Radon is an invisible, odourless gas that can build up in any home, and the only way to know the level is to test. Health Canada's guideline is 200 Bq/m³, measured with a long-term test of at least 91 days during the heating season in the lowest lived-in level. Above that, Health Canada recommends fixing the home within a year, most often with a sub-slab depressurization system installed by a C-NRPP certified professional.
This guide covers testing and fixing existing homes and planning new ones. It is general information drawn from Health Canada, Indigenous Services Canada (ISC) and National Research Council code material, not legal or engineering advice. Confirm program and code questions with ISC, CMHC, your lands office or your building inspector.
What is radon, and why should a housing department care?
ISC describes radon as "a radioactive gas that has no colour, smell or taste," formed when uranium in soil, rock and groundwater breaks down. Outdoors it is diluted, but in enclosed spaces like basements "it can sometimes accumulate to high levels" (Indoor air safety, ISC). Health Canada says radon gets in through cracks in foundation walls and floor slabs, construction joints, gaps around pipes and support posts, floor drains and sumps, and that all homes have some radon: "The question is how much and the only way to know is to test" (Radon: What you need to know, Health Canada).
The health risk is lung cancer, and it builds over years. Health Canada estimates that 16% of lung cancers are from radon exposure, resulting in more than 3,000 lung cancer deaths in Canada each year, and calls radon the number one cause of lung cancer in non-smokers. People who smoke and are exposed to radon have an even higher risk. Health Canada also says 1 in 5 homes in Canada have high radon levels.
Levels are hard to predict. ISC notes that "Even homes on the same street can have very different levels of radon" (ISC). A community cannot test one house and assume the rest. For a housing department, that makes radon a task for every home, like smoke alarms or furnace servicing.
What is the Canadian radon guideline?
The guideline for homes is 200 becquerels per cubic metre (200 Bq/m³). Health Canada's measurement guide, updated in 2026, says the guideline "applies to your average annual radon level, not short-term measurements." If a long-term result is above it, Health Canada recommends that people "mitigate within 1 year for radon levels higher than 200 Bq/m³" and act sooner if the level is higher, reducing radon to as low as reasonably achievable (Guide for radon measurements in homes, Health Canada).
Older Health Canada material allowed up to 2 years for levels between 200 and 600 Bq/m³ and 1 year above 600 (Radon: Reduction Guide for Canadians, Health Canada). Where the two differ, follow the newer measurement guide. Health Canada is also clear that below 200 the risk is small but "there is no level that is considered risk free."
How should homes be tested?
The key rules from Health Canada's current guide:
- Long-term only. Health Canada says to test for "a minimum of 3 months" (Testing your home for radon, Health Canada). The measurement guide says at least 91 days of the test should fall in the heating season, and recommends tests of 3 to 12 months. Short-term tests "are not appropriate for informing mitigation decisions."
- Heating season. Readings are usually higher in colder months because windows stay closed and the stack effect draws more soil gas in. A result below 200 with fewer than 91 heating-season days may be an underestimate, so retest the next heating season.
- Right level, right room. Place the detector on the lowest lived-in level, in a room someone uses more than 4 hours a day, such as a bedroom or living room. Do not use the kitchen, bathroom, laundry room or storage rooms, and keep detectors away from sump holes, crawl spaces and foundation cracks.
- Upper floors too. Homes whose lowest lived-in level does not touch the ground "should still be tested."
- Reliable devices. Use a long-term detector or an electronic radon monitor that appears on the C-NRPP list, or hire a C-NRPP certified measurement professional. Residents should not change their habits during the test.
Keep a proper record for each home. Health Canada's guide lists what a test report should include: the room and floor, the device's serial number, type and model, its validity (such as expiry or calibration date), photos of the device in place, and a statement of the guideline (Health Canada). It also says all residents of the home "should be informed of the radon level they are being exposed to."
Help is available locally. ISC's indoor air page says test kits can be bought in stores, by phone or online, and to "Ask your local Environmental Health Officer (EHO) for help if needed" (ISC).
What support does ISC offer for radon?
We could not find a dedicated, national ISC radon testing program for on-reserve homes on ISC's public pages. What the pages do show:
- Guidance and EHOs. ISC's indoor air page explains radon, points residents to test kits and EHOs, and lists simple steps if a level is above 200 Bq/m³: air out basements and crawl spaces, seal foundation cracks and openings around pipes and drains, and cover exposed dirt floors with plastic sheeting (ISC).
- The First Nations Environmental Contaminants Program (FNECP). ISC funds community-based research, monitoring, risk assessment, risk communication and knowledge integration on environmental hazards. Projects need qualified scientific or academic partners, and First Nations in British Columbia apply through the First Nations Health Authority instead (FNECP, ISC). The most recent intake listed closed on September 22, 2025; check the page for the next call.
- Past radon projects. ISC's FNECP outcomes page describes community projects that placed detectors in homes for "90+ days," mitigated homes that measured above Health Canada's guidance, and retested afterward to confirm the reduction (FNECP outcomes, ISC).
- ISC-funded construction. ISC's infrastructure protocol lists the Government of Canada Radon Guideline and Health Canada's radon measurement guides among its air quality references (Protocol for ISC-Funded Infrastructure).
We also could not find an ISC or CMHC page that names radon mitigation as an eligible expense under a specific housing repair program. Ask your ISC regional office and your CMHC Indigenous and the North Housing Solutions Specialist before budgeting. For the main federal housing programs, see our funding guide for First Nations modular buildings.
How is a high radon level fixed?
