What radon is and the number that matters
Radon is a radioactive gas that comes from uranium breaking down in soil and rock. You cannot see it or smell it. It gets into houses through cracks, floor drains, sump pits and gaps around pipes, and it builds up in basements.
The Government of Canada guideline is 200 becquerels per cubic metre (Bq/m³). Health Canada's current guideline page says that if your home is above 200 Bq/m³, you should take action to lower it within one year, and sooner the higher the level. It also says no level is risk free, so a result under 200 is good news, not a guarantee.
What the Ottawa numbers show
Health Canada's Cross-Canada Survey tested 13,807 homes with three-month detectors during the fall and winter of 2009-10 and 2010-11. In the City of Ottawa health unit, 6.2% of the 64 homes tested were above 200 Bq/m³. Ontario as a whole came in at 8.2%, and 6.9% nationally.
These surveys sampled different places and homes; neither predicts an individual property. The 2024 Cross-Canada Radon Survey reported 17.0% of tested Ottawa–Gatineau metro houses at or above 200 Bq/m³. Test your own home for a usable result.
The only way to know your number is to test your own home.
How to run a proper test
Use a long-term test. Health Canada's measurement guide calls for at least 91 days, and 3 to 12 months gives a better average. Short tests of a few days swing too much with weather to base a repair decision on.
Test in the heating season. The guide asks that at least 91 days of the test fall during the heating season, when windows are shut and the house draws more soil gas. In Ottawa, starting in October or November works well.
Place it right. The detector goes on the lowest level where someone spends time, often a finished basement. Keep it at least 30 cm above the floor and 30 cm from walls, and at least 1 m from vents, windows and doors. Do not test in a kitchen, bathroom or laundry room.
Leave it alone for the full period. When it is done, seal it and mail it to the lab straight away, with the start and end dates filled in.
Test kit or C-NRPP professional
Costs vary with the property, testing method, system design and provider. Ask for a current itemized quote and confirm what testing and follow-up are included.
Costs vary with the property, testing method, system design and provider. Ask for a current itemized quote and confirm what testing and follow-up are included.
Health Canada does not recommend radon testing during a real estate transaction. Ask for existing long-term results, or plan a long-term test after purchase.
Reading your result
Under 200 Bq/m³ on a representative long-term test is below the Canadian guideline, although no radon level is risk free. Retesting may be appropriate after changes to the home.
Over 200 Bq/m³: plan a fix within the year. Health Canada recommends a C-NRPP certified mitigation professional. Installation time and reduction vary by home; follow-up testing confirms the result.
Well above 200: move faster. The guideline says the higher the level, the sooner you should act.
Keep the lab report. You will want it when you compare the retest after mitigation, and a buyer may ask to see it.
Common testing mistakes
A test with fewer than 91 days during the heating season may underestimate the annual average. If such a result is below the guideline, Health Canada advises retesting during the next heating season.
Follow Health Canada’s placement guidance: use a normally occupied room on the lowest lived-in level, away from windows, vents and other conditions that could distort the measurement.
Stopping early. A kit pulled after six weeks is no longer a long-term test. Mark the end date on your calendar when you start.
Waiting too long to mail it. Most kits ask you to send the detector to the lab right away once the test ends. Read the instructions on the day you open the package.
Relying on a short reading from a home sale. It cannot establish an annual average; arrange a long-term test during the heating season.
Sources
- Health Canada, Government of Canada radon guideline
- Health Canada, Guide for radon measurements in homes
- Health Canada, Cross-Canada Survey of Radon Concentrations in Homes, final report (2012)
- Ottawa Public Health, Radon in your home
- Evict Radon National Study, Radon levels in Canada's six largest cities