Canadian homes have been getting more energy-efficient for decades and a large part of this is due to improved airtightness. Keeping the air that is already in the home at the right temperature and humidity is easier and cheaper than treating air from the outdoors. However, builders often encounter a bewildering set of standards for airtightness and procedures for testing it.

In an article originally published in Winter 2022 in Better Builder Magazine, Gord Cooke, President of Building Knowledge Canada, demystifies the issue.

Code requirements for airtightness have been getting more rigorous for decades in Canada, partly because better insulation has led to a greater chance of moisture condensation in the wall and attic cavities during cold weather. Canada’s 2020 National Building Code has a voluntary standard for airtightness, at 2.5 air changes per hour at 50 pascal (2.5 ACH@50Pa) pressure difference. While air tightness testing is currently required only in the British Columbia building code, air tightness levels of less than 3 air changes per hour at a pressure difference of 50 Pascal (ACH50Pa) are encouraged in every provincial code to limit risks for builders.

How air leakage occurs

As Gord explains, there are three main mechanisms for air leakages in homes:

• Wind causes pressure differences that push air into or out of the building.
• Mechanical systems such as fans, dryers, and venting push warm air out which in turn forces cool air in.
• Stack effect—the tendency of warm air to rise—causes heat to escape through the upper storeys, while cool air leaks in through the lower levels.

All of these mechanisms depend on leaks in the building enclosure, whether through poorly sealed building penetrations, improperly applied caulking or sealing tapes, or ill-fitting windows and doors.

Measuring air leakage

The standard test for air leakage is a blower door test. This involves installing a large fan on an exterior door, creating an even pressure difference of negative 50 Pascal across the entire building enclosure, and then measuring the airflow required to create this pressure. The airflow rate can be easily converted into air changes per hour rate based on the total volume of air in a home. As Gord points out, there are several tools for measuring air flow but they all generally deliver results within a few percentage points. From these, one can determine the ACH of a home, a value that buyers can readily understand. The leakage characteristics of a home as the “equivalent leakage area”— the size of a theoretical hole in a wall if you combined all the airflow from leakage points in a house into one spot.

Learn more

Given the trends in both codes and energy initiatives, Gord says, builders and trade contractors should be working to make homes ever more airtight and that means learning more about the codes, emerging technologies for improving airtightness such as the AeroSeal Envelope System, and the testing procedures.

Building Knowledge Canada not only offers airtightness testing but also helps builders and contractors understand how to make the best use of innovative and emerging systems and technologies to optimize their housing designs. Get in touch to see how we can support your design and business goals.

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_{Originally published in Better Builder Magazine, Issue 44 / Winter 2022}