Radon Health Risks: What Every Canadian Homeowner Should Know

The bottom line up front

Radon causes approximately 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 is no "safe" level of radon, but Health Canada's guideline of 200 Bq/m³ is the threshold at which action is strongly recommended.

What is radon and why is it dangerous?

Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil and rock. It seeps into buildings through cracks in foundations, floor drains, and construction joints, and can accumulate to dangerous levels indoors.

The danger isn't radon gas itself — it's the radioactive particles it releases as it decays. When you breathe radon-contaminated air, these decay products attach to lung tissue and emit radiation. Over years of exposure, this radiation damages DNA and can cause lung cancer.

Because radon is colourless and odourless, there's no way to detect it without a test. Many people live for years in homes with elevated radon without knowing.

How common is it?

Radon is present in virtually every home — the question is at what concentration. In Canada:

• Approximately 7% of Canadian homes exceed Health Canada's guideline of 200 Bq/m³
• In some provinces like Saskatchewan, Manitoba, and New Brunswick, the proportion is significantly higher
• Average indoor radon concentrations vary widely by region, soil type, and building construction

You cannot predict your home's radon level based on your neighbourhood or province alone. Testing is the only way to know.

What does the research say?

The health evidence on radon is well-established:

IARC classification: The International Agency for Research on Cancer classifies radon as a Group 1 carcinogen — meaning there is sufficient evidence it causes lung cancer in humans.

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

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

Who is most at risk?

Smokers: The combined effect of smoking and radon is multiplicative, not additive. Smokers living in homes with elevated radon face a dramatically elevated cancer risk compared to either risk alone.

People who spend significant time in basements: Radon concentrations are typically highest on the lowest floor. If your home office, bedroom, or living space is in the basement, you're accumulating more exposure than average.

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

Long-term residents: Risk accumulates over time. Someone who has lived in a home with elevated radon for 30 years has experienced far more cumulative exposure than a recent buyer.

Understanding the 200 Bq/m³ guideline

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

Many countries use 100 Bq/m³ as their action level. The World Health Organization recommends a reference level of 100 Bq/m³. Canada's guideline was lowered from 800 Bq/m³ to 200 Bq/m³ in 2007, and some experts advocate for further lowering it.

Mitigation works

The good news: radon mitigation is highly effective. Sub-slab depressurization — the most common approach — involves installing a fan that draws radon from beneath the foundation before it can enter the home. This typically reduces indoor radon levels by 80–99%.

Mitigation systems cost $1,500–$3,500 in most Canadian markets and last the lifetime of the home with minimal maintenance. The fan runs continuously, the system requires no ongoing consumables, and it can usually be installed in a single day.

For a family that spends decades in a home, mitigation is one of the highest-value 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. Professional mitigation is fast, effective, and durable.