Is There Radon in Toronto? What the Data Can and Cannot Say

About 1 in 22 Toronto-area houses tested above Health Canada's radon guideline in the 2024 survey, and a further 12.2 percent sat between 100 and 199 Bq/m3. The 2024 Cross-Canada Survey of Radon Exposure is a research report by the Evict Radon National Study team, university researchers who worked with Health Canada, CAREX Canada and the BC Centre for Disease Control. For Toronto it says: "The average radon level for a Toronto area residential building is 43.0 Bq/m³". It adds that "1 in 22 (4.5%) of houses exceeded 200 Bq/m³, while 12.2% are between 100 and 199 Bq/m³".

Radon is measured in becquerels per cubic metre of air (Bq/m3). Health Canada's radon guideline says: "The Canadian guideline for radon is 200 becquerels per cubic metre (Bq/m³)". For a home above that line, the same page says: "Health Canada recommends that you take corrective action to lower the level within 1 year". How to read a result against that line is covered in what the 200 Bq/m3 guideline means.

The report's Toronto area is wider than the city. It is the census metropolitan area, which the 2024 report describes as "the city itself and surrounding commuter towns", home to about 6.2 million people. Its results come from long-term tests of 90 days or more, as the report describes them, and the report weights them to the 2021 Census mix of single-detached, semi-detached and row houses.

An average leaves out the homes at the top of the range, and the 2024 report found one far above the guideline. The 2024 report warns that "there are people living in those cities whose houses contain as high as 1,013 Bq/m³ in Toronto". It says Toronto-area houses show lower levels than Edmonton, Calgary, Montréal and Ottawa, yet "still carry notable risks". For Ontario as a whole, the same report puts the chance of a building at or over 200 Bq/m3 at 1 in 8, or 12.4 percent.

The 12.2 percent of Toronto-area houses that the 2024 report puts between 100 and 199 Bq/m3 matter too. The World Health Organization (WHO) radon fact sheet recommends that countries set a reference level of 100 Bq/m3, and no higher than 300 Bq/m3 where 100 cannot be reached. Canada's line stays at 200, and Health Canada's guideline page says: "While the health risk from radon exposure below the Canadian guideline is small there is no level that is considered risk free". The same page adds: "The higher the radon concentrations, the sooner action should be taken to reduce levels to as low as practically possible". Health Canada's 1-year timeline applies only above 200 Bq/m3. Below that, the page says: "It is the choice of each homeowner to decide what level of radon exposure they are willing to accept". How a system lowers the level is explained in how a radon mitigation system works.

The report's authors set the limit of their own figures. They write that "these numbers cannot tell you if you are at risk in your own home", and that the way to know is a long-term test of 90 days or more where you live.

Health Canada's 2012 survey found 2.7 percent of the 73 homes it tested in the City of Toronto Health Unit above the guideline, and none above 600 Bq/m3. That figure sits in Table 5 of the 2012 survey report, whose tests ran over the 2009-10 and 2010-11 fall and winter seasons. The same report says: "This survey's results should not be used as a tool to determine radon risk potential or whether or not to test a home for radon".

Toronto's 2012 figure rests on a small sample. The report says Toronto was one of 10 health regions that "had been destined for under sampling originally", so extra recruits were sent there in the second year. With only 73 homes, one home reading differently moves the share a long way. The survey also left out renters, and it says "high-rise condo units that were above the second floor" did not qualify. The 2012 figure is a snapshot from more than a decade ago, and the 2024 survey is the current picture.

The 2 surveys measured different places, different homes and different years, and the 2024 authors think radon levels may also have risen. The 2012 row covers the City of Toronto Health Unit only. The 2024 figure covers the whole metro area, commuter towns included. The 2024 report says the 2012 data "was not re-used".

The 2024 authors list several reasons their national results run higher, and building practice comes first. They write: "The simplest explanation is that Canadian residential radon levels have actually increased over the past decade due to changing build practices". Most of the other reasons are about method, such as more of their detectors sitting below ground: 68 percent of their results came from rooms below ground, against 31 percent in 2012.

Because the area, the homes and the methods all changed, the 2 Toronto figures do not make a trend line. How the provinces compare, and every reason the report gives, is in radon levels by province.

Toronto Public Health gives a third figure, for all buildings rather than houses. Its radon page says: "An estimated seven per cent of buildings in Toronto, including homes, workplaces and schools, have levels of radon that may pose a health risk". The page does not say how that estimate was made.

Toronto Public Health also puts a local number on the risk: it says "10 deaths related to radon exposure could be prevented each year" in Toronto if levels were brought below the 200 Bq/m3 guideline. Its advice ends where the surveys do: "Radon levels can only be determined by testing". The same page notes that Ontario's 2024 Building Code requires new houses to have a rough-in for a radon system from January 1, 2025, which the guide to radon rough-ins in new Ontario homes explains.

A household finds its own level with a long-term test that runs through the heating season. Health Canada's guide for radon measurements in homes says: "Testing should be conducted so that a minimum of 91 days of the test is during the heating season". The same guide places the detector on "the lowest level or floor of the home where someone spends 4 or more hours a day". It adds: "Only the long-term average value should be used for comparing to the guideline".

The steps are in the guide to testing a GTA home for radon, kit sources are in where to get a radon test kit in Ontario, and published prices are on the radon testing cost guide. Which floor counts is covered in radon in the basement vs the first floor. The 2024 Toronto shares describe houses, so condo residents should start with radon in a Toronto condo. Why the house next door can read very differently is in where radon gets into a Toronto home.

RadonIndex lists 7 companies with a street address in Toronto, the same 7 counted on its Toronto area page. The site files 5 under radon testing: Inch By Inch Inspections, Radon Inspections, Restoration Mate, Safe Air Environmental Inc. and Trillium Home Inspections. It files 2 under radon mitigation, which means installing a system to lower the level: Radon Gas Expert and The BearStar Group Inc. It files none of the 7 under both. The names are in alphabetical order, not a ranking.

Most of the 7 do radon work inside a wider business. By the business type Google Maps gives each one, they are 2 home inspectors, 1 building inspector, an environmental consultant, an asbestos testing service, a water damage restoration service and a demolition contractor.

Of the 7, only Trillium Home Inspections says on its own website that it is certified by the Canadian National Radon Proficiency Program (C-NRPP), the national certification for people who measure or reduce radon.

Four more companies publish no street address but name Toronto among the places they serve. In all, 12 of the 35 companies in the index publish no address, so the site does not place them in a city. Of those 12, the 4 that name Toronto are Pillar To Post Home Inspector (The Gonneau Team) and Radon Inc, filed under testing, RadonSafeToronto, filed under mitigation, and RBM Group, filed under both. Radon Inc's own wording is the Greater Toronto Area (GTA). Three more of the 12 say they serve the GTA, but the website text RadonIndex stored for them does not name Toronto.

Across the index, 5 of the 35 companies say on their own website that they are C-NRPP certified. Among the Toronto companies, only Trillium Home Inspections and RadonSafeToronto say it. That certification belongs to a person, not a company, and RadonIndex checked no certificate. Health Canada's Radon Reduction Guide suggests asking: "Can the contractor provide proof of C-NRPP certification?" Then look the name up on the C-NRPP certification check. Full lists are on the radon testing and radon mitigation pages, and published system prices are on the radon mitigation cost guide.