By Ted McIntyre

Canada’s radon threat is getting worse, and code adjustments are likely to follow

“In 2012, my wife Janet was diagnosed with lung cancer and given four months to live unless she underwent immediate surgery to remove the tumors in both of her lungs,” Alan Whitehead relates. Two years of surgeries ensued. 

“Touch wood, Janet is doing well now,” Whitehead says. “But she’s in the minority. Lung cancer survivors are rare.”

The mystery with Janet was that she had never smoked, nor had she even been regularly exposed to second-hand smoke. But Alan had an inkling. Five years earlier, he had helped found Radon Environmental, which provides consumers, mitigation professionals and builders with high-performance options for preventing radon exposure. “We were living in B.C. when Janet was diagnosed, but had previously lived in Rockcliffe Park in Ottawa, and I knew Ottawa was a major hot spot for radon—rich in uranium,” Alan says. “When we reached out to the occupants of our former home in Ottawa to suggest they test for radon gas, it came back at 3,200 Becquerels per cubic metre (Bq/m³). That’s 32 times the World Health Organization’s action guideline and 16 times Health Canada’s guideline of 200 Bq/m3.”

Naturally occurring, invisible and odourless, radon gas is formed when radioactive metal (radium, thorium or uranium) breaks down in rocks, soil or groundwater. While it quickly dissipates outdoors, it can build up in higher concentrations indoors, where it can enter a home from anyplace that’s in contact with the ground—from cracks in foundation walls and floor slabs, to construction joints, gaps around service pipes, support posts, window casements, sumps and floor drains or interior wall cavities.

As the Whiteheads learned the hard way, radon is the leading cause of lung cancer in non-smokers, accounting for 3,200 deaths in Canada annually (16% of overall lung cancer fatalities), according to Health Canada. The good news is that it’s exactly the same number of fatalities the federal government was reporting five years ago. The bad news is that the number of homes measuring beyond the guideline appears to be increasing, with the Canadian government now noting it as close to 10%. Recent data gathered by researchers from the University of Calgary, however, suggest that number could actually be closer to 20%—with 5,600 of 30,000 homes tested nationwide exceeding the 200 Bq/m³ ceiling. 

The trend is supported by a 2021 study produced by Evict Radon, a trans-disciplinary national non-profit enterprise aimed at both understanding and ‘engineering out’ radon from the Canadian residential environment. The study, which compares Canadian and Swedish houses, found that “homes built from the 1950s to the 1970s in Sweden tended to contain higher radon versus those built in Canada in the same period, (but) by the 1980s, houses built in Canada and Sweden were constructed with the same—relatively high—radon level. From then on, radon in new Swedish properties decreased, while the reverse occurred in Canada, such that new Canadian homes are now built with an average of 467% higher radon levels compared to a new house built in Sweden.

“Our goal is to gather the essential building, health and economic data needed to make a clear case to implement meaningful changes to the next Canada Building Codes (in 2025),” the study indicates. “By changing our building practices to fundamentally reduce the way houses capture and concentrate radon, we can protect everybody from the health risks of radon exposure.”

The study, published in the journal Scientific Reports, predicts “that without intervention, by 2050 the average radon level of a new Canadian home will increase another 25% over current levels, which are already third highest in the world.”


While researchers are not yet 100% sure why Canada has seen such an increase in radon compared to Sweden, they note “that there is a major difference between Canada and Sweden in terms of how properties are heated, with natural gas-based furnaces (57%), electric baseboard heaters (27%) and boilers (radiators) (5%) encompassing the majority of heating in Canada. By contrast, Sweden began to phase these methods out during the mid-20th century, replacing them with district heating. District heating uses the combustion of biomass fuels in a centralized facility to produce steam that is then forced through a pipe network to individual properties for radiant heat distribution. By the 2010s, district heating accounted for more than 70% of heating in Sweden, while natural gas-based furnaces encompassed less than 10%. Natural gas-based furnaces require forced-air ventilation from lower to upper property levels to distribute heat, a process that has major implications to air dynamics and pressures within a given building. (This) might be a major reason why introducing HRV has corresponded with an increase in innate radon risks, versus the decreases observed in Sweden and elsewhere.”

