Radon in the Eastern Townships (Estrie): Magog, Coaticook, and the Risk Areas

General information for Eastern Townships homeowners, buyers, and renters, drawn from public sources (the Direction de santé publique de l'Estrie, Health Canada, the Gouvernement du Québec, and 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 the Estrie a high-radon area? Yes. The Direction de santé publique de l'Estrie estimates that about 1 home in 4 in the region has a radon level above the guideline — well above the provincial average of roughly 1 in 10. The Appalachian bedrock under the Eastern Townships is rich in uranium, which is the source of the gas. But a regional figure is only a flag: living in the Estrie is not a result, and the only way to know your own home's level is a long-term test of at least 91 days.

This guide is the regional deep-dive for the Eastern Townships: why the Estrie runs so high, which towns and MRCs are flagged, what the public-health authority recommends, and exactly how to test. For the city of Sherbrooke specifically, see our dedicated page, Radon in Sherbrooke. For the province-wide picture, start with the pillar, Radon in Quebec, and for the regional map, see the radon map of Quebec and its risk regions.

See the Estrie radon map — measured results for every surveyed area, searchable by postal code.

Why is the Estrie one of Quebec's highest-radon regions?

Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil and rock. Outdoors it disperses harmlessly; indoors it seeps in through foundation cracks, floor drains, sumps, and gaps around pipes, then accumulates in the lowest, least-ventilated rooms — typically the basement and ground floor.

What sets the Estrie apart is what's under it. The region's public-health authority is explicit: about 1 home in 4 in the Estrie has a level above the guideline, compared with roughly 1 home in 10 across Quebec. That is more than double the provincial rate, and it is geology rather than housing stock (see the next section).

Two modern habits make the regional risk worse. Homes are built tighter for energy efficiency, and people increasingly keep windows closed year-round — even in summer — because of extreme heat and wildfire smoke, which lets radon accumulate more. And the rise of remote work, with basements converted into offices, family rooms, and children's bedrooms, means people now spend far more hours in exactly the part of the house where radon is highest. The combination is why the Estrie is treated as a priority region for testing.

What does the geology of the Eastern Townships have to do with radon?

Everything. The Eastern Townships sit in the Appalachian geological belt, formed during ancient mountain-building events that folded, faulted, and metamorphosed the rock. The result is a landscape of metasedimentary rocks (mica schists and related rocks), volcanic units, and granitic intrusions — precisely the rock families most often associated with elevated indoor radon, especially where they are highly deformed, sheared, or uranium-bearing.

Here is the chain in plain terms:

1. Uranium in the bedrock decays over geological time, producing radium.
2. Radium decays into radon gas, which — being a gas — can migrate.
3. The gas moves up through soil and rock fractures and reaches the surface.
4. Where a building sits on that ground, it seeps in through the foundation and collects indoors.

The amount of uranium varies sharply across the Townships, which is why radon levels can differ dramatically between two neighbouring homes of the same design. Soil type matters too: a tight clay cap can hold gas back, while permeable, fractured ground lets it travel freely toward foundations. The Gouvernement du Québec lists the soil's uranium content, the climate, the ventilation, how well-sealed the house is, and indoor negative pressure as the factors that together set a home's concentration.

The practical takeaway: geology tells you the Estrie is a higher-probability region, but it can never tell you the number for your specific address. Only a test can.

Which Eastern Townships towns and MRCs are at risk — Magog and Coaticook?

Because the elevated radon is regional, every MRC in the Estrie carries higher-than-provincial risk — including the MRC de Memphrémagog (Magog), the MRC de Coaticook, the MRC du Val-Saint-François, the MRC du Granit, the MRC du Haut-Saint-François, and the MRC des Sources, along with Sherbrooke. The "1 in 4" estimate is a regional figure that applies broadly across the Eastern Townships, not a single town.

A few local signals are worth knowing:

• Magog has published its own residential-radon page (December 2025), repeating the estimate that radon is present in 1 home in 4 in the Estrie and urging residents to test during the cold season, when houses are sealed and the gas concentrates most.
• Coaticook sits in the same Appalachian belt, so the regional risk applies; we did not find a Coaticook-specific municipal radon program confirmed at the time of writing.
• Sherbrooke, the regional hub, has been the focus of awareness efforts and Health Canada free-kit distributions; in a Radio-Canada report the share of Sherbrooke homes with a concerning level was put at about 1 in 4, against a Quebec average nearer 1 in 10. We cover the city on the Radon in Sherbrooke page.

