Question 1

How much radon is safe in Thornhill?

Accepted Answer

Health Canada's action guideline is 200 Bq/m³ — at or above this level, active soil depressurization (ASD) mitigation is recommended. The World Health Organization recommends action at 100 Bq/m³, recognizing that lung cancer risk increases proportionally with radon exposure at any concentration. Roughly 7% of Canadian homes exceed Health Canada's guideline. Ontario's granite and shale geology produces elevated soil gas radon in many regions, and Thornhill properties should be individually tested rather than assumed safe. There is no level at which radon exposure carries zero risk, which is why testing and mitigation where warranted are the responsible approach.

Question 2

How long does radon testing take?

Accepted Answer

Long-term testing using a certified alpha track detector takes 90+ days and is the most accurate method, providing a reliable annual average radon level for your Thornhill home. This is the Health Canada-recommended approach for homeowners. Short-term testing over 2–7 days is available for real estate transactions where a closing deadline requires faster results — these tests provide a useful screening result but are less accurate because radon levels fluctuate seasonally. In Ontario, radon levels typically rise in winter when homes are sealed, making winter long-term tests the most representative of peak exposure.

Question 3

What happens if radon is high?

Accepted Answer

If your Thornhill home tests above Health Canada's 200 Bq/m³ guideline, active soil depressurization (ASD) is the recommended mitigation approach. An ASD system involves drilling through the basement slab, inserting a PVC pipe, and using a continuously running fan to draw radon-laden soil gas from beneath the foundation and exhaust it safely above the roofline before it can enter the home. ASD systems reliably reduce radon levels by 80–99% and are installed by licensed radon mitigation contractors. Costs in Ontario typically run $1,500–$3,000 depending on foundation type and system complexity. ASADS provides mitigation guidance and can coordinate post-mitigation confirmation testing.

Question 4

Is radon testing required to buy a home in Thornhill?

Accepted Answer

Radon testing is not legally required as a condition of purchasing a home in Thornhill or anywhere in Ontario. However, it is strongly recommended — particularly for homes with basements and lower-level living space, which are common throughout Thornhill's residential stock. Radon is completely invisible and odourless; there is no way to detect elevated levels without testing. As awareness of radon risks grows in Ontario, more Thornhill buyers are including radon testing as a purchase condition alongside the standard home inspection. A $149 long-term test is modest protection against a carcinogen that causes approximately 3,300 Canadian lung cancer deaths per year.

Radon Testing Thornhill | Health Canada Certified | ASADS