Learn More About Radon

What Is Radon and Where Does It Come From?

How Does Radon Get Into the Home?

Which Homes Might Have A Problem?

Why are so many Canadians only learning about radon gas now?

Radon Health Risks

Why Is Radon More Harmful to Children than Adults?

What Is Radon Mitigation?

What’s in the code?  What can you do to mitigate?

How Effective Is Sub-Slab Depressurization?

How do we know that mitigation is working and that radon levels are as low as possible?

When To Call Canada Radon?

What Is Radon and Where Does It Come From?

Radon gas is a colourless, odourless, radioactive gas and known carcinogen that is released during the decay of uranium in rocks and soils. It is generated naturally by the bedrock below our homes all across Ontario and Canada, and dilutes to non-hazardous levels in outside air.

Radon is the number one cause of lung cancer in non-smokers. Radon induced lung cancer kills more than house fires and carbon monoxide combined and is 10 times more dangerous to children (source: Airthings).

In Canada, radon levels are measured in the units of Becquerels per cubic meter (Bq/m3). Concentrations in the outside air we breathe are considered non-hazardous and typically in the range of 5-30 Bq/m3. Radon becomes a health hazard at higher levels.

While Health Canada recommends radon mitigation at radon levels of 200 Bq/m3, the US EPA recommends 150 Bq/m3 while the World Health Organization (WHO) recommends a level of 100 Bq/m3.

Radon becomes a health issue when it enters the home and concentrations rise and remain high in the living space. Radon levels indoors are influenced by:
• Geography, as uranium and radon levels vary naturally in soils across the country
• Household construction methods and architectural design
• Natural ventilation options, ventilation systems and ultimately, the use of a radon mitigation system.

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How Does Radon Get Into the Home?

Radon can enter buildings through cracks and openings in floors, leading to higher levels, especially in basements and lower floors. Over time, exposure to radon increases the risk of developing lung cancer. Health Canada estimates that over 3,000 Canadians die each year due to radon gas exposure (Chen et al., 2012).

(source: ncceh.ca/environmental-health-in-canada/health-agency-projects/radon)

For most of the year, the air pressure inside your home is lower than the pressure in the soil surrounding your foundation. This difference in pressure can draw air and other gases in the soil, including radon, into the house.

Gas containing radon can enter your home at any opening where the house contacts the soil. These openings can be present even in well-built and new houses.

Potential entry routes for radon in homes with poured concrete foundations include cracks, areas with exposed soil or rocks, openings for utility fixtures or hollow objects such as support posts.

Radon is a monatomic gas that is much smaller than a water molecule and can find its way into a home's basement by several different routes:

  • Open cracks, seams or gaps in the basement slab, foundation walls, windows, plumbing, or conduit entering the home below grade
  • Open sump wells, floor drains, and crawlspaces
  • Through our water taps and shower heads

The air pressure inside your home is usually lower than in the soil surrounding the foundation. This difference in pressure draws air and other gases, including radon, from the soil into your home.[1]

Because newer homes are generally more airtight, even with the use of heat recovery ventilation, radon can accumulate to hazardous levels indoors.[2]

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 Which Homes Might Have A Problem?

Almost all homes have some radon. The levels can vary dramatically even between similar homes located next to each other.  The amount of radon in a home will depend on many factors including:

  • Soil Characteristics: Radon concentrations can vary enormously depending on the uranium content of the soil. As well, radon flows more easily through some soils than others, for example sand versus clay.
  • Construction Type: The type of home and its design affect the amount of contact with the soil and the number and size of entry points for radon.
  • Foundation Condition: Foundations with numerous cracks and openings have more potential entry points for radon.
  • Occupant Lifestyle: The use of exhaust fans, windows and fireplaces, for example, influences the pressure difference between the house and the soil. This pressure difference can draw radon indoors and influences the rate of exchange of outdoor and indoor air.
  • Weather: Variations in weather (e.g., temperature, wind, barometric pressure, precipitation, etc.) can affect the amount of radon that enters a home.

Because there are so many factors, it is not possible to predict the radon level in a home; the only way to know for sure is to test.

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Why are so many Canadians only learning about radon gas now?

Just like asbestos, radon in high concentrations is a known carcinogen and a serious threat to lung health that has been studied for decades in the US and Europe. Unlike asbestos, radon has only recently gained widespread attention and notoriety on a national and provincial level across Canada. 

1975 - The Environmental Measurements Laboratory of the US Department of Energy conducted the first detailed indoor radon survey in the USA.

