Air tightness and blower door test
A low energy building design requires maximum air tightness and no or nearly no thermal bridges in order to minimise its energy consumption. This requires both thoughtful design and skillful construction workers who know how to make the building envelope completely tight. Cracks and gaps in the building envelope typically occur in the following places:
- Joints in the airtight layer
- Penetrations of the airtight layer, e.g. by technical installations and lighting
- Joints by the foot of the roof or where two different surfaces meet
- Joints around doors and windows
- Joints around the foundation
- Joints between the ground deck and crawlways
Air tightness is important, not only in relation to energy use, but also with regard to a healthy construction and indoor climate. A tight vapour barrier prevents the moisture produced by the people living or working in the building from penetrating into the structure and causing problems of dampness and condensation. Moisture may allow fungi to grow that can cause allergies and decay of building materials.
The need for a high air-tightness level has an impact on the building design. Complicated shapes with many details, cumbersome cabling for HVAC systems and electrical installations in the construction are all elements that increase the risk of errors and air leaks.
The level of tightness in a building can be tested by performing a so-called blower door test.
