CROSS-CANADA SURVEY OF RADON EXPOSURE IN RESIDENTIAL BUILDINGS OF URBAN AND RURAL COMMUNITIES

Made possible by funding from: Canadian Institutes of Health Research – Healthy Cities Research Initiative; Health Canada’s National Radon Program; the Alberta Real Estate Foundation; and the Canadian Cancer Society.

Report prepared and published by the: Evict Radon National Study team (including researchers at the British Columbia Cancer Agency, the Arnie Charbonneau Cancer Institute at the University of Calgary, University of Saskatchewan, and Dalhousie University) in collaboration with the staff and researchers at Health Canada, CAREX Canada, and the British Columbia Centre for Disease Control.

PREFACE

Radon is an important human health hazard. Between 2007 and 2012, Health Canada’s National Radon Program undertook an initiative to characterize the problem by measuring radon concentrations in thousands of homes across the country, generating a large national data set to support what was then the most up-to-date and comprehensive assessment of residential radon exposure in Canada. Since that time, we’ve seen changes in the way people build, renovate, and use their homes, including in response to influences such as climate change and high energy costs. At the same time, commercial radon testing has become widely available, enabling more individuals to test their homes and facilitating research studies.

As new data accumulates, researchers have been seeing a trend towards higher radon levels in many parts of Canada, demonstrating a need to update our understanding of radon within our diverse and developing communities. To this end, Health Canada welcomes this report. The results presented herein represent a major collaborative effort to create and review the largest Canadian radon dataset to date, providing a picture that better reflects the realities of radon exposure in 2024, and providing authorities with data and evidence to more effectively address the challenge of protecting public health. 

-Health Canada

EXECUTIVE SUMMARY

The 2024 Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities summarizes the findings of a multi-year project. This project was led by a consortium of researchers comprised of the Evict Radon National Study team (including researchers at the British Columbia Cancer Agency, University of Calgary, University of Saskatchewan, and Dalhousie University) in collaboration with the staff and researchers at CAREX Canada, the British Columbia Centre for Disease Control, and Health Canada’s National Radon Program.

The aims of this project were to (i) estimate the proportion of the Canadian population living in residential properties with radon gas levels above the Canadian guideline level of 200 Bq/m³ when radon mitigation is recommended, and the World Health Organization (WHO) reference level of 100 Bq/m³; (ii) understand how radon exposure in Canada differs by region, community, and residential building types; and (iii) empower Canadians to make informed decisions about health and policy, using recent and reliable data that accurately reflects Canada today.

It is important to emphasize that while the health risks from radon exposure below the Canadian Guideline or WHO reference level are small, there is no level that is considered risk-free. It is the choice of each individual to decide what level of radon exposure they are willing to accept. Regardless of radon level, any action taken that reduces an individual’s radon exposure corresponds to a decrease in their health risk.

All radon test outcomes included in the 2024 Cross-Canada Radon Survey were from tests carried out by people living in Canada following instructions consistent with best practices for radon testing indicated by Health Canada and the Canadian National Radon Proficiency Program (C-NRPP). All results encompass the outcomes from long-term alpha track radon tests provided by an accredited radon test supplier, with 99.7% of tests occurring between 2009 and 2024. Multiple groups supplied the source data used for this survey, including The Evict Radon National Study, Health Canada, Radonova Inc., the British Columbia Centre for Disease Control, and multiple provincial Lung Associations. All data was assigned to a Statistics Canada census division, and expressed as a function of region, urban-to-rural community type, and building design.

The results from this study indicate that approximately 1 in 5 (17.8%) of people residing in Canada live in buildings with radon levels at or above the current radon guideline of 200 Bq/m³. An additional 24.2% of people reside in houses with radon levels between 100-199 Bq/m³. These estimates are greater than the previous Cross-Canada Survey results obtained in the late 2000s, which indicated 6.9% of houses that at the time were at or above 200 Bq/m³. Overall, 83.6% (245/293) of current Census Divisions had at least one house whose radon level was at or above 200 Bq/m³. Of the 171 Census Divisions in which we obtained at least 25 radon readings, there were 51 Census Divisions where approximately 25-50% of houses contained radon at or above 200 Bq/m³.

The average radon level of a Canadian residential building (including single-detached, semi-detached, and row-style residential houses) is 84.7 Bq/m³, weighted by the distribution of these houses across Canadian regions and urban-to-rural communities, based on data from the 2021 Canada Census. The 2024 survey finds that radon levels vary significantly across regions, urban-to-rural communities, and by building design types. There are areas of Canada where high indoor radon levels are more prevalent, including Atlantic Canada, Prairie Canada, the North, and the British Columbia Interior.

Among different building types, single-detached houses are more likely to be at or above 200 Bq/m³ relative to semi-detached houses, which are more likely to be at or above 200 Bq/m³ relative to row-style houses. While limited data was available for multi-family housing (i.e. apartments), current information suggests that some of these property types have high radon exposure. Residential buildings of any type in rural Canadian communities (meaning population centres of 1-29,999 people) generally demonstrated a greater likelihood of being at or above 200 Bq/m³ relative to urban equivalents.

The percentage of houses with residential radon levels at or above the current radon guideline of 200 Bq/m³ is generally high across Canadian municipalities, with four of Canada’s largest cities with populations exceeding 1 million people (Montreal, Ottawa-Gatineau, Calgary, and Edmonton) demonstrating a 1 in 6 chance and weighted average residential radon levels between approximately 80-110 Bq/m³.

Based on available data in this report, Canadian towns and cities where at least one quarter to half of residences contain radon at or above 200 Bq/m³, include Whitehorse (YT), Nelson (BC), Kelowna (BC), Prince George (BC), Vernon (BC), Penticton (BC), Trail (BC), High River (AB), Okotoks (AB), Strathmore (AB), Regina (SK), Brandon (MB), Winnipeg (MB), Thunder Bay (ON), Kingston (ON), Sherbrooke (QC), Bathurst (NB), and Halifax (NS). Many of these municipalities contain houses with average residential radon levels greater than 130 Bq/m³. Therefore, we recommend that public health stakeholders who are active in these communities take particular care to increase the promotion of radon awareness and access to radon reduction resources at this time.

There are no areas of Canada that are ‘radon-free’. The results of this study can be used by federal, provincial, and municipal governments as well as health, occupational, and building safety professionals to help prioritize radon outreach and education efforts, and to encourage testing and remediation where necessary.

It is important to note that the outcomes reported in this survey expand upon and validate the results of the previous cross-Canada survey, in that, even for regions where average results indicate a lower incidence of elevated radon, there are houses containing radon at or above Health Canada and/or WHO reference levels for radon action. As such, the results in this report should not be used as a tool to determine personal radon risk potential, or to decide whether to test a specific household for radon. 

Since radon levels are influenced by both building features and the behaviour of the people occupying it, the only way to know if a house that people are living in has an elevated level of radon is to test, regardless of region or community.
The 2024 Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities represents an important new starting point in reporting residential radon exposures in Canada on a more regular timeline, and we are committed to consistent updates of Canadian radon exposure statistics as new data becomes available. We highlight the near-term need to improve radon test information across the Canadian North, especially in the province of Nunavut, and for multifamily housing. Additional radon test information connected with key geographic and building type data is also required for communities in census divisions that we have, as yet, been unable to report radon exposure estimates.

AN INTRODUCTION TO RADON and its HEALTH EFFECTS

• What is radon gas, and how is it formed?

Radon is a colourless, odourless radioactive gas that is the second largest contributor to lung cancer worldwide, and the leading cause of lung cancer among people who have had a limited tobacco smoking history or have never smoked tobacco at all[1–3].

Radon gas is produced deep under the ground. It starts when uranium and thorium, which are found in rocks and soil, break down; this process, called “radioactive decay,” changes these elements into radium, a solid radioactive metal. Radium then breaks down further into radon gas. This radon gas mixes with other gases in the soil and can quickly move from underground to the Earth’s surface as part of what is called “free-phase” gas movement.

Soil gases containing radon constantly migrate to the surface of the Earth, where they escape into outside air and are diluted quickly in the atmosphere. Radon emerging at the Earth’s surface may also enter buildings that are in direct contact with the ground, where dilution is limited, and high radon levels can accumulate.

Once formed, radon gas undergoes further decay within only a matter of days, releasing ‘alpha’ (α) particle radiation and precipitating as solid ‘radon decay products.’ For any given amount of radon gas entering a building, it takes just under four days for half of that gas to become a solid radon decay product.

• Why is breathing in high amounts of radon gas so harmful?

When radon gas and/or its decay products are inhaled into the lungs, the lung cells are directly exposed to alpha radiation. Exposure to this radiation increases the risk of those lung cells transforming into a cancer, especially if they are exposed over many years and/or to very large amounts of radon.

Alpha radiation is made up of ‘alpha particles’ that move at 15,000 kilometres per second with enough energy to break apart and damage most molecules they encounter. For example, a single alpha particle emitted by decaying radon has enough energy to produce a microscopic dent in impact-resistant CR39 polycarbonate plastic. Four alpha particles are emitted during the decay of every radon atom and its subsequent short-lived decay products (see the infographic below for additional details about radon decay). Thankfully, alpha particles cannot move very far. Inside our lungs, however, radon decay emits alpha particles right next to very sensitive lung cells that absorb oxygen from the air. These particles may hit the cells’ DNA—the fundamental building block of all life on Earth.

Infographic showing the radioactive decay series of the substances that lead to the formation of radon gas. Uranium (U) decays to radium (Ra), which are all solids that remain under the ground. Radon – the only gas in this series of events – can move to the surface, entering outside and indoor atmospheres, and then follows a radioactive decay series that transforms it into solid radioisotopes starting with polonium (Po) and progressing into stable lead (Pb) over many decades. Once inhaled, these ‘radon decay products’ can become embedded in our lungs (and bodies), emitting radiation for prolonged periods.

Alpha radiation can damage the DNA in the cells of our lungs, increasing the risk of genetic mutation. Genetic mutations triggered by radon exposure have the potential to alter how lung cells control their growth, increasing the risk of developing lung cancer later in life [4,5]. 

Radon gas is considered our most significant source of lifetime radiation exposure. Evidence indicates that radon exposure is responsible for 1 in 6 of all lung cancers [6], which equates to about 1 in 50 of all cancer deaths. The high rate of mortality associated with lung cancer is because it remains challenging to treat since it is typically diagnosed very late, at a cancer stage where it has already spread beyond the lungs to other parts of the body.

A brief history of radon discovery and how we know it impacts human health.

1940-1970s – Radon exposure in underground miners.

In the 1940s, Dr. Wilhelm C. Hueper, a USA National Cancer Institute pathologist, highlighted the potential health risks of radon within an occupational setting. Hueper’s research and the subsequent 1942 report “Occupational Tumors and Allied Diseases” concluded that radon inhalation was a probable cause of lung cancer[14,15] and that radon was likely responsible for the premature deaths of more than 50% of European miners within 10-20 years of employment. Remarkably, the report had little impact on safety regulations for miners in the workplace at the time but marked the start of a period of a more comprehensive understanding of radon as a public health concern in occupational settings. In time, the link between radon and lung cancer became evident through the larger-scale studies of lung cancers in uranium miners in Canada, East Germany, and Czechoslovakia during the mid-20th century[16–19]. High levels of radon gas were prevalent in early Cold War-era uranium mines, and miners exposed to these conditions showed significantly increased rates of lung cancer. These large epidemiological studies provided the first conclusive evidence of the carcinogenic nature of radon to humans.

During the winter of 1984, when construction engineer Stanley Watras (pictured ABOVE, with his family) entered the Limerick County nuclear power plant in Pennsylvania, USA, he unexpectedly set off the radiation contamination alarms. The event was considered remarkable as there was no nuclear material on-site because the plant was still under construction, and when Mr. Watras left at the end of the day, the alarms did not sound. Further investigation by authorities found that the indoor air of his nearby residential house contained an astonishing 99,900 Bq/m³ radon gas and that the source of the radiation that triggered the alarms was likely large quantities of radon decay products attached to his clothing[20]. The incident led to widespread radon testing in residential properties across the United States and other countries, prompted the development of residential radon testing and mitigation technology, and underscored the significance of residential radon exposure as a public health issue[21].

1988 – IARC classification of radon inhalation as cancer-causing exposure.

The International Agency for Research on Cancer (IARC) is the specialized cancer agency and part of the World Health Organization (WHO). Their main objective is to coordinate and conduct research on the causes and prevention of cancer globally. One of the agency’s key roles is to assess the cancer-causing (carcinogenic) risks of various substances and exposures and classify these risks accordingly. A Group 1 carcinogen is, based on all available evidence, a substance that is conclusively cancer-causing in humans. Ultimately, in 1988, the IARC categorized radon and radon decay products as an IARC Group 1 carcinogen[22].

1990s-2000s – Linking residential radon exposure to lung cancer.

The epidemiological study of how radon exposure within the residential built environment (homes) relates to lung cancer in large populations was carried out throughout the 1990s-2000s. Like the earlier work on underground uranium miners, these very large studies were crucial to understanding whether long-term exposure to residential radon increased the risk of developing lung cancer. By 2005, three major studies on this were released, including (i) a pan-European study where collaborative analysis combined data from thirteen separate European studies, encompassing 7,148 people experiencing lung cancer and 14,208 healthy volunteer controls[17]; (ii) seven pooled North American case-control studies involving 3,662 people experiencing lung cancer and 4,966 health volunteer controls[23]; and (iii) two large case-control studies conducted in China, which included a total of 1,050 people experiencing lung cancer and 1,996 health volunteer controls[24]. Collectively, all these studies found that the average radon concentration in the homes of people diagnosed with lung cancer was higher than that of the healthy volunteer control groups and consistently showed that population centres with higher residential radon levels have higher lung cancer rates. Overall, there was a statistically significant increase in excess relative risk of lung cancer of 16% per 100 Bq/m³ increase in long-term average radon exposure.

REGION. Radon gas can move easily through cracks, faults, and openings in the ground. It rises to the surface at a rate dictated by the geology of a given location. In Canada, all regions have some radon-generating geologic source material, with most regions displaying average indoor air radon levels at the high end of those documented for other global regions[32]. In part, high indoor radon occurs in Canada because our geology has some of the world’s most abundant reserves of uranium-containing (and thus radon-generating) minerals. Therefore, when thinking about radon risk in a given household, it is important to consider region.

COMMUNITY. Both earth and atmospheric factors influence the movement of radon upwards and into buildings, as well as ground-penetrating human infrastructure such as groundwater wells. Recent research[33] indicates that rural communities relying on groundwater wells have properties with higher radon levels compared to nearby urban communities. The higher radon trend for more rural (lower population density) communities has been demonstrated across Canadian regions, so when accounting for factors contributing to the risk of radon exposure within a given household, it is important to consider community type.

BUILDING DESIGN. Over the past decade, a variety of research studies have shown that Canadian buildings are experiencing high and increasing levels of radon gas. The design, construction, and ventilation systems of a building are key factors that impact indoor radon levels[33–35]. For example, recent research indicates a trend of higher radon levels in newer residential buildings in Canada[34]. It is important to recognize that how our properties are built is a function of continuously evolving build practices and regulatory codes and that not all new residential properties in the world necessarily contain higher radon. For example, in Sweden – a comparable cold-climate nation to Canada – indoor air radon levels have decreased in new buildings over time. Thus, when accounting for factors contributing to the risk of radon exposure within a given household, it is important to consider a building’s design type, age, and other property metrics.

Radon testing and reduction (mitigation of a building to reduce radon entry)

Residential radon exposure is highly variable between populations and individuals but is also highly modifiable and, therefore, preventable. To understand whether a given building contains sufficient radon levels to be of concern, it is first recommended that Canadians test all residential properties which they occupy for substantial periods of time. For most people, this will be their primary place of residence. As radon is invisible to human senses, performing a long-term radon test is the only way to determine if a given building has high radon levels.

Testing a residential building for radon is relatively easy and widely accessible to the public through commercial and non-profit sector radon testing options. One of the most effective and reliable tests is called an ‘alpha track’ device, which requires no electricity and is often in the shape of a small hockey puck or ant trap. The general advice is ‘to test the air you breathe’ so the radon test devices should be placed in the lowest level of the home, where an occupant spends four or more hours on average each day. A long-term radon test is required to obtain a reliable outcome, with test period recommendations typically being 90 or more days to reduce the chances of an undesirable false-low or false-high outcome [36].

Taking action to reduce radon levels at or greater than 100 Bq/m³ is recommended by various health organizations, including the World Health Organization, to reduce the risk to individuals living in high radon-containing built environments. The Canadian Radon Guideline I level is 200 Bq/m³ and is considered the actionable threshold [6], with specific advice to reduce exposure to as low as reasonably achievable. Action to reduce radon levels above the guideline is strongly advised, and the level of urgency increases as radon levels rise. While the health risk from radon exposure below the Canadian Guideline is small, there is no level that is considered risk-free. It is the choice of each individual to decide what level of radon exposure they are willing to accept. Regardless of radon level, any action taken that reduces an individual’s radon exposure corresponds to a decrease in their health risk.

If a radon test outcome is considered high (at or exceeding 100-200 Bq/m³) or otherwise unacceptable by the occupants, then a radon reduction retrofit (commonly called radon mitigation) can be done. Thankfully, the technology needed to retrofit a residential building to permanently reduce radon entry is well-established, highly effective in Canada, and relatively quick to install.

SURVEYING RESIDENTIAL RADON IN 21st CENTURY CANADA

The purpose of the 2024 Cross-Canada Radon Survey

The purpose of the 2024 “Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities” is to gather long-term (three months or longer) indoor radon test results that have been carried out in a large number of residential buildings from across diverse Canadian communities ranging from the most densely populated urban areas to the least populated rural regions, in order to:

• Estimate the proportion of the Canadian population living in residential properties with radon gas levels above the Canadian guideline level of 200 Bq/m³ and WHO recommended level of 100 Bq/m³.
• Understand how radon exposure in Canada differs by region, community, and residential building types.
• Empower Canadians to make informed decisions about health and policy, using recent and reliable data that accurately reflects Canada today.

