Radon and energy-efficiency renovations: why you must test after the work

General information for Quebec homeowners, buyers and renters, drawn from public sources (Health Canada, CMHC, the Government of Quebec, Natural Resources Canada). It is not medical, legal or building-engineering advice. Results are presented in relation to Health Canada's guideline of 200 Bq/m³; RadonTest.ca coordinates the logistics of testing and does not interpret individual results.

Can an energy retrofit raise radon? Yes — and it's well documented. Making a house tighter (caulking, insulation, new windows, weatherstripping) reduces air exchange, which can trap radon and drive its concentration higher indoors. That's why Health Canada recommends you re-test after work that affects structure, ventilation or air-tightness — and, ideally, that you test beforehand too. Only a long-term test of at least 91 days reveals your home's real level.

It's one of the lesser-known paradoxes of renovating: the very steps that lower your heating bill — a legitimate goal in Quebec — can concentrate a cancer-causing gas in the air you breathe. The answer isn't to skip the renovation, but to measure. This article explains why air-sealing has this effect, which renovations are involved, the role of ventilation, where Rénoclimat fits in, and when to test. For the full picture of the topic (risk, rules, mitigation, funding), start with our pillar page, Radon in Quebec: concentrations, risks and what to do.

Why can air-sealing raise radon?

To understand this, you need to know how radon gets into a house. Produced by the breakdown of uranium in soil and rock, it seeps in through cracks in the slab, floor-wall joints, pipe penetrations, the crawl space and the sump. But it doesn't simply "drift" in — it is drawn inside.

This is the stack effect (or thermal draft): in winter, warm air rises and escapes through the top of the house, creating a slight negative pressure in the basement. That suction acts like a giant straw and pulls soil air — laden with radon — indoors. The more a house is heated and closed up, the stronger the pull.

Enter the energy retrofit. By sealing cracks, fitting airtight windows, adding insulation and caulking air leaks, you reduce natural air exchange — that's the whole point: less cold air in, less heat out. But a house that "breathes" less also vents the radon that has entered less effectively: the gas that would have been diluted in a leakier home stays trapped and builds up.

Health Canada puts it plainly: "Airtight buildings reduce energy loss, but they can also affect indoor air quality. Energy retrofits can reduce air exchange and unintentionally increase radon concentrations. Research has identified links between building energy-efficiency improvement programs and increased radon exposure."

How large is the effect? Health Canada draws on a synthesis from the U.S. Department of Energy (the BEX study, 2020) finding that reducing energy costs increased radon concentrations by 22% on average. Other international studies, cited by Health Canada, go further still:

These figures are study averages, not a prediction for your home: a very low starting concentration can double and still stay below the guideline, while a home already near the threshold can tip above it. That's why you don't guess — you measure.

Which renovations are involved?

Any renovation that makes a house tighter, changes how air moves, or disturbs the soil around the foundation can change your radon concentration. Health Canada recommends re-testing after work that affects the structure, the ventilation or the air-tightness, as well as after excavation near the foundation. In practice, here are the most common projects in Quebec.

• Insulation (attic, walls, basement, crawl space). Adding insulation reduces heat loss, but also the air leaks through which radon used to dilute. Basement insulation is especially worth watching: it's the floor closest to the soil, and radon's main entry point.
• Window and door replacement. This is the work most directly tied to radon increases in the studies above: new, well-sealed windows remove much of the old home's "accidental" air exchange.
• Caulking and weatherstripping (sealing cracks, joints, the perimeter of doors and windows, and pipe penetrations). Taken on its own, each step seems minor; added up, they can meaningfully cut air exchange.
• Finishing a basement. Turning a basement into living space compounds the effects: you seal it, insulate it and spend more time in it — so you breathe radon there for longer. A finished, occupied basement should always be tested. See Radon in the basement on this point.
• Replacing the heating or ventilation system. Changing a furnace, closing off a chimney or altering the combustion-air intake shifts the balance of pressures — and therefore the suction of radon.
• Excavation or work near the foundation (weeping tile, waterproofing, an addition, slab repair). Disturbing the soil or the slab can open — or close — entry pathways.

What these projects share: they change air-tightness, pressure or the time spent near the soil — and none of them, on its own, tells you which way your concentration will move. Hence the simple rule: after any of these jobs, re-test the following heating season.

What is the role of ventilation (HRV/ERV)?

Here's the most important nuance in the whole article: air-sealing without ventilation is the problem. A well-built modern house can be both very tight and healthy — provided it brings in fresh air in a controlled way rather than through accidental leaks.

That's the job of a heat-recovery ventilator (HRV) — a "VRC" in French. It exhausts stale air outdoors and brings fresh air indoors, the two streams crossing in an exchanger that transfers heat from the outgoing air to the incoming air. You renew the air without throwing your heat out the window.

