Radon in Toronto (2026): What the Data Shows, Why You Should Still Test, and What Toronto Homeowners Should Do

Flat-vector map of Canada with a coral red pin marking Toronto, Ontario, alongside a circular badge showing 7% — City of Toronto's estimated share of buildings with radon levels that may pose a health risk

A note before you read. This article is general health and home-testing information for Toronto homeowners, drawn from Health Canada, the City of Toronto, Cancer Care Ontario, and the Canadian Cancer Society. It is not medical advice. See full disclaimers at the bottom.

If you live in Toronto and you've been told radon is "more of a Calgary or Winnipeg problem," there's truth to that — but it's not the whole story. Toronto has measurably lower average residential radon levels than most other major Canadian cities: per the Evict Radon National Study, the average Toronto Metro Area home tests at about 43 Bq/m³ with about 1 in 22 properties above the Health Canada 200 Bq/m³ guideline. The City of Toronto itself estimates that about 7% of Toronto buildings — homes, workplaces, and schools combined — have radon levels that may pose a health risk.

That 7% sounds small, but Toronto has roughly 1.2 million private dwellings in the city alone (and several million more in the broader Greater Toronto Area). 7% of that population is tens of thousands of Toronto homes with elevated radon — and the only way to know whether yours is one of them is to test it.

This guide walks through the Toronto data honestly, explains why Toronto's average is lower than other major cities (and why that doesn't mean you should skip testing), and lays out the practical step-by-step from "I want to know" to "result in hand."

TL;DR for Toronto homeowners

Toronto has measurably lower average residential radon than most other major Canadian cities — average about 43 Bq/m³, well below the 200 Bq/m³ guideline.

But about 7% of Toronto buildings are estimated to have elevated radon (City of Toronto) — that's tens of thousands of Toronto homes given the city's size.

The only way to know your specific home's level is to test it — Toronto's geographic averages don't reliably predict individual home levels.

For new-build Toronto homeowners (Agreement of Purchase and Sale signed on or after February 1, 2021, and within the 7-year window), elevated radon may trigger up to $50,000 of Tarion warranty coverage for mitigation.

A long-term radon test costs $89 all-in. Order a kit →

What the published Toronto radon data actually shows
Why Toronto's average is lower than other major cities
Why testing still matters in Toronto
What to do as a Toronto homeowner
Tarion warranty coverage for Toronto new-build owners
Local Toronto and Ontario resources
FAQ — Toronto-specific questions
Disclaimers
Sources

What the published Toronto radon data actually shows

Toronto has multiple data sources, and they consistently show Toronto on the lower end of the Canadian radon spectrum:

Evict Radon National Study: Toronto Metro Area average residential radon level of about 43 Bq/m³ — among the lowest of Canada's six largest cities. About 1 in 22 properties (~4.5%) above the Health Canada 200 Bq/m³ guideline.
City of Toronto: estimates that about 7% of Toronto buildings (homes, workplaces, and schools) have radon levels that may pose a health risk (Toronto.ca).
Ontario provincial average (2012 Cross-Canada Survey): about 8% of homes above the guideline.

Sources: Evict Radon National Study; City of Toronto — Radon & Your Health; Health Canada Cross-Canada Survey

The takeaway: Toronto is a lower-radon city by Canadian standards. That's the honest framing — most Toronto homes test well below the guideline, and the city's average is meaningfully lower than Calgary, Winnipeg, Saskatoon, or Halifax. But "lower" doesn't mean "zero" — at the city's population scale, 7% of buildings is a lot of homes.

Order a $89 long-term radon test kit →

Why Toronto's average is lower than other major cities

Toronto's geology is the main reason its residential radon profile is lower than prairie or Atlantic Canadian cities:

Geology. Toronto sits on the St. Lawrence Lowlands sedimentary basin, on glacial soils of mostly Ordovician shale and limestone bedrock. This geology contains lower uranium concentrations than the Canadian Shield bedrock under prairie cities (Winnipeg, Saskatoon) or the Halifax Group bedrock under Halifax. Less uranium in the soil = less natural radon production = lower background residential radon levels.

Climate and construction are similar to other Canadian cities (long heating season, full-basement housing, tighter modern envelopes), but the geology is doing most of the protective work in Toronto.

That said — and this is important — geological averages are city-wide. Individual Toronto homes can still test high depending on local geology variations, foundation construction, ventilation, and how the home is operated day-to-day.

Why testing still matters in Toronto

Three reasons even Toronto homeowners should test:

1. The 7% of Toronto buildings with elevated radon are real homes with real people. At the City of Toronto's population scale, 7% is tens of thousands of dwellings. The only thing those homes had in common before testing was that the owners assumed they were probably fine. Testing is the only way to know whether yours is in the 93% or the 7%.