Survey Design 

The following list summarizes important-to-understand features of the 2024 survey:

• All radon results are from long-term alpha track tests (of 90 days or more in duration) performed by people living in Canada advised to place their test on the lowest floor (storey) of a residential property in which a person spends an average of four or more hours per day. 
• The majority of radon testing took place in winter heating months, with any outcomes based on radon testing periods that included a summer month being primarily in the context of a longer radon testing period of six months to a year.
• Both homeowners and renters were eligible to participate in radon testing for this survey. Similarly, people living in multi-story buildings, Indigenous reserves, or any other type of property or community were eligible to participate.
• Participants were recruited through a combination of geographically targeted direct invitation, convenience sampling, and/or arbitrary invitation administered by a wide variety of organizations and in English and/or French, depending on the organization. No quotas were used.
• In terms of communication, participants were informed of the opportunity to perform a radon test in their house via a combination of in-person radon awareness events, social media, paid online advertising, direct phone calls, and/or word-of-mouth.
• A mixture of paid-for, cost-subsidized, and at-cost radon test kits were deployed, depending on the specific group or organization administering the radon tests to participants.
• Data is associated with basic information regarding general location, test period, and other property type data, with a majority of data points also linked to exact geographic location and precise property metrics.
• Radon results are sorted into census divisions, as defined by Statistics Canada, rather than other potential units such as provincial health regions. Where possible, household radon results within a census division were further linked to a smaller census sub-division, and/or metropolitan area, and/or designated place.

Quality controls during radon testing

To our knowledge, all data included in the 2024 Cross-Canada Radon Survey was carried out according to the best practices for radon testing advised by Health Canada and indicated by the Canadian National Radon Proficiency Program (C-NRPP). At a minimum, data are from long-term alpha track radon test devices provided by an accredited supplier who also performed internal quality controls during device production, test analyses, and provided participants (and/or groups administering the radon testing programs for a community) with a certified radon test outcome. Please see the methodology section for more details.

For all radon test programs administered by agencies such as Health Canada or the Evict Radon National Study teams, the radon testing process is verified to have included quality controls to determine the reliability of results in terms of accuracy and precision, which are explained in the graphic above. To illustrate quality controls used to assess accuracy and precision, data from radon tests conducted by the Evict Radon National Study team are shown in the examples below.

To assess radon test ACCURACY (how close a given set of measurements are to their true value), we deployed ‘blanks’, which are tests put through the postal system without being deployed in a house, to control for test quality and background signal, as well as ‘spikes’, which are tests exposed to a known amount of radon in a certified radon chamber, as an independent check of the laboratory analysis results.

To confirm PRECISION, which is how close otherwise identically performed measurements are to each other, duplicate radon tests were provided at no cost to randomly selected participants, and then deployed at the same time and in the same place.

For these true duplicates (illustrated in panel A of the figure above), identical radon tests were placed no more than 10 cm apart and carried out at the same time in the same room within a house.

We also examined tests that were conducted by participants in the same house and at the same time, but in different rooms on the same floor, or in different rooms on different floors (see panels B and C of figure to the above). While these are not true duplicates, they provide a good idea about similarities and differences in radon testing performed within different locations within the same house.

IN SUMMARY, we have a high degree of confidence in the radon test outcomes that form the basis of this survey, as the accuracy controls indicate that tests reflect known amounts of radon 99.5% of the time. The precision controls (true duplicates) indicate that two tests performed together obtain the same outcome 97% of the time.

Achieving a balanced representation of Canadian residential radon levels

By linking all residential radon test results with a specific Statistics Canada ‘census division’, the radon test outcomes for different building design types in this survey could be reported as a function of geographic region, and/or urban-to-rural community type.

Why was it important to do this?

Grouping the readings in this way allowed us to use all three of these specific categories to ensure the average radon outcomes reported in this survey were appropriately weighted, meaning that they better represent how residential houses in Canada actually exist, as opposed to just those households who performed a radon test.

By applying statistical weighting of all data to calculate average radon levels, we aimed to ensure that results are as representative as possible of the current distribution of Canadian housing stock as it has been measured by the most recent (2021) Canada Census (for more details, see BOX #5).

In short, the 2024 Cross-Canada Radon Survey was designed so that radon information about indoor radon concentrations reflects the mix of residential housing that exists in Canada today. In the following sections, we define the categories of data classification used in this report.

Defining Region Type Categories

It is important to note that, for statistical purposes of preparing the data for this report, we were required to group the provinces of Canada into five larger regions that either include multiple provincial jurisdictions grouped together or, in one case, part of a provincial split between two regions. Please see the Box #6 for a more detailed explanation.

These five regions reflect areas of Canada where indoor air radon levels demonstrate a degree of consistency (for example Ontario and Quebec), or acknowledge large differences within a province (for example the BC coast versus BC interior), and/or are already commonly understood geographical groups (for example, Prairie or Atlantic Canada).

The five regions are:

• Atlantic (NL, PE, NS, NB)
• Central (ON and QC)
• Prairies and NWT (AB, SK, MB, NT)
• Pacific Interior and Yukon Territory (Northern and Interior BC, eastern Fraser Valley from Chilliwack onwards, and YT)
• Pacific Coastal BC and Island (Vancouver Island, Sea-to-Sky Corridor, Sunshine Coast, the northern BC coast, Lower Mainland and western Fraser Valley up to Chilliwack)

Defining Building Design Type Categories

The four major building design type categories we used are:

• Single-detached Properties
• Semi-detached (Duplex) Properties
• Row (Attached) Properties
• Other (including Multi-Family Dwellings, Cabins, Mobile Homes, etc.)

Of these, we had access to only limited data for the ‘other’ category that included multi-family dwellings such as apartments. As such, a majority of radon test outcomes discussed in the 2024 report will be restricted to the first three categories, with a special section that discusses preliminary outcomes for multifamily residential buildings.

Defining Community Type Categories

Using Statistics Canada’s definitions of Population Centres and Designated Places that include census metropolitan and rural areas, all household radon readings were assigned to these two community group categories.

• More “Urban” communities, which are a combination of cities and large towns. Specifically, large towns are formally classified as communities that have a population of 30,000-99,999 people, while cities are communities with a population greater than 100,000 people. The grouping acknowledges that the infrastructure of these more urban communities (and the experiences of the people living there) are generally distinct from those of lower population densities. For simplicity, moving forward, we will refer to all city and large town communities as “urban”.
• More “Rural” communities, which are a combination of small towns and rural areas. Specifically, rural areas refer to communities/isolated residences with a population of 1-999 people, while small towns are communities with a population of 1000-29,999 people. The grouping acknowledges that the infrastructure of these more rural communities (and the experiences of the people living there) are generally distinct from those of higher population densities. For simplicity, moving forward, we will refer to all small towns and rural/isolated communities as “rural”.

Glossary and definitions of other important terms

As discussed above, Statistics Canada 2021 census data was used to re-weight our radon data so that it best reflected the “reality” of radon exposure in Canada in the 2020s. To achieve this, all household radon results were first sorted into Census Divisions (with other units including Census Subdivisions, Census Agglomerations, Census Metropolitan Areas (urban areas), and Designated Places (rural areas)).

The glossary below will help the reader understand what is meant by all these terms (and for more details, please see Statistics Canada):

• Census Agglomeration: An area formed by one or more nearby municipalities with a core population (i.e. the population of the largest municipality in the group) of at least 10,000 people. All areas within a Census Agglomeration that are not within the border of a population centre or designated place are considered rural areas.

• Census Division: are one of the most stable administrative areas of intermediate geographic size, between the provincial/territory and municipality levels. They are most often used in long-term studies. Census divisions are used for regional planning and managing common services, and are established by provincial law, or in cooperation with Statistics Canada and provincial/territorial authorities.

• Census Metropolitan Area: An area formed by one or more nearby municipalities with a total population of at least 100,000 people and the core population of at least 50,000 (i.e. the population of the largest municipality in the group). All areas within a Census Metropolitan Area that are not within the border of a population centre or designated place, are considered as rural areas.

• Census Subdivision: A geographic area that is provincially or territorially legislated as a municipality, or areas that are treated as a municipal equivalent for statistical purposes.

• Designated Place: An area that does not meet the criteria of a population centre but is a small community or place of importance. If a designated place has a population of fewer than 1,000, it is considered a rural area.

• Population Centre: A geographic area centred on a municipality with a population of at least 1,000 and a population density of at least 400 people per square kilometre. If an area falls outside the population centre, and is not a designated place, for the purposes of this report, it is considered a rural area.

• “Urban”: Communities that are large towns and cities with populations of 30,000 people or greater

• “Rural”: Includes small towns, villages, hamlets and isolated properties where the population ranges from 1 person to 29,999 people in the community.

RADON LEVELS FOR CANADA AS A WHOLE, AND BY BUILDING TYPE

A total of 69,478 unique long-term radon test outcomes were assembled for this survey, with 68% having been completed in a basement or cellar (below grade floor of property), 30% completed on the ground floor or walkout level (floor or property entirely or partly level with the ground), and 2% on an upper floor at least one storey above ground level. The average radon test duration was a geometric mean of 126 days (approximately 4 months), with 99.7% of tests carried out between calendar years 2009-2024. The complete ‘raw’ outcomes of the data collected for the 2024 Cross-Canada Radon Survey are shown below.

Residential radon across Canada, weighted by region, community, and building type

When all Canadian data (for all regions, communities, and building types) are combined in a manner that is balanced by distribution of these factors as established by the 2021 Canada Census, the geometric average household radon level was 84.7 Bq/m³, with just under 1 in 5 (17.8%) of single-detached, semi-detached, and row-type residential buildings containing radon levels that are at or over 200 Bq/m³.

KEY FINDING = Nearly 1 in 5 Canadian single-detached, semi-detached, and row-type residential buildings are at or above 200 Bq/m³ radon

Overall, 83.6% (245/293) of Census Divisions had at least one house whose radon level was at or above 200 Bq/m³. Of the 171 Census Divisions in which we obtained at least 25 radon readings, there were 51 Census Divisions where approximately 25-50% of houses contained radon at or above 200 Bq/m³. The highest Canadian residential radon level observed within this dataset was 32,321 Bq/m³.

