What Is Radon? The Complete Guide for Canadian Homeowners

Radon is a naturally occurring radioactive gas that forms underground when uranium in soil and rock slowly breaks down. It's colourless, odourless, and tasteless. You can't see it, smell it, or detect it without a test. Outdoors it disperses harmlessly, but inside an enclosed space like your home it can build up to dangerous levels.

In Canada, radon is the second leading cause of lung cancer after smoking, responsible for roughly 3,200 deaths per year.

Where does it come from?

Radon originates in soil and bedrock. The amount produced depends on local geology: areas with granite, shale, or uranium-rich soils tend to produce more than areas with limestone or sandy soils.

Every home in Canada has at least trace levels of radon indoors. The question is how much.

How does it get into a home?

Air pressure inside most homes is slightly lower than in the soil beneath them. That pressure difference draws soil gases, including radon, upward and into the building through any available gap.

Common entry points:

• Cracks in foundation walls and floor slabs
• Construction joints and gaps around service pipes
• Floor drains and sump pits
• Exposed soil in crawl spaces
• Gaps around support posts

Once inside, radon builds up, especially in basements and lower floors where there's less air exchange.

Why is it dangerous?

Radon itself isn't the direct problem. The decay products it releases are. When radon decays, it produces radioactive particles that lodge in lung tissue and emit bursts of radiation when you breathe them in.

Over months and years, that radiation damages the DNA in lung cells. The process is slow and silent. There are no symptoms of radon exposure until lung cancer develops, often decades later.

The risk comes down to two things: the concentration of radon in your home, and how much time you spend in it.

Radon and smoking: it's not additive, it's multiplicative

For smokers, the danger is far higher. Radon and tobacco smoke don't just stack on top of each other. They multiply. Radon damages lung tissue, and smoke impairs the lung's ability to clear those radioactive particles. The combination is dramatically worse than either alone.

If you smoke and haven't tested your home, that's worth taking seriously.

How common is elevated radon in Canada?

Health Canada estimates about 7% of Canadian homes exceed the national guideline of 200 Bq/m³. In Saskatchewan and Manitoba, the number is considerably higher.

You can't predict your home's radon level from:

• Your province or city
• How old your home is
• Whether it has a basement
• What your neighbours tested

The only way to know is to test.

What levels are considered safe?

Health Canada's guideline is 200 Bq/m³. At or above that, action is recommended. But "below the guideline" doesn't mean zero risk.

The World Health Organization recommends 100 Bq/m³, and many countries use that lower threshold.

How do you test?

Testing is straightforward and cheap. Two options:

Long-term alpha track detector (the right call for most people): A small passive device placed in the lowest livable area of your home for 91 days or more. It captures seasonal variation and gives you the most accurate picture of your actual exposure. Kits run $30–$60 and are available online or at hardware stores.

Short-term test: Lasts 2–7 days. Less accurate because radon levels fluctuate naturally. Useful for a quick initial read, but Health Canada recommends confirming any elevated short-term result with a long-term test before acting on it.

For either test: place the device on the lowest floor you regularly use, not a storage room or mechanical room. Follow the instructions, then mail it back to the lab.

What if your levels are high?

If your home tests above 200 Bq/m³, the fix is active sub-slab depressurization:

1. A hole is drilled through the foundation slab
2. A PVC pipe is connected to a continuously running fan
3. The fan creates negative pressure beneath the slab, drawing radon out before it enters the home
4. Radon is vented outside

This system typically reduces indoor levels by 80–99% and costs $1,500–$3,500 in most Canadian markets. It's usually done in a single day and needs minimal maintenance.

Always hire a C-NRPP certified professional for mitigation. That's Health Canada's recognized standard for radon professionals in Canada.

Next steps

• Haven't tested yet? Get a test kit. Long-term kits start around $30.
• Have a result? Use our result interpreter to understand what your number means.
• Ready to act? Find a certified professional near you.