Building Air Permeability / Air Leakage

Building energy consumption is dependant on several different factors, one of the most important factors is building air permeability, also known as air leakage/airtightness.

Bear with me, it will sound a little crazy, although it’s critical there are no statutory requirements or regulations governing air leakage/airtightness, the Hong Kong BD requirements and BEC (Building Energy Code) are equally silent.

Leaky buildings waste vast quantities of energy, in the absence of statutory and regulatory goals, green building systems do include criteria for air leakage/airtightness measurement, such as the BEAM PLUS Interiors rating tool.

Why is not compulsory is puzzling. The early versions of HK-BEAM included criteria encouraging whole building air leakage/ airtightness measurement. Unfortunately, no measurement equipment or expertise was available in Hong Kong to conduct such site measurements.

In the absence of local firms and no local equipment suppliers, firms from US and UK are engaged, at great expense, to conduct this relatively simple and straightforward task. This is a global issue, even ASHRAE, a leading energy efficiency authority in USA, does not specify any air leakage criteria for buildings.

Even for energy modelling there are few references that can be used to account for air leakage when computing energy consumption using energy simulation models techniques.


How to determine air leakage in a building, the rate of air leakage needs to be measured on-site before the interior works commence. Essentially two common methods include 1) tracer gas concentration or 2) an airflow test, often called blower door test. However, both these methods tend to be used for room measurement, not whole buildings.

In the UK for nearly a decade the building regulations in the approved document Part L have specified the permitted air permeability for domestic and non-domestic buildings, requiring certification, some EU countries also have air permeability requirements, but Asia lags a long way behind.

Effectively every building needs two air permeability tests, it is wise to test the building when the envelope is complete but before the finishes are installed. This allows any defects to be fixed before the finishes are installed. Similarly, for hotel rooms, pre-test the air permeability before the cabinetry, millwork, and finishes are installed. And test after the room is completed to verify the result. However testing requires a very clean site, any dust or dirt will be immediately apparent and could damage the instruments.