Radon Map of Quebec: The Risk Regions

General information for Quebec homeowners, buyers, and renters, drawn from public sources (Health Canada, INSPQ, MSSS, regional public-health authorities, the cross-Canada radon survey). This is not medical or legal advice. Results are presented against Health Canada's guideline of 200 Bq/m³; RadonTest.ca coordinates the logistics of testing and does not interpret individual results.

Is there a radon map of Quebec? Yes and no. There are maps of radon emission potential — geological tools that show which areas are more likely to have homes with elevated concentrations. But there is no official map that tells you the radon level at a specific address: a map predicts risk across a territory, never the level in your own house. The only way to know your real concentration is a long-term test of at least 91 days.

This article is the detailed regional guide to radon in Quebec: where the gas runs highest, what the public-health authorities say, and why Quebec's geology produces such sharp differences. For the big-picture portrait (health risk, rules, mitigation, funding), start with our pillar page, Radon in Quebec: concentrations, risks, and what to do.

Radon potential vs. measured concentration: two different things

This is the single most important distinction in the whole subject, and the one that most "radon maps" blur.

• Radon potential is a geological prediction. It is built from how much uranium sits in the bedrock and soil, the intensity of gamma radiation at the ground surface, and the nature of the surface deposits. It answers the question: "In this area, how likely is it that a home has an elevated level?"
• Measured concentration is the result of an actual test in an actual home, in becquerels per cubic metre (Bq/m³). It answers the only question that matters to you: "How much radon is in my house?"

The two are never substitutes for each other. A home in a low-potential area can show an elevated level (a crack in the slab, strong depressurization, a well); a home in a high-potential area can be low (good impermeable clay deposits over the bedrock, a sealed slab). Health Canada is unequivocal on this point: "Radon concentrations will vary from one house to another, even if they are similar in design and are next door to each other. The only way to know the radon level in your home is to test."

In other words, a map is for prioritizing and raising awareness — it helps a government target which regions to test first. It is never a way to excuse you from testing.

Radon by region in Quebec

Quebec's radon "map" is very uneven, and a few regions stand out clearly because their public-health authorities have published data. Here is the portrait, from best-documented to least-documented.

Outaouais — among the highest concentrations in Quebec

The Outaouais is the best-documented region and one of the most affected. The CISSS de l'Outaouais reports an average basement concentration of about 68.3 Bq/m³ — well above the provincial average — which it attributes to the high uranium concentrations in the bedrock of certain parts of the territory. The municipalities of Chelsea, Cantley, and the Pontiac are explicitly flagged as higher-risk because of the composition of the bedrock.

In its Radon Awareness Month news release (November 2025), the CISSS also reminds residents that, in Quebec, 10 to 16% of lung-cancer deaths are linked to radon, or more than 1,000 deaths per year. For the region's central city, see our guide Radon in Gatineau.

Estrie (Eastern Townships) — about 1 home in 4

The Direction de santé publique de l'Estrie estimates that about 1 home in 4 there has a radon level that is too high, above the provincial average — one of the highest regional proportions in Quebec. The geology explains it: the Estrie sits on the Appalachians, whose metasediments are in places particularly uranium-bearing (see below). The same authority notes that very few homeowners have tested (on the order of 1 in 8, per Statistics Canada), which means most at-risk households still do not know their concentration. Local details in our guide Radon in Sherbrooke.

Greater Montréal — about 1 home in 6

People often assume, wrongly, that big cities are spared. The 2024 cross-Canada survey (Evict Radon / University of Calgary) ranks Montréal among the large Canadian cities showing a risk of roughly 1 home in 6 above 200 Bq/m³ (alongside Ottawa–Gatineau, Calgary, and Edmonton), a proportion comparable to the Quebec average (16.7%). Across Canada as a whole, urban communities show a similar proportion (17.4% at or above 200 Bq/m³), plus a substantial share of homes in the 100–199 Bq/m³ band. The St. Lawrence Lowlands, over which the region spreads, combine shales, glacial deposits, and Monteregian intrusions. We publish a guide for every major city in Greater Montréal and the Montérégie: Montréal, Laval, Longueuil, Terrebonne, Saint-Jean-sur-Richelieu, Saint-Jérôme, and Saint-Hyacinthe.

