Predicting Envelope Leakage in Attached Dwellings (Fact Sheet)

The most common method of measuring air leakage is to perform single (or solo) blower door pressurization and/or depressurization test. In detached housing, the single blower door test measures leakage to the outside. In attached housing, however, this 'solo' test method measures both air leakage to the outside and air leakage between adjacent units through common surfaces. Although minimizingleakage to neighboring units is highly recommended to avoid indoor air quality issues between units, reduce pressure differentials between units, and control stack effect, the energy benefits of air sealing can be significantly overpredicted if the solo air leakage number is used in the energy analysis. Guarded blower door testing is more appropriate for isolating and measuring leakage to theoutside in attached housing. This method uses multiple blower doors to depressurize adjacent spaces to the same level as the unit being tested. Maintaining a neutral pressure across common walls, ceilings, and floors acts as a 'guard' against air leakage between units. The resulting measured air leakage in the test unit is only air leakage to the outside. Although preferred for assessing energyimpacts, the challenges of performing guarded testing can be daunting.