Radon testing and long-term monitoring in Simcoe County

In Health Canada’s 2012 survey, 0.9% of 110 homes tested in the Simcoe Muskoka District Health Unit were above the guideline.

The larger 2024 Cross-Canada survey reports 12.4% (1 in 8) of homes at or above the guideline for Ontario as a whole. The two surveys aren't directly comparable: the 2024 study pooled about 69,000 volunteer tests, more of them in basements, which partly explains its higher numbers. Neither can tell you about a single house, because neighbouring homes can differ widely.

The health unit says the best time to test is fall to spring, that lower levels such as basements are at greater risk, and that Tarion's warranty covers radon mitigation in new Ontario homes 7 years old or less.

Health Canada's measurement guide asks for a long-term test with at least 91 days in the heating season, when closed windows and the stack effect make readings higher, so the result is a conservative estimate of the yearly average. It recommends testing for 3 to 12 months.

• Alpha track detectors record radon's alpha particles on a plastic film; you mail them to a lab when the test ends.
• Electret ion chambers lose charge as radon ionizes the air inside; a lab reads the voltage drop.
• Digital (electronic) monitors read continuously and show results on a screen or an app. For a long-term test, Health Canada says to use one that has passed C-NRPP performance testing, and it still has to run at least three months.

Place the detector on the lowest level where someone spends more than four hours a day, at least 30 cm above the floor and 30 cm from walls, and at least 1 m from vents, windows and doors; avoid kitchens, laundry rooms and bathrooms. A digital monitor left running after mitigation lets you watch for changes between the long-term tests below.

• Borrow a monitor. Take Action on Radon lists Tay Township Public Library among the libraries that lend radon monitors; a borrowed digital monitor is good for screening, and a long-term test needs at least three months.
• There's no provincial free-kit program in Ontario; long-term kits, about $30–$80 including the lab fee (Windsor-Essex County Health Unit), are sold online and at hardware stores.
• For a professional measurement or mitigation, search the C-NRPP directory ↗ by postal code; it lists certified measurement and mitigation professionals, and you can confirm they cover Innisfil and the rest of Simcoe County.

Health Canada recommends fixing levels above 200 Bq/m³ within a year, and sooner the higher the level. The usual fix is a sub-slab depressurization system (a sealed pipe through the floor and a fan venting outside), which Health Canada says costs about $2,000 to $3,000 including material and labour and cuts radon by more than 80% in most homes. Hire a professional certified for mitigation under C-NRPP.

After a system goes in:

• A C-NRPP professional runs a short test starting at least 24 hours after the fan is turned on.
• A long-term three-month test follows in the next fall or winter, done by a company other than the installer.
• With an active system, Health Canada recommends a long-term test within two years of activation and every five years after that, and again after renovations.
• Check the system's pressure gauge (manometer) regularly and never switch the fan off. It costs about $50 to $75 a year to run; a replacement fan is $200 to $300.

Since January 1, 2025, the Ontario Building Code requires new houses to include a soil-gas barrier and a radon rough-in. Tarion's new-home warranty covers radon remediation for seven years from possession, and the Canadian Lung Association's Lungs Matter program offers up to $1,500 toward mitigation for households with low to moderate incomes or a lung cancer diagnosis.

Read more: The radon testing guide.