Airtightness is simply the control of airflow within a building. This means there is no unexpected air leakage (losing warm air) or no cold air infiltration.
In passive construction the building is made airtight in order to prevent the unwanted movement of air. This has many benefits, some of which include:
- Reduced heat loss.
- Reduced energy costs (Space Heating).
- Improved thermal performance of the structure. (Prevents wicking of insulation - diagram on the right of the page)
- Improved thermal comfort. (A steady temperature is maintained throughout the building).
When building a passive house it is important to get an accurate measurement of the airtightness; to obtain this a "Blower Door Test" is used.
- The blower door fan is set up in the doorway of the main entrance of the dwelling.
- Windows and doors are closed while vents and fans are sealed.
- The fan is then turned on and tested for overpressurisation; the house is subjected to 50 Pascals of pressure for one hour whilst the air flow rate is measured.
- The goal of the first stage is for the dwelling to maintain the excess pressure of 50 Pascals.
- The fan is then turned around and the test is repeated; this time testing for underpressurisation; 50 Pascals of pressure is pumped out of the house. The results of the test are based on the buildings capability to maintain this negative pressure
- The average of the two tests are then calculated to determine the airtightness of the building. ( 48 Votes )