Radon in BC Homes: How to Test and How to Reduce It

Radon is a radioactive gas that seeps into homes from the ground, and you can't see, smell or taste it, so a test is the only way to know your level. Here is how to test a BC home properly, what the result means, how radon is reduced and how it fits into buying or selling.

The short version

What radon is and why it matters

Radon is a radioactive gas that comes from the breakdown of uranium in soil and rock. Health Canada says it is found in almost all homes in Canada, and it gets in wherever a house touches the ground: through cracks in foundation floors and walls, gaps around service pipes, floor drains, sumps and cavities inside walls.

• It varies from house to house. Levels differ even between similar homes next door to each other, so a neighbour's result doesn't tell you yours.
• The risk is lung cancer. Health Canada calls radon the second leading cause of lung cancer after smoking and the leading cause for non-smokers, and HealthLinkBC says about 16% of lung cancer deaths in Canada are linked to indoor radon. There are no immediate symptoms.
• Smoking adds to it. Health Canada estimates that a non-smoker exposed to high radon levels over a lifetime has about a 1 in 20 chance of getting lung cancer, and a smoker exposed to the same level about 1 in 3.

Radon in BC

HealthLinkBC says high radon levels are found throughout most of the province. Some regions typically run higher: in the Northern and Interior health regions, the share of homes reporting levels above the guideline ranged from 6% to 30%. Everyone is encouraged to test, including in the Lower Mainland and the Fraser Valley.

Health Canada's guideline is 200 Bq/m³, measured as the average over a year in the normal occupancy area: any part of the home where someone is likely to spend more than four hours a day. Crawl spaces, unfinished basements, storage rooms, furnace rooms and laundry rooms don't count.

How to test your home

Health Canada recommends testing every home, including homes above ground level. Its measurement guide sets out how:

• How long. At least 91 days for a valid estimate of the yearly average, and Health Canada recommends three to 12 months. Don't base a decision to mitigate on a shorter test.
• When. At least 91 days of the test should fall in the heating season, generally the colder months, so plan to start in the fall or early winter.
• Where. On the lowest lived-in level, in a room used more than four hours a day, with bedrooms first. Avoid kitchens, bathrooms, laundry rooms and crawl spaces.
• How to place it. At least 30 cm above the floor and 30 cm from walls and ceilings, at least 1 m from vents, windows and doors, and at least 10 cm from other objects. Keep it away from drafts, heat sources, direct sunlight, sump holes and foundation cracks.
• Kit or professional. HealthLinkBC lists BC Lung among the sources of do-it-yourself kits, and puts a kit, including the analysis, at about $30 to $50. You can also hire a measurement professional certified under the Canadian National Radon Proficiency Program (C-NRPP). If you use an electronic monitor, choose one that has passed C-NRPP performance testing for long-term home measurements.

What your result means

• Below 200 Bq/m³. Health Canada's guideline doesn't call for action, but HealthLinkBC notes that no level of radon is considered harmless, so reducing a level near the guideline can still be worth considering.
• Above 200 Bq/m³. Health Canada recommends taking action to lower the level within one year, and sooner the higher it is.
• Other units. One picocurie per litre (pCi/L) equals 37 Bq/m³, so the guideline is about 5.4 pCi/L.
• Testing again. Retest after a renovation that affects the structure or ventilation, after an energy retrofit, or when a floor that wasn't tested, such as a newly finished basement, becomes the lowest lived-in level.

How radon is reduced

Health Canada recommends hiring a professional certified under C-NRPP to reduce radon, and says levels in most homes can be reduced by more than 80%. Its reduction guide describes the main options:

• Active sub-slab depressurization. A pipe runs through the foundation floor, and a small fan draws radon from beneath the slab and vents it outside. Health Canada calls it the most effective and reliable technique, and it is the method C-NRPP certified professionals use most.
• Crawl spaces. Where a crawl space has a soil floor, a similar system draws radon from under a plastic membrane laid over the soil.
• Sealing and ventilation. Sealing cracks and openings helps, but it is hard to find and permanently seal every one, so it is used alongside other methods. A heat recovery ventilator gives only a modest reduction.
• Cost. It varies by home, but Health Canada says it is about the cost of other common repairs, such as replacing a furnace or air conditioner. Its 2023 reduction guide estimated about $2,000 to $3,000 for a sub-slab or crawl space system, plus about $50 to $75 a year to run the fan.

