Radon is a naturally occurring radioactive gas that can build up inside homes and other buildings. Long-term exposure to elevated radon levels increases the risk of lung cancer.

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What radon is

Radon is a naturally occurring colorless, odourless, tasteless radioactive gas produced by the breakdown of uranium in rocks and soil.

Since radon is a gas, it can easily move through soil and thawing permafrost, into the air we breathe. Outdoors, radon is diluted and is not a concern. In enclosed spaces such as homes and buildings, radon can build up to levels that may pose a health risk.

How radon affects your health

When radon gas is inhaled, it continues to break down, creating radioactive particles. These particles can damage lung tissue over time.

Repeated exposure to high radon levels increases the risk of developing lung cancer. The risk depends on both radon level and how long a person is exposed to it.

In Canada, radon exposure is the leading cause of lung cancer among non-smokers and the second leading cause of lung cancer among people who smoke.

The combined effects of radon exposure and tobacco use greatly increase the risk of lung cancer. 

For more information on the health effects of tobacco, visit:

• Health effects of tobacco

Canadian guideline for indoor radon

Radon is measured in becquerels per cubic meter (Bq/m³), a measure of radioactivity.

Radon levels can vary throughout the year and even from day to day. For this reason, health risks are assessed using an annual average radon level.

Health Canada recommends that the annual average radon level indoors stay below 200 Bq/m³. This guideline applies to indoor spaces where people regularly spend more than four hours per day. 

Radon in NWT homes and buildings

Radon can be found in homes and buildings across Canada.

Radon levels can vary between communities, neighbourhoods and even neighbouring buildings. Factors such as local geology, building design, ventilation practices and seasonal weather conditions can affect indoor radon levels.

Many northern buildings are built on piles or cribbing rather than directly on the ground. Air movement beneath these buildings may help reduce the buildup of radon indoors. However, airflow conditions can change during the year. For example, snow accumulation in winter may restrict airflow beneath a building and affect radon levels.

Many northern buildings are also located on permafrost. Frozen permafrost can help slow the movement of radon gas. As permafrost changes over time, its ability to limit radon movement may also change in some areas. Testing every five years can help identify changes in indoor radon levels over time.

How radon enters buildings

Radon can enter homes and buildings through opening where the structure comes into contact with the ground, including:

• cracks in foundation walls
• cracks in floor slabs
• construction joints
• gaps around service pipes
• support posts
• window casements
• floor drains
• sumps
• wall cavities

Factors that affect indoor radon levels
Several factors influence how much radon can build up indoors:

• Soil characteristics: Radon concentrations can vary greatly depending on soil composition.
• Building construction: Design, condition and contact with the ground affect radon entry.
• Foundation condition: Cracks and openings create potential for entry points.
• Occupant activities: Exhaust fans, windows, and fireplaces can influence air movement and pressure differences.
• Weather conditions: Temperature, wind, barometric pressure, and precipitation can affect radon movement.

What we know about radon in the NWT

Preliminary northern radon testing reported in the 2024 Cross Canada Radon Survey found that the average radon level was 70 Bq/m³. The survey also found approximately 1 in 5 homes tested in the Northwest Territories had radon levels above the Canadian guideline value of 200 Bq/m³.

These findings were based on a small sample size from homes in the North Slave and South Slave regions and may not reflect radon exposure risk in all NWT communities.

Because radon cannot be seen, smelled, or tasted, testing is recommended to determine the radon level in your home or building.

Additional Resources

• Radon (Government of Canada)
• Canadian population risk of radon induced lung cancer (national estimate study) (external)
• Cross Canada Radon Survey
• Take Action on Radon (TOAR)