These outcomes emphasize that Canadian radon exposure in residential buildings is a serious public health concern. Based on the total number of single-detached, semi-detached, and row-type residential buildings and the average number of occupants per house in Canada at this time, the observation that nearly 1 in 5 houses contain radon levels that are at or exceed 200 Bq/m³ equates to an estimated 4.6 million out of 25.7 million people (living in these home types) who would benefit most from radon reduction to lower their exposure below current radon action guidelines. Further to this, an additional 1 in 4 (24.2%) of Canadian houses record radon levels between 100 and 199 Bq/m³, which is important to note as 100 Bq/m³ is the WHO reference level [17,23,24]. Thus, 42% of the Canadian house types we report on will contain radon that is at or exceeds 100 Bq/m³.

Radon levels across different Canadian residential building types

Radon levels in a building can vary significantly depending on various factors, including how that building is designed. To understand how differing building structures influence radon concentrations in Canada, household radon levels were sorted to allow a detailed examination of trends of high radon by building type. The three building type categories listed below encompass 69.6% (25.7 million people) of the total population of Canada (36.99 million people in the 2021 Census), with multifamily dwellings (such as apartments) making up the remaining 30.4%.

Single-detached houses: Single-detached houses, which encompass 53% of Canadian residences, exhibit the highest average indoor radon levels at 93.4 Bq/m³.  In Canada, 1 in 5 (20.4%) Single-detached houses contain radon at or over 200 Bq/m³. 1 in 4 (26.4%) of these dwellings record levels between 100 and 199 Bq/m³.

• 1 in 5 Single-detached properties are at or above 200 Bq/m³ radon

Semi-detached houses: Semi-detached houses represent 10% of all Canadian residences, and show average radon levels of 61.5 Bq/m³. On average, semi-detached houses contain lower levels of indoor radon than detached houses. In Canada, 1 in 9 (11.1%) semi-detached houses contain radon at or over 200 Bq/m³. 1 in 5 (18.8%) semi-detached houses record levels between 100 and 199 Bq/m³.

• 1 in 9 Semi-detached properties are at or above 200 Bq/m³ radon

Row-style (attached) houses: Row type houses represent 7% of all Canadian residences and show average radon levels of 51.8 Bq/m³. On average, row houses contain lower levels of indoor radon than detached or semi-detached houses, but these levels are still considered high in a global context. In Canada, 1 in 13 (7.9%) for row houses contain radon at or over 200 Bq/m³. 1 in 6 (15.6%) row houses record levels between 100 and 199 Bq/m³.

• 1 in 13 Row-style properties are at or above 200 Bq/m³ radon

The pan-Canadian data underscores significant differences across residential building types that impact indoor radon levels. These outcomes also emphasize that assessing the probability of high radon in the Canadian residential built environment needs to carefully consider housing type wherever possible.

RADON LEVELS IN CANADA, BY URBAN TO RURAL COMMUNITY

As many different factors influence indoor radon levels, the analysis of household radon in Canada can be broken down further into separate variables such as community type. In this section, we report Canadian residential radon data for two distinct types of communities, those that are considered (i) ‘Urban’ and (ii) ‘Rural’ based on community population size.

• 1 in 6 Urban community properties are at or above 200 Bq/m³
• 1 in 4 Rural community properties are at or above 200 Bq/m³

IMPORTANT: As a reminder, whether a community is considered more “Urban” versus more “Rural” is entirely dependent on population size. Our rural community group includes small towns, villages, hamlets and isolated properties where the population ranges from 1 person to 29,999 people in the community. By contrast, communities that are large towns and cities with populations of 30,000 people or greater are classed under the urban community group.

Urban communities: 62% of Canadian detached, semi-detached, and attached residences are found in more urban communities. Of these, 53% are in cities of 100,000 or more people, and 9% live in large towns of 30,000-99,999 people.

The average urban household radon levels were found to be 86.3 Bq/m³, with 1 in 6 (17.4%) of these buildings containing radon levels at or above 200 Bq/m3, while 1 in 4 (26.4%) were between 100 and 199 Bq/m³. Within more urban communities, radon levels across building types were:

• 1 in 6 Urban Single-detached properties are at or above 200 Bq/m³
• 1 in 8 Urban Semi-detached properties are at or above 200 Bq/m³
• 1 in 11 Urban Row-style properties are at or above 200 Bq/m³

Rural communities: 38% of Canadian detached, semi-detached, and attached residences are found in rural communities. Of these, 15% are in small towns of 1,000-29,999 people, and 23% live in villages, hamlets or isolated properties of 1-999 people.

The average rural household radon levels were found to be 99.9 Bq/m³, with 1 in 4 (23.8%) of these buildings containing radon levels at or above 200 Bq/m³, while 1 in 4 (25.7%) were between 100 and 199 Bq/m³. Within rural communities, radon levels across different building types were:

• 1 in 4 Rural Single-detached properties are at or above 200 Bq/m³
• 1 in 8 Rural Semi-detached properties are at or above 200 Bq/m³
• 1 in 8 Rural Row-style properties are at or above 200 Bq/m³

From these findings, people living in Canadian rural communities experience higher average radon levels relative to those in urban communities, and a greater proportion of the rural Canadian population lives in houses with radon levels at or exceeding 200 Bq/m³. Canadian scientists have recently suggested that, in addition to differences in single-detached houses being more common in rural areas, another factor that contributes towards the higher rural radon trend is that rural community houses are more likely to be near one or more drilled groundwater wells. In this scenario, borehole gaps surrounding well casings may increase how easily underground radon can migrate up towards the soils underneath properties. Thankfully, the recommended solution to high radon in a rural property (following a standard radon mitigation process for the house) remains effective and no direct action regarding wells is suggested at this time.

RADON LEVELS ACROSS CANADIAN REGIONS, AT-A-GLANCE

The total area of Canada is 9,985 km², with a major factor influencing indoor air radon levels of residential buildings being the geological source of radon in the ground, meaning the amount of radium, thorium and uranium in the rock and soil of a given geographic area.

In the following sections, we provide average radon for residential properties grouped across five regions: Atlantic Canada, Central Canada, The Prairie and Northwest territories, Pacific Interior and Yukon and finally, Pacific Coastal Canada shown in the graphic below.

The KEY FINDINGS for a Canadian regional overview of residential radon levels are:

• 1 in 3 Atlantic properties are at or above 200 Bq/m³
• 1 in 6 Central properties are at or above 200 Bq/m³
• 1 in 5 Prairie and NT properties are at or above 200 Bq/m³
• 1 in 3 Pacific Interior and YT properties are at or above 200 Bq/m³
• 1 in 75 Pacific Coastal Canadian properties are at or above 200 Bq/m³

IMPORTANT: As a reminder, these groupings were based on the following considerations: (i) commonly-grouped geographic areas (e.g. the Prairies, Atlantic region), (ii) areas with relatively comparable radon levels (e.g. Ontario and Quebec), (iii) a need to combine data for provinces or territories with relatively smaller populations in order to weight outcomes, and/or (iv) a need to divide some regions where radon levels were highly divergent within a province (e.g. British Columbia). At this time, we were not able to obtain sufficient radon results for the territory of Nunavut to report outcomes, and so regrettably this important area will need to be studied further and reported on at a later date.

RADON LEVELS IN ATLANTIC CANADA

The Atlantic Canadian Region encompasses the provinces of Nova Scotia (NS, pop. 969,383), New Brunswick (NB, pop. 775,610), Newfoundland and Labrador (NL, pop. 510,550), and Prince Edward Island (PEI, pop. 154,331), and contains 8% of all Canadian residential building types reported on in this study.

1 in 3 (33.3%) of Atlantic Region households contain radon levels at or above 200 Bq/m³, with an average radon level of 116.8 Bq/m³, the second-highest average level of household radon among all five Canadian regions. In total, 22.3% of Atlantic Canadian residential properties contained radon in the 100-199 Bq/m³ range.

FOR PROVINCES in this regional group, we find that radon levels in residential buildings are broadly comparable and generally considered high, with geometric mean radon levels ranging between 80.8 Bq/m³ in PEI (note: unweighted value), to 90.1 Bq/m³ in NL (note: unweighted value), to 99.4 Bq/m³ in NB (weighted value), and 125.3 Bq/m³ in NS (weighted value). The likelihood of a building containing at or over 200 Bq/m³ ranges between 1 in 5 for NL and PEI (unweighted values), to 1 in 4 (24.6%) for NB (weighted value) and more than 1 in 3 (36.8%) for NS (weighted value). Please note, we aim to report fully weighted radon outcomes for all Canadian provinces in a future update to this report.

IN SUMMARY, the residential radon statistics of Nova Scotia, New Brunswick, Newfoundland, and Prince Edward Island in Atlantic Canada highlight significant variations based on community setting and housing type. Atlantic rural area properties follow a national trend of having higher indoor radon when compared to more urban communities. Similarly, Atlantic region single-detached properties contain higher radon than semi-detached. Unusually, Atlantic Region row houses have higher average radon than semi-detached houses, although overall, few of them exceed 200 Bq/m³ compared to other types. Atlantic Canadian residential radon levels are amongst the highest observed for any geographic area in Canada and should be considered a priority area for radon testing and mitigation.

