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It matters because Health Canada calls radon the leading cause of lung cancer in non-smokers, and warns that radon exposure combined with smoking significantly increases the risk. There are no symptoms and nothing to see in the house itself: the only way to know your level is to test. Testing is simple, and when a result is high, proven reduction methods exist.
This page covers how radon gets in, how to test properly, when to hire a certified professional, how mitigation systems work, why retesting matters and what the building code expects in new homes.
How radon gets into Canadian homes, with no warning signs
Radon moves from the soil into any part of a house that touches the ground. Health Canada notes it can be found in almost all Canadian homes, and because it can't be seen or smelled, a dry, well-kept basement tells you nothing about its level. Your neighbour's result is no substitute for testing your own home.
- Cracks in the foundation floor and walls.
- Construction joints, including the joint where the slab meets the wall.
- Gaps around service pipes that pass through the foundation.
- Floor drains and sump pits.
How to test for radon: a long-term test during the heating season
The Canadian guideline is 200 becquerels per cubic metre (Bq/m³). Health Canada recommends a long-term test lasting at least 3 months, and its measurement guide calls for at least 91 days of the test to take place during the heating season.
Put the detector on the lowest level where someone spends more than four hours a day, follow the kit's instructions and leave it in place for the whole test. When the result comes back above the guideline, Health Canada recommends acting to lower it, and the higher the level, the sooner.
DIY radon test kit or a C-NRPP certified professional
Health Canada lists two ways to test: buy a do-it-yourself long-term kit, or hire a radon measurement professional. The Canadian National Radon Proficiency Program (C-NRPP) trains and certifies radon measurement and mitigation professionals and offers an online tool to find one nearby. Health Canada's Take Action on Radon page also points homeowners to long-term kits sold online and to certified professionals.
- A DIY kit: you place the detector, send it to the lab when the test ends and read the report yourself.
- A certified measurement professional: places the device, records the conditions and explains the result, which helps for a sale, a rental unit or a result close to the guideline.
- Either way, choose a long-term test; a reading over a few days can't stand in for the long-term result Health Canada relies on.
- A certified mitigation professional: the person Health Canada recommends hiring when a result is above the guideline.
Radon mitigation methods: sub-slab depressurization, sealing and ventilation
Health Canada's reduction guide describes active sub-slab depressurization as the most effective and reliable technique, and the most common one used by C-NRPP certified professionals. A pipe is installed through the basement floor slab and connected to a fan that runs continuously, drawing radon from beneath the house and releasing it outdoors, where it quickly dilutes.
Other measures play a supporting role. Sealing cracks and openings can help, but the guide says it isn't a standalone technique, since every opening is hard to locate, reach and close for good. A sump can be capped and sealed so it keeps draining water while serving as the suction point, and a heat recovery ventilator brings in outdoor air, which the guide says might reduce radon by 25 to 50 per cent in most homes.
- An assessment of the slab, the sump, the fill under the floor and the best route for the pipe to the outdoors.
- A discharge point outdoors, placed so the radon doesn't come back in through windows, doors or air intakes.
- A pressure indicator on the pipe so you can see that the system is running.
- Sealing of the sump, cracks and the floor-wall joint where needed, as a complement to the fan system.
Retesting after radon mitigation and checking the system over time
Only a new measurement proves a system works. Health Canada's reduction guide recommends a short-term test by a C-NRPP certified professional, started at least 24 hours after the fan is turned on, followed by a long-term three-month test the next fall and winter to confirm the annual average is below the guideline.
- Measure again with a long-term test within two years of activation, then every five years, as the guide recommends.
- Glance at the pressure indicator regularly and call the installer if the reading changes or the fan stops.
- Test again the heating season after renovations that affect the structure or ventilation, such as finishing the basement.
- Keep the test reports and system documents; they are useful when you sell.
Radon in new homes: building code rough-ins and what buyers should check
According to Health Canada's reduction guide, the 2010 National Building Code requires every building to have granular fill under the slab and a rough-in for a future radon reduction system, so one can be completed if testing shows the need. Provinces adopt the national code on their own schedule, so ask your builder or municipality what applies where you live. A rough-in doesn't lower radon until it is connected to a working fan, and a new home still needs its own long-term test once it's lived in.
- Ask the builder where the rough-in pipe is and whether it is capped and labelled.
- Ask whether the soil gas barrier under the slab was sealed at the edges and around penetrations.
- Plan a long-term test during your first heating season in the home.
Radon Testing & Mitigation: frequently asked questions
What radon level is safe?
Health Canada's guideline is 200 Bq/m³, and it recommends lowering any level above it. Lower is always better: the reduction guide says to bring levels as low as practically possible, and the higher the result, the sooner you should act.
Can a short-term radon test replace a long-term one?
Not for deciding whether to mitigate. Health Canada recommends a long-term test of at least 3 months; a short-term test mainly serves to check that a new mitigation system is working.
Will sealing basement cracks fix high radon?
Rarely on its own. Health Canada says sealing isn't a standalone technique; it works best as a complement to sub-slab depressurization.
Can I install a radon mitigation system myself?
Health Canada recommends hiring a C-NRPP certified professional when your level is above the guideline. The job involves cutting through the slab, wiring the fan and placing the discharge correctly, and certified installers follow recognized standards of practice.
My new house has a radon rough-in. Do I still need to test?
Yes. A rough-in doesn't reduce radon by itself; only a long-term test shows whether it should be completed with a fan.
Sources
- About radon — Health Canada
- Government of Canada radon guideline — Health Canada
- Guide for radon measurements in homes — Health Canada
- Testing your home for radon — Health Canada
- Radon: A reduction guide for Canadians — Health Canada
- Canadian National Radon Proficiency Program (C-NRPP)
- Take Action on Radon — Health Canada
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides