Determination of the Airtightness of Building Envelopes by the Fan Depressurization Method

1              SCOPE AND FIELD OF APPLICATION

1.1          Scope

This is a standard method of tests (SMOTs) for the determination of the airtightness of building envelopes. This Standard contains three test options, two types of assessments and, for attached zones, two pressure boundary set-ups. The test options are the multi-point test, the two-point test and the single-point test. The types of assessments are as-operated and closed-up. The pressure boundary set-ups are guarded and unguarded.

Each test can be used to determine the airtightness characteristics including combined area of leaks in the building envelope. It is the responsibility of the user, specifically the referencing code, standard or program, to specify what test and results are required.

These tests are not intended for determining the actual air leakage that occurs through a building envelope under the natural influences of wind and buoyancy pressures, or as a result of pressures produced by the operation of mechanical systems.

1.2          Applicability

These test methods are applicable to buildings or portions of buildings that are suitable for testing as a single zone (e.g. detached houses, townhouses, apartments with self-contained heating and ventilation systems, and commercial buildings) and are generally limited to three storeys above grade  .

1.3          Choice of standard method of test

The choice of one test option over another is a balance of the following factors: time commitment for the user in the field, repeatability, accuracy and the measurement of airtightness descriptors that are required versus the pressure differential(s) at which the test is performed.

Uncertainty analysis is only available with the multi-point test option, and the ability to extrapolate the results to different pressures is not available with the single-point test option without using an assumed n value.

The choice of assessment type is based on ease of testing, safety, and what elements of the building envelope are to be assessed.

The pressure boundary set-up is chosen based on ease of testing and availability of multiple blower door systems, access to adjacent zones and whether leakage through the common surfaces of adjacent zones is of importance.

Any standard that refers to CGSB 149.10 should be assumed to be referring to the multi-point test option, the as-operated assessment type and an unguarded pressure boundary set-up unless it specifies otherwise.

1.4          Combustion spillage

This Standard does not predict the risk of combustion spillage. Users are advised to refer to Standards written specifically for that purpose.

1.5          Uncertainty

This Standard is applicable to small indoor-outdoor temperature differentials and low wind conditions. The uncertainty of the test results increases with increasing wind speeds and temperature differentials. Appendix A contains recommendations to mitigate wind effects.