Every home in Quebec and Canada has some radon. All of them. The question is never "is there any in my house?" — it's "how much?" And that question is one no map, no neighbour, and no year of construction can answer for you. Two identical houses, same street, same soil, same builder: one at 40 Bq/m³, the other at 400. It's documented right across the country.
This guide covers what a homeowner actually needs to know: where radon in a home comes from, what makes it rise, what level is acceptable, how to measure it properly — and what to do if the number is high.
What radon is, in two paragraphs
Radon is a naturally occurring radioactive gas. It comes from the decay of uranium in the soil — everywhere, not just "in certain regions." It's invisible, odourless, and tasteless: your nose will never detect it, and neither will your smoke detector.
Outdoors, it disperses and poses no problem. The problem is when it builds up in an enclosed space — your home, especially from fall to spring, with the windows closed and the heat running. Over the long term, breathing in too much radon damages the lungs: it's the leading cause of lung cancer among non-smokers in Canada, and roughly 1,000 deaths a year in Quebec according to public health. We don't say that to frighten you; we say it because it's measurable and correctable — which makes it, frankly, one of the few health risks you can fix with a reasonable bill.
How radon gets into a home
Your home literally draws air up out of the soil. In winter, warm air rises and escapes at the top; the house makes up for it by pulling air in from below — that's the stack effect. That air passes through everything that touches the ground:
- cracks in the slab and in foundation walls;
- the sump and floor drains;
- the joints between the slab and the walls;
- pipe and cable penetrations;
- an earth-floor crawl space, if there is one.
That's why the basement almost always shows the highest concentrations — and it's why you test at the lowest level where you spend time. A finished basement with an office, a playroom, or a teenager's bedroom: that's where you measure. See exactly where to place your detector.
And what about new homes? Often worse, not better: because they're more airtight, they hold the air — and the radon — inside. "New home" is not a free pass; in fact, the Quebec Construction Code requires radon-preparedness measures precisely because the problem is real in new construction.
What level is acceptable?
The Canadian guideline is 200 Bq/m³ (becquerels per cubic metre), as an annual average, in the lowest lived-in area. It's an action threshold, not a sharp line between an acceptable level and a level of concern: the risk rises gradually with concentration and length of exposure.
| Your result (long-term measurement) | Health Canada recommendation |
|---|---|
| Below 200 Bq/m³ | No remediation required. Retest after major renovations, or every ~5 years. |
| 200 to 600 Bq/m³ | Remediate the home within 2 years. |
| Above 600 Bq/m³ | Remediate the home within 1 year. |
Average in Quebec basements: around 35 Bq/m³. But homes above 200 are found in every region — Outaouais, Capitale-Nationale, Estrie, Montérégie, and yes, Montreal. See our guide Radon in Quebec: regions and data.
How to test your home (the right way)
There's only one method aligned with the guideline: a long-term measurement, 91 days minimum, ideally during the heating season (October to April).
In practice:
- Place a detector (the small passive detector, no battery) at the lowest lived-in level, between 0.8 and 2 m off the floor, away from drafts and moisture.
- Forget about it for three months. It's the only health test that asks you to do nothing.
- Return it to the lab — our kit is analysed by a C-NRPP certified Canadian lab, prepaid return included.
- Receive your documented result: your Certificate of Analysis, with your average in Bq/m³ and what it means.
Why not a digital monitor with a screen? A good approved monitor has its place — tracking trends, checking a mitigation system. But to make a decision, the reference remains the long-term, lab-analysed measurement: independent and documented. And a word of caution: non-approved monitors, some of them recalled by Health Canada, are still sold online. To understand the labels, read "Health Canada approved": what that really means.
A free test is sometimes possible — participating libraries, public-health campaigns. If you have access to one and you're patient, it's a real option; the important thing is to test, full stop.
Result above 200: what do you do?
First: no panic, and don't sell the house. Radon can be fixed — properly, and for good.
The standard solution is called active soil depressurization (the well-known "radon mitigation system"): a pipe sealed into the slab, a dedicated fan, and the soil gas is vented above the roof before it enters your home. Installed by a C-NRPP certified professional, it typically reduces radon by 80 to 90% and more, in a single day's work. In Quebec, expect generally between $2,000 and $3,500 depending on the home. See the breakdown in Radon mitigation cost: the full details.
Then you retest (a long-term measurement again) to confirm the system is doing its job — and that's where your before/after certificate becomes the proof in black and white, useful too on the day you sell. Follow the step-by-step action plan for a result above 200 Bq/m³.
The questions everyone asks
My house is new, am I in the clear?
Not tested = no answer. New homes, being more airtight, hold more radon. The Code requires preparation (a sealed pipe under the slab) in new construction — but preparation isn't mitigation: you have to measure.
Does radon cause symptoms in the home?
No — no odour, no headache, nothing in the short term. The only "symptoms" are long-term and affect the lungs. That's exactly why you measure instead of waiting for signs. For the full answer, see Symptoms of radon exposure.
My neighbour tested at 50 Bq/m³. Does that reassure me?
Unfortunately not. Radon varies from one house to the next on the same street — foundation, cracks, drainage, ventilation: everything differs. Your neighbour's test tells you about your neighbour's house.
Does an air purifier or opening the windows work?
HEPA filters don't remove radon (it's a gas). Opening the windows dilutes it temporarily — until you close them. The only lasting solution above 200 Bq/m³ is mitigation at the source.
I'm a renter — what do I do?
Test all the same (the detector can go anywhere) and raise it with your landlord, documented result in hand.
What's the difference between Bq/m³ and pCi/L?
Two units for the same thing — Canada uses Bq/m³, the United States uses pCi/L (1 pCi/L = 37 Bq/m³; the Canadian guideline of 200 Bq/m³ ≈ 5.4 pCi/L).
Sources
- Health Canada — Radon: canada.ca/fr/sante-canada — radon
- Government of Quebec — Residential radon: quebec.ca — radon domiciliaire
- Institut national de santé publique du Québec (INSPQ) — Radon in Quebec: health risk assessment: inspq.qc.ca/publications/352