Two key points, according to CMHC:

1. Air exchange dilutes radon. By continually replacing some of the indoor air, the HRV reduces the concentration of contaminants that accumulate in a closed-up house — radon among them.
2. A properly set HRV is balanced. Installed correctly, it delivers equal incoming and outgoing airflows, without creating positive or negative pressure in the house. This matters: a poorly balanced unit that depressurizes the basement could, on the contrary, draw more radon from the soil. Balanced airflows are the condition to meet.

One caution, though: an HRV is an air-quality tool, not a certified radon-mitigation system. Health Canada lists it among ways to reduce radon ("a balanced heat-recovery and energy-recovery ventilation system"), but if your test exceeds 200 Bq/m³, the reference solution remains an active soil depressurization system designed by a certified professional — with the HRV as a complement, never a replacement. Ventilate for air quality, but measure first.

In one sentence: if you tighten your house, plan for adequate mechanical ventilation — and test for radon to confirm the whole system works as intended.

Rénoclimat and radon: what you need to know

In Quebec, the main residential energy-retrofit program is Rénoclimat, administered by the Government of Quebec. The program is built around an energy evaluation of your home, carried out by an advisor before and then after the work, and it provides financial assistance for measures such as insulation, air-sealing, door and window replacement, and the installation or replacement of certain mechanical systems (heating, ventilation). As of 2026, Rénoclimat remains active.

Why mention it here? Because the list of work eligible under Rénoclimat — insulation, air-sealing, windows, ventilation — corresponds precisely to the measures Health Canada links to a possible rise in radon. A Rénoclimat project is therefore, by its very nature, a project that can change your concentration.

Two essential things to remember:

• Rénoclimat does not fund radon mitigation. The program targets energy performance, not indoor air quality, and not the installation of a soil depressurization system. The assistance you receive to tighten your house does not cover the work that may become necessary if radon climbs afterward. That's one more reason to know your concentration before committing the money.
• The Rénoclimat evaluation is the perfect moment to fold in a radon test. Since an advisor is already assessing your home before the work, take the opportunity to start a long-term test in parallel: a "before" measurement while the project is being planned, an "after" measurement the following heating season. The test isn't a step in the program, but nothing stops you from running it yourself.

Finally, note that at the federal level, the Canada Greener Homes Grant no longer accepts new applications (the program is closed), and the Canada Greener Homes Loan stopped accepting applications on October 2, 2025. So don't count on these federal supports for new projects; turn instead to the Quebec programs currently in force.

When to test: before and after the work?

The ideal is to test twice: once before the renovation, once after. Here's why each measurement matters.

Before the work, a test establishes your baseline. If it already reveals a high concentration, you can plan mitigation at the same time as the renovation — often simpler and cheaper than coming back once the walls are closed up. If your concentration is low, you have a reference value against which to judge the real effect of the work.

After the work, a new test confirms whether the air-sealing has pushed your concentration up. Health Canada recommends re-testing the following heating season: with the house closed up, radon generally reaches its highest concentrations then — the most cautious measurement. In Quebec, that season runs roughly from November to April. (Radon also varies by region: see the Quebec radon map and high-risk regions.)

In both cases, the same measurement rules apply:

• A long-term test of at least 91 days (three months). Radon fluctuates enormously from day to day, week to week and season to season; only an average over 91 days or more reflects your real exposure. Short-term tests are useful only for quickly checking a mitigation system — never for deciding whether to act.
• At the lowest lived-in level (the basement if it's used, otherwise the ground floor), in a room occupied more than four hours a day, about 1 m off the floor, away from drafts, vents, heat sources and direct sunlight. Avoid the kitchen, bathroom and laundry room.
• A kit analyzed by a C-NRPP-certified laboratory (the Canadian National Radon Proficiency Program, overseen with Health Canada).

You can order a RadonTest.ca kit for your "before" measurement as soon as the project is being planned, then run another "after" the following heating season.

A word on new construction. Since June 2, 2022, the Quebec Construction Code has required, in new dwellings, passive soil-gas measures — notably a passive extraction column connected to the piping beneath the slab — that make it easier to add a mechanical mitigation system later. It's a useful measure — but it is not an active system, and it is not a test. A new home, airtight by design, must also be tested once occupied. For the details, see our guide to the Quebec Construction Code and radon.

What to do if your concentration is high?

If your long-term test exceeds Health Canada's guideline of 200 Bq/m³ (annual average), don't panic: radon's risk comes from cumulative exposure over years, and proven solutions exist.

Health Canada recommends acting within one year, and sooner if the concentration is clearly high. (Note: Health Canada no longer recommends a tiered timeline of the "two years / one year" type based on concentration — the current guidance is simply to act within the year, sooner if the concentration is high.)

The reference solution is an active soil depressurization (ASD) system: a fan draws air from beneath the slab and vents it outdoors before it enters the house. Well designed, it reduces the concentration dramatically, often by 80 to 90%. Have it installed by a C-NRPP-certified professional, as Health Canada recommends: that's your assurance of compliant work, verified by a follow-up test. For the range of costs across Canada, see How much does radon mitigation cost?.

For the complete, step-by-step process, read What to do if your radon level is above 200 Bq/m³.