The single most important point about this table: a town-level flag is not a home-level result. A high-risk MRC contains plenty of low-radon homes, and a "lower-risk" pocket still contains homes above the guideline. The flag tells you to test; it never tells you what you'll find.

What does the Estrie public-health authority say about radon?

The Direction de santé publique de l'Estrie's guidance is consistent with Health Canada and the Gouvernement du Québec:

• Radon is the leading cause of lung cancer in non-smokers and the second leading cause overall (after smoking). In Quebec, 10 to 16% of lung-cancer deaths are linked to radon — more than 1,000 deaths a year province-wide.
• About 1 home in 4 in the Estrie is above the guideline, yet, per Statistics Canada, only about 1 homeowner in 8 has tested in the past decade. That gap — high regional risk, low testing — is the core of the regional message.
• Test in winter (roughly October to April), when windows stay closed and concentrations are typically highest, using a passive monitor left in place for at least three months and then sent to a specialized laboratory.
• Radon causes no short-term symptoms — no cough, no allergy, no asthma. You cannot feel, smell, or see it, so measurement is the only way to know.
• Don't rely on a neighbour's result: the authority stresses that the amount of radon can vary greatly within the same neighbourhood.

The authority frames testing as "simple and affordable" and stresses that effective fixes exist if your level comes back high.

How should Eastern Townships residents test for radon?

The method is the same everywhere in Canada, and it is straightforward:

1. Use a long-term test of at least 91 days (3 months). Health Canada is explicit that you should conduct a long-term test for a minimum of three months. A long-term alpha-track test captures the weather-driven swings in radon that a quick "snapshot" test misses — and a short-term test can mislead you in either direction.
2. Test during the heating season (about October to April), since sealed-up winter homes show the highest concentrations.
3. Place the detector in the lowest occupied level — basement or ground floor — in a room where you spend at least four hours a day, about a metre off the floor, away from drafts and exterior walls.
4. Have it analyzed by a C-NRPP-certified laboratory. Canadian National Radon Proficiency Program (C-NRPP) certification is recognized by Health Canada and Quebec's Ministère de la Santé et des Services sociaux.

A managed long-term kit handles the parts people get wrong on their own — choosing a compliant detector, running the full 91 days, and getting the device to an accredited lab. RadonTest.ca's kit is an alpha-track detector deployed for 91+ days and analyzed by a C-NRPP-certified laboratory, with prepaid return shipping and the option to have the analysis done entirely in Canada — useful for Townships households that want a Canadian lab and no cross-border shipping.

A note on electronic monitors: Quebec's guidance accepts a continuous electronic monitor only if it has passed C-NRPP performance testing and is run for at least one month, ideally three — and some inexpensive online models have been recalled or are unreliable. For a definitive number, a long-term passive test analyzed by a certified lab remains the standard. For how the methods compare and the full provincial picture, see Radon in Quebec.

What should you do if your Estrie home is above 200 Bq/m³?

First, the framing: 200 Bq/m³ is Health Canada's action guideline, not a "risk-free" line. There is no level considered free of risk — the World Health Organization suggests a reference level of 100 Bq/m³ — so the goal is always to get the concentration as low as reasonably achievable, whatever your starting number.

How quickly to act depends on how high the result is. Health Canada's current guidance is a single timeline: if your level is above the 200 Bq/m³ guideline, take corrective action to lower it within one year — and the higher the reading, the sooner you should act. (Some older Quebec public-health material still shows a graduated "two years for 200–600 Bq/m³" version, but Health Canada's guideline page now recommends acting within one year for any result above 200 Bq/m³.) Whatever your number, the goal is to reduce the radon concentration as low as practically possible.

The fixes are well-established and routinely effective. The most common is active sub-slab depressurization — a certified contractor cores a small hole in the foundation slab and installs a fan that draws the gas from beneath the house and vents it above the roofline before it enters the living space. Supporting measures include sealing foundation cracks, covering and venting sumps, and improving basement ventilation. Most homes can be brought well below the guideline.

