What Is Radon? The Complete Guide for Canadian Homeowners
Radon is a colourless, odourless radioactive gas that causes 3,200 lung cancer deaths in Canada each year. Learn what it is, where it comes from, and what to do about it.
March 15, 2026
What is radon?
Radon is a naturally occurring radioactive gas. It forms underground as uranium — found in soil, rock, and groundwater across Canada — slowly breaks down. As uranium decays, it produces radium, which in turn produces radon gas.
Radon is colourless, odourless, and tasteless. You cannot see it, smell it, or detect it without a test. It rises from the ground constantly, disperses harmlessly outdoors, but can accumulate to dangerous concentrations when it enters an enclosed space like your home.
In Canada, radon is the second leading cause of lung cancer after smoking — responsible for an estimated 3,200 deaths per year.
Where does radon come from?
Radon originates in soil and bedrock. The amount produced depends on the local geology: areas with granite, shale, or uranium-rich soils tend to produce more radon than areas with limestone or sandy soils.
All soil produces some radon. This means every home in Canada has at least trace levels of radon indoors — the critical question is how much.
How does radon enter a home?
Air pressure inside most homes is slightly lower than in the soil beneath them. This pressure difference draws soil gases — including radon — upward and into the building through any available gap.
Common entry points include:
- 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 and window casements
Once inside, radon can accumulate — particularly in basements and lower floors where there is less air exchange with the outdoors.
Why is radon dangerous?
Radon itself isn't the direct problem — the decay products it releases are. When radon decays, it produces radioactive particles called "radon progeny" or "radon daughters." When you breathe these particles, they lodge in lung tissue and emit bursts of radiation.
Over months and years of exposure, this radiation damages the DNA in lung cells. Repeated damage increases the likelihood of those cells becoming cancerous. The process is slow and silent — there are no symptoms of radon exposure until lung cancer develops, often decades later.
The risk is proportional to: the concentration of radon in your home × the time you spend in it. A home with high radon levels is more dangerous than one with moderate levels, and someone who has lived in an affected home for 20 years has accumulated more risk than a recent resident.
Radon and smoking: a compounding risk
For smokers, the danger is significantly higher. Radon and tobacco smoke don't just add together — they multiply. Radon damages lung tissue, and smoke impairs the lung's natural ability to clear those radioactive particles. The combination makes each risk dramatically worse.
| Exposure scenario | Estimated lifetime lung cancer risk |
|---|---|
| Non-smoker, low radon (<100 Bq/m³) | ~1 in 200 |
| Non-smoker, elevated radon (200 Bq/m³) | ~1 in 20 |
| Smoker, low radon (<100 Bq/m³) | ~1 in 10 |
| Smoker, elevated radon (200 Bq/m³) | ~1 in 3 |
If you smoke and haven't tested your home, testing should be an immediate priority.
How common is elevated radon in Canada?
Radon is present in every home — the question is the level. Health Canada estimates that approximately 7% of Canadian homes exceed the national guideline of 200 Bq/m³. In high-risk provinces like Saskatchewan and Manitoba, the figure is considerably higher.
You cannot predict your home's radon level based on:
- Your province or city (neighbouring homes can have very different levels)
- Your home's age or construction type
- Whether your home has a basement
- Whether your neighbours have tested
The only way to know your home's radon level is to test it.
What are safe radon levels in Canada?
Health Canada's guideline is 200 Bq/m³ (becquerels per cubic metre). At or above this level, action is strongly recommended. However, "below the guideline" doesn't mean zero risk — lower is always better.
| Level | Recommendation |
|---|---|
| Below 100 Bq/m³ | Low risk — no action required; re-test if you renovate |
| 100–200 Bq/m³ | Moderate — consider mitigation; re-test within 2 years |
| 200–600 Bq/m³ | Elevated — mitigate within 2 years |
| Above 600 Bq/m³ | High — mitigate within 1 year |
The World Health Organization recommends a reference level of 100 Bq/m³, and many countries use this lower threshold.
How do you test for radon?
Testing is straightforward and inexpensive. There are two main options:
Long-term alpha track detector (recommended): A small passive device placed in the lowest livable area of your home for 91 days or more. This is the most accurate method because it captures seasonal variation in radon levels. Kits cost $30–$60 and are available online or at hardware stores.
Short-term test: A test lasting 2–7 days. Less accurate due to natural fluctuation in radon levels, but useful for a quick initial reading. Health Canada recommends confirming any elevated short-term result with a long-term test.
For either test, place the device on the lowest floor you regularly occupy (not a storage room or mechanical room). Follow the instructions and mail the device back to the lab when complete.
What happens if your levels are high?
If your home tests above 200 Bq/m³, the solution is radon mitigation. The most effective and common method is active sub-slab depressurization (ASD):
- A hole is drilled through the foundation slab
- A PVC pipe is installed and connected to a continuously running fan
- The fan creates negative pressure beneath the slab, drawing radon out before it enters the home
- Radon is vented safely to the exterior
This system typically reduces indoor radon levels by 80–99% and costs $1,500–$3,500 in most Canadian markets. It can usually be installed in a single day and requires minimal maintenance.
Other methods include improved ventilation, sealing entry points, and heat recovery ventilators — but sub-slab depressurization is the most reliable approach for homes with elevated levels.
Who should perform radon mitigation?
Always hire a certified radon professional for mitigation. Look for C-NRPP certification (the Canadian National Radon Proficiency Program) — Health Canada's standard for radon professionals. Certified professionals have completed specific training, passed exams, and committed to ongoing professional development.
A certified professional will assess your home, design an appropriate system, install it correctly, and perform post-installation testing to confirm the radon level has been reduced.
Next steps
- Haven't tested yet? Get a test kit — long-term kits start around $30 and are the most accurate way to know your home's radon level.
- Already have a result? Use our result interpreter to understand what your reading means and what to do next.
- Ready to mitigate? Find a certified professional near you.
Ready to test your home?
Find a certified radon professional near you and request a free quote.