You should plan to test any GTA home for radon, but a reliable result takes at least 3 months, so for most buyers the real test happens after closing. Health Canada's guideline is 200 Bq/m³: if a long-term test averages above that, Health Canada recommends fixing it within 1 year. During a short condition period, the best you can do is a short-term screening, a question to the seller about past results, or a holdback negotiated with your lawyer.

Quality Inspections does not test for radon. This guide explains how radon testing in Ontario works and when to bring in a certified radon professional.

What Is Radon?

Radon is a radioactive gas that forms when uranium in soil and rock breaks down. According to Health Canada, it has no colour, smell or taste. Outdoors it disperses, but indoors it can build up to high levels.

Radon gets into a house because the air pressure inside is usually lower than the pressure in the soil around the foundation. That difference pulls soil gas in through:

  • Cracks in foundation floors and walls
  • Construction joints
  • Gaps around service pipes
  • Support posts and window casements
  • Floor drains and sumps
  • Cavities inside walls

Health Canada says the only way to know the radon level in a home is to test. Two houses on the same street can have very different results, so a neighbour's number doesn't tell you much about yours.

How Dangerous Is Radon?

Radon is the leading cause of lung cancer in people who don't smoke. Health Canada calls it "the #1 cause of lung cancer in non-smokers" and notes that the risk depends on both the radon level and how long you're exposed. Combining radon exposure with smoking "can significantly increase your risk of lung cancer."

The national and Ontario numbers:

  • The Canadian Cancer Society says Health Canada estimates about 16% of lung cancer deaths are related to radon exposure in the home, and that more than 3,000 lung cancer deaths a year in Canada are related to radon.
  • A Public Health Ontario infographic attributes about 850 lung cancer deaths a year in Ontario, or 13% of the province's lung cancer deaths, to radon.

Because exposure builds over years, radon is a long-term health question, not an emergency. That matters for buyers: you have time to test properly after you move in.

What Is Health Canada's Radon Guideline?

Health Canada's radon guideline is 200 becquerels per cubic metre (Bq/m³), measured as an annual average in the part of the home people normally occupy. The Government of Canada radon guideline says to "take corrective action if the average annual radon level exceeds 200 Bq/m³ in the normal occupancy area of a building," and to act within 1 year. It adds that "the higher the radon concentrations, the sooner action should be taken."

You'll still see an older two-tier timeline online. The C-NRPP website lists remediation within 1 year above 600 Bq/m³ and within 2 years between 200 and 600 Bq/m³. Health Canada's current guideline page uses a single 1-year timeline for anything above 200, so that's the one to follow.

Long-term test resultHealth Canada's current recommendationOlder timeline still shown by C-NRPP
Below 200 Bq/m³Within the guideline. Take Action on Radon suggests considering a retest within 5 years—
200 Bq/m³ or moreReduce the level within 1 yearRemediate within 2 years (200–600 Bq/m³)
Above 600 Bq/m³Reduce within 1 year, and sooner the higher the levelRemediate within 1 year
After mitigationAim for as low as reasonably achievable; a final level under 200 Bq/m³ is usually achievableRetest to confirm the system works

Sources for the table: Health Canada guideline, C-NRPP, Take Action on Radon — interpreting results.

Why Does Health Canada Recommend a 3-Month Radon Test?

Health Canada recommends a long-term test of at least 3 months because radon levels change from day to day and season to season, and only a long average shows your real exposure. Health Canada's testing page says "it is important that you conduct a long-term test for a minimum of 3 months."

Health Canada's Guide for Radon Measurements in Residential Dwellings adds the details:

  • Tests should run 3 to 12 months, with at least 91 days during the heating season. C-NRPP describes the heating season as October through April.
  • Place the detector in a normal occupancy area on the lowest lived-in level, at least 30 cm above the floor and 30 cm from walls and ceilings.
  • Anything shorter than 91 days counts as a short-term test, and "short-term measurements are not appropriate for informing mitigation decisions."

Testing in fall and winter tends to give a conservative result, because windows are closed and radon is usually higher in colder months.

What Are Your Radon Testing Options?

You can test with a do-it-yourself kit, an electronic monitor, or a certified radon measurement professional. None of the sources below publish standard prices, so get prices from the supplier or professional directly.

Test typeDurationApprox. costWhen to useLimitations
Short-term screening (C-NRPP listed device or monitor)96 hours to 90 days; real estate screening is a minimum of 4 days under CARST guidelines (C-NRPP)Not published; ask a C-NRPP professionalA quick indicator during a purchase; checking a new mitigation systemHealth Canada says short-term results shouldn't drive mitigation decisions (Health Canada guide)
Long-term DIY kit (single use)91 days or more (Take Action on Radon)Not published; described as the lowest-cost optionAfter you move in, during the heating seasonYou must follow set-up instructions and mail it to a lab; no result for 3+ months
Electronic radon monitorMinimum 3-month test, then can stay in place for ongoing readingsNot publishedOngoing monitoring after an initial long-term testHealth Canada says to choose one that has passed C-NRPP performance testing (Health Canada)
C-NRPP certified professionalLong-term test of at least 3 monthsGet quotesWhen you want proper placement, quality control and results explainedSame 3-month wait; costs more than a kit

Health Canada and Take Action on Radon list kit suppliers and a directory to find a radon measurement professional. Health Canada also runs a radon line at 1-833-723-6600.

Can You Test for Radon During a 5-Day Condition Period?

