Radon Testing a Home in Quebec

Your pre-purchase inspector will not measure radon. It is not an oversight: the only measurement Health Canada considers valid requires a device left in place for at least three months, while an inspection lasts a few hours. Here is how radon is actually measured in Quebec, and the mechanism the forms provide for a test that finishes long after you sign at the notary.

What radon is, and why it concentrates in the basement

A gas that comes out of the ground. Health Canada describes it as “a radioactive gas that comes from the natural breakdown of uranium in soil and rock”. It is invisible, odourless and tasteless. Outdoors it dilutes and poses no risk. The problem begins with enclosure: it gets in through cracks in foundation walls and slabs, through construction joints and through the openings around pipes. That is why the measurement is taken on the lowest lived-in level, never on the second floor.

On the risk, let us quote the health authorities word for word. Health Canada writes that “long term exposure to high levels of radon is the leading cause of lung cancer in non-smokers”. The Regie du batiment du Quebec (Quebec’s building authority, the RBQ) reports that in Quebec, 10 to 16% of lung cancer deaths are associated with radon, which is more than 600 deaths a year.

The 200 becquerels per cubic metre guideline

Radon concentration is measured in becquerels per cubic metre of air, written Bq/m³. The Canadian guideline recommends remedial action when the annual average concentration exceeds 200 Bq/m³ in the normally occupied areas of a building. Three words in that sentence deserve your attention.

Annual average. Not a peak, and not the value of one afternoon, but an average over the year, estimated from a long term test.

Guideline. For an existing home, no law forces you to fix anything. The Government of Quebec recommends doing it within a year.

Normally occupied areas. A crawl space does not count. A finished basement where a teenager sleeps does.

The Government of Quebec indicates that the average concentration in Quebec basements is around 37 Bq/m³, but that it can exceed 1,000 Bq/m³. The average is reassuring. It says nothing about your address.

Radon in Quebec, region by region: what the public tests show

Health Canada’s cross-Canada survey publishes its results by health region. Here are the Greater Montreal regions, plus one point of comparison.

These are raw percentages, drawn from small samples of volunteer homes. For Quebec as a whole, the survey gives 10.1% of tested homes above the guideline, and Health Canada adds a sentence that is worth the whole table: “There is no radon free region in Canada.”

Quebec has in fact given up on carving up its territory. The RBQ reports that mapping by the ministere de la Sante et des Services sociaux (Quebec’s health ministry) shows that every region of Quebec contains, to varying degrees, sectors with high radon emission potential, without being able to delimit their extent at the municipal scale. In the Laurentides, a screening campaign by the INSPQ (Quebec’s public health institute) in elementary schools found 4 schools out of 22 above the federal guideline; in the Outaouais, only 2 schools.

The OACIQ (Quebec’s real estate regulator) is blunt about this: nobody should extrapolate the concentration in one building from results obtained in another, because of differences in ground conditions and construction. Whether you are shopping in Laval or anywhere else, radon cannot be deduced from a postal code. It gets measured, one house at a time.

Testing radon in a Quebec home: three months, in the heating season

Health Canada’s measurement guide requires the test to be conducted so that a minimum of 91 days fall within the heating season. The Government of Quebec translates that into practice: a passive detector for at least three months, ideally from October to April. An electronic detector can run for a minimum of one month, but if the result exceeds 100 Bq/m³ after that month, the measurement has to be extended over at least three months or validated with a passive detector. The device goes in the lowest normally occupied area, at least 30 centimetres away from walls and ceilings.

And the 48 hour test sold at the hardware store? Health Canada settles it: “short term measurements are not appropriate for informing remedial action decisions”. Two days in July with the windows open teach you nothing you can use. A detector can be bought from the Association pulmonaire du Quebec (the Quebec lung association), from CAA-Quebec or at a hardware store; otherwise, a professional certified by the Programme national de competence sur le radon au Canada, the PNCR-C, will measure for you.

A three month radon test against the deadline in a promesse d’achat

The OACIQ names the problem directly: “The main issue with radon in the context of a real estate transaction is the time of year and the time required to carry out the test.” Your inspection condition is counted in days, the test is counted in months. The two never meet.

There is, however, a mechanism built into the forms. Standard clause 3.21, Radon measurement test, instructs the officiating notary to hold back a sum out of the proceeds of the sale. It is remitted to the buyer if a report produced by a professional certified in radon measurement establishes that the annual average concentration in the living space is equal to or greater than 200 Bq/m³, and if a copy of the report is given to the seller within the number of days written in following the signing of the deed of sale. Past that deadline, the sum goes to the seller.

Two details change everything, and they are discussed with your notary before signing. The amount held back and the deadline are blanks to be filled in: 90 days signed in May cover no part of a heating season. And the clause states that on receipt of that sum, the buyer waives any claim and any other recourse in that respect. You are trading a recourse for an amount set before you know the result.

The result is above 200 Bq/m³: what the fixes involve

The least expensive measures come first, and the OACIQ lists them: sealing foundation cracks, sealing openings in contact with the ground, covering sumps and venting them to the outside, improving basement ventilation. If the concentration is very high, they will not be enough.

The real solution has a name: active sub-slab depressurization. A pipe goes through the foundation, a fan draws the gas from under the house and discharges it outdoors before it gets in. Health Canada writes that such a system will reduce concentrations by more than 80%, that it is installed in one day only, and for the same price as other common home repairs. The work goes to a mitigation professional certified by the PNCR-C.

What I cannot give you is an invoice: no government source consulted publishes a Quebec price range. Treat this item as a reserve to plan for, in the same way as the other amounts on the closing costs list, and insist on two written quotes.

New construction, the seller’s declaration, and what nobody can quantify

The construction code. Since a regulation that came into force on 2 June 2022, with a transition period that ended on 8 July 2023, protection against soil gases applies across all of Quebec: the notion of “recognized risk zones” has been removed. A basic conduit, a 100 millimetre pipe running vertically through the slab on grade, is mandatory everywhere, and the RBQ puts it at 300 dollars for a 90 square metre home. It is a starting point, not a system: the owner completes it with passive or active extraction if concentrations above 200 Bq/m³ are observed. A new home therefore has to be tested too, and the RBQ makes the point: the radon concentration in a building cannot be known before its construction is finished.

What the seller has to say. The results of prior expert assessments, including detector analyses, must be made available to the buyer through the answers to clauses D12.1, D12.2 and D13.9 of the Declarations du vendeur (the seller’s declaration form). The listing broker must question the seller to find out whether tests or corrective work have already been done, and disclose that information to anyone proposing to acquire the property. A high result kept quiet is the territory of the seller’s declaration and of the latent defect.

And the price? No public source allows anyone to quantify the effect of a radon result on the value of a property in Quebec. The only official figure that touches the subject is a sentence from the RBQ about its own basic conduit requirement: “This measure has no influence on the resale price of properties.” Anyone who announces a percentage to you is making it up.

Frequently asked questions

Can my pre-purchase inspector measure radon during the visit? No. The inspection is a visual examination done in a few hours; a valid measurement takes 91 days in the heating season. The inspector can recommend the test, and that is all.

The seller refuses a three month deadline. What now? That is the normal case, not bad faith. The route provided for is holding back a sum with the notary under standard clause 3.21, with an amount and a deadline that you negotiate. Have the wording reviewed before you sign.

Can renovations increase radon? According to the OACIQ, research conducted abroad shows that energy renovations, windows, doors, insulation, can reduce air renewal and increase indoor concentrations. A result is therefore not a permanent licence: after major work, you measure again.

To go further, read what a pre-purchase inspection checks and the signals that justify walking away.

A detector showing a number above 200 Bq/m³, or looking for how to word the clause in your promesse d’achat? Write to me. I will tell you what gets negotiated and what gets settled at the notary.

Georges Matar

Residential Real Estate Broker · RE/MAX DU CARTIER INC.

Contact Georges