Bottom line: an energy retrofit is a sound investment — for your comfort, your bill and the climate. The only reflex to add is to measure radon before and after. A test costs a fraction of the work, and it remains the only way to know whether your tighter house is also a healthier one.

Table: effect of renovations on radon and the recommended action

No renovation, on its own, tells you which way your concentration will move — only a long-term test reveals it.

Frequently Asked Questions

Can a renovation really raise the radon in my home? Yes. Health Canada confirms that renovations which increase air-tightness (insulation, windows, caulking) can reduce air exchange and unintentionally raise radon — studies cited by Health Canada report +22% on average, and up to +100% in some cases. That's why it matters to test after the work.

Should I test before or after an energy retrofit? Both, ideally. A test before establishes your baseline and lets you plan mitigation at the same time as the work. A test after — the following heating season — confirms whether the air-sealing has pushed your concentration up. In both cases, use a long-term test of at least 91 days.

If I install an HRV, am I protected against radon? Not automatically. A well-balanced HRV renews the air and helps dilute radon (CMHC notes it creates neither positive nor negative pressure when properly installed), but it is not a certified mitigation system. If your test exceeds 200 Bq/m³, the reference solution remains an active soil depressurization system installed by a C-NRPP-certified professional. Test first.

Does Rénoclimat cover the installation of an anti-radon system? No. Rénoclimat funds energy-performance measures (insulation, air-sealing, windows, mechanical systems), not radon mitigation. It's precisely because this work can drive radon up that it's better to know your concentration before committing to it, and to re-test afterward.

Is the Canada Greener Homes Grant still available? No. The federal grant is closed to new applications, and the federal loan stopped accepting applications on October 2, 2025. In Quebec, the provincial programs currently in force (such as Rénoclimat) remain the route to favour; always confirm the up-to-date parameters on Québec.ca.

My home is new and very airtight. Do I still need to test? Yes. Since June 2, 2022, the Quebec Construction Code has required a passive rough-in in new dwellings, but this waiting conduit is neither an active system nor a test. A new home, airtight by design, must be tested once occupied — precisely because low air permeability can concentrate radon.

What type of test should I use after my work? A long-term test of at least 91 days, ideally during the heating season (November to April in Quebec), placed at the lowest lived-in level and analyzed by a C-NRPP-certified laboratory. Short-term tests aren't suitable for deciding whether to act.

Is there a acceptable radon level after a renovation? No level is entirely without risk. Health Canada's guideline is 200 Bq/m³ (annual average): it's the threshold above which it recommends acting within one year, sooner if the concentration is high. The goal after the work is to verify that your concentration hasn't crossed that threshold — and to reduce exposure as much as reasonably possible.

Order your radon test kit → — all-in, analyzed in Canada, prepaid return shipping.

Whether you're planning a Rénoclimat renovation, you've just installed new windows, or you've finished your basement, the RadonTest.ca kit gives you a reliable measure of your real concentration: an alpha-track detector (91 days or more), analysis by a C-NRPP-certified laboratory with the option of analysis entirely in Canada, prepaid return shipping, and your result delivered with Health Canada context — all in a single kit. Test before your work, test after, and know where you stand.

Sources

• Health Canada — Radon and energy renovations — airtight buildings can reduce air exchange and unintentionally increase radon; BEX study (DOE, 2020): +22% on average; table Germany +100% / United Kingdom +67% / Switzerland +33%; ventilation via balanced HRV; mitigation by active soil depressurization (published 2023-10-23).
• Health Canada — Radon action guides: Energy efficiency — guides and standards linking energy efficiency and radon (modified 2026-02-18).
• Health Canada — Test your home for radon — re-test after renovations affecting structure, ventilation or air-tightness, or after energy-efficiency work (windows, insulation, sealing); long-term test of 90 days or more.
• Health Canada — Government of Canada radon guideline — 200 Bq/m³ (annual average); act within one year, sooner if the concentration is high; no level entirely without risk.
• CMHC — Heat Recovery and Energy Recovery Ventilators — how an HRV works; balanced airflows, with neither positive nor negative pressure when properly installed.
• Government of Quebec — Rénoclimat — residential energy-efficiency program (evaluation, insulation, air-sealing, doors and windows, mechanical systems); administered by the Government of Quebec.
• Natural Resources Canada — Canada Greener Homes Grant (closed) — the federal grant no longer accepts new applications.
• Natural Resources Canada — Canada Greener Homes Loan — stopped accepting applications on October 2, 2025.
• NCCEH — Energy-efficient renovations and indoor air quality: prioritizing health — evidence synthesis on balancing energy renovation with indoor air quality (a Health Canada footnote).

Laboratory analysis is performed independently by a C-NRPP-certified laboratory. Results are presented in relation to Health Canada's guideline of 200 Bq/m³. RadonTest.ca coordinates only the logistics of the kits and the submission of samples — it does not interpret or alter results and does not provide medical, legal or building-engineering advice. Financial-assistance program parameters may change; confirm them with government sources before planning your work.