1984 - Very high concentrations of radon found in Pennsylvania homes set the wheels in motion and gave birth to the US Radon Industry. The US EPA expanded its involvement in radon issues and assumed an active role by establishing the National Radon Proficiency Program to evaluate the effectiveness of radon measurement and mitigation methods.  https://pubmed.ncbi.nlm.nih.gov/25911413/

2007 -  The Canadian Radon Guideline reference level of 200 Bq/m3 was established.  It was four times lower than the previous Canadian level of 800 Bq/m3.  Canada’s reference level is still higher than the guidelines set by the World Health Organization (100 Bq/m3) and the United States (4 pCi/L, equivalent to about 148 Bq/m3).  (Source: CELA.CA Radon in Indoor Air: A Review of Policy and Law in Canada Nov 2014 p4-173)

2008  - Health Canada’s National Radon Program (NRP) was established to educate the Canadian public about radon, conduct research to better understand the radon situation in Canada, and establish the Canadian infrastructure and resources needed to take action to reduce indoor radon. (Source: NRP-Behavioural-Study-Final-Report-ENG-2020.pdf)

2011 - The Canadian Association of Radon Scientists and Technologists (CARST) was established to provide a bridge between policy makers, radon professionals, private industry and homeowners to support the effective and responsible management of radon levels in Canadian homes, schools and workplaces.

2014 - The C-NRPP was established as an agreement between the Canadian Association of Radon Scientists and Technologists (CARST) and Health Canada to fulfill the need for a certification program with established guidelines for Canadian radon professionals.

2014 to PresentCities across Canada and Ontario establish their own radon mitigation requirements for residential new construction.

2020 -  The City of Hamilton implemented its own radon mitigation requirements for residential new construction.

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Radon Health Risks

Today we know that radon levels should be reduced as much as possible and kept there with mitigation. A 2015 study showed that radon-induced deaths could be reduced by almost 50% when radon levels were reduced to 50 Bq/m3 and kept there.

“… radon gas inhalation is the 2nd leading cause of lung cancer4,7–13 and is responsible for tens of thousands of new cases and related deaths per year7,10–16[worldwide].”

(Source:  https://www.nature.com/articles/s41598-021-86096-3.pdf p1)

Smoking places people at higher risk from radon exposure, increasing the odds of developing lung cancer from 1 in 20 to 1 in 3 (Health Canada, 2010).





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Why Is Radon More Harmful to Children than Adults?

 “Lifetime relative risk of lung cancer from radon is inversely proportionate with age, with the youngest being the most at risk due to innate pediatric radiosensitivity, faster breathing rates, lower body mass and, most potential years of life lost at time of exposure15,16,26

(Source: https://www.nature.com/articles/s41598-021-86096-3.pdf p1)

  • Children’s organs are still developing; their replicative tissue is more vulnerable to DNA damage.
  • Children breathe faster; they actually respire 2-3 times faster than adults as their lungs are much smaller.
  • Children weigh less; their exposure is greater, as it is measured in concentration per kilogram.
  • Children have more life left; and thus could live long enough to get cancer from early life radon exposure.


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What Is Radon Mitigation?

Radon mitigation - the process of reducing radon gas concentrations in the living zones of occupied buildings, or radon from water supplies. [Wikipedia]

Radon gas is present in ALL homes, new and old, and cannot be detected or measured until a home is ready for move in.

The Good News: While modern medicine can only do so much to cure lung cancer, radon mitigation by sub-slab soil depressurization is highly effective at keeping radon out of the home, and hence cancer out of your lungs.


The amount of radon that enters a building can be reduced by decreasing the flow of soil gas into the home by:

  • sealing the basement to prevent soil gas entry;
  • decreasing the pressure in the soil beneath the building or beneath a membrane so that soil gas no longer flows from the soil into the building. This is known as soil depressurization.

Does your new home construction plan incorporate radon mitigation?

Is it the lowest risk plan for you and your homeowners?

Many cities, regions and municipalities are now requiring radon mitigation plans as part of their permit process.

Any home found to have hazardous radon levels     (> 200 Bq/m3) will require mitigation and on-going measurement to ensure homeowner safety.

Tarion insures new homeowners against hazardous radon levels for 7 years.

Radon awareness is a priority for Health Canada, Public Health Ontario, and advocacy groups.  Over 50% of Canadians are now aware of radon and its harmful effects.

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What’s in the code? What can you do to mitigate?

  • Gravel sub-membrane layer
  • Poly membrane beneath the slab
  • Proper foundation sealing
  • Properly sealed sump pit
  • Properly located soil depressurization rough-in and passive vent system
  • Complete Active Soil Depressurization (ASD) system

Radon mitigation by soil depressurization - Passive vs. Active options

An active radon system relies on a specially designed, low power (e.g., less than a 60W light bulb), all weather in-line fan that draws radon gas from beneath the foundation to the outside of the living space, through a continuous run of 4” vent pipe.

A passive system is designed to accomplish this exhaust action without the use of a fan and requires roof venting while active systems can often be side vented for additional cost savings and often lower design complexity.

Designing in a passive radon mitigation system when building a new house will improve the property's value and market appeal by ensuring radon protection and improving indoor air quality.

A basic passive radon mitigation system for new construction can easily be made into an active system (if necessary) simply by installing an in-line fan.


Benefits of Installing an Active System during New Home Construction

If you live in an area of the country that has moderate to high radon levels, Canada Radon recommends the installation of an active radon mitigation system during construction. An active system is similar to a passive system, except it has a very low draw radon fan installed. It consumes very little energy (e.g., less than a 60W light bulb) and greatly reduces soil gas and moisture intrusion.

