Is radon a problem in Calgary?

How common is high radon in Calgary homes?

Common enough that a high result should not surprise anyone. The Cross-Canada Survey of Radon Exposure put about 1 in 6 Calgary-area houses (15.5%) at or above 200 Bq/m³, with a further 36.9% between 100 and 199 Bq/m³ and an average of 102.5 Bq/m³source.

The middle group deserves attention. Health Canada's guideline is 200 Bq/m³ as an annual average, the point above which it recommends corrective actionsource. A house in the middle band is under that line, yet its owner is not looking at a low number, and plenty of Calgary households are in exactly that position.

These are figures for a region. They describe how often a high result turns up, not where. For the area-by-area picture and the public maps, with their limits, see what is published about radon by area in Calgary.

Has the picture changed between studies?

The share of homes over the guideline is higher in the newer survey than in the earlier local study. In 2017 a University of Calgary-led team reported on 2,382 homes in Calgary and the surrounding area and found about 1 in 8 at or above the guidelinesource. Nearly half of those homes, 47.6%, measured 100 Bq/m³ or more, and their average was 126 Bq/m³source.

We treat the Cross-Canada Survey as the current reference and the 2017 paper as the historical one. The two were not run the same way, so the gap between them is not proof that radon in the city rose over those years. What both show is the same broad result reached twice, with different samples of homes, several years apart.

An older federal number still circulates as well. Health Canada's 2012 cross-Canada survey found 8.1% of the 86 homes it sampled in the Calgary health region above 200 Bq/m³, and Health Canada itself states that those results should not be used to judge radon risk potential or to decide whether a home needs testingsource. With a sample that small, we mention it only so that readers who meet it elsewhere know where it comes from.

Why does the Calgary region test high?

Two things have to be present for a house to have high radon: a source in the ground, and a building that draws the gas in and holds it. Radon is a radioactive gas produced as uranium in soil and rock breaks down naturally, and it has no colour, smell or tastesource. Dr. Aaron Goodarzi of the University of Calgary has said that southern Alberta ranks in Canada's top five for radon exposure, and that the Okotoks and Foothills area is among the most exposed regions observedsource.

We will not go further than that on geology. The sources we cite establish that the ground here supplies radon. They do not single out one formation or one cause, and we would be guessing if we named one. The research is far more specific about the second ingredient, the house.

Soil gas gets in through cracks in foundation floors and walls, construction joints, gaps around service pipes, support posts, window casements, floor drains and sumps, because the air pressure indoors is usually lower than the pressure in the soilsource. Basements are the norm in Calgary houses, which puts a large area of concrete, with all of those openings, in contact with the ground. Many families also use that level as everyday living space.

Why do newer homes test higher?

On average they do, and the finding has been repeated. In the 2017 southern Alberta study, homes built in 1992 or later averaged 142 Bq/m³ against 108 Bq/m³ for older homes, a difference of 31.5%source. University of Calgary-led research later reported that radon in new Canadian houses has been climbing since about 1980, and that new Canadian homes averaged 467% more radon than new Swedish onessource. A 2021 study gave averages of 131 Bq/m³ for Canadian houses built in the 2010s and 2020s and 28 Bq/m³ for Swedish houses of the same periodsource.

The comparison with Sweden matters because it points away from the ground as the only explanation. Two countries with cold winters ended up with very different indoor radon in houses of the same age. The way a house is designed, sealed and ventilated is part of the answer, and that is something builders and owners can change.

The same research projects that, without intervention, average radon in new Canadian homes will rise by about another 25% by 2050source. Alberta's building code now requires a radon rough-in, with a pipe stub, in new homessource. A rough-in is a provision for a future system. It moves no air until someone tests the house and, if the result calls for it, connects a fan. Our page on turning a builder's rough-in into a working system explains that step.

For a Calgary buyer this reverses a familiar assumption. A recent build in a new community is not the low-risk case. On the averages, it is the one more likely to need attention.

Which building features are linked with more radon?

A 2019 study of 11,727 buildings across the Prairies linked higher radon with more recent construction, larger floor area, fewer storeys, higher ceilings and less window openingsource. Those are associations found across thousands of buildings. They are not a checklist that convicts or clears one house.

Read as a description, though, the list looks a lot like the houses that have gone up around Calgary's edges in recent decades: large footprints, tall ceilings, and windows that stay shut for most of the year. A wide bungalow has more floor touching the soil for each person living in it than a narrow two-storey does. A house whose windows are rarely opened exchanges less air with the outdoors. The study measured the links. Explanations like these are reasonable readings of them, and we offer them as nothing more.

Setting matters too. A 2024 study covering 42,051 Canadian residential properties found that people in rural, lower population density communities experience as much as 31.2% greater average radon than urban equivalentssource, and it attributed most of that gap to proximity to drilled groundwater wells, not to the use of well watersource. Acreage owners outside the city have no reason to assume the Calgary-area figures overstate their own odds.

Does Calgary's long heating season make it worse?

It makes the high season longer. Health Canada wants at least 91 days of any test to fall in the heating season, when windows are closed and indoor radon tends to be highestsource. The mechanism is simple. Warm air rises and leaks out near the top of a heated house, replacement air is pulled in low down, and some of that replacement comes from the soil. Health Canada notes that the stack effect increases radon entry in the cold monthssource.

In a city where furnaces run from early fall well into spring, the closed-up months outnumber the open-window ones. That does not appear as a separate line in any study we cite, and we do not put a number on it. It is simply the reason a summer reading taken here says little about the year as a whole.

What does the research not tell us?

Quite a lot, and the gaps are as useful to know as the findings. The table separates statements the published work supports from ones it does not.

The last row is the one people find hardest to accept. Health Canada states that radon differs from house to house, including between similar houses side by side, and that testing is the only way to know a home's levelsource. Research can tell a city how worried to be. It cannot tell a household what is in its basement.

Why does a high radon level matter?

Because of one long-term health risk. Health Canada lists an increased risk of lung cancer as the only known health effect of radon, and describes the risk as long-term, not immediate, depending on the level, the length of exposure and smokingsource. It identifies radon as the leading cause of lung cancer among people who have never smoked and the second leading cause overall, after smokingsource.

Dr. Goodarzi has put the provincial toll at roughly one new radon-induced lung cancer case every day in Albertasource. That figure is his, not ours. We repeat it because it explains why researchers in this city have spent years measuring basements.

The calm reading of all this: a high result is not an emergency tonight, and it is not something to leave indefinitely either. Above the guideline, Health Canada recommends reducing the level within one year, and sooner the higher it issource. Radon gives no sign of its presence, so the decision has to start from a measurement.

Is Calgary worse than the rest of Canada?

The published figures do not settle that, because they count different things. The same national survey estimated that about 1 in 5 residential buildings in Canada (17.8%) are at or above 200 Bq/m³source. The Calgary-area figure quoted earlier on this page counts houses and the national one counts residential buildings, so the two sit side by side here and are not directly comparable.

So the honest answer to the question in the title is that radon is a Canadian problem which Calgary shares in full. What sets the city apart is how closely it has been studied: several of the papers quoted on this page were led from the University of Calgary. That is a reason for confidence in the numbers.

What should a Calgary homeowner do about it?

Measure first. Health Canada recommends testing every home, wherever it is and whatever kind of building it issource, and it recommends a measurement of 3 to 12 months, with 91 days as the minimumsource.

• Not tested yet: start a long-term test this heating season. Our step-by-step guide to testing a home covers the method, and professional radon testing in Calgary covers having it done for you.
• Tested, with a result under the guideline: keep the report. No level is free of risk and lower is better, so some owners in the upper part of that range still choose to act.
• Tested, with a result above the guideline: read how radon mitigation works in Calgary homes and plan the work within the year Health Canada recommends, sooner if the level is high.
• Holding a result and unsure what it means: the radon result checker places it against the guideline.

Health Canada reports that a reduction system can usually be installed in less than a day and lowers radon by more than 80% in most homessource. The problem described on this page is common. It is also one of the more fixable ones a house can have.