Enforcing Airtightness

In the last installment of the Window Geeks: Master Class, we explored the air and water tightness of windows and what the BC Building Code says on these two important subjects. Turns out, it’s not a huge amount, though the building code does reference NAFS and what it has to say on these matters.

So if the Building Code doesn’t place strict rules on a window’s airtightness… are there any BC-specific rules that do?

By the end of this lesson, you will:

• Be prepared for regulatory changes in BC.
• Be informed on difficulties calculating home airtightness.

How is the air and water tightness of a window enforced?

As you undoubtedly know by now, rules constantly change over time – and they certainly aren’t getting more lax. We’ve seen the rules regulating windows grow stricter as we strive to achieve higher building performance.

As the BC Energy Step Code is adopted in more municipalities, whole-building air tightness testing will be required and rules on minimum air leakage will be specified. This directly impacts windows, and it’s through these standards and regulations that their airtightness will be enforced.

Why is it hard to predict whole-home airtightness through window airtightness?

When it comes to windows, airtightness is measured in L/m2.S, and is labelled as an “A” rating. Windows are tested and labelled based on an area calculation, which poses a challenge when trying to determine whole home airtightness, which is instead based on volume.

It’s worth noting that windows are not the only source of air leakage. In fact, they only typically account for around 10% of it. Other building elements will have to be taken into account as regulations around this issue tighten.

It’s also a misconception that the more airtight a window is, the better it is. Windows and doors actually need to be engineered for venting to minimize heat exchange and a pressure differential can be incorporated to reduce water ingress and improve drainage to limit the risk of mould growth.

Speak to your Centra Experts to learn more about how windows are designed for pressure equalization.

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