Should You Test Your Ontario Home for Radon? What to Test, How, and What to Do If It’s High
Invisible, odourless, and the #1 cause of lung cancer in non-smokers — yet testing and fixing it both cost less than you’d think
Does an Ontario home need a radon test, and what counts as ‘too high’?
Yes — every home in contact with the ground should be tested. Radon is a naturally occurring radioactive gas that seeps up from the soil into your home; you can’t see or smell it. Per Health Canada, radon is the leading cause of lung cancer among non-smokers in Canada. The Canadian guideline is 200 Bq/m³; above that, Health Canada recommends fixing it within one year. Public Health Ontario estimates that about 4.6% of Ontarians live in homes above the guideline. The reliable way to test is a long-term test: at least 3 continuous months, ideally over the closed-window fall/winter season.
Sources: Health Canada, "Radon guideline" and "Testing your home for radon" (canada.ca); Public Health Ontario. Guideline: 200 Bq/m³.
Most clients give me a blank look the first time I mention radon: “My house is fine — why would I test for that?” That’s exactly the problem. Radon has no colour and no smell; your body feels nothing, yet it’s the top cause of lung cancer in non-smoking Canadians. The good news: testing is cheap (a kit costs a few dollars), and even a high reading is usually fixed by installing a simple mitigation system. Here’s what to test, how to test it properly, what to do if it’s high, and how to handle radon in a purchase or sale.
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What radon is, and why it matters
Radon is a radioactive gas produced as uranium in soil naturally decays. It enters through cracks in the foundation, around pipes, and through basement floors, then concentrates in enclosed spaces. As you breathe, radon’s decay products lodge in lung tissue and release radiation; over years, that raises lung-cancer risk. Per Health Canada, radon is the number-one cause of lung cancer in non-smokers, and higher still for smokers. Key point: this isn’t an “old house” or “certain neighbourhood” issue — any ground-contact home can be high, and two houses next door to each other can read very differently.
Step 1: Use a long-term test, not a quick one
ℹ️Don’t be reassured by “the air upstairs feels fresh.” Radon seeps up from the foundation, so the basement and main floor read highest — exactly where many families sleep and relax. Test the lowest level where you actually spend time.
Step 2: Buy a certified kit, or hire a C-NRPP professional
Step 3: Above 200, fix it — don’t panic
⚠️Ignore the number from a short (few-day) kit, high or low. Radon swings too much day to day; the only reliable basis for a decision is a long-term reading of 3+ months.
Handling radon when buying or selling
Buyers: if you’re buying a detached, semi, or townhouse (a ground-contact home), add radon testing to your inspection conditions, or test yourself in the first year after closing — the cost is tiny for the peace of mind. Sellers: you aren’t legally required to test, but if you know the home is above guideline and conceal it, you may run into trouble over failing to disclose a dangerous latent condition. Having tested and mitigated is actually a selling point. High-floor condo owners are generally lower risk, but ground-floor and townhouse owners should still pay attention.
Frequently Asked Questions
Is radon testing expensive?
No. A DIY long-term kit is typically $30–$60 including lab analysis — one of the best-value home-safety investments there is. Hiring a C-NRPP professional costs more but is worth it for a transaction or if you want it handled end to end.
If radon is high, is the home still liveable and buyable?
Yes. It’s a solvable engineering problem — the common sub-slab depressurization system is usually installed in a day or two and brings the reading below the guideline. In a purchase, you can negotiate for the seller to mitigate or reflect it in price rather than walking away.
When is the most accurate time to test?
Health Canada recommends a long-term test of at least 3 continuous months over fall and winter, when doors and windows stay closed — closest to your true long-term exposure. Testing in summer with windows open gives a falsely low, unreliable reading.
Do condo residents need to test?
High-floor units are generally lower risk, since radon enters from the ground. But ground-floor units and ground-contact townhouses should still test once — the cost is low and the peace of mind is worth it.
Arthur Zhao
Real Estate Broker · FRI · ABR · SRS · PSA · MCNE · E-PRO · CLHMS & GUILD Elite · REAIS
VP & Branch Manager, Bay Street Group Inc.
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