Ontario has widely varying radon risk depending on geography. The Ottawa Valley, eastern Ontario, and areas underlain by the Canadian Shield, including parts of Sudbury, Elliot Lake, and the Bancroft region, have elevated radon due to uranium-rich granite bedrock. Southern Ontario's clay and limestone geology generally produces lower levels, though local hotspots exist in any region. The 2024 Cross-Canada survey found about 13% of Ontario homes exceed the guideline.

Typical Mitigation Cost in Ontario

$2,200–$3,800

Near national average

Costs vary significantly between the GTA, Ottawa, and northern Ontario due to labour markets and home construction types.

•Foundation type: poured concrete, block, or slab
•Basement finish level: unfinished installs are faster and cheaper
•Pipe routing complexity in finished or split-level homes
•GTA vs. rural Ontario labour rate differences
•Age of home: older homes may require additional sealing work

Local radon data

How common is high radon in Ontario?

Moderate

1 in 7.6

homes in Ontario have radon above Health Canada's action level of 200 Bq/m³. That's lower than Canada as a whole (1 in 5.6).

Check your postal code on the radon map

Cities in the 2024 survey

Thunder Bay1 in 3 homes
Kingston1 in 3 homes
St. Catharines - Niagara1 in 6 homes
Ottawa - Gatineau1 in 6 homes
Guelph1 in 6 homes
Hamilton1 in 8.7 homes
Windsor1 in 10 homes
Kitchener - Cambridge - Waterloo1 in 12 homes
London1 in 37 homes
Toronto1 in 59 homes

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Frequently Asked Questions: Radon in Ontario

Ottawa, Kingston, Sudbury, and communities in the Ottawa Valley and Canadian Shield region tend to report higher radon levels. However, localized hotspots can exist anywhere in Ontario, so testing is recommended province-wide.

Radon testing is not legally required in Ontario real estate transactions, but it is increasingly common in home inspection agreements, particularly in Ottawa and the surrounding region where awareness is higher.

Ontario follows Health Canada's national guideline of 200 Bq/m³. If your home tests above this level, Health Canada recommends taking action to reduce radon within two years (or sooner if levels are very high).

The Canadian Shield's granite and gneiss bedrock contains naturally elevated uranium concentrations, which decay into radon gas. Homes built directly over or near Shield geology, particularly in eastern and northern Ontario, face a higher risk of elevated indoor radon.

Health Canada recommends a long-term test of at least three months, conducted in the lowest livable area of the home during the heating season (fall through spring) when windows and doors are kept closed most of the time.

Units on upper floors of high-rise condos are generally at low risk because radon dissipates quickly above grade. Ground-floor units and basement suites are more susceptible and worth testing. Townhouse-style condos with basements should always be tested.

Use the city search above to find certified radon professionals serving your area. All listings on RadonFinder.ca hold current C-NRPP certification.

Most Ontario homeowners pay between $1,800 and $3,200 for a complete active sub-slab depressurization system. Ottawa homes with complicated configurations or multiple entry points may reach the higher end of this range.

Radon Resources for Ontario

Tools and guides to help you understand radon risk and take action.

Check your radon risk

Estimate your risk based on province, home age, and foundation type.

Understand your test results

Learn what Bq/m³ means and when action is required.

DIY radon test kits

Compare test kit options starting from $10.

Radon guides & articles

In-depth guides on testing, mitigation, and health risk.

Radon map of Canada

See how common high radon is in your postal code.

Radon FAQ

Answers to the most common questions about radon.