Radon Testing Before Finishing a Basement in Manitoba

Radon is a radioactive gas that comes from uranium in the ground. You can’t see, smell or taste it, and it tends to build up most in basements, the part of a house closest to the soil. Health Canada calls radon the leading cause of lung cancer in non-smokers. Manitoba Health, citing Health Canada’s 2012 cross-Canada survey, says about 19 per cent of Manitobans live in homes above the radon guideline.

If you’re about to turn a basement into living space, this is the easiest time to find out, and a test takes little effort: you place a detector, leave it for the test period, then send it to a lab.

Why test for radon before finishing a basement?

Because finishing changes two things: people start spending hours down there, and the space often gets tighter. Health Canada notes that energy retrofits can reduce air exchange and raise radon levels. If a test shows a problem, the usual fix draws soil gas from under the floor and vents it outside, which is easier to route before drywall goes up.

Radon gets in through cracks in foundation walls and floor slabs, construction joints, and gaps around pipes, floor drains and sumps. A newer house isn’t immune; Health Canada’s advice is that all homes need to be tested.

How do you test for radon?

Use a long-term test. Health Canada recommends at least three months, ideally in fall or winter, with the detector on the lowest lived-in level in a room used four or more hours a day. You can buy a test kit or hire a professional certified under the Canadian National Radon Proficiency Program (C-NRPP).

• Where to get a kit: the Province’s radon page points to Take Action on Radon’s list of Manitoba test kit providers and to the Manitoba Lung Association.
• When: Manitoba Health suggests testing during the winter, for example between October and April, and notes that longer tests give a more accurate picture of the annual average.
• Where: once the basement is finished, it becomes the lowest lived-in level, so tell your test provider about your plans when you choose a spot.
• How long: a test shorter than 91 days that misses most of the heating season can underestimate the annual average.

Based on Health Canada and Manitoba Health guidance, checked October 13, 2026.

What do the results mean?

Health Canada’s guideline is 200 becquerels per cubic metre (Bq/m³), measured as the average level in your home. Above that, Health Canada recommends fixing the home, generally within a year, and sooner if the level is higher. The guideline isn’t a safe threshold to stop at; if it’s reasonable to get the level lower, Health Canada encourages it.

How is radon reduced?

Health Canada calls active soil depressurization (ASD) the most trusted and effective solution, able to cut radon by 90% or more: a fan draws soil gas from below the foundation and vents it outside. Health Canada recommends a C-NRPP certified mitigation professional and says a system can usually be installed in less than a day.

Health Canada describes the cost as similar to other common home improvements. Other measures help less: balanced ventilation with an HRV or ERV generally lowers radon by only 20% to 50% and has to run continuously, and sealing cracks and gaps around pipes supports other measures rather than replacing them.

How do you plan a basement around a radon system?

Treat the mitigation system like any other mechanical item in the layout. Share your test result at the on-site visit, then settle where the pipe, fan and exterior vent will go with the mitigation professional before framing, so walls, bulkheads and storage are planned around them rather than built and cut open later.

• Agree on the order of work: who installs what, and whether the system goes in before or during framing.
• Keep the sump pit reachable. Health Canada notes that certified installers adapt the system to the house, including homes with a sump pit.
• Plan any bulkhead or chase the pipe needs, and keep the fan’s location accessible for service.
• Put the retest on the calendar for the first heating season after the work is done.

Do you need to retest after the basement is finished?

Yes. Health Canada advises retesting in the next heating season after any renovation that affects the structure or ventilation of the home, and after a mitigation system is installed, to confirm it works. Homes with an active mitigation system should be retested every five years.

If the renovation includes new insulation or air sealing, the same advice applies. Our guide to insulation rebates during a renovation covers the envelope side of a basement upgrade.

Next step

Start the test this fall and use the three months to plan. Our basement renovation projects begin with a free on-site visit and a free written quote. Get a starting range from the instant estimate, read about planning a winter basement development, or book your visit.