Residential radon

Radon is a radioactive gas that forms from uranium present naturally in Earth’s crust. Radon is found in soil, everywhere on Earth’s surface. Levels of radon in the soil can vary greatly from one place to another. Radon can also be present in groundwater.

Radon can seep into buildings, particularly through foundations. It can sometimes accumulate and reach levels that can lead to health risks. Given it is a gas with no smell, taste or colour, it is impossible to detect with the senses.

Health effects

Radon enters the lungs with the air we breathe. Big organisations and international health agencies recognise radon as a carcinogen. It emits radiation that may cause lung cancer in the long term.

Radon is the second leading cause of lung cancer, after smoking. It is also the leading cause of cancer in non-smokers. In Québec, 10 to 16% of lung cancer deaths are attributed to radon. This represents over 1000 deaths each year. Of these deaths:

  • 60% occur in smokers
  • 30% occur in former smokers
  • 10% occur in non-smokers

Risk of radon-related lung cancer increases with the following:

  • Levels of radon: the more a person is exposed to high levels of radon, the higher the risk of cancer.
  • Duration of exposure to radon: risk of cancer increases for a person exposed to radon for several decades.
  • Smoking: smokers exposed to radon are at higher risk of having lung cancer than non-smokers.

Radon does not cause the following:

  • Breathing difficulties, such as chronic bronchitis and emphysema
  • Allergies
  • Asthma
  • Birth defects

Identifying sources of radon in a building

Outdoor radon levels are usually very low. Radon disperses in the ambient air fast and therefore does not cause health problems.

However, radon can seep into buildings through various openings, including:

  • Dirt floors
  • Cracks in concrete slab or foundation walls
  • Drains
  • Crawlspaces
  • Joints
  • Openings around vent pipes and service lines, pipe fittings, for example
  • Faucets, especially ones in the shower. Faucets can in fact be a point of entry for radon coming from groundwater rich in the gas. Hence, they can contribute to increasing levels of radon in indoor air.

Source : Natural Resources Canada This hyperlink will open in a new window.

Radon accumulates mainly in the lower and least ventilated rooms of a building, such as in the basement. Levels of radon in indoor air depend on several factors:

  • Levels of uranium and radon in the soil
  • Climate
  • Ventilation of the premises
  • Sealing and insulation of the house
  • Negative air pressure, meaning air pressure is less inside the building than outside. This pressure difference has the effect of transforming the dwelling into a sort of vacuum. Radon can then seep through cracks and other entry points that are in contact with the soil

The only way of knowing if there is radon in the dwelling is by measuring. 

Measuring levels of radon in a building

To know the concentration of radon in your house, you must use a measuring instrument called a dosimeter. It is advisable to conduct that measurement over a period of at least three months and to perform radon measurement during winter. You can measure radon concentration in your house by yourself or hire a professional.

Do not rely on test results from a neighbouring house or dwellings in your neighbourhood. Radon concentration may vary widely between houses, even if they are close to each other.

To measure radon concentration levels in your house by yourself, you need to get a dosimeter and use it according to the manufacturer’s instructions. It will cost you about $45 to purchase a dosimeter and to have the results analysed by a lab.

You can get a dosimeter the following ways:

  • Order one from the Québec chapter of The Lung Association’s This hyperlink will open in a new window. website, which offers certified dosimeters approved by Health Canada
  • Go to CAA Québec’s This hyperlink will open in a new window. website, which has information on getting a dosimeter in the ‘At Home’ section
  • Buy a test kit for analysing radon in the air. They are available in some hardware stores

To obtain a list of professionals certified to measure radon in Québec, use the search tool provided by the Canadian National Radon Proficiency Program This hyperlink will open in a new window. (C-NRPP). This certification program is recognised by Health Canada and the Ministère de la Santé et des Services sociaux du Québec.

Measures to take if radon concentration exceeds the Canadian guideline

Radon is measured in units of becquerels per cubic metre (Bq/m³).

In Canada, a guideline stipulates that radon concentration in dwellings should not exceed 200 Bq/m3. In general, radon concentration is not very high in Québec homes. The average concentration of radon in basements is about 35 Bq/m³. However, concentrations can sometimes reach very high levels, which exceed 1,000 Bq/m³.

Personal protective measures

If you are a smoker, the first thing to do in order to protect yourself against lung cancer due to radon is stop smoking. It is the fastest and cheapest way to reduce risk of radon-related lung cancer. Someone exposed to both tobacco smoke and radon greatly increases this risk.

Corrective measures for your home

Health Canada recommends taking corrective action whenever the average annual radon concentration exceeds 200 Bq/m³ in occupied spaces of a home. If this is the case in your home, you must take action, whether or not you are a smoker.

The recommended time to take corrective action depends on the average concentration of radon in your home:

  • If the concentration exceeds 600 Bq/m³, you should take corrective action within less than a year
  • If the concentration is between 200 Bq/m³ and 600 Bq/m³, you should take corrective action within less than 2 years

You will get better results by applying more than one corrective measure. For instance, you can do the following:

  • 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

If radon concentration in the house are too high, these measures will not be enough because they do not completely prevent radon from seeping through. In such case, you need to hire a qualified contractor. A qualified contractor will install a system that allows radon beneath the foundation to be evacuated before it reaches the building’s living spaces.

Health Canada recommends that people taking corrective measures try to reduce radon concentration to the lowest possible levels. Hence, in order to verify their effectiveness, it is recommended that you measure radon concentration again once corrective measures have been applied.

Many specialised companies can help you reduce radon concentration levels and its infiltration into your house. It is very important that you deal with a certified company. You can consult a list of these companies on Health Canada’s Canadian National Radon Proficiency Program This hyperlink will open in a new window. (C-NRPP) website.

Measures for new buildings

During construction of a new home, you can request that your contractor use mitigation techniques to minimise infiltration of radon into the house. If necessary, these techniques can also be applied to facilitate elimination of radon once the house is built. However, it is much easier and cheaper to do so at the beginning of construction. 

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Last update: October 4, 2023


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