RADON LEVELS IN CENTRAL CANADA

The Central Canadian Region encompasses the provinces of Ontario (ON, pop. 14,223,942) and Quebec (QC, pop. 8,501,833), and contains the greatest portion (59%) of all Canadian residential building types reported on in this study.

Collectively, 1 in 6 (16.4%) of Central Region households contain radon levels at or above 200 Bq/m³, with an average radon level of 76.9 Bq/m³. In total, 22.9% of Central Canadian residential properties had radon levels in the 100-199 Bq/m³ range.

FOR PROVINCES in this regional group, we find that radon levels in residential buildings are very similar between Ontario and Quebec, with weighted geometric mean radon levels ranging between 71.9 Bq/m³ in ON, to 77.7 Bq/m³ in QC. The likelihood of a building containing at or over 200 Bq/m³ ranges between 1 in 8 (12.4%) for ON and 1 in 6 (16.7%) for QC.

IN SUMMARY, the residential radon statistics of Ontario and Quebec in Central Canada highlight significant variations based on community setting and housing type. Central Canadian rural area properties follow the national trend of having a higher indoor radon when compared to more urban communities. Similarly, Central Canadian single-detached properties contain higher radon than semi-detached, which are higher than row (attached) residential houses. The Central Canadian region has lower residential radon concentrations relative to the Atlantic, Prairie, or Pacific Interior regions of Canada. However, with 1 in 6 properties still at or above 200 Bq/m³, radon testing is still strongly advised.

RADON LEVELS IN THE CANADIAN PRAIRIES and NW TERRITORIES

The Prairie Canada and the Northwest Territory Region encompasses the provinces of Alberta (AB, pop. 4,262,635), Manitoba (MB, pop. 1,342,153), Saskatchewan (SK, pop. 1,132,505), and the Northwest Territories (NT or NWT, pop. 41,070), and contains 20% of all Canadian residential building types reported in this study.

Collectively, 1 in 5 (20.0%) of Prairie and NWT Region households contain radon levels at or above 200 Bq/m³, with an average radon level of 113.6 Bq/m³. In total, 37.2% of Prairie and NWT Canadian residential properties contained radon in the 100-199 Bq/m³ range.

FOR PROVINCES and the TERRITORY in this regional group, we find that radon levels in residential buildings are all considered high but are somewhat divergent from one another, with geometric mean radon levels ranging from 70.3 Bq/m³ in NWT (unweighted value), to 106.1 Bq/m³ in AB (weighted value), to 140.7 Bq/m³ in SK (unweighted value), and 168.6 Bq/m³ in MB (unweighted value). The likelihood of a building containing at or over 200 Bq/m³ ranges between just over 1 in 6 (16.7%) for AB (weighted value), to 1 in 5 for NWT (unweighted value), to approximately 1 in 3 for SK and MB (unweighted values). Please note, we aim to report fully weighted radon outcomes for all Canadian provinces in a future update to this report.

IN SUMMARY, the residential radon statistics of Alberta, Saskatchewan, Manitoba, and the Northwest Territories highlight significant variations based on community setting and housing type. The region follows national trends of having a higher rural area radon when compared to more urban communities. Similarly, Prairie and NWT region single-detached properties contain higher radon than semi-detached, which are higher than row (attached) residential houses. Prairie and NWT Canadian residential radon levels are amongst the highest observed for any geographic area. Radon testing and effective mitigation systems should be considered a high priority.

RADON LEVELS IN THE CANADIAN PACIFIC INTERIOR and YUKON

The Pacific Interior and Yukon Region encompasses Northern and Interior British Columbia, eastern Fraser Valley from Chilliwack onwards (estimated pop. 1,450,756), and Yukon Territory (YT, pop. 40,232), and contains 4% of all Canadian residential building types reported on in this study.

Collectively, 1 in 3 (31.6%) of Pacific Interior and Yukon Region households contain radon levels at or above 200 Bq/m³, with an average radon level of 126.9 Bq/m³, the highest level observed for all regions of Canada we examined. In total, 28.3% of Pacific Interior and Yukon Canadian residential properties contained radon in the 100-199 Bq/m³ range.

For the PROVINCIAL sub-region and the TERRITORY in this regional group, we find that radon levels in residential buildings are all considered high and comparable to one another, with geometric mean radon level being 97.3 Bq/m³ in YT (weighted value), to 125.2 Bq/m³ in the BC Interior (weighted value). The likelihood of a building containing at or over 200 Bq/m³ ranges between just over 1 in 4 (23.7%) for YT (weighted value), and 1 in 3 for the BC Interior (weighted value). 

IN SUMMARY, the residential radon statistics of northern and interior British Columbia, Chilliwack and more eastern communities in the Fraser Valley, as well as Yukon Territory, highlight significant variations based on community setting and housing type. The region reflects national trends with higher radon levels in rural areas when compared to more urban communities. Similarly, single-detached properties in this region contain higher radon levels than semi-detached, which are higher than row (attached) residential houses. Pacific Interior and Yukon residential radon levels are the highest observed nationally. Therefore, radon testing and effective mitigation systems should be considered a high priority.

RADON LEVELS IN PACIFIC COASTAL CANADA

The Pacific Coastal Canadian Region (estimated pop. 3,590,355) encompasses Vancouver Island, the Sea-to-Sky Corridor, the Sunshine Coast, the northern BC coast, Lower Mainland and western Fraser Valley up to but not including Chilliwack, and contains 9% of all Canadian residential building types reported on in this study.

Collectively, 1 in 75 (1.3%) of Pacific Coastal Canadian households contain radon levels at or above 200 Bq/m³, with an average radon level of 20.4 Bq/m³, the lowest level observed for all regions of Canada we examined. In total, 3.7% of Pacific Coastal Canadian residential properties contained radon in the 100-199 Bq/m³ range.

IN SUMMARY, the residential radon statistics of Pacific Coastal Canada, including the Lower Mainland, and Vancouver Island, show generally low residential radon levels compared to the rest of British Columbia and Canada in general. Similar to the rest of Canada, there are significant variations based on community setting and housing type, and the region follows national trends of having higher rural indoor radon concentrations versus more urban communities. While radon levels in Pacific Coastal Canada are lower on average versus other regions, this area is by no means free of risk, and residents should still be aware of potential exposure and test for radon, especially those in rural communities.

RADON LEVELS IN CANADA’S SIX LARGEST (pop. >1M) CITIES

In this section, we compile data on average household radon levels across the six Canadian metropolitan areas with populations of at least 1 million. Collectively, these six urban areas are home to 17.52 million residents of Canada, or nearly half of the entire population.

The information below is ranked in order of largest to smallest population and encompasses the broader census metropolitan areas (that is, the city itself and surrounding commuter towns) as defined within the 2021 Canada Census.

Table of Metropolitan Areas with Census Weighted Radon Outcomes

IN SUMMARY, the greatest average residential radon levels of the six largest Canadian metropolitan areas are observed in the Prairie cities of Edmonton and Calgary, with substantial levels also occurring in Montréal and Ottawa. Houses in the Toronto metro area, while displaying lower overall radon levels compared to Edmonton, Calgary, Montréal and Ottawa, still carry notable risks. Fitting with the overall regional trends for the Pacific Coastal area of Canada, radon levels in the Vancouver metro area are much lower relative to the other large cities. However, they are still at risk, and residents are therefore encouraged to test for radon.

RADON LEVELS IN OTHER MAJOR CANADIAN MUNICIPALITIES

In this section, we examine radon in 41 Canadian municipalities whose populations range from just under 15,000 to 999,999 people according to the most recent (2021) census conducted by Statistics Canada, for which we had enough data to draw conclusions. The location of these municipalities is shown in the map below.

The 2024 report includes radon information for 7 in 10 of all cities in Canada whose population exceeds 100,000 people, and half (54.8%) of all municipalities with populations greater than 50,000 people. We emphasize that we aim to report on as many additional cities and towns (census metropolitan areas) as possible, in near-future updates of this survey.

Please note that the radon results we obtained for some of these towns and cities did not have sufficiently detailed information about building design type or the exact postal address to allow us to assign a precise house- and/or community-type coding. Therefore, in the table below, we will present two sets of data for average household radon:

• For cities and towns where we had sufficient data to apply weighting, we report the weighted average radon level that is considered representative of the distribution of house and community types in that area based on the current census outcomes. For comparison, we also show the average (geometric mean) radon level that is obtained from the unweighted data.
• For all cities and towns where we are not (yet) able to apply weighting to calculate a balanced average (geometric mean) radon level, we report the unweighted average radon level obtained from the ‘raw’ data in order to provide a far larger number of Canadians with a more localized idea of residential radon exposure within their municipality.

IMPORTANT: Readers are advised to consider that all unweighted values may increase or decrease somewhat once appropriately weighted to reflect the actual distribution of housing in their community. We also note that the real differences between weighted and unweighted average radon levels emphasize the need to capture additional housing and community type metrics associated to enable radon levels for all Canadian cities to be re-weighted into the most representative value possible. As indicated earlier, we have sufficient data for 70% of all Canadian cities, which are defined formally by Statistics Canada as census metropolitan areas with populations exceeding 100,000 people. To increase the scope of the next update to this report, the remaining 30% of cities where additional radon testing is required in the near future are, in order of population size: St. Catharines-Niagara (ON), Oshawa (ON), Barrie (ON), St. John’s (NL), Greater Sudbury (ON), Saguenay (QC), Trois-Rivières (QC), Brantford (ON), Peterborough (ON), Nanaimo (BC), Belleville – Quinte West (ON), Chatham-Kent (ON), and Drummondville (QC).

