Radon gas: what homeowners, buyers, and sellers need to know

Updated January 26, 2024

When you’re thinking about buying a house, your thoughts turn to things like price, location, and the age of the home. One of the last things on your checklist is probably the presence of radon gas (if it’s there at all).

However, radon gas is definitely a factor to consider. Radon is a naturally occurring substance in the ground that could have repercussions on you and your family’s health. If you own a home, or you’re planning to buy or sell one, you should be aware of radon gas.

Read on to learn more about radon gas, its effects on your health, and how to detect it in your home.

Radioactive gas sign in a green field

What is radon gas?

Radon is an invisible, odourless, tasteless, and radioactive gas that forms from the breakdown of uranium in rock and soil. It’s found everywhere on the earth’s surface, although the levels of radon in the soil vary from region to region. Radon is also sometimes present in groundwater.

How can radon affect your health?

Radon is known to cause health problems.

Radon is the leading cause of lung cancer among non-smokers. International health agencies have recognized radon as a carcinogen. In Quebec, 10–16% of lung cancer deaths are attributed to radon, which amounts to over 1,000 deaths a year in the province. Smokers are at a higher risk of developing lung cancer from radon. The gas doesn’t directly cause breathing difficulties, however, nor is it known to cause issues such as chronic bronchitis, asthma, allergies, or birth defects.

Radon can seep into a house through dirt floors, drains, crawlspaces, joints, faucets, cracks in the foundation walls or concrete slab, and openings around vent pipes and service lines. Upon inhalation into the lungs, radon breaks down into radioactive particles that release small burst of energy. This energy is absorbed by lung tissue which damages the lung cells. Damaged cells can become cancerous when they reproduce.

Radon gas is harmless outdoors, as it quickly becomes diluted by the fresh air.

How to detect radon

Homeowners can purchase a radon gas detector from a local hardware store or have a professional perform tests.

Radon is measured in becquerels per cubic meter (Bq/m³), which are a gauge of radioactivity. The detector will give you two readings: a short-term reading (usually a seven-day average) and a long-term reading (an average of all measurements taken). Radon levels can change from day to day and month to month in the same space.

Place the detector in the basement or in an area on the lowest floor of the home where people usually spend more than four hours a day. Place the device at height of no more than 6 feet. Don’t place the device in humid areas (above 85%), or within 3 feet of ventilation sources such as vents, fans, windows, or doors. An influx of fresh air will skew the results.

Health Canada recommends that radon levels within living spaces do not exceed 200 Bq/m³.

If the reading is higher, Health Canada recommends corrective action:

  • For a reading of between 200 Bq/m³ and 600 Bq/m³, take corrective action within two years.
  • For a reading greater than 600 Bq/m³, take action within one year.

We will look at corrective measures below.

Implications for homebuyers and sellers


As a seller and a homeowner, you should have your home tested for radon, even though you are not legally required to do so. A prospective buyer may ask about the radon levels in your home.

However, readings above 200 Bq/m³ constitute a material latent defect which you and your real estate agent or broker would be obligated to disclose to potential buyers. Additionally, if you’re unable to provide the results of a radon test, the buyer may reduce their offer price or hold back funds until the house is tested.


As a buyer, you should ask the seller if they have long-term radon gas readings and request a copy of the results. If the seller has tested, ask where in the house they got readings, especially if the house has a basement. If the house hasn’t been tested, make sure that tests get done before you close the deal.

It’s also wise to start running long-term tests after you move in, just to be safe.

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Corrective measures

You can reduce radon levels in your home with some basic measures:

  • Seal cracks in the foundation.
  • Seal openings in contact with soil.
  • Ensure that drains are covered and ventilated to the outside.
  • Improve ventilation in your home, especially in the basement.

Ultimately, it comes down to blocking radon’s passage into your home. There are many places that radon gas can get inside a building:

Graphic of a home's basement foundation showing possible entry points for radon gas: Exposed soil in crawlspaces, cracks in foundation, around utility penetrations, hollow support posts, cracks in floor, floor drains, and floor/wall joints.

Hiring a professional, certified contractor is also highly recommended. They can install a system which evacuates radon beneath the foundation before it penetrates the living area of the dwelling. You can find a list of certified contractors on the Canadian National Radon Proficiency Program (C-NRPP) website.

Commonly asked questions

What areas in Canada have high levels of radon?

Radon exists throughout all of Canada. However, it’s more prevalent in Manitoba, Saskatchewan, and New Brunswick. It’s also prominent in parts of BC’s interior and northern regions, as well as certain locales in Quebec.

What types of homes have the most radon?

Any type of building is susceptible to radon gas infiltration. If it’s on the ground, radon can seep inside. As a general rule, the greater the on-ground footprint of a home, the higher is susceptibility to radon gas. However, radon can be an issue in any home — big or small, old or new.

That’s why it’s so important to test for it.

Where in the house are radon levels highest?

Radon forms in the ground, so areas of a home in contact with the ground tend to have the highest concentrations of radon gas. Basements, cellars, crawlspaces, or other sections at the lowest level of a home will usually collect the most radon.

However, it’s important to note that even homes without basements are susceptible to radon, and it could potentially reach any room in the home.

Does home insurance cover radon mitigation?

If there’s radon in your home, home insurance won’t cover any repairs or mitigation. Steps taken to reduce radon gas in a home, while important, are considered maintenance. Home insurance is meant to cover damage from sudden and accidental events. If you find radon gas in your home, it won’t be from a sudden occurrence.

Want to learn more? Visit our Home and Personal Safety resource centre to find more information about protecting your family and your home. Or, get an online quote in under 5 minutes and find out how affordable personalized home insurance can be.


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