Montreal Radon Map

The RadonTest.ca Montreal radon map — drawing on a 69,478-test national dataset of measured long-term results — puts Montreal at 17.4% of homes at or above Health Canada’s 200 Bq/m³ action guideline (about 1 in 6 homes), with a typical (geometric mean) level of 82.4 Bq/m³. Nationally the figure is 17.8%, and Quebec as a whole reads 18.6%. The highest reading anywhere in the Montréal metro catchment was 14,652 Bq/m³, recorded in La Vallée-du-Richelieu on the South Shore — over 73× the guideline. On the island of Montréal itself the highest was 2,126 Bq/m³.

See Montreal on the interactive map

Open the Canada Radon Map zoomed to Montreal → Search a postal code to find your immediate area.

The underlying survey data is public; the RadonTest.ca Canada Radon Map is the free tool that makes it searchable — by province, city and postal code, in English and French, no signup.

Montreal compared with its province and Canada

Nearby areas — where Montreal sits in context

Areas with few tests carry a wider margin of uncertainty — treat small-sample percentages as indicative rather than precise. A 0% reading means no home tested above 200 Bq/m³ among those measured there, not that the area is radon-free.

The same area at three different thresholds

Canada’s action guideline is 200 Bq/m³. The World Health Organization uses a stricter 100 Bq/m³ reference level, and the US EPA acts at 148 Bq/m³ (4 pCi/L). Measured against each, RadonTest.ca’s Montreal data reads:

No level of radon is completely risk-free — the risk rises with exposure, which is why the WHO line sits lower than Canada’s. Health Canada recommends acting within a year above 200 Bq/m³, sooner at higher levels.

Why this differs from older Health Canada figures

Health Canada’s 2009–11 national survey put Quebec at about 10.1% of homes at or above 200 Bq/m³, from 1,774 valid tests (2009–11 figures as re-tabulated by the 2024 survey team), with a typical level near 42 Bq/m³. This page uses the 2024 Cross-Canada Survey of Radon — 69,478 long-term tests, the largest residential radon dataset in Canada — which puts Quebec at 18.6% from 6,506 tests, typical level 86 Bq/m³.

Two things differ. First, the sampling: the 2009–11 survey recruited by random digit dialling across 121 health regions and deliberately over-sampled sparsely populated regions for geographic coverage, while the 2024 dataset aggregates long-term tests from homes whose occupants chose to test — which skews toward older housing, ground-contact basements and areas where radon is already a known concern. Second, the weighting: the 2009–11 figures quoted above are the raw, unweighted results. Because that survey deliberately over-sampled some regions, Health Canada also published population-weighted estimates, and its headline national result is 6.9%; the 11.3% raw figure comes from the 2024 survey team’s re-tabulation of the same dataset. None of these numbers is wrong — they answer different questions. For a population-representative estimate of Canadian housing, Health Canada’s weighted 6.9% is the right figure. For the largest body of actual measured results, use this page. Both are shown on the Canada Radon Map, and both can be switched between on the RadonTest.ca map. Full detail on methodology and sources.

Montréal: a moderate island surrounded by much higher ground

The Montréal metro figure is 17.4% and the island census division reads 16.6% across 650 tests. What makes Montréal notable is not the average but two things sitting either side of it.

The island versus the couronnes

Montréal's suburbs read consistently higher than the island. On the north shore, Deux-Montagnes reads 27.6%, Thérèse-De Blainville 21.5% and Mirabel 18.5%. On the south shore, Marguerite-D'Youville reads 29.8%, La Vallée-du-Richelieu 26.4%, Roussillon 19.8% and Le Haut-Richelieu 17.9%. Laval sits at 17.8%, close to the island. Longueuil is the outlier in the other direction at 7.5%.

The pattern follows the geology: the island sits on Trenton limestone and glacial marine clays from the Champlain Sea, which are relatively poor radon transmitters, while the north-shore couronne sits at the edge of the Canadian Shield, and the South Shore’s readings track the uranium-bearing intrusive rock of the Monteregian Hills and more permeable glacial sediments. If you moved off the island for a bigger lot, you probably moved onto ground that emits more radon into a house that is more likely to let it in.

