interior doors left open.

Air flows can be located using a flow meter or through an infrared camera for hard-to-reach areas.

In the case of passive houses, the air renewal rate, which is equal to the quantity of air escaping through building leaks divided by the volume of the building, must not exceed 0.6 renewals per hour (n50).

airtightness-in a-passive-house-étanchéité-dans-une-maison-passive-blower-door-test