Radon is the second leading cause of lung cancer in Canada after smoking. Ontario has significant radon risk zones. Here is what homeowners need to know in 2026.
What Is Radon?
Radon is a naturally occurring radioactive gas that forms from uranium decay in soil and rock. It enters homes through foundation cracks, sump pits, floor drains, and construction joints. Odourless and colourless — only testable, not detectable by senses.
Ontario Risk Areas
Notable elevated radon areas: parts of Ottawa, Bancroft, Sudbury, and scattered locations across GTA and cottage country. Health Canada action level: 200 Bq/m3. Approximately 7% of Canadian homes exceed this level.
How to Test
Long-term alpha track test (90-day minimum): most accurate. Place detector in lowest liveable area. Send to certified lab. Cost: $30-$60 DIY kit. Recommended for all Ontario homes — especially those with finished basements.
Mitigation: Active Soil Depressurization (ASD)
ASD is the standard Ontario mitigation method. A pipe and fan draws radon from under the foundation slab and exhausts it outside. Installed by C-NRPP certified contractor. Cost: $1,500-$3,000. Reduces radon by 80-99%.
When to Test
Test any home before purchasing. Test after significant air sealing work. Test periodically (every 2-5 years) as radon levels can change.
Discuss radon testing results and find Ontario mitigation contractors at home.renovation.reviews.