Millions of Canadian homes have high levels of cancer-causing radon. Is yours one of them?

You can’t see or smell radon, the cancer-causing gas lurking inside millions of Canadian homes.

Roughly one in five residential buildings in Canada has high radon levels — a figure that’s more than doubled since the late 2000s — while radon-induced lung cancer kills an estimated 3,200 people each year, federal figures show.

This radioactive gas is released from the ground and flows into buildings across the country, but scientists say modern designs and renovations likely play a role in why more Canadians are being exposed in their own homes.

“We are pretty good at keeping air inside of our homes because we want to keep the heat inside … especially in this kind of cold climate that we live in,” said Pawel Mekarski, head of radon technical operations at Health Canada. 

“A lot of the time when we are doing renovations and retrofits, we're typically trying to make the building more airtight, without necessarily introducing any sort of other ventilation.”

There’s hope that could change. A long-awaited update to the national building code, just released in late December, requires newly built homes to include a passive radon stack, which acts like a chimney to help reduce indoor radon buildup.

Though that code sets out the guidelines for construction projects throughout the country, it still needs to be adopted by provinces and territories.

“We hope to see these systems introduced in future homes in Canada,” Mekarski said.

But what about existing homes that are at risk of having high radon levels? And how do you know if your own house is a danger zone?

Experts say the only way to know if your home contains a high amount of radon is to test for it.

The process is simple: You can either hire a radon measurement professional or buy your own test kit. (Some communities provide free radon monitors through libraries or local public health units. You can find out more information through the federal Take Action on Radon program.)

Health Canada recommends testing your home for at least 91 days, and ideally for a period of three to 12 months to get the most accurate results. It’s also important to test during the colder months when windows and doors are likely shut, trapping more radon in your home. 

The current national guideline for indoor radon levels is 200 becquerels — the standard unit of radioactivity, which refers to the rate of nuclear decay — per metre cubed (Bq/m3).

If your home’s readings hit that threshold, the Take Action on Radon program offers a searchable list of certified radon professionals who can install mitigation systems. These typically involve a pipe that runs from the foundation floor up through the roof, with a small fan attached, to draw radon outside before it can enter the house. Installations usually take a day or less.