2. Geographic averages don't predict individual homes. Even within "low-radon" Toronto neighbourhoods, individual home levels vary substantially based on foundation construction, ventilation, basement use, and small-scale geological variations. The Evict Radon National Study and Health Canada both emphasize that home-to-home variability dwarfs neighbourhood-level averages.

3. The cost is small relative to the information value. A $89 long-term test answers the question definitively for your specific home. If you test below the guideline, you can stop wondering for the next 5 years. If you test above, you can mitigate and remove a lifetime lung-cancer risk factor for your family.

Order a $89 long-term radon test kit →

What to do as a Toronto homeowner

Step-by-step:

Step 1: Test (long-term, 91+ days). Health Canada's recommended test for a homeowner mitigation decision is a long-term alpha-track lab test, deployed for at least 91 days during the heating season (October–April in Toronto), in the lowest lived-in level of your home. The test costs $89 all-in with RadonTest.ca — kit, tracked outbound, prepaid tracked Canada Post return label, and analysis at Lex Scientific in Guelph, Ontario (a C-NRPP-listed Canadian lab).

Step 2: Read your result. Below 200 Bq/m³, no mitigation is required (Health Canada recommends retesting every 5 years). Above 200 Bq/m³, mitigation is recommended. See our How to Read Your Radon Test Results and What to Do If Your Radon Level Is Above 200 Bq/m³ guides.

Step 3: Mitigate, if needed. A C-NRPP-certified mitigation contractor installs a sub-slab depressurization system at a typical Ontario cost of $2,500–$4,500. These systems typically reduce radon by up to 95%. Find a Toronto-area C-NRPP-certified mitigator via the C-NRPP Find a Professional tool.

Step 4: Apply for Tarion warranty coverage (if applicable) AND/OR the Lungs Matter grant. See the Tarion section below. The Lungs Matter program offers up to $1,500 for eligible Canadians.

Step 5: Verify. Once mitigation is complete, run an independent post-mitigation test to confirm levels are below 200 Bq/m³.

Order your Toronto kit — $89 →

Tarion warranty coverage for Toronto new-build owners

If you bought a new home in Toronto with an Agreement of Purchase and Sale signed on or after February 1, 2021, and the home is within its 7-year warranty window, Tarion covers up to $50,000 of radon mitigation if a qualifying long-term test shows levels above 200 Bq/m³. The warranty travels with the home to subsequent owners.

For the full claim process, see our Tarion radon warranty claim guide. Note: meeting the test-type criteria is one of several conditions for a Tarion claim.

Local Toronto and Ontario resources

City of Toronto — Radon & Your Health (toronto.ca) — the City's public-health radon resource page
Cancer Care Ontario — Risk of Residential Radon Exposure (cancercareontario.ca)
York Region — Radon: Test Your Home (york.ca) — for GTA homeowners north of Toronto
Tarion — Radon warranty coverage (tarion.com)
Take Action on Radon — Ontario (takeactiononradon.ca/provinces/ontario)
Canadian Lung Association — Lungs Matter mitigation grant (lung.ca)
C-NRPP Find a Certified Professional (c-nrpp.ca) — Toronto-area certified measurement and mitigation professionals

Note on Ontario building code. New-build Toronto homes are subject to the 2024 Ontario Building Code, which requires a Level 1 radon "rough-in" province-wide.

Note on Ontario real estate disclosure. Ontario uses OREA's Form 220 (SPIS), which is voluntary but, once completed, requires truthful answers. Independent of the SPIS, the latent-defect doctrine applies. See our Real Estate Radon Guide.

FAQ — Toronto-specific questions

How common is high radon in Toronto? Toronto has lower average residential radon than other major Canadian cities. Per the Evict Radon National Study, about 1 in 22 Toronto Metro Area properties (~4.5%) test above the Health Canada guideline. The City of Toronto estimates about 7% of Toronto buildings overall have elevated radon. Both figures are meaningfully below the Canadian average — but at Toronto's population scale, even 7% is tens of thousands of homes. The only way to know your home's specific level is to test it.

Why is Toronto's radon lower than Calgary or Winnipeg? Geology. Toronto sits on the St. Lawrence Lowlands sedimentary basin (Ordovician shale and limestone bedrock), which contains lower uranium concentrations than the Canadian Shield bedrock under prairie cities like Calgary or Winnipeg. Less uranium = less natural radon production.

Should I bother testing if Toronto is mostly low-radon? Yes. Toronto's average is low, but individual home levels vary substantially. Even in "low-radon" Toronto neighbourhoods, individual homes can test high based on foundation construction, ventilation, basement use, and small-scale geological variations. A $89 long-term test answers the question definitively for your specific home.

Are some Toronto neighbourhoods worse than others? Toronto's geology is broadly similar across the city (St. Lawrence Lowlands sedimentary), but individual home levels vary substantially based on factors that have nothing to do with neighbourhood. Neighbourhood-level statistics don't reliably substitute for a home-specific test.