Not reliably. A condition period of a few days is far shorter than the 3-month minimum, and Health Canada's real estate guidance says plainly: "Health Canada doesn't recommend conducting a radon test during a real estate transaction." It says "a three-month test is the only way to accurately find out what the radon level is in a home."

That leaves buyers with five practical options:

  1. Ask the seller. Ask whether the home has been tested with a long-term test and whether a mitigation system is installed. According to Take Action on Radon, "there are no provincial databases in Canada" of past results, so the seller is your only source.
  2. Look for an existing system. Take Action on Radon says a system installed by a C-NRPP professional is an advantage. Look for its label and a U-tube manometer, which shows the fan is running.
  3. Use a short-term screening as an indicator only. C-NRPP notes CARST guidelines for real estate screening of at least 4 days. Treat the result as a flag, not an answer.
  4. Negotiate a holdback. Health Canada notes that some real estate professionals use a holdback so testing can happen after closing, and "mitigation can be completed using the hold back funds" if the level is high. Ask your real estate lawyer how to word it.
  5. Test after you move in. Health Canada encourages buyers to run a long-term test once they've moved in. Start it in the fall so it covers the heating season.

For sellers, Health Canada suggests testing before listing, so a low result can be shared with buyers.

How Is Radon Fixed?

Radon is usually fixed with a sub-slab depressurization system, a pipe through the basement floor and a small fan that pulls soil gas from under the house and vents it outside. According to Health Canada:

  • The system reduces radon by more than 80% in most homes.
  • It can be installed in less than a day.
  • It costs "about the same cost as other common home repairs."
  • Hire a contractor certified through the Canadian National Radon Proficiency Program (C-NRPP).

Take Action on Radon calls the same approach active soil depressurization. Get quotes from C-NRPP mitigation professionals, because the price depends on the foundation, the slab and where the pipe can run.

Sealing cracks and adding ventilation can help, but Health Canada says their effect depends on the radon level and the house. After any system goes in, C-NRPP recommends a short post-mitigation test followed by a long-term test the next heating season.

How a Home Inspection Handles Radon

A home inspection doesn't measure radon, and Quality Inspections doesn't offer radon testing. A pre-purchase inspection is a visual review of the home's systems, as described in what a home inspector checks in Ontario.

What an inspection can do is note visible things related to radon entry and mitigation:

  • Open sumps, floor drains and visible foundation cracks, which Health Canada lists as entry points
  • An existing mitigation pipe and fan, or a capped radon rough-in pipe in a newer home
  • Whether the basement is finished, which affects where a system could run

What's out of scope: measuring radon, judging whether a system is working, and estimating your exposure. For those, call a C-NRPP certified measurement or mitigation professional.

Radon in Toronto and the GTA: What Do Local Data and Rules Say?

GTA survey results have been low on average, but averages don't predict an individual house. Health Canada's Cross-Canada Survey of Radon Concentrations in Homes, based on 2009–2011 testing, found:

Health regionHomes testedAbove 200 Bq/m³
Ontario (province)—8.2%
City of Toronto732.7%
Peel (Mississauga, Brampton)890.0%
York (Markham, Richmond Hill, Vaughan)950.0%
Halton (Oakville, Burlington)1024.9%
Durham950.0%

These samples are small and more than a decade old. The same Health Canada page notes a 2024 update that found about 1 in 5 (17.8%) houses in Canada at or above the 200 Bq/m³ guideline. Whether you're buying in Toronto, Mississauga or Burlington, test your own house.

Two Ontario rules matter for newer homes:

  • Ontario Building Code. According to the Home Construction Regulatory Authority, the 2024 Ontario Building Code requires all new homes to include a capped, sealed and labelled radon rough-in pipe, with the 2024 updates in full effect as of April 2025.
  • Tarion warranty. Tarion says a freehold builder's warranty includes up to $50,000 of coverage for radon above Health Canada's 200 Bq/m³ guideline, for the full seven years of the warranty. You need test results covering at least three months, using C-NRPP certified devices and professionals. Coverage is as of October 2026; check Tarion for current terms.

If you're buying a home under seven years old, ask the seller for the warranty start date. Our new home warranty inspection covers the visible construction items, not radon.

Frequently Asked Questions

Is radon a problem in Toronto?

Health Canada's 2009–2011 survey found 2.7% of 73 Toronto homes tested above 200 Bq/m³, but every region in Canada has homes with elevated radon. The only way to know a specific home's level is a long-term test.

What radon level is safe in Ontario?

Health Canada's guideline is 200 Bq/m³ as an annual average, and it recommends fixing levels above that within 1 year. Take Action on Radon notes that no radon level is entirely risk-free.

Can I make my offer conditional on a radon test?

Health Canada doesn't recommend radon testing during a real estate transaction, because an accurate test takes at least 3 months. Ask your real estate lawyer about a holdback or other clause instead.

How long does a radon test take?

A long-term test runs at least 3 months (91 days), ideally during the heating season. Anything shorter is a short-term test and isn't used for mitigation decisions.

Does a home inspector test for radon?

Quality Inspections does not test for radon. Hire a C-NRPP certified radon measurement professional or use a long-term kit after you move in.

How much does radon mitigation cost?

Health Canada says a system costs about the same as other common home repairs. Get quotes from C-NRPP certified mitigation professionals.

Does Tarion cover radon in new homes?

Yes, as of October 2026. Tarion says freehold new homes have up to $50,000 of radon coverage for seven years if a 3-month test shows levels above 200 Bq/m³.

Sources

Book an Inspection

A pre-purchase inspection gives you a digital report with photos within 24 hours, so you can plan radon testing alongside everything else. Call (416) 899-8116 or send the property details to book.