Radon is invisible, odourless and tasteless. You cannot confirm a home’s level during a walkthrough, and a neighbour’s result does not answer the question for the house you are considering. The useful response is simple: test correctly, understand what the result represents, and make a plan for any action.
For Greater Sudbury buyers, the timing can be awkward. Health Canada recommends testing for 3 to 12 months to estimate the annual average. A long-term test must run for more than 91 days, and the current guide includes additional heating-season rules when less than 91 days of the test falls in that season. An offer condition may be much shorter. That does not make radon unknowable. It means the transaction plan and the long-term health measurement need to be kept honest.
Check the current guidance: Health Canada’s testing, placement, guideline and mitigation guidance can change. Recheck the official guidance before starting a test or acting on a result.
What radon is—and why the house matters
Health Canada describes radon as a radioactive gas produced by the breakdown of uranium in soil and rock. Outdoors it is diluted. Indoors it can enter through openings where a building contacts the ground and accumulate. Long-term exposure to elevated radon increases lung-cancer risk; Health Canada identifies radon as the leading cause of lung cancer among non-smokers.
The amount can vary from home to home because buildings, entry pathways, ventilation, weather and occupant habits differ. A map, postal code, construction year or neighbouring test may provide context, but Health Canada is clear that testing is the only way to know a home’s level.
Use the right test for the decision
Health Canada describes two consumer paths: purchase a do-it-yourself kit or hire a radon measurement professional. Its current measurement guide recommends 3 to 12 months to estimate the annual average, with more than 91 days required for a long-term test and additional heating-season rules described in the guide.
Choose a device and laboratory service that follow current Health Canada guidance. If you are considering an electronic radon monitor, check the current guidance and cited C-NRPP performance-testing information rather than assuming every consumer device is suitable. If you hire a provider, Health Canada recommends a certified professional who will perform the long-term measurement.
A short reading can show what the device measured during that shorter period. It is not the minimum three-month long-term result Health Canada recommends. Do not let a precise-looking number erase that difference.
Place the device where the result will mean something
Health Canada guidance says to test a normal occupancy area on the lowest lived-in level. That means a space where someone spends, or soon will spend, at least four hours per day—such as a bedroom, office, playroom or living room.
The kitchen, bathroom, laundry room, crawl space and a rarely used storage or furnace area are not substitutes for the occupied room the guidance describes. Follow the device instructions and keep it away from direct sunlight, exterior walls, high humidity, heat sources, windows, doors, vents, fans and electronics that could interfere with the measurement. Leave space around it and do not move it during the test.
Plan radon due diligence during a purchase
Ask for the complete record
If the seller has tested, ask for the full report—not only a screenshot of a number. Look for the device or laboratory, test dates, duration, room and placement, result, and any mitigation documents. If a system was installed, ask for the installer information, commissioning details, maintenance instructions and follow-up test.
Compare the record with the home you are buying
A result from an unfinished basement may not represent a now-finished bedroom. A test taken before new windows, foundation work, ventilation changes or an addition may not describe the current building. Health Canada recommends retesting after changes that affect the structure or ventilation, after significant excavation beside the home, and after a mitigation system is installed.
Address the timing gap directly
If there is no suitable long-term result and your transaction window cannot accommodate more than 91 days, discuss options with your REALTOR® and lawyer before the offer is firm. Depending on the seller, property and agreement, that may mean negotiating access for a long-term test, obtaining specialist advice, reviewing mitigation feasibility, or planning a compliant test after possession. The contract language and allocation of cost or risk are legal questions; do not improvise them from a generic checklist.
What the Canadian guideline means
The Canadian radon guideline is 200 becquerels per cubic metre (Bq/m³), based on the average annual level in a normal occupancy area. If a home’s long-term result is above 200 Bq/m³, Health Canada recommends corrective action and says it should be taken sooner as the level rises. Its current guideline page recommends lowering a home above the guideline within one year.
The guideline is an action level, not a promise of zero risk below it. Health Canada also recommends reducing radon as much as practicable when work is done. For a result above the guideline, it recommends a C-NRPP-certified mitigation professional to determine an appropriate approach for the building.
High radon is a repair question, not a verdict on the home
Radon-reduction methods are established, but the design has to fit the building. Health Canada identifies sub-slab depressurization as the most common approach: a fan and pipe system draw soil gas from beneath the foundation and exhaust it outdoors before it enters the house. Sealing and ventilation may also form part of the work, but their effectiveness depends on the home and the measured level.
Get a property-specific scope and keep testing in the plan. After mitigation, confirm performance through the follow-up measurement recommended by the professional and Health Canada guidance. Keep the reports with the house records for future maintenance, renovations and resale.
Red flags to slow down for
- A seller says the neighbourhood is “low radon” but has no result for the home.
- A number is provided without the room, dates, duration, device or report.
- A short test is presented as if it were the recommended long-term measurement.
- The tested room is not on the lowest lived-in level or the device was beside a vent, window or heat source.
- The home was materially renovated after the test and no retest followed.
- A mitigation system is present but its installer, operating instructions or follow-up result cannot be found.
This is general consumer information, not medical, legal or environmental advice. Follow current Health Canada guidance and obtain property-specific advice from the qualified professionals responsible for the measurement, contract and mitigation work.
Expect Moore for Your Real Estate.
— Chad Moore, REALTOR®
— Lake City Realty Ltd., Brokerage