Capitale-Nationale and Chaudière-Appalaches — watched, not fully mapped

The Direction de santé publique de la Capitale-Nationale publishes general information on residential radon and the action to take above 200 Bq/m³, but with no published regional figure to date. On the Chaudière-Appalaches side, public health states clearly that there is not yet a complete mapping of the region's risk zones, and that measurement projects in homes and schools are underway to document any areas of overexposure. The lesson is plain: the absence of a detailed regional map is no guarantee that radon is absent — it is one more reason to test. See Radon in Quebec City, Radon in Lévis, and, for the neighbouring Centre-du-Québec, Radon in Drummondville.

Laurentides, Mauricie, and Centre-du-Québec — limited regional data

Several regional authorities (including the Laurentides) publish information pages and testing advice, but few precise, recent regional proportions are publicly available. In the absence of a reliable regional figure, the only certainty remains that you must test house by house. Local guides: Saint-Jérôme (Laurentides) and Trois-Rivières (Mauricie).

Abitibi-Témiscamingue and Saguenay–Lac-Saint-Jean — often lower, but never zero

In Abitibi-Témiscamingue, the CISSS reports that radon concentrations are among the lowest in Quebec — but that some homes still exceed the 200 Bq/m³ guideline. It is the perfect illustration of why a map is not enough: "low-potential region" does not mean "your house is fine." The same reasoning applies to Saguenay–Lac-Saint-Jean, where the Canadian Shield creates locally uranium-rich pockets. See Radon in Saguenay.

What this means for you: living in a "low-risk" region is not a result. Two homes side by side can show very different values depending on the soil, the foundations, and the ventilation. Only a long-term test reveals your own concentration.

Table: radon by administrative region

The table below summarizes each region's risk signal, as documented by public sources. "Published data" means a public-health authority or a study has released a regional figure; "no published regional figure" means you have to rely on geological potential and, above all, on testing.

Reading the table: an area with no published data is not a "risk-free" area. Where public-health authorities do not yet have a regional figure, geological potential — and the test — take precedence.

To place Quebec in the national context, see our comparison of radon levels by province.

How a radon potential map works (and what the science says)

Quebec has one of the strongest scientific foundations in Canada for mapping radon potential. The Ministère de la Santé et des Services sociaux (MSSS), working with the INSPQ and the Institut national de la recherche scientifique (INRS), developed a GIS-based (geographic information system) mapping approach to portray the high-emission-potential zones, in order to prioritize interventions there.

The foundational study (Drolet et al., 2013, Journal of Environmental Radioactivity) compared 1,417 basement radon measurements against three radiogeochemical indicators: the equivalent uranium (eU) concentration measured by airborne gamma surveys, the uranium concentration in sediments, and the geology of the bedrock and surface deposits. The results establish a direct relationship between uranium in the ground and radon indoors:

• Where equivalent uranium in the ground is below 0.75 ppm, 18% of homes exceed 150 Bq/m³ in the basement.
• Between 0.75 and 1.25 ppm, that proportion climbs to 33%.
• Above 1.25 ppm, it exceeds 40%.
• Where sediments contain more than 20 ppm of uranium, the geometric mean of radon reaches 215 Bq/m³, with more than 69% of homes above 150 Bq/m³ and more than 50% above the Canadian guideline of 200 Bq/m³.

The study also concludes that emission potential is higher where a uranium-rich bedrock unit is not covered by a low-permeability surface deposit (silt or clay). That is exactly why two areas with uranium-bearing bedrock can behave very differently depending on what covers them.

These figures are probabilities at the scale of an area, not a verdict on any one home: even where "more than 40%" of homes exceed the threshold, the majority do not — and the reverse is true in areas thought to be low. The map points the way; the test decides.