The study’s researchers are calling for proactive radon mitigation systems to be included in all new residential properties constructed using the 2025 Building Code, says Dr. Aaron Goodarzi, an associate professor with the University of Calgary’s Department of Biochemistry & Molecular Biology and founder and scientific director at Evict Radon.

“Radon ‘take action’ guidelines vary around the world, but our goal in mitigation is to keep indoor levels as low as possible, and ideally below 100 Bq/m3,” suggests Robert Maccarrone of Stoney Creek-based GoTek Radon. “While Canada recommends that corrective action is taken if the average annual radon level exceeds 200 Bq/m3 in the normal occupancy of a building, the U.S. Environmental Protection Agency recommends corrective action at 150 Bq/m3, while the World Health Organization (WHO) recommends it at 100 Bq/m3,” Maccarrone notes. “And for reference, the Kentucky Association of Radon Professionals has published an infographic that compares exposure to an average annual radon level of just 148 Bq/m3 to smoking eight cigarettes per day.   

“The National Building Code of Canada 2020 was released March 28, 2022, and there have been only slight updates to the radon-relevant references in the code,” Maccarrone shares. “At the CARST (Canadian Association of Radon Scientists and Technologists) annual conference in April, we learned that work is being done to prepare recommendations for more significant changes, and it was suggested that there may be an update this fall.”

“Around the same time, we’re told that the Canada Labour Code will be amended to require radon testing provisions to protect workers in all workplaces,” says Whitehead, a former president of CARST. 

As for current rules across the land, “it’s a patchwork quilt,” Whitehead says. “Atlantic provinces, not including Newfoundland and Labrador, and Saskatchewan and Alberta have all adopted 2015 National Building Code recommendations, including the rough-in and soil depressurization systems for new builds. Quebec has quietly been testing 20,000 homes over three years, with 25% well above Health Canada guidelines, so they’re looking hard at adopting something in the next 12 months. Half of B.C. requires radon control measures to be put in place during construction and went beyond national code recommendations. The vent pipe that used to go four feet above the slab is supposed to be capped and sealed. In many cases, it wasn’t being capped and sealed, so you were literally creating a four-inch-wide airway into the home. So B.C. said, ‘We’re going to extend that vent pipe through the roof space during construction.’ We’re expecting that to be recommended in the next National Building Code cycle, hopefully later this year.”

For now, the Ontario Building Code lists only three areas as mandated to meet the 200 Bq/m3 guideline: the City of Elliot Lake, the Township of Faraday in the County of Hastings, and the township of Hyman in Sudbury. The rest of the province continues to decide for itself. “Over the past few years, Guelph, Thunder Bay, North Bay, Peterborough, Kingston, Hamilton and Ottawa have all changed their radon requirements,” Whitehead notes. 

In Guelph’s case, residents seeking a building permit must proactively address radon risks with steps that include mandatory rough-in and testing, sealing the foundation or installing a full mitigation system. “I don’t hear any complaints about it anymore. It’s just part of building a house,” Nicholas Rosenberg, a program manager at the City of Guelph, told the Toronto Star last year.


It’s not as though Ontario builders have had it easy, though. The statutory Tarion new-home warranty includes radon remediation coverage for seven years from the original possession date. For all purchase agreements signed on or after February 1, 2021, there is a maximum of $50,000 (up from $25,000) for warranted damage caused by environmentally harmful substances or hazards, including excessive levels of radon. Tarion advises builders to check if the municipality they’re building in has supplemental soil gas control measures as part of their requirements, in addition to any standard requirements within the OBC. 

“Tarion was the first insurer to include radon in its coverage, but it surprised us that they made it seven years retroactive,” says Whitehead. “That caused some consternation, particularly in Ottawa region, which is a major hotspot.”

For retroactive fixes, it’s important to employ qualified radon professionals, stresses Whitehead, who has seen bigger problems pop up when poor work under the slab created a new airway to allow even more radon gas in.

Though not yet a requirement everywhere in Ontario, some builders have recently chosen to include rough-ins for radon mitigation in their new homes. But where can mistakes get made? Although part of new builds, “it’s common to see failures with the capped rough-in vent stack, installed as part of local and OBC requirements, where the capped rough-in cannot be used due to improper location or installation,” Maccarrone notes. “Another issue that’s hard to control is the eventual development of gaps along the expansion joint between the foundation wall and the floor slab. Unless properly sealed during construction, these gaps, even minor ones, can lead to elevated radon concentrations.

“We saw a home with radon levels of 1,500 Bq/ m3 in the basement, where the levels were in the 700-900 Bq/m³ range on the main floor,” Maccarrone says. “This was a very well-built home, approximately 10 years old, but there were cracks in the floor slab and gaps at the expansion joint between the slab and the wall. The homeowners had just moved in and were using the basement regularly as a study and as a play area for their four-month-old daughter. We repaired and sealed all basement gaps and cracks (approx. 600 lin. ft.) and an active radon mitigation system was installed over a two-day period. Average radon levels now range from 50 to 100 Bq/m3 in the home.”

Following B.C.’s example and “extending the pipe through the roof costs little during construction. But the cost to retrofit a home with that system is typically $3,000 to $5,000—and you have to find a straight run for that pipe,” Whitehead explains. “What we do is go beyond code, and we have the only code alternatives approved by the Canadian Construction Materials Council.” 

Instead of four inches of gravel serving as a filter beneath the slab, Radon Environmental worked with an architect to design an alternative, RadonGuard, which creates large voids beneath the slab to move air and moisture more efficiently. Composed of expanded polystyrene (EPS), it also provides a thermal break, adding insulation. “You can put it down on compacted ground, then put our Radon Block, a radon-blocking barrier membrane, on top. Instead of just being a vapour barrier, ours is specifically designed to block radon gas and methane. The costs of the two different systems is very similar, especially when you consider finding and shipping the prescribed type of gravel, which loses efficiency over time anyway.

“The other way of addressing the problem) is to use a ventilation system with a sensor that pilots the air exchange system when it detects a peak of radon and the fan runs until it’s dissipated, as opposed to fans in the roof space or basement that need to run 24/7,” Whitehead says. “Installed, you’re typically looking at $2,000 to $3,000. The builders we work with will usually build above code and install both the Radon Guard and Radon Block during construction. It takes six to eight hours, whereas it takes quite a lot longer to put down gravel and a vapour barrier.”


Expect more demand for such measures from new-home buyers. “I saw that Health Canada conducted a behavioural study in 2020 after sending a radon awareness postcard to around 1.5 million Canadians. They found a 4,188% increase in visits to the radon website by Canadians in areas that received the postcards!” Maccarrone says. Health Canada followed with a distribution of another 3 million radon-info postcards between November 2021 and January 2022. 

“We have designers, developers, builders and renovators reaching out to us right now who are interested in learning more about radon and how to keep it out of their projects where the local building code requires a mitigation plan. We also have a growing group of builders working with us to control radon in all of their new projects,” adds Maccarrone, whose company is also an authorized dealer of the Airwell treatment system for radon in groundwater.

It’s a similar story for Whitehead, whose clients include Empire Communities, Wastell Homes and ERTH Homes, the latter of which is installing the company’s products into new homes where it’s not yet required by code.

Ontario builders have recognized that this is an issue and are starting to proactively address the challenges, assures Luca Bucci, CEO of the Ontario Home Builders’ Association.

 “We are encouraged to see that our members are working with radon mitigation companies to proactively manage the levels of radon for the health and safety of our customers,” Bucci says. “Our association looks forward to working with government and all stakeholders to develop unique solutions that maintain those high standards and expectations without negatively impacting housing affordability that is already strained.”

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