Radon testing

Radon is a radioactive gas from uranium breaking down in soil and rock. It seeps into a house through floor cracks, the gap where slab meets wall, floor drains, sump pits and the holes cut for pipes, then builds up in the lowest level. You cannot see it, smell it or taste it, and your neighbour's result tells you nothing useful about yours.

The number that matters is 200 becquerels per cubic metre. That is the Canadian guideline, and Health Canada applies it to the normal occupancy area, which it defines as any part of the building where a person is likely to spend more than four hours a day (Health Canada, Government of Canada radon guideline). Above 200, the advice is to lower the level within one year, sooner the higher the reading. Health Canada also says plainly that no level is risk free, so a result of 150 is good news rather than a certificate.

Place the detector in a normally occupied room on the lowest lived-in level. Health Canada defines normal occupancy by time spent there, including spaces expected to be occupied soon. Avoid kitchens, bathrooms and laundry rooms; follow the device instructions and measurement guide.

Health Canada’s placement guidance calls for the device to be at least 30 cm above the floor and from walls or ceilings, and at least 1 m from vents, windows and doors. Follow the device instructions for any additional limits.

Step three: run a long-term test for 3 to 12 months, with at least 91 days during the heating season. Normal household routines should continue during the test.

Step four: record the start and end dates and return the detector according to the manufacturer or lab instructions, including any expiry date.

How long it takes. Device placement time and lab processing depend on the provider. The long-term measurement itself must run for at least 91 days, with at least 91 days during the heating season. A short reading varies with weather and cannot be compared with the annual-average guideline. Health Canada does not recommend testing during a real estate transaction; plan a long-term test before listing or after purchase.

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.

What makes an Ottawa house different. Two studies give two pictures of this city and both are worth knowing. Health Canada's Cross-Canada Survey, using three-month detectors in the winters of 2009-10 and 2010-11, found 6.2% of the 64 homes tested in the City of Ottawa health unit above 200 Bq/m3 (final report, 2012). The 2024 Cross-Canada Radon Survey reports 17.0% of tested Ottawa–Gatineau metro houses at or above the guideline (Evict Radon). The studies covered different areas and samples; neither predicts a particular home’s result.

Ground conditions and construction details vary across Ottawa and between individual homes. Neither neighborhood geology nor house age predicts a home’s radon result; a long-term test does.

Homeowners can use a suitable long-term test kit according to Health Canada’s instructions. If hiring someone to measure or mitigate radon, check the relevant C-NRPP certification for that work.

What to ask before you hire. Are you C-NRPP certified for measurement, and what is your certificate number. Which lab processes the detector. How many detectors are you placing and where. Will the report state the start date, the end date, the placement height and the level of the house. If the result comes back high, do you also sell mitigation, and who arranges the independent follow-up test. Get the answers on the quote rather than over the phone.

A test measures one spot over one window of time, so a retest after major work is worth the small cost.