Radon is one of the few building risks you can't see, smell or taste — and yet Health Canada describes it as the leading cause of lung cancer among non-smokers. For a buyer or owner, the good news is simple: radon can be measured, and when a level is high, it can be reduced. This page explains what radon is, what Health Canada says, and why measurement is the only way to know a home's real level.
What is radon?
Radon is a naturally occurring radioactive gas. It comes from the breakdown of uranium found naturally in soil and rock. Because it's a gas, it migrates through the ground and can seep into a building through its points of contact with the soil: slab and foundation cracks, joints, crawl spaces, openings around pipes and drains, and sump pits. Once inside, it tends to accumulate in the lowest, least-ventilated spaces — typically the basement and ground floor.
Radon is odourless, colourless and tasteless. No human sense can detect it, and its concentration can't be guessed by eye during a visit. That's exactly what sets it apart from other building issues: there is no reliable "visible sign" of radon the way there can be for moisture or a crack.
Why radon matters for Quebec homes
According to Health Canada, radon exposure in homes is the leading cause of lung cancer among people who do not smoke, and the second leading cause of lung cancer overall (after smoking). The risk is not "all or nothing": it increases with the radon concentration and with the length of exposure. In other words, the lower the level the better, and prolonged exposure matters more than brief exposure. The risk is also substantially higher for smokers. These statements come from Health Canada; this page does not provide medical advice and does not assess any individual's personal risk.
Radon is present everywhere in Canada, including Quebec. It is not limited to a few "problem" regions.
Why measurement is the only way to know
Because radon is invisible and varies from building to building, you cannot infer a home's level from its neighbourhood, its age, or a regional map. A "radon potential" map shows a geological probability across a territory — it says nothing about the actual level behind one specific door. Likewise, a visual building inspection can document possible entry pathways (cracks, basement openings, drainage condition), but it does not measure radon concentration.
The only reliable data point is a measurement taken in the home itself, over a sufficient duration, then compared to the Health Canada guideline.
The Health Canada guideline: 200 Bq/m³
Health Canada expresses radon concentrations in becquerels per cubic metre (Bq/m³). The Canadian guideline recommends taking corrective action when the annual average radon concentration exceeds 200 Bq/m³ in the normal occupancy areas of a building.
Two important nuances:
- It's an annual average, not a single reading. Radon levels fluctuate with the seasons, the weather and how the home is used — which is why a quick few-day snapshot is not representative.
- It's not a sharp "safe / unsafe" boundary. Since risk increases with concentration and duration, aiming for the lowest reasonably achievable level is preferable, even below 200 Bq/m³.
Long-term or short-term testing?
Health Canada recommends the long-term test as the reliable method to estimate the annual average:
- Long-term (recommended) — the detector stays in place for at least 91 days (about 3 months). Ideally the measurement is done in fall or winter, when windows are mostly closed and levels tend to be highest. This best reflects real year-round exposure.
- Short-term — a few days to a few weeks. Useful as a quick first indication, but less reliable for estimating the annual average. A short-term result should generally be confirmed with a long-term test.
How a long-term test is placed
A long-term measurement follows a simple but precise protocol:
- Location — the detector is placed in the lowest lived-in level that's regularly occupied (for example a finished basement or ground floor), in a used room, away from direct drafts, heat sources and excess humidity.
- Duration — it stays in place for at least 91 days, undisturbed, with the home occupied normally.
- Analysis — at the end of the period, the detector is analyzed (depending on the device, by a lab) to obtain an average expressed in Bq/m³.
- Comparison — the result is compared to Health Canada's 200 Bq/m³ guideline.
For a formal measurement, you can obtain a recognized test kit or engage a qualified radon professional (notably a C-NRPP–certified professional — the Canadian National Radon Proficiency Program).
What the result can — and cannot — conclude
A radon measurement answers one specific question: what is the average concentration in this home, relative to the 200 Bq/m³ guideline? It does not tell you:
- whether a person will develop an illness — that's for a physician and Health Canada's public-health statements, not a building measurement;
- what the level will be after remediation — that depends on a mitigation system designed by a professional;
- the level of another home, even next door — each building must be measured separately.
Inspecteur Élite's role is to document a building's apparent, visible and accessible condition during an inspection — including signs of infiltration, the state of the basement and drainage. We do not perform radon testing and do not interpret radon results; for a measurement, contact a qualified professional.
What to do if the level is high
If the annual average exceeds 200 Bq/m³, Health Canada recommends undertaking corrective action. The good news: radon can usually be reduced significantly. The most common method is sub-slab depressurization, which captures radon beneath the building and vents it outside before it enters.
Designing and installing a mitigation system is the role of a C-NRPP–certified radon mitigation professional. This is not a do-it-yourself job: a poorly designed system can be ineffective or even make things worse. After work is done, a new measurement confirms the mitigation's effectiveness.
Radon in the context of buying
For a buyer, radon is one of the elements to weigh in an informed decision — alongside the condition of the roof, structure or plumbing. Because long-term testing takes about three months, it rarely fits within the tight timelines of a condition removal; it's often a check a new owner performs after purchase, or that a buyer negotiates depending on context. Some sellers already have a recent measurement result, which can reassure both parties.
A pre-purchase inspection does not measure radon, but it helps you understand the building's apparent condition and spot infiltration pathways and basement moisture issues — useful context when you're also considering an independent radon measurement by a qualified professional. For indoor air quality in general, see also our mold & air quality service.
Radon is a real but manageable risk: you measure it, compare it to the Health Canada guideline, and reduce it if needed with a qualified professional. The first step is always the same — measure the home itself.