Before you sign, ask for proof of certification, get more than one estimate and read the written contract. Afterwards, Health Canada recommends a short-term test by the professional, started at least 24 hours after the fan is turned on, then a long-term test the next fall or winter that isn't done by the installer. With an active system, retest every five years.

Radon and new homes in BC

The 2024 BC Building Code dropped the old exemption for some areas of the province, so houses and other small residential buildings now need a radon rough-in, for building permits applied for on or after March 8, 2024. Under the 2018 code, the requirement applied mainly in listed areas. Vancouver has its own building bylaw, so check the City's rules there.

• What a rough-in is. A gas-permeable layer under the floor slab, separated from the living space by an air barrier and connected to a labelled radon vent pipe that runs to the outside, with room left to add a fan.
• What it isn't. The code doesn't require a fan or a radon test. The Province's bulletin recommends testing, which is up to the owner after occupancy.
• Older homes. A home built under an earlier code may have no rough-in, and the bulletin advises owners of existing homes to test.

Buying or selling a home

A long-term test takes at least three months, which a subject period rarely allows. Health Canada doesn't recommend testing during a real estate transaction, and suggests testing before a sale or after a purchase instead.

• If you are buying. Ask whether the seller has done a long-term test, for the results and where the detector was placed; if it wasn't in the area you will use most, a new test may be needed. Ask too whether the home has a mitigation system, and have a certified professional assess it.
• Holdbacks. Buyer and seller can agree to hold back part of the price so a long-term test, and any mitigation, can follow completion, with the money released to the seller if no problem is found. Your lawyer or notary can help set the terms.
• Price. BCFSA notes that a buyer can also factor the likely cost of mitigation into the offer.
• If you are selling. There is no legal requirement to test, but BCFSA treats a known radon level above 200 Bq/m³ as a material latent defect, which a seller's real estate professional must disclose. If a buyer asks about a lower result, answer truthfully or decline to answer, and update your Property Disclosure Statement if you learn something new. Health Canada suggests testing, and mitigating if needed, before you list, so a low result works in your favour.
• Strata homes. BCFSA notes that for a townhouse in a strata, the strata council must approve the work and hire the mitigation professional; a bare land strata can differ.

Questions buyers often ask me

How long does a radon test take?

At least 91 days. Health Canada recommends three to 12 months, with at least 91 days in the heating season, so start one in the fall.

What is a safe radon level in Canada?

Health Canada's guideline is 200 Bq/m³ as a yearly average, and above it, Health Canada recommends lowering the level within a year. No level is considered harmless, so lower is better.

Can I test for radon during my subject period?

Not reliably. A valid test takes at least 91 days, and Health Canada doesn't recommend testing during a transaction, so ask for the seller's long-term results, consider a holdback, or test after you move in.

How much does radon mitigation cost?

It varies by home. Health Canada's 2023 reduction guide estimated about $2,000 to $3,000 for a sub-slab system, plus about $50 to $75 a year to run the fan, so get more than one estimate from a certified professional.

Do new homes in BC have radon protection?

Under the BC Building Code, houses and other small residential buildings with a building permit applied for on or after March 8, 2024 need a radon rough-in. The code doesn't require a fan or a test, so test a new home after you move in.

Buying a home? Read what your inspector checks, and what they don't, how subject clauses work and what sellers disclose.

This article is general information, not medical or legal advice. The details come from Health Canada, HealthLinkBC, the Province's Building Code bulletin, BCFSA and BCREA, and were current at the time of writing. For Health Canada's guide, see Radon: reduction guide for Canadians.