Radon Health Risks: What Every Canadian Homeowner Should Know

Radon causes roughly 3,200 lung cancer deaths in Canada every year, making it the second leading cause of lung cancer after smoking. The risk is entirely preventable with testing and mitigation. There's no completely "safe" level of radon, but Health Canada's guideline of 200 Bq/m³ is the threshold where action is strongly recommended.

What makes radon dangerous?

Radon is a naturally occurring radioactive gas that seeps into buildings through foundation cracks, floor drains, and construction joints. It can build up to harmful levels indoors.

The gas itself isn't the direct problem. It's the radioactive particles radon releases as it decays. When you breathe air with elevated radon, those decay products attach to lung tissue and emit radiation. Over years of exposure, that radiation damages DNA and can cause lung cancer.

Because radon is colourless and odourless, there's no way to detect it without a test. People can live for years in homes with elevated levels and have no idea.

How common is it?

Radon is present in virtually every home. In Canada:

• About 7% of Canadian homes exceed Health Canada's guideline of 200 Bq/m³
• In Saskatchewan, Manitoba, and New Brunswick, the numbers are much higher
• Average indoor concentrations vary by region, soil type, and how homes are built

You can't predict your home's level from your neighbourhood or province alone. Testing is the only way to know.

What the research shows

The health evidence is well-established:

IARC classification: The International Agency for Research on Cancer classifies radon as a Group 1 carcinogen. That means there's sufficient evidence it causes lung cancer in humans.

Combined risk with smoking: The risk of lung cancer from radon is far higher for smokers. A lifetime non-smoker exposed to 200 Bq/m³ has roughly a 1 in 20 chance of developing lung cancer from radon. For a smoker at the same level, it's closer to 1 in 3.

Linear no-threshold model: Health agencies apply a linear no-threshold model to radon risk, meaning there's no exposure level considered completely safe. Lower is always better.

Who faces the highest risk?

Smokers. The combined effect of smoking and radon isn't additive, it's multiplicative. Smokers in homes with elevated radon face a dramatically higher cancer risk than either factor alone would suggest.

People who spend a lot of time in basements. Radon concentrations are highest on the lowest floor. If your home office, bedroom, or main living space is below grade, your exposure is above average.

Children. Some research suggests children may be more sensitive to radiation-induced cancer risk because of faster cell division rates, though the evidence is less definitive than for adults.

Long-term residents. Risk accumulates over time. Someone who's lived in a home with elevated radon for 30 years has far more cumulative exposure than someone who moved in recently.

Understanding the 200 Bq/m³ guideline

Health Canada's guideline is 200 Bq/m³ (becquerels per cubic metre). At or above that level, action is recommended. But being below the guideline doesn't mean there's no risk.

Many countries use 100 Bq/m³ as their action level. The World Health Organization recommends 100 Bq/m³. Canada's guideline was lowered from 800 Bq/m³ to 200 Bq/m³ in 2007, and some experts advocate going lower still.

Mitigation works

Radon mitigation is highly effective. Sub-slab depressurization installs a fan that draws radon from beneath the foundation before it can enter the home. This typically reduces indoor levels by 80–99%.

A system costs $1,500–$3,500 in most Canadian markets and lasts the lifetime of the home with minimal maintenance. The fan runs continuously, uses about the energy of a light bulb, and requires no ongoing consumables. Most jobs are done in a single day.

For a family spending decades in a home, mitigation is one of the best health investments available.

Next steps

If you haven't tested your home, start with a DIY test kit. Long-term alpha track kits (91+ days) are the most accurate and cost $30–$60.

If your results are above 200 Bq/m³, find a certified mitigation professional in your area. The sooner you act, the better.