What applies to you in Montréal

Québec's GCR warranty covers new-home construction defects, and since 17 April 2025 the Code de construction du Québec requires a full passive radon stack — not just a capped rough-in — in the new dwellings its building chapter covers (buildings of two storeys or less with eight dwellings or fewer are outside that chapter; for a typical new house, GCR enforcement does the work instead). Note that Québec has, as of 2026, no radon-specific workplace exposure limit — radon is absent from the Règlement sur la santé et la sécurité du travail, unlike in Ontario and several other jurisdictions. Employers still owe a general duty of care under the LSST, which matters in a city with as much basement commercial space as Montréal, but there is no numeric ceiling. On resale, Québec has no obligation to test for radon — but the OACIQ seller’s declaration, a mandatory form for brokered residential sales under five units, asks at section D13.2 (tests and expert assessments) whether tests — radon is named among them — have been done, and the Civil Code latent-defect warranty can apply to a known elevated result.

A map cannot test your home

Every figure on the RadonTest.ca Montreal radon map is an area figure. Two identical houses on the same street in Montreal can test very differently, because radon depends on your foundation, your soil, your ventilation and how you live in the house. The map tells you the odds. Only a long-term test tells you your number.

Health Canada recommends a long-term test of at least 91 days, and you can start it any time of year. Ideally at least 91 of those days fall in the heating season (roughly October to April), and there is a simple rule for when they don’t: if your result comes back below 200 Bq/m³ on a mostly-summer test, Health Canada suggests re-testing next heating season, because a summer test can read low. If it comes back above 200, Health Canada says no re-test is needed — act on it. Test your Montréal home — order a long-term radon kit →

What to do if your result is above 200 Bq/m³

Health Canada recommends taking corrective action within a year above 200 Bq/m³, and sooner the higher the reading. Most Canadian homes are fixed with sub-slab depressurisation — a pipe running from beneath the foundation slab to a fan that vents above the roofline, which, when properly installed, reduces levels by more than 80% in most homes (Health Canada); results vary by house. In Québec homes built under the Code's 2021 radon provisions — and especially since April 2025, when a full passive stack became required for covered new dwellings — sub-slab piping may already be in place, which usually reduces the job to connecting a fan.

Work should be done by a professional certified through the Canadian National Radon Proficiency Program (C-NRPP), and the home should be re-tested afterwards to confirm the fix worked. You can also look up radon by address or postal code anywhere in Canada on the RadonTest.ca map.

Montreal radon map — questions

How high is radon in Montreal?

RadonTest.ca’s Montreal radon map puts about 17.4% of Montreal homes — 1 in 6 — tested at or above Health Canada’s 200 Bq/m³ guideline in the 2024 Cross-Canada Survey of Radon, with a typical level of 82.4 Bq/m³. Against the WHO’s 100 Bq/m³ reference level, 45.4% are over.

What is the highest radon reading recorded in Montreal?

On the RadonTest.ca map: 14,652 Bq/m³, recorded in La Vallée-du-Richelieu on the South Shore, in the 2024 Cross-Canada Survey dataset — over 73 times Health Canada’s guideline. Readings like that are rare, and no map predicts them; only testing finds them.

Is there a free radon map for Montreal?

Yes. The RadonTest.ca Canada Radon Map is free and needs no signup, and covers Montreal at census-division and postal-area level.

Does the map show my street or postal code?

The RadonTest.ca map shows measured results for Montreal by census division and, for many postal areas, by postal prefix (FSA). It does not show individual addresses — no radon map anywhere does, because radon is measured house by house, not street by street.

Related

• Ottawa radon map
• Carte radon Montréal (français)
• Radon in Montreal: testing and mitigation
• Canada Radon Map
• Radon in Laval
• Radon in Québec condos
• Methodology and data sources

Recommended citation: Montreal Radon Map, RadonTest.ca, 2026. Data: 2024 Cross-Canada Survey of Radon (v1.1 (CCSR.24.1.1), ISSN 2818-8195). https://radontest.ca/pages/montreal-radon-map Data licensed CC BY 4.0 — attribution required: “RadonTest.ca Canada Radon Map”.