Short answer
The most common radon myths in Southern Ontario are that it only affects the Canadian Shield, that a neighbour’s low result applies to you, that new homes are immune, and that a few days of testing is enough. In fact, about 1 in 8 Ontario homes test at or above the guideline, results vary widely between neighbouring houses, newer homes have tended to test higher, and Health Canada recommends at least three months of testing.
Key facts
- Southern Ontario has radon sources of its own: glacial soils and black shales.
- Neighbouring homes can have very different levels.
- Newer homes have tended to test higher, not lower.
- Long-term (91+ day) tests are the standard for decisions.
1. “Radon is a Shield problem, not a Southern Ontario one.”
Southern Ontario’s glacial soils include ground-up Shield rock, and black shales add uranium in parts of the southwest. The 2024 Cross-Canada Survey estimated about 1 in 8 Ontario homes at or above 200 Bq/m³, and a Hamilton public health survey found about 14% of tested homes above the guideline.
2. “My neighbour tested low, so I’m fine.”
Radon depends on the ground directly under your foundation, the condition of your slab, your sump and drains, and how your house is heated and ventilated. Neighbouring homes regularly get very different results. Only your own test counts.
3. “New homes don’t have radon.”
Research from the University of Calgary found newer Canadian homes have tended to test higher than older ones. Homes built under the 2024 Ontario Building Code have a soil gas barrier and a rough-in pipe, but the rough-in is passive until a fan is added.
4. “A few days of testing tells you what you need to know.”
Radon levels swing with weather and season. Health Canada’s guideline is based on tests of at least three months, ideally through the heating season. Short tests are useful screens, not verdicts.
5. “If it were harmful, we’d notice symptoms.”
Radon causes no headaches, coughs or other short-term symptoms. Its harm, lung cancer, appears after years of exposure. That’s why it’s called invisible, and why testing is the only way to know.
6. “We tested years ago and passed.”
If that test was before June 2007, it was judged against an 800 Bq/m³ guideline. Today’s guideline is 200. Renovations, new windows, a finished basement or a new furnace can also change levels. Re-test.
7. “Opening the windows fixes it.”
Ventilation dilutes radon temporarily, but it isn’t practical through an Ontario winter, costs energy, and stops working the moment windows close. A sub-slab system works continuously at a fraction of the cost.
8. “Sealing the cracks will solve it.”
Sealing is part of every good mitigation, but on its own it rarely brings levels down reliably: there are too many hidden openings, and slabs keep cracking. Depressurizing the soil under the slab is what makes the difference.
9. “A radon problem makes a house hard to sell.”
Radon is fixable, usually in a day. A home with an installed, documented system and a low follow-up result is a home with one less unknown. Many buyers see that as a plus.
Common questions
Is radon real or overblown?
Radon’s link to lung cancer is well established by decades of research. In Canada, it’s attributed to about 16% of lung cancer deaths. The risk is real, and also very manageable: test, and fix if needed.
Do apartments and condos get radon?
Units on the ground floor or below grade can. Upper-floor units are much less likely to have elevated radon because they’re far from the soil.
Sources
- Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities (2024)
- Global News — Hamilton public health survey of 294 homes
- Simms et al., Scientific Reports (2021) — radon in newer North American residences
- Health Canada — Government of Canada radon guideline
- Health Canada — Guide for Radon Measurements in Residential Dwellings (Homes)
- CMAJ (2023) — Radon is responsible for 16% of lung cancer deaths in Canada