What is the Health Canada action level for radon and what percentage of Toronto homes exceed it?

Health Canada has set the radon action level at 200 becquerels per cubic metre (Bq/m³), and approximately 7-10% of homes in the Greater Toronto Area exceed this threshold, with basement levels typically showing the highest concentrations.

Radon is a naturally occurring radioactive gas that seeps into homes through foundation cracks, floor drains, sump pits, and gaps around utility penetrations. It's completely odourless and invisible, making testing the only way to know your exposure level. Health Canada identifies radon as the second leading cause of lung cancer after smoking, responsible for approximately 3,200 deaths annually in Canada.

The 200 Bq/m³ action level represents the point where Health Canada recommends taking corrective action to reduce radon levels in your home. For context, the average outdoor radon level is about 10 Bq/m³, while the average indoor level across Canada is approximately 40 Bq/m³. However, basement levels can be significantly higher than main floor readings, particularly in homes with poor foundation sealing or inadequate ventilation.

GTA-specific radon considerations are particularly important for basement renovation planning. Toronto sits on glacial till and clay soils that can trap radon gas, and the city's older housing stock often has foundation vulnerabilities that allow gas infiltration. Homes in areas like North York, Scarborough, and parts of Etobicoke built on clay soils may show elevated readings, especially in basements with limited air circulation.

Before starting any basement renovation, radon testing should be completed using a long-term test kit (minimum 3 months) to get an accurate annual average. Short-term tests can fluctuate significantly based on weather, season, and ventilation patterns. Test kits are available at most hardware stores for $30-50, or you can hire a certified radon measurement professional for $150-300.

If your basement tests above 200 Bq/m³, radon mitigation should be integrated into your renovation plans. Common mitigation strategies include sealing foundation cracks and penetrations, installing a sub-slab depressurization system (essentially a fan that draws radon from beneath the concrete floor and vents it outside), and improving basement ventilation. Professional radon mitigation typically costs $1,500-4,000 and can reduce levels by 80-90%.

During basement finishing, radon mitigation becomes more complex and expensive if not planned initially. Installing a sub-slab system after the basement is finished requires cutting through flooring and potentially removing sections of framing. It's far more cost-effective to test first and address any radon issues during the renovation phase rather than afterward.

For basement renovations, proper foundation sealing with polyurethane crack injection, installing a vapour barrier system, and ensuring adequate ventilation through HRV/ERV systems can significantly reduce radon infiltration while also addressing moisture concerns. Many basement waterproofing contractors are also trained in radon mitigation techniques.

Need help finding a basement contractor experienced with radon mitigation? Toronto Basement Remodeling can match you with professionals who understand both waterproofing and radon reduction strategies for your renovation project.