Does my Toronto home have a radon rough-in? If your home was built under the 2024 Ontario Building Code (in force January 1, 2025), yes — there should be a capped vent pipe stub through the basement slab. Older Toronto homes (built before 2025) generally do not have a radon rough-in, since the prior 2012 Ontario Building Code only required a rough-in in three designated areas (none of which were in Toronto).

Can I claim Tarion warranty coverage if my Toronto home tests above 200 Bq/m³? Possibly. If your home is in its 7-year Tarion warranty window from the original possession date, and you have a qualifying long-term test result above 200 Bq/m³, you may be able to claim up to $50,000 of Tarion-covered mitigation (for Agreements of Purchase and Sale signed on or after February 1, 2021). See our full Tarion radon warranty claim guide for the step-by-step process.

How much does radon mitigation cost in Toronto? Typical Ontario residential mitigation costs are $2,500–$4,500 for a sub-slab depressurization system installed by a C-NRPP-certified contractor. The Canadian Lung Association's Lungs Matter program may offset up to $1,500 for eligible homeowners.

Where can I buy a long-term radon test kit in Toronto? You can order a RadonTest.ca $89 all-in long-term kit online and receive it within a few business days anywhere in the Greater Toronto Area — kit + tracked outbound + prepaid tracked Canada Post return label + analysis at a C-NRPP-listed Canadian lab.

Do I have to disclose elevated radon when I sell my Toronto home? Ontario uses OREA's Form 220 (SPIS), which is voluntary but, once completed, requires truthful answers. Independent of the SPIS, the latent-defect doctrine applies under common-law principles, and a known elevated radon reading is generally treated as a material defect requiring disclosure. See our full Real Estate Radon Guide.

When is the best time of year to test in Toronto? The heating season — October through April — produces the highest indoor radon levels and is the recommended testing window per Health Canada. A long-term test (91+ days) started in early October gives you a strong heating-season reading.

Where can I find a C-NRPP-certified radon mitigator in Toronto? The C-NRPP Find a Certified Professional directory lists certified measurement and mitigation professionals by area. Toronto and the GTA have a substantial certified-mitigator network.

Test your Toronto home — $89, all in

Toronto has lower average residential radon than other major Canadian cities — but "lower average" isn't "zero," and the only way to know whether your specific home is in the 93% below the guideline or the 7% above is to test it. A long-term lab-analyzed result for $89 answers the question definitively for the next 5 years.

RadonTest.ca — $89 all-in (plus applicable tax). Long-term 91-day alpha-track test kit. C-NRPP-listed device. Analysed at Lex Scientific in Guelph, Ontario — Canadian lab, C-NRPP listed, ISO/IEC 17025 accredited by CALA. Tracked Canadian shipping both ways. Written lab report PDF delivered to your inbox.

Order — $89 →

Important disclaimers

Not medical, legal, or warranty advice. This article provides general health and home-testing information for Toronto homeowners drawn from publicly available Health Canada, City of Toronto, Cancer Care Ontario, Tarion, Canadian Cancer Society, and Evict Radon National Study materials. It is not medical advice, legal advice, or warranty advice. Consult a qualified professional for specific decisions.

Statistics and citations. The 1-in-22 Toronto Metro Area figure and 43 Bq/m³ average are from the Evict Radon National Study. The "about 7% of Toronto buildings" figure is from the City of Toronto — Radon & Your Health page. National figures are from Health Canada's Radon: What You Need to Know fact sheet (2025). Sources update published figures periodically.

Local Toronto data. Statements about Toronto radon levels reflect published research and government materials. Radon levels vary substantially even between adjacent homes; community-level statistics do not substitute for a home-specific long-term test.

Mitigation cost. The $2,500–$4,500 mitigation cost range is a typical Ontario residential figure. Actual costs vary by home, foundation, complexity, and contractor.

Tarion qualification. Statements that the alpha-track test "qualifies" or "meets Tarion test-type criteria" mean only that the test method matches Tarion's published test requirements. They are not a representation that any specific home, test, or claim will be approved. A complete Tarion radon warranty claim requires several conditions — see our Tarion claim guide. RadonTest.ca is independent from Tarion.

Lungs Matter grant. Eligibility, grant amounts, and program availability for the Canadian Lung Association's Lungs Matter program may change. Verify directly at lung.ca before relying on the program.

Real estate disclosure. Statements about Ontario real estate disclosure reflect general OREA / common-law latent-defect principles. Specific obligations for any individual transaction depend on the facts; consult an Ontario real estate lawyer.

No diagnosis or treatment claims. RadonTest.ca sells radon test kits. We do not diagnose, treat, or prevent disease.

No warranty as to completeness. RadonTest.ca makes no warranty as to the completeness or accuracy of the information herein and accepts no liability for decisions made in reliance on this article.

Sources & further reading

Toronto- and Ontario-specific

Health Canada / national

National associations and grants

Related RadonTest.ca articles

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