Radon in Ontario homes: Health Canada's guideline, the test, and what the Building Code now requires

• "The Canadian guideline for radon is 200 becquerels per cubic metre (Bq/m³)."
• Above the guideline, "Health Canada recommends that you take corrective action to lower the level within 1 year."
• "The higher the radon concentrations, the sooner action should be taken to reduce levels to as low as practically possible."

Health Canada's Radon: what you need to know describes "a long term test, for 3 months, ideally during the fall or winter time", with a do-it-yourself radon test kit or a C-NRPP certified measurement professional. Its Take action on radon page says: "A long-term (3-month) radon test kit is the most accurate way to find out if you have a dangerous level."

Health Canada's page on reducing radon in the home says: "The most common radon reduction method is called sub-slab depressurization", and that it reduces the level by more than 80% in most homes. It recommends that the contractor be certified as a radon mitigation professional by the C-NRPP and links to a list of certified professionals. On cost, the current page says "about the same cost as other common home repairs"; Health Canada's 2009 brochure gave a range of $2,000 to $4,000.

Health Canada's cross-Canada survey of 2009 to 2011 (published 2012) weighted Ontario at 4.6% of homes above 200 Bq/m³, with health-region figures of 6.2% for the City of Ottawa, 2.7% for the City of Toronto and 5.0% for the City of Hamilton. The report itself says these figures should not be used to decide whether to test a particular home. Health Canada's page for provinces and territories says: "The 2024 cross-Canada radon survey estimates that about 1 in 5 homes will have a high radon level."

The Home Construction Regulatory Authority's technical brief (October 2025) describes "New Ontario Building Code requirements that came into effect on April 1, 2025": "The 2024 Code requires every new home where a wall, roof, and floor assembly is in contact with the ground to have a soil gas rough-in pipe, as specified in subsection 9.13.4." The same brief says Tarion's new-home warranty covers radon above 200 Bq/m³ in homes less than 7 years old, based on a long-term test of 91 days or more.

No public record gives a home's radon level; only a test does. The permits on file and the soil at the lot are public records a buyer's report reads. The entries below name each record and where it is published.

• What building permits are on record for the home?Permits and renovations
• What soil do the provincial surveys record at the lot?Soil at the lot