Here are the benefits of installing an active system during construction:

  1. Can actually be lower cost than a passive system (i.e. can often be side vented)
  2. Radon levels will be extremely low (passive systems are only 60% effective- many need to be activated after construction).
  3. Active systems can remove litres of water vapour/day during wet months and prevent musty odors and mold growth caused by dampness. Active systems complement existing building envelope technologies to ensure a dry basement free of mold growth and musty smells.

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How Effective Is Sub-Slab Depressurization?

Radon mitigation systems installed by certified professionals are very effective at reducing radon levels even when results far exceed the recommended guideline.     (source: ncceh.ca/environmental-health-in-canada/health-agency-projects/radon

 The Active Soil Depressurization system is the most effective way to mitigate radon as well as other soil gas entry into the home. 

During new home construction, we offer 3 levels of service, all of which comply with the relevant sections of the Ontario Building Code (OBC) requirements for radon gas mitigation:

Protection Level



Typical Radon Reduction %, (compared to pre-installation levels)

Level 1

Sub-floor Depressurization Rough-In Only


Level 2

Passive Sub-floor Depressurization (PSD)

Up to 60%

Level 3

Active Sub-floor Depressurization (ASD)

Up to 95%


Level 1: Rough-in
Level 2 and 3: Passive (no fan) or Active (with fan)

Our level 1 service is our lowest cost option but does not lower home radon levels.  This option ensures the home is ready for the addition of an active subfloor depressurization system in the future.  For this reason, our level 2 or 3 service options provide the greatest value over the lifetime of the home by keeping radon levels as low as possible, lowering risks associated with radon, and working to ensure healthier air quality in general.


Example of change in Radon Concentration after Mitigation with an Active Sub-floor Depressurization (ASD) system [3]

While our prime focus is prevention of radon gas entry, studies show that subfloor depressurization systems can offer the added benefit of drier basement air due to the extraction of sub-slab moisture which further protects against basement odors, dampness and mold growth over time.1

“Results … indicate that ASD operation can produce significant moisture reductions in the basement air and walls … The findings are consistent with anecdotal reports of drying and odor improvement in basements during ASD operation, and suggest that microbial growth may also be reduced.“ 2  (p.1/61)

“The average moisture extracted by the full ASD system configuration ranged from approximately 13 to 19 gal/day, while the single-pipe systems extracted approximately 10 to 13 gal/day. These data are averages of one or more seasons.“ 3  (p.8/61)

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How do we know that mitigation is working and that radon levels are as low as possible?

The only way to know that radon levels inside a home are safe is to measure them, and yet most homes have yet to be tested.

Health Canada recommends that all homes be tested (Health Canada, 2013) and those over 200 becquerels per meters cubed (Bq/m3) should be mitigated. This standard applies to public buildings as well, including schools, libraries and childcare facilities.

Despite this recommended level of 200 Bq/m3, there is a large and growing body of evidence to suggest that radon levels should be kept as close to outside air levels as possible. 

Because the amount of radon gas rising from the earth varies with changes in weather, wind and pressure, concentrations vary seasonally with the highest levels often occurring in winter months when we tend to keep our windows and doors shut more often.  Although radon can be measured with a short 48-hour test, the best way to accurately determine the radon concentration in a home is to perform a long-term test lasting at least 91 days.  

Radon levels vary from home to home.  It is not uncommon that a home with safe radon levels sits right next door to a home with hazardous radon levels, even if both homes were built at the same time to the same construction standards!  In a recent study carried out by the City of Hamilton, 1 in 7 homes were found to have hazardous radon levels.

The Good News:  Radon mitigation systems installed by certified professionals are very effective at reducing radon concentration to safe levels even when results far exceed the recommended guideline.    

(source: ncceh.ca/environmental-health-in-canada/health-agency-projects/radon )

Once a radon mitigation system has been installed and move-in has occurred, Canada Radon will conduct a long term home radon study of at least 91 days.  This is because Radon levels in a home change significantly over time. They can rise and fall from one hour or day to the next and seasonally. For this reason, measurements taken over a longer period of time are more accurate

Canada Radon repeat these tests as needed and can also help by performing radon measurement tests in homes where no mitigation system has been installed.

Health Canada recommends performing long-term testing every 2 years using an approved test kit that includes a calibrated radon detection device and analysis by a certified radon measurement lab.  In homes that use an active radon mitigation system will be equipped with system status and performance indicators that may range from a simple U-Tube manometer to wifi enabled digital monitoring systems.

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When To Call Canada Radon

If you are starting a new build, please let us know as soon as you have the plans. We will work with your team on a detailed radon mitigation strategy that can be planned in from the outset - saving time and ensuring compliance with local building code requirements.

If your home is already under construction or complete, we can work with you on retrofit strategies and discuss the different options. When installed properly, retrofit radon mitigation systems are highly effective at ensuring safe radon levels in the home.


Click here to book a consultation now!