Health Canada recommends hiring a contractor certified as a radon mitigation professional through the Canadian National Radon Proficiency Program (C-NRPP). The most common method is sub-slab depressurization, also called active soil depressurization: "a pipe is installed through the foundation floor to an outside wall or up through to the roof line" with a small fan that draws radon from below the house to the outside. Health Canada says a system "can be installed in less than a day" and in most homes cuts radon by more than 80% (Reducing radon levels in your home, Health Canada).
Health Canada's reduction guide describes variations for different foundations (Health Canada):
- Sump-hole depressurization: a sump can be capped and sealed so it still drains water and serves as the suction point.
- Drainage system depressurization: suction on weeping tile that forms a complete loop around the foundation.
- Sub-membrane depressurization for crawl spaces: a thick plastic sheet sealed over the soil and to the foundation walls, with a fan drawing radon from beneath it.
- Cold-climate detail: fans and pipes in an unheated attic or garage can collect condensation and ice. The guide notes that placing the fan indoors with a short, near-ground discharge reduces this.
- Combustion safety: confirm that the system does not cause backdrafting of a furnace, water heater, fireplace or wood stove. A trained radon specialist or heating contractor can test for this.
Sealing cracks is not enough on its own. In Health Canada's national follow-up study, homeowners who only sealed entry routes saw an average reduction of about 13%, while active soil depressurization installed by a contractor or certified professional averaged around 83% (Residential Radon Mitigation Actions Follow-Up Study, Health Canada).
Cost. Health Canada's reduction guide puts sub-slab or sub-membrane systems at "about $2,000 to $3,000 including material and labour," plus roughly $50 to $75 a year for fan electricity (Health Canada). That guide dates from about 2016, so treat the figure as a starting point and get current written quotes. The reduction guide suggests getting more than one estimate, checking references, and getting a written cost estimate covering all the work.
Upkeep. After installation, Health Canada recommends retesting to confirm the system works, and testing homes with an active system "every 5 years" (Health Canada). Most systems have a pressure gauge, usually a U-tube manometer, that shows whether the fan is working. Add a check of the gauge to your regular maintenance visits.
Follow-through. This is where programs fail. In Health Canada's follow-up study, only about 29% of homeowners who tested at or above the guideline took steps to reduce it. The most common reasons for not acting were not considering the level high (35%) and concern about cost (18%) (Health Canada). A housing department that tests homes should budget for fixing them, and explain results to tenants plainly.
What does the building code require in new homes?
Health Canada's reduction guide explains that the 2010 National Building Code (NBC) added radon requirements. Part 9, which covers houses, includes a sealed plastic membrane under the foundation slab, granular fill under the slab and "a rough-in for a future radon reduction system" (Health Canada). Health Canada's building code guide for municipalities, updated October 2026, describes the NBC rough-in as a "stub": "a short vent pipe which rises from the floor and is capped." It lists Saskatchewan and Manitoba among the provinces that follow the National Building Code (Radon action guide for municipalities: Building codes, Health Canada).
Health Canada is candid that a stub is a minimum, not a fix. The same page says "There is a significant risk that high radon environments remain untested and unmitigated" and that current best practices require more complete systems, such as a passive pipe vented at the roofline or an active system with a fan. It points to the Canadian General Standards Board's 2024 "Radon control options for new buildings." The NRC's intent statement for Sentence 9.13.4.3.(3) of the 2015 NBC explains that the granular layer, pipe and airtight seal exist to prevent depressurization under the slab from being "ineffective" (NRC Codes Canada).
Which code applies on reserve depends on your agreements and funding. ISC's infrastructure protocol says that in the absence of provincial or territorial building statutes, "the national codes will apply" (ISC). Confirm with ISC and your building inspector.
What should you ask a builder about radon?
Health Canada says "It is not possible to predict before construction whether or not a new home will have high radon levels," and that "It is more practical and less expensive to install the pipe through the foundation slab while your new home is being constructed" (Health Canada). Questions to put in your tender or ask at the design meeting:
- Will the slab sit on at least 100 mm (4 in.) of coarse gravel, with a polyethylene membrane of at least 6 mil and taped seams underneath?
- Will all slab penetrations, the floor-wall joint and the sump lid be sealed, and will floor drains have traps that block soil gas?
- Will there be a rough-in pipe of at least 100 mm (4 in.) through the slab, capped, sealed and labelled for radon? Will it be extended to a passive stack, or fitted with a fan, rather than left as a stub?
- For crawl spaces, will exposed soil be covered with a sealed membrane?
- For the foundation type you choose, such as a basement, slab, crawl space or other support, how will radon entry be controlled and how could a system be added later?
- Will the handover package tell the household to test? Health Canada recommends testing a new home in the first heating season after occupancy and again 2 years after the year of construction (Health Canada).
Where does a builder fit in?
A builder controls the details that make radon easier to manage: the membrane, the sealing, the rough-in and the foundation choice. Herauf Modular, a division of Herauf Enterprises, builds homes and community buildings as finished sections indoors in its Saskatchewan and BC plants, then delivers and sets them on site. Every unit meets or exceeds CSA A277 and the National Building Code for climate zones 6 through 8. Most builds are manufactured and delivered in about 16 weeks, with foundations, pads and services prepared on site at the same time, so radon details belong in the site and foundation scope from the start.
If you are planning new homes and want to talk through foundations and radon details, send us an enquiry. We reply within one business day.
This guide is general information, not legal or financial advice. Program rules change: confirm the details with the program, your Indigenous Services Canada regional office or CMHC before relying on them. Herauf does not administer any program or apply on a community's behalf.