Radon: should you test before buying a house?

In short

Radon is a natural radioactive gas, odourless and colourless, that comes from the ground and builds up in basements. Health Canada ranks it as the second leading cause of lung cancer in the country after smoking, and estimates that about 7% of Canadian homes exceed the guideline of 200 becquerels per cubic metre. It cannot be seen or guessed from the neighbourhood: only a test measures it, and a reliable test lasts at least three months.

Why the inspection is not enough

The inspection report does not measure radon unless you ordered a separate test. A short-term test (a few days) gives an indication; Health Canada recommends a test of at least three months, ideally during the heating season, to decide.

Two neighbouring houses can have very different concentrations. Regional maps indicate a probability, not a result.

What it changes for the purchase

The inspection condition does not last three months. Common practice is to test after purchase and plan the correction if the result exceeds the guideline.

The correction, called mitigation, most often consists of a sub-slab depressurization system that vents the gas outside. It is effective and well mastered by certified contractors.

Orders of magnitude

A long-term detector costs a few tens of dollars. A mitigation system installed by a certified contractor most often runs a few thousand dollars. Orders of magnitude to confirm with a quote.

What to do before buying

Ask the seller whether a test was done and its result.
Buy or borrow a long-term detector and place it on the lowest lived-in level as soon as you move in.
If the result exceeds 200 Bq/m³, call a certified mitigation contractor.

What Clarity does with it

Clarity adds the radon test to the first-year roadmap when the house has a finished basement and the report mentions no test.

Does your report mention this? Clarity tells you in five minutes what is priority, what to have checked and what to ask the seller.

Analyze my report

Frequently asked questions

Is radon common in Quebec?

It is present everywhere in Canada to varying degrees. Some Quebec regions have higher exceedance rates, but none is exempt; only the test answers.

Is a short radon test useful?

It serves to detect a very high concentration quickly. To decide on mitigation, Health Canada recommends a test of at least three months.

Does an unfinished basement change anything?

Radon enters through the ground whatever the finish. The question is how much time occupants spend on the lowest level.

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