Two rules matter: hire a C-NRPP-certified mitigation professional (Health Canada and Quebec both point to the C-NRPP directory), and re-test after the work to confirm the system actually lowered your level. For the step-by-step, read what to do if your radon level is above 200 Bq/m³, and for budgeting see radon mitigation cost in Canada.

The Estrie's geology means the odds are genuinely higher here than almost anywhere else in Quebec — but the regional rate is not your result, and a long-term test is the only way to turn "1 in 4" into a real number for your own home.

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

Frequently Asked Questions

Is the Estrie really one of Quebec's highest-radon regions? Yes. The Direction de santé publique de l'Estrie estimates that about 1 home in 4 in the region has a radon level above Health Canada's guideline of 200 Bq/m³, compared with roughly 1 home in 10 across Quebec. The reason is the region's uranium-rich Appalachian bedrock. A high regional rate is a reason to test, not a substitute for testing.

Does living in Magog or Coaticook mean my home has high radon? No. A regional or town-level flag tells you the probability is higher; it can never tell you your home's actual level, which varies enormously between neighbouring houses because of the soil, the foundation, and how the home is sealed and ventilated. The only way to know is a long-term test of at least 91 days in your own home.

Why is radon so high in the Eastern Townships? The Townships sit on Appalachian metasedimentary rocks and granitic intrusions that are relatively rich in uranium. As uranium decays it produces radium and then radon gas, which migrates up through soil and rock fractures and seeps into buildings through the foundation. The more uranium in the local ground, the more radon is generally available to enter homes.

What is the radon action level in Quebec? Canada's guideline, used in Quebec, is 200 Bq/m³. Above that, take corrective measures to reduce the level as much as possible — within one year, sooner if the reading is very high. There is no level considered completely free of risk; the WHO suggests aiming for 100 Bq/m³.

When should I test my Estrie home for radon? During the heating season, roughly October to April, when homes are sealed against the cold and concentrations are typically at their highest. Use a long-term test left in place for at least three months.

Is there a free radon test kit program in the Estrie? Health Canada and partners have distributed free kits in the region in the past (notably in Sherbrooke), and the national 100 Radon Test Kit Challenge runs in participating Quebec municipalities each year. Availability changes annually and kits are limited, so check with your municipality or MRC. If none is running, a managed long-term kit is inexpensive and available year-round.

Will a hardware-store kit give me a reliable result? It can, if it is a long-term (91+ day) test analyzed by a C-NRPP-certified laboratory and you place and run it correctly. The common pitfalls are a short-term snapshot test, poor placement, or skipping lab analysis. A managed kit removes those variables with a compliant detector and prepaid return shipping to an accredited Canadian lab.

Sources

• Direction de santé publique de l'Estrie — Radon — the regional public-health authority's radon page: the "about 1 home in 4 above the guideline," the ~1-in-8 testing rate (Statistics Canada), the 10–16% lung-cancer link, and winter testing with a 3-month passive dosimeter. (Note: this page still displays an older graduated "200–600 Bq/m³ → two years" remediation table; Health Canada's current guidance is to act within one year of any result above 200 Bq/m³.)
• Ville de Magog — Radon domiciliaire (Dec 18, 2025) — municipal page repeating the "1 home in 4 in the Estrie" estimate and recommending cold-season testing.
• Gouvernement du Québec — Residential radon — provincial guidance: the factors that set a home's concentration, the 200 Bq/m³ guideline, remediation within one year, C-NRPP certification, and that radon varies sharply between neighbouring homes.
• Health Canada — Radon and Testing your home for radon — the federal guidance, including the minimum 3-month long-term test and C-NRPP performance testing for electronic monitors.
• Evict Radon — 2024 Cross-Canada Radon Survey — national results, including roughly 16.7% of Central-region (Ontario/Quebec) homes at or above 200 Bq/m³.
• Radio-Canada — "Une maison sur quatre recèle une dose inquiétante de radon à Sherbrooke" — the ~1-in-4 figure for Sherbrooke vs. ~1-in-10 provincially, and a Health Canada free-kit distribution.
• Canadian National Radon Proficiency Program (C-NRPP) — directory of certified measurement and mitigation professionals and the consumer electronic-monitor performance report.
• Geology context (Appalachian metasedimentary rocks, granitic intrusions, and uranium as the radon source): Geology of Quebec and the U.S. Geological Survey on radon potential in the Appalachians — general geological background, not Estrie-specific measurements.