The geology that explains everything

Why is radon so uneven in Quebec? Because everything hinges on how much uranium sits in the soil and bedrock, and the province is made up of three broad geological domains that behave very differently.

• The Canadian Shield (the north and part of the southeast) — a basement of ancient crystalline bedrock, uranium-rich in places (acidic igneous rocks, pegmatites, carbonatites). This is what creates locally elevated pockets in Saguenay–Lac-Saint-Jean and in parts of the Outaouais.
• The St. Lawrence Lowlands — the valley where most Quebecers live, made of sedimentary rocks (shales) often covered by thick glacial deposits, and cut through by the Monteregian magmatic intrusions (the Montérégie hills). The black shales can be surprisingly uranium-bearing, which is why Greater Montréal is not spared.
• The Appalachians (Estrie and the southeast) — a belt of metasediments, some horizons uranium-bearing, which goes a long way to explaining why the Estrie ranks among the most affected regions.

The counterintuitive lesson: Quebec's radon does not follow a simple "North = high, South = low" rule. Some of the most affected areas (Estrie, Outaouais) sit on sedimentary or metamorphic formations that are especially uranium-rich, in the deep south of the province. And as the INRS study reminds us, what covers the bedrock (an impermeable clay deposit or, conversely, a permeable soil) can count as much as the bedrock itself.

Why a map cannot predict YOUR home

Even the best radon potential map fails to say what is happening under a specific foundation, for concrete reasons:

1. Local geology varies at the scale of a street. A lens of uranium-bearing bedrock, a fault, a change in soil permeability can make two neighbouring lots diverge.
2. The house counts as much as the soil. The number and size of cracks in the slab, the state of the joints, the presence of a sump or a crawl space, and above all the depressurization created by heating and ventilation determine how much radon is actually drawn inside.
3. Lifestyle matters. A finished, occupied basement, a heat pump, a recent sealing renovation all change the picture.
4. Well water can be an additional entry point in certain areas.

That is why Health Canada, the INSPQ, and every public-health authority in Quebec converge on the same message: a map helps to know where to raise awareness, but it never replaces a test. The map is an "area to watch" sign; the test is the diagnosis.

How to test your home in Quebec

Testing is simple, inexpensive, and the only way to know your real concentration.

• Use a long-term test of at least 91 days (three months). Radon fluctuates from day to day and season to season; only an average over 91 days or more reflects your real exposure. Short-term tests are only good for checking a mitigation system, never for deciding whether to act.
• The heating season (roughly November to April) is ideal, because the closed-up house gives a conservative reading — but you can start in any season.
• Place the detector on the lowest lived-in level (often the basement if it is used), in a room occupied more than four hours a day, about 1 m off the floor, away from drafts, vents, and direct sun. Not the kitchen, bathroom, or laundry room.
• Choose a test analyzed by a C-NRPP-certified lab (the Canadian National Radon Proficiency Program, overseen by Health Canada). RadonTest.ca kits use an alpha-track detector analyzed by a C-NRPP-certified lab.

Where to get a test: order a RadonTest.ca kit — the alpha-track detector (91 days or more), analysis by a C-NRPP-certified lab (with an option to analyze entirely in Canada), prepaid return shipping, and your result delivered with Health Canada context are all included.

If your result is 200 Bq/m³ or higher, Health Canada recommends taking corrective measures within one year — and sooner if the level is high. No radon level is entirely without risk, but it is a measurable, fixable problem. See our guide What to do if your radon level is above 200 Bq/m³.

Order your radon test kit → — all-in, analyzed in Canada, prepaid return shipping.

Frequently Asked Questions

Is there an official radon map of Quebec? There are maps of radon emission potential, developed by the MSSS with the INSPQ and the INRS from geological indicators (uranium in the ground, gamma radiation, surface deposits). There is, however, no official map showing the level at a specific address. A map predicts regional risk; only a long-term test reveals your home's concentration.

Where is radon highest in Quebec? Among the documented regions, the Outaouais (average basement concentration ≈ 68.3 Bq/m³; Chelsea, Cantley, the Pontiac) and the Estrie (≈ 1 home in 4) rank among the most affected; Greater Montréal is at ≈ 1 home in 6. But any home, in any region, can show an elevated level — only the test tells.

If my region is "low-risk," should I still test? Yes. In Abitibi-Témiscamingue, for example, concentrations are among the lowest in Quebec, but some homes still exceed 200 Bq/m³. A low regional potential says nothing about your particular home.

What is the difference between "radon potential" and "measured concentration"? Radon potential is a geological prediction at the scale of an area. Measured concentration is the result of an actual test in your home, in Bq/m³. A map helps to prioritize; it does not replace the test.

Can I use a map instead of testing? No. A potential map cannot account for the cracks in your slab, your ventilation, your well, or the geology at the scale of your lot. Health Canada is clear: the only way to know your concentration is to do a long-term test.

What is a acceptable radon level in Quebec? No level is entirely without risk. Health Canada's guideline is 200 Bq/m³ (annual average): it is the threshold above which it recommends acting within one year. The risk below the guideline is lower, but not zero.

How long should a radon test last? At least 91 days (three months) for a valid long-term result. Short-term tests are not suitable for deciding whether to act.

Sources

• Health Canada — About radon — concentrations vary from one house to another even when next door; "the only way to know the radon level in your home is to test" (modified 2025-09-24).
• Health Canada — Radon guideline — 200 Bq/m³; corrective measures within one year, sooner if high.
• Drolet, Martel, Poulin et al. (2013), J. Environ. Radioact. 124:57-67 — foundational study of radon potential mapping in Quebec (1,417 measurements; eU thresholds 0.75 / 1.25 ppm; 18% / 33% / >40%; sediments >20 ppm → 215 Bq/m³). DOI: 10.1016/j.jenvrad.2013.04.006.
• INSPQ — Mapping radon emission potential (BISE scientific summary) — MSSS/INSPQ/INRS GIS approach to prioritize high-potential zones.
• INSPQ — Radon in Quebec (publication 352) — risk assessment and geological foundations.
• CISSS de l'Outaouais — Radon Awareness Month news release (Nov. 2025) — average basement concentration 68.3 Bq/m³ (CISSS Radon page); 10 to 16% of deaths / >1,000 per year; testing season Nov.–Apr.
• CISSS de l'Outaouais — Radon — Chelsea, Cantley, Pontiac flagged higher-risk.
• Direction de santé publique de l'Estrie — Radon — about 1 home in 4 above the provincial average.
• Santé Québec Chaudière-Appalaches — Radon — no complete mapping; measurement projects underway.
• Santé Québec Capitale-Nationale — Residential radon — information and the action to take above 200 Bq/m³.
• CISSS de l'Abitibi-Témiscamingue — Radon — concentrations among the lowest in Quebec, but some homes > 200 Bq/m³.
• Santé Québec Laurentides — Radon — regional information and testing advice.
• 2024 cross-Canada radon survey (Evict Radon / University of Calgary) — Quebec ≈ 16.7% (1 in 6) at or above 200 Bq/m³; Montréal named among the large Canadian cities at ≈ 1 in 6; Canadian urban communities 17.4%; national average 84.7 Bq/m³, 17.8% across Canada.
• Gouvernement du Québec (MSSS) — Residential radon — average basement concentration ≈ 37 Bq/m³; >1,000 deaths/year in Quebec (updated 2025-11-20).

Laboratory analysis is performed independently by a C-NRPP-certified lab. Results are presented against Health Canada's guideline of 200 Bq/m³. RadonTest.ca coordinates only the logistics of the kits and sample submission — it does not interpret or alter results and does not provide medical or legal advice. Regional data are summarized from the public sources above; some proportions may evolve as new measurements are compiled.