IN SUMMARY, high radon levels are observed across a large number of Canadian municipalities. A number of cities and towns that have particularly elevated average residential radon levels, where at least one-quarter to one-half of residences have indoor radon levels at or above 200 Bq/m³. These eighteen municipalities include (in west to east order):

• Whitehorse (YT)
• Nelson (BC)
• Kelowna (BC)
• Prince George (BC)
• Vernon (BC)
• Penticton (BC)
• Trail (BC)
• High River (AB)
• Okotoks (AB)
• Strathmore (AB)
• Regina (SK)
• Brandon (MB)
• Winnipeg (MB)
• Thunder Bay (ON)
• Kingston (ON)
• Sherbrooke (QC)
• Bathurst (NB)
• Halifax (NS)

These outcomes highlight the need for households to strongly consider doing a radon test; it is the only way to know. Most importantly, we remind the reader that high indoor radon is a solvable problem (via professionally-installed mitigation), that can significantly reduce your risk of lung cancer. Some amount of radon is found in every house in Canada. Having high radon and obtaining a mitigation does not negatively impact your property value – indeed, reducing radon makes for a healthier home, and is of value.

SPECIAL CASE-REPORTS

The following section highlights some special cases of interest where we obtained sufficient data for a more focused analysis. These case reports include a more in-depth analysis of:

1. Residential Radon Levels in Multifamily Buildings – Preliminary Outcomes.
2. Radon levels in Northern Canada as a collective whole, acknowledging that this region of Canada is home to peoples with unique communities and experiences.
3. Comparative radon levels across building types between three major cities, including Halifax NS, Montréal QC, and Calgary AB.
4. Trends in changing radon levels as a function of the year that the residential building was constructed.
5. Examining differences in residential radon levels as a function of building floor.

Residential Radon Levels in Multifamily Buildings – Preliminary Outcomes

The data in this report encompasses data from single-detached, semi-detached, and row-style residential properties in which 69.6% of the Canadian population live.

The remaining 30.4% of Canadians live in residential buildings that include multifamily dwellings such as low and high-rise apartments, trailer / mobile houses, cottages, and cabins, each of which has its own unique building design considerations in terms of radon exposure.

With these considerations in mind, and in the interests of inclusivity, we report the preliminary finding that approximately 1 in 10 (9.3%) of [the mostly low-rise] multifamily buildings surveyed contain radon that is at or exceeds 200 Bq/m³, and 1 in 7 (14.3%) record radon levels between 100 and 199 Bq/m³.

• 1 in 10 multifamily residential properties are at or above 200 Bq/m³

We emphasize that better understanding radon exposure in the diverse types of multifamily dwellings that exist in Canada is important work to carry out in the future, especially as these early findings suggest these buildings can have high radon exposure for the people who live in them.

Special Region Overview – Residential Radon of the Canadian North

The North is an area of special interest in Canada due to its unique communities, peoples, climate, and built environment that spans the Arctic and near-Arctic regions. It is home to 0.3% of the Canadian population (pop. 0.12 million).

For the many residential buildings in Northern communities that have always existed on ground not subject to permafrost, radon risks may be comparable to other areas of Canada – that is to say, potentially very high. In other communities of the Canadian North, permafrost (ground that remains frozen for at least two sequential years) is thought to act as a barrier to the movement of underground gases, including radon. In areas with still-undisturbed permafrost, radon gas movement toward the surface may be slowed, meaning that indoor air radon levels may be substantially lower. Further, the need for buildings resting on permafrost to be built on piles or stilts (common in this region) often separates regional residences from the ground in such a way that they are unlikely to experience increased indoor radon at all. However, as climate change disrupts Canada’s permafrost, previously hindered radon gas can start to gain better entry to the surface, while also compromising the structural integrity of buildings otherwise designed to exist on frozen ground. Scientists are currently speculating that many Northern communities may be – some for the first time – experiencing increased radon exposure.

IN SUMMARY, the residential radon statistics of the two Canadian Territories in the North highlight consistently higher radon levels across all building types and across the region. While single-detached properties in this region contain higher radon levels than semi-detached and row (attached) residential houses, these differences are modest. Northern Territory residential radon levels are considered high, therefore radon testing and effective mitigation systems should be considered a high priority for the people of this region.

A Comparative Analysis – A Closer Look at Residential Radon by Building Type in the Halifax, Montreal, and Calgary metropolitan areas

In this section, we compare and contrast the greater metropolitan areas of three large Canadian cities for which we have sufficient data for a more in-depth examination of radon as a function of community and build type. We chose the census metro areas of Halifax on the East Coast, Montréal in Central Canada, and Calgary in the West near the Rocky Mountains.

In future years, updates to this report will feature as many other Canadian metro areas as possible.

The Greater Halifax Metropolitan Area

The city of Halifax is located on the Atlantic coast in the eastern part of Canada, and is the capital of the province of Nova Scotia. Halifax, whose name in the language of the Indigenous Mi’Kmaq people is Kjipuktuk and means ‘Great Harbour’, is a major economic centre within Eastern Canada, having been founded in 1749. The local geography features rugged terrain with coastal cliffs, and encompasses a large area with >200 neighbourhoods with a strong maritime and naval tradition.

Halifax reported a population of 0.47 million people in the 2021 Canada Census, and is the largest city on Canada’s Atlantic coast. 78.5% of Halifax residential properties are single-detached houses, 15.5% are semi-detached properties, and 6% are row (attached) properties.

The Greater Montréal Metropolitan Area

The city of Montréal is located in the province of Quebec, positioned in southeastern Canada. The city is centred on the island of Montréal, which has a unique geography and a greater metropolitan area consisting of 19 large boroughs that span several periphery islands and mainland Quebec. The heart of the city surrounds the triple-peaked, namesake mountain called ‘Mount Royal’. Founded in 1642 as ‘Ville-Marie’ by early French settlers, Montréal is considered an important cultural and commercial centre, with the second largest GDP of all Canadian cities. The land of Montréal shows evidence of occupation by Saint Lawrence Iroquoians, as early as 4000 years ago and in the Ojibwe language, the land is called Mooniyaang or Moon’yaang which translates as “the first stopping place”.

Montréal reported a population of 4.3 million in the 2021 Canada Census, making it the largest city in Canada’s French-speaking regions. 66.0% of Montréal residential properties are single-detached houses, 27.2% are semi-detached properties, and 6.8% are row (attached) properties.

The Greater Calgary Metropolitan Area

The city of Calgary is situated in the western part of Canada in the province of Alberta, at the transition between foothills that lead up to the Rocky Mountains, and the Canadian Prairies. Calgary was founded in 1875, and its name is derived from the Gaelic word Calgairidh, meaning “cold garden”. In the language of the Indigenous Blackfoot peoples (Siksiká), the area in which Calgary exists is referred to as Mohkínstsis. In contrast, the Indigenous Stoney Nakoda people refer to it as Wîchîspa Oyade – both translating as “Elbow” in reference to the sharp bend of local rivers. Calgary is a major economic and transportation hub in the west of Canada.

Calgary reported a population of approximately 1.5 million in the 2021 Canada Census, making it the largest city in the Canadian Prairies. 73.9% of Calgary residential properties are single-detached houses, 13.3% are semi-detached properties, and 12.7% are row (attached) properties.

Case-Study: Albertan residential radon levels by construction year

Several factors have already been demonstrated to impact household radon. With the amount of data received from Alberta, it was possible to study how the year of construction may impact the levels of household radon.

The graphs show increasing Alberta household radon levels as a function of the year that a residential property was constructed, with an overall increase in 39.2 Bq/m³ geometric mean radon level over the roughly 50-year period between 1971 to 2024. Albertan residential properties are currently being constructed with record-high radon levels documented within a short number of years post-completion, averaging 131.6 Bq/m³.

These trends are consistent between single-detached houses, semi-detached, and row-style dwellings, as well as across urban to rural communities. In future updates to the Cross-Canada Radon Survey, it will be important to gather sufficient information to perform this analysis for all Canadian provinces.

Examining differences in residential radon level as a function of building floor.

Radon gas is generated within the Earth and typically enters a building via surfaces in direct contact with the ground such as basement-level floors, walls, and foundation penetrations such as pipes. It has, therefore, been generally understood that the highest radon levels are observed typically on the lowest floor or storey of the building being tested; this does not mean, however, that levels of a building at or above ground level are free of risk.

To understand differences in Canadian radon exposure across the typical levels of a residential building, we calculated the average (geometric mean) radon outcome obtained from the 68% of tests that were carried out on a floor of property that is entirely below ground (such as basements or cellars), or from the 30% of tests carried out on a ground floor or walkout level (either entirely or partly level with the ground), or from the 2% of tests that were carried out on an upper floor (at least one storey above ground level).

With all outcomes weighted to the distribution of regions and building types based on the 2021 Canada Census, we find that the average radon reading on floors entirely below ground is 89.9 Bq/m³, the average radon reading on floors at ground level is 68.8 Bq/m³, and the average radon reading on floors entirely above ground is 54.4 Bq/m³. These outcomes indicate an average of 23.5% more radon in rooms in the basement or cellar of a typical Canadian residential building, relative to rooms that are on floor level with the ground. Similarly, there is an average of 20.9% more radon in rooms on the floors level with the ground, relative to ‘upstairs’ rooms on floors that are at least one storey above ground level.

These outcomes indicate that, in Canada, there remain substantial radon risks in rooms on levels that are at or above ground level. It is also correct that the greatest levels of radon are often observed on the level of the building that is below ground (and most likely in direct contact with the building foundation). Building scientists believe that the most probable explanation for somewhat lower radon levels observed on higher floors is that there are more opportunities for radon to be diluted with air from openings such as windows and doors, as indoor air migrates through the building to these levels (following entry via the foundation).

DISCUSSION and INTERPRETATION

Synopsis of Major Outcomes and Recommendations

The 2024 Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities finds that there are no areas of Canada that are ‘radon free’, and that approximately 1 in 5 (17.8%) of people residing in Canada are living in buildings with radon levels at or above the current radon guideline of 200 Bq/m³. The results of this study can be used by federal, provincial, and municipal governments as well as health, occupational, and building safety professionals to help prioritize radon outreach and education efforts, and to encourage or enable radon testing and remediation where necessary.

Of the Census Divisions in which we obtained at least 25 radon readings, approximately 30% encompassed communities in which 25-50% of houses contained radon at or above 200 Bq/m³. A majority of (7 in 10) Canadians live in single-detached, semi-detached, and row-style residential dwellings, and we report that the average radon level in these property types is 84.7 Bq/m³, weighted by their distribution across Canadian regions and urban-to-rural communities.

We also find that radon levels vary significantly across regions, urban-to-rural communities, and by building design types. Areas where high indoor radon levels are especially prevalent include Atlantic Canada, Prairie Canada, the North, and the British Columbian interior. Of the building types we have examined, single-detached houses generally demonstrate the highest risk of being at or above 200 Bq/m³ relative to semi-detached houses, which in turn have a higher risk relative to row-style houses. While limited data was available for multi-family housing (i.e. apartments), current information suggests these property types do carry some risk of high radon exposure. Residential buildings of any type in rural Canadian communities (meaning population centres of 1-29,999 people) generally demonstrated a greater risk of being at or above 200 Bq/m³ relative to already high-risk urban community equivalents.

For Canadian municipalities, the risk of residential radon levels being at or above the current radon guideline of 200 Bq/m³ is generally high, with four of Canada’s cities with populations exceeding 1 million people (Montréal, Ottawa-Gatineau, Calgary, and Edmonton) demonstrating a 1 in 6 risk, and weighted average residential radon levels between approximately 80-110 Bq/m³. Other towns and cities where at least one-quarter to half of residences contain radon at or above 200 Bq/m³ include Whitehorse (YT), Nelson (BC), Kelowna (BC), Prince George (BC), Vernon (BC), Penticton (BC), Trail (BC), High River (AB), Okotoks (AB), Strathmore (AB), Regina (SK), Brandon (MB), Winnipeg (MB), Thunder Bay (ON), Kingston (ON), Sherbrooke (QC), Bathurst (NB), and Halifax (NS). Many of these municipalities contain houses with average residential radon levels greater than 130 Bq/m³. Therefore, we recommend that public health stakeholders who are active in these communities take particular care to increase the promotion of radon awareness and access to radon reduction resources.

The results of the 2024 Cross-Canada Radon Survey show that, even for those regions, cities, and towns where the overall results indicate a lower incidence of residential buildings with elevated radon levels, there are still houses with high radon levels and higher increases in occupants relative lifetime risk of lung cancer. Therefore, it is important that readers be aware that the results in this report should not be used as a tool to determine personalized radon risk potential, or to decide whether or not to test a specific household for radon. Radon levels are influenced by several factors, including building features and the behaviour of the people occupying it. Ultimately, the only way to know if a house has an elevated level of radon is to test it, regardless of region or community.

Comparing the 2012 and 2024 Cross-Canada Radon Surveys

The 2024 survey of residential radon in Canada is an update of Cross-Canada radon reporting, and does not invalidate the previous work carried out in 2012, which is a robust snapshot of Canadian radon exposure of that time period. That said, it is important to address differences in observations between the 2012 and 2024 Cross-Canada Radon Surveys.

The 2024 Cross-Canada Radon Survey found that 17.8% of Canadian residential properties contain an average radon level that is at or exceeds 200 Bq/m³, a nearly 2.5-fold increase compared to the 6.9% of households that tested at or over 200 Bq/m³ in the 2012 Cross-Canada Radon Survey. We speculate that this substantial increase in average radon levels could be attributed to the following factors:

Building Construction. The simplest explanation is that Canadian residential radon levels have actually increased over the past decade due to changing build practices, meaning newer houses contain substantially higher radon versus their older equivalents. It has been suggested that evolving Canadian building codes (and practices) have unintentionally led to higher radon levels in newer buildings due to factors such as increased air tightness coupled with limited or imbalanced fresh air exchange, changes in concrete used within foundations, and more. These ideas have been discussed in detail within the academic literature [34] and the trends supporting this phenomenon are summarized within the Albertan Case Study.

Distribution of Tests by Floor. As determined in by the 2024 report, we find that radon test outcomes from rooms located on floors below ground (such as basements or cellars) are 23.5% higher in radon, on average, than outcomes from tests placed in rooms on the (main) floor of the building that is level with the ground. In the 2012 Cross Canada Radon Survey, 31% of results were from radon test devices placed in rooms below ground and 58% were from rooms on floors level with the ground – a major difference to the 2024 report, where 68% of results were from rooms below ground and 30% were from rooms level with the ground. We speculate that this difference explains part of the increase in outcomes between the two surveys. We emphasize that participants in both surveys were advised to place the test device on the lowest floor of the household where a person spends, on average, four or more hours per day. Since this modality of testing increases the likelihood that test results reflect radon levels in the air that people are being exposed to, we chose not to re-weight any outcomes in the report to harmonize the floor on which the tests were placed. We speculate that the increase in people choosing to test on lower levels of properties may reflect the increased use of such spaces as living areas, such as ‘basement suites’.

Building Retrofit and Renovation. Another contributor to high radon levels could possibly be the increased airtightness of older building envelopes produced by energy efficiency retrofits installed without increasing the rate of mechanical ventilation. This change that can increase how radon-laden soil gases are retained at high levels within indoor air. Indeed, over the past decade, federal and provincial incentive programs have increased the uptake of energy-efficient retrofits in older buildings. It is possible that part of the difference in outcomes between the 2024 and 2012 surveys can be attributed to the unintentional impact of certain energy efficiency measures. It is important here to note that increased energy efficiency does not, in of itself, necessarily result in high radon. Indeed, in other cold-climate nations such as Sweden, the most energy-efficient houses display the overall lowest average indoor radon levels [34]. This highlights the need to consider the way in which buildings circulate and exchange air as a whole when considering retrofits, and that energy efficiency can be improved without inadvertently increasing radon.

Overall Scale of Data Collection. The 2024 report collected five times more long-term radon results than the 2012 report (~70,000 results versus ~14,000 results), and applied multiple re-weighting factors to increase the balance between the distribution of surveyed houses versus what is known to exist in Canada based on the most recent census. To our knowledge, this is the first time national radon outcomes have been adjusted for regional, community, and building design type factors at the same time, a process only made possible by the larger sample size that covers a greater proportion of Canada in greater depth. Part of the difference in outcomes between the 2024 and 2012 surveys may be due to this enhanced balance.

Recruitment Strategies. There were differences in participant recruitment strategies between the 2024 and earlier surveys. For example, during the 2012 survey, participants were recruited via phone calls to landlines via a process intended to be random and administered by a third-party company, with no digital or word-of-mouth recruitment. At the time, landline recruitment was an appropriate strategy for constructing representative surveys, a fact that is no longer true in our modern digital society. By contrast, the 2024 survey compiled data obtained via varied recruitment modalities, including digital recruitment, which likely increased the diversity of participants. Therefore, differences in recruitment strategy possibly accounts for some of the underlying differences in survey outcomes.

Sampling techniques. As indicated earlier, the 2024 survey compiled data from a number of different sources using different sampling techniques such as tests provided for free, subsidized radon tests provided using citizen science-based initiatives, and tests purchased at market cost through varied vendors in different sectors. Participants were selected randomly, through semi-random processes, or by convenience sampling. We acknowledge that using raw and unweighted radon data from convenience sampling alone has the potential to introduce bias to outcomes, since people may be more likely to opt for radon testing if they have a history of lung cancer, hear about testing via neighbours whose radon test outcomes are high, and/or live in a single-detached house. The impact of many of these potential biases can be mitigated if participant houses are well understood (i.e. building type and age). The regions and the communities in which radon test outcomes are from can be appropriately re-weighted in reference to independently collected census data to avoid over-representation of house types, communities and any regions with unusually high radon. Indeed, this is precisely what has been done in the 2024 survey to produce outcomes that are as ‘symmetric’ as possible with the reality of the Canadian built environment.

Participant demographics. Understanding the people who participate in radon testing matters as there is evidence that population demographics are not randomly distributed across Canadian housing types or locations (See Box #12 for further details). While we do not have access to complete demographic data for all participants who performed a radon test as part of this survey, approximately 6,000 people from the 32% of readings in this survey that were contributed by The Evict Radon National Study have been polled for age, gender, socioeconomic demographics, as well as personal and family cancer history. These polls indicated that those who consented to carry out radon testing between 2018-2024 were, overall, balanced by gender, were an average of 50 years of age (with a broad spread across ages 30-70), were not over-represented by people with a history of lung cancer, and have household incomes near the average reported in the 2021 Canada Census. Nevertheless, complete demographic characteristics for the 2024 (and indeed earlier) Cross-Canada Radon Survey participant cohorts are not fully understood, and they are a potential factor influencing survey outcomes.

In summary, we suggest that the differences observed in the 2024 report versus the 2012 report are likely due to the following:

• Increases in residential radon due to changing build practices;
• The use of weighting as a function of building design and community type to improve data symmetry with the Canadian built environment;
• The increased adoption of building retrofits without balanced mechanical ventilation by Canadians may unintentionally increase household radon;
• The increased testing on floors that are entirely below ground;
• The increased sample size of the 2024 survey, and inclusion of diverse sampling methodologies.

Radon – a modifiable, preventable source of radiation exposure and lung cancer

Ultimately, it is the cumulative dose of radiation (to the lungs) from radon that a person experiences that modifies their lifetime risk of lung cancer. Radon and its decay products are the most significant contributors to a person’s lifetime dose of ionizing radiation exposure, accounting for nearly half of the effective dose received from all background radiation sources. In addition to region, community, and building design type factors that influence radon levels in air, the major influence on the actual dose of radiation that people absorb from radon exposure is behaviour, and how much time a given person spends within an indoor air environment containing radon.

For example, people’s behaviour may modify how a building draws on and retains radon-containing soil gas. Regularly maintaining a household’s air balance (by cleaning fresh return air filters), ensuring correct operation of HVAC systems, having gas-sealed sump pumps, and/or how likely a person is to open (and keep open) windows all can influence a building’s radon level. Beyond radon-modifying behaviours, lifestyles, personal demographics, and/or occupational choices can also impact the total radiation doses that people absorb from indoor radon exposure, and therefore their relative risk of subsequently developing cancer [41–43]. For example, two adults may occupy a single property with an identical radon level, but each experiences distinct radiation doses from it, as one person works from home five days a week (more time spent in the house equates to a greater annual dose of radiation from radon). In contrast, the other person works away at a large commercial office with little radon (low annual relative dose). In the years during and since the end of the Canadian response to the COVID-19 pandemic, the proportion of people working from home some or all of the time has increased [41]. From a radon exposure policy perspective, the outcomes of this radon survey may be considered by occupational health and safety stakeholders as such work environments become more widespread for some job types, compared to pre-pandemic periods.

A similar phenomenon of differential risk is anticipated between an adult without any other lung health risks/exposures and someone who has experienced another exposure or health event that increases the risk of lung cancer, such as inhalation of tobacco smoke, asbestos fibres, or other combustion particulates [45–47], and/or severe lung inflammatory events such as tuberculosis, chronic obstructive pulmonary disease (COPD), and/or severe pneumonia [48]. Based on this, people who are aware of an exposure to another cause of lung cancer (such as a history of tobacco smoking) or whose medical history includes a severe lung inflammatory event are strongly recommended to test the buildings in which they live for radon.

Future Directions and the next update of the Cross-Canada Radon Survey

The 2024 Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities represents an important new starting point in reporting residential radon exposures in Canada on a more regular timeline, and we are committed to consistent updates of Canadian radon exposure statistics as new data becomes available.

• We also anticipate presenting the primary information contained within this survey to Canadians as a more interactive data dashboard by Spring 2025.

Achieving this will enable increasingly complete reporting of Canadian radon exposure risks through future versions of the survey, and for all provinces, cities, towns, and rural areas in a manner that is appropriately weighted by building and community type. We look forward to helping Canadians understand the scale and nuances of residential radon gas exposure through these near-future activities.

Methodology

Assembly of Radon Test Outcome Databases

The 2024 Cross-Canada Radon Survey includes long-term (> 90-day test duration) radon test outcomes obtained from the analysis of certified alpha track radon tests performed by Canadians who consented to test their primary households. Participant recruitment and support, test device quality control, and subsequent data stewardship and security were administered by multiple groups as outlined below.

All activities required for database assembly using the information provided by data-sharing partners were pre-approved by the Conjoint Health Research Ethics Board, Research Services, University of Calgary (IDs = REB17-2239, REB19-1522), adhering to research ethics best practice, and in accordance with all regional guidelines and regulations to preserve participant privacy and ensure rigorous data security.

Where applicable, data-sharing agreements between the study team and partner groups were established in advance of data being transferred, and/or data had been integrated into working radon datasets by agreement via previously published peer-reviewed academic articles.

Long-term alpha track device radon test data was entirely from residential properties located across Canada. Test outcomes were contributed by the following organizations, distributed per the pie chart below. A total of 69,478 readings were assembled for this survey.

• Evict Radon National Study Team (including researchers at the British Columbia Cancer Agency, University of Calgary, University of Saskatchewan, and Dalhousie University).
• Radonova Inc.
• BC Centre for Disease Control*
• Health Canada, Radiation Protection Bureau**
• The Lung Associations of Nova Scotia and PEI, of New Brunswick, of Saskatchewan, and of Alberta.

*It should be noted that BC CDC radon test data is, of itself, comprised of data collected from a variety of data providers. Special care was taken to remove any duplicated data points that existed between the BC CDC compilation data and that held by another organization providing data for this survey.

**Data from the 2012 Cross-Canada Radon Survey was not re-used in the 2024 dataset, and the Health Canada dataset provided for the 2024 survey represents new readings collected after the completion of the 2012 survey.

Funding for database assembly and report preparation was provided by a project grant from the Canadian Institutes of Health Research – Healthy Cities Research Initiative held by A. Goodarzi, J. Taron and D. Brenner (University of Calgary (AB) with C. Peters at the University of British Columbia (BC); a radon outreach program contract from Health Canada’s National Radon Program to the Evict Radon National Study team; via a research grant held by A. Goodarzi at the University of Calgary (AB) from the Alberta Real Estate Foundation; and via team grant funding from the Canadian Cancer Society Breakthrough program to diverse researchers working on the “Changing the Narrative of Lung Cancer” program, based at the University of British Columbia (BC), University of Calgary (AB), Queens University (ON), and Dalhousie University (NS).

Radon Test Devices and Testing Advice for Participants

As discussed earlier, participants were instructed to follow current best practices for residential radon testing carried out by occupants, as indicated by Health Canada and the Canadian National Radon Proficiency Program (C-NRPP). To our knowledge, the majority of participants had access to online and telephone support from qualified persons to address any questions regarding the correct placement and use of radon test devices. As part of standardized advice given to all persons in Canada performing a radon test, participants were advised to place at least one test device on the lowest level (floor/storey) of the building where a person spends an average of four or more hours per day.

Alpha track radon test devices were all closed passive etched track detectors made from CR-39 plastic film inside antistatic holders enclosed in electrically conductive housing with filtered openings to permit gas diffusion, intended for long-term (>90 days) use with a typical linear range of 15 to 25,000 Bq/m³. All devices were sourced from certified radon testing laboratories, and included the RadTrak2 and RadTrak3 from Radonova, Inc., the AT100 from Accustar Labs, and long-term alpha track radon tests from the Saskatchewan Research Council, Lex Scientific Inc., and RPC Science and Engineering. To be read, CR-39 films are etched in 5.5 N NaOH at 70°C for 15.5 min and scored using software such as TrackEtch (Radonova laboratories, Sweden, EU) or comparable programs.

Time Period of Radon Testing

The majority (99.7%) of radon tests included in this survey were conducted between 2009 and 2024, with a very small set of legacy data (0.3%) dating between 1997-2008 (with no readings from 2004).

A complete breakdown of the number of tests included in this survey by year that the test was performed is shown in the graph below. 

Graphics, Photos and Data Access Statement.

All figures, charts, and infographics shown in this report have been designed and produced by our team and should not be altered by third parties in any way if shared. All photos used in this report were obtained through license to the Adobe Stock or Canva Images.

Administration and stewardship of the raw data used in this report are held independently by the five groups previously described, with each dataset governed separately by the rules and regulations of that group. As such, any public-sector research organization that is interested in obtaining access to these datasets is required to contact each group separately and follow the specific data access process indicated by that team.

In general, access to raw data is only permitted for researchers at public organizations governed by a Canadian research ethics board. It is not available to private sector groups or individuals in order to adhere to data privacy rules and the informed consent agreements signed between research groups and people in Canada testing their properties for radon.

Statistics Canada Data and Weighting Procedure

Statistics Canada Census 2021 data: Publicly available data on Census 2021 population, property type distribution, Census Division, Census Metropolitan Areas, and others were retrieved from Statistics Canada. 

Regional Building Year of Construction Data: To understand the year of construction across regions, Housing completion data were accessed from the Canadian Mortgage and Housing Corporation Data hosted on the Government of Canada Statistics website. The data were accessed from Statistics Canada.

Assigning Community type. Using Statistics Canada provided census information and Census Boundary files (available at Statistics Canada) radon entries were assigned to i) a Province, ii) a census division, iii) a population centre, iv) a designated place and v) a census metropolitan area using ArcGIS Pro 3.1.0. Using population density and overall population, radon results were assigned to a Large city (population ≥ 100,000), Large Town (population = 30,000 – 99,999), Small Town (population = 1,000 – 29,999) or rural area (population ≤ 999).

Community and Building Type Weighting of Data (See Example Weighting Method): Taking Canada Overall as an example, the geometric mean radon was determined for each property type (Single-detached, Semi-detached and Row House) across urban and rural communities. To determine the community-type weighted geometric mean radon, the percentages of Statistics Canada properties in each building category were determined for urban and rural communities. Using the percentages as a weighting factor, the geometric mean