Airtightness testing of dwellings

Fan pressure testing allows the permeability, or airtightness performance, of the dwelling to be assessed. The technique is straightforward and can be carried out when the envelope is complete.

The airtightness test can be used in several ways:

• Assessing the air permeability of the building, i.e. the air leakage for the whole envelope area of the building.

• Identifying the air leakage paths, which will allow targeted remedial sealing.

• Measuring the effectiveness of remedial sealing.

In the UK the testing methodology should conform to BS EN 13829 Thermal Performance of Buildings – Determination of air permeability of buildings – Fan pressurisation method (2001) and CIBSE TM:23 Testing buildings for air leakage (2000). Further details on post construction testing can be found in the Further Information section.

To carry out the test, a fan is mounted in a temporary screen (the original door remains in place, but is held open to enable the screen to be mounted in the rebate, see Figure 22). The fan is used to move air into or out of the building. The air leakage characteristics are determined by measuring the rates of air flow through the fan while a range of pressure differences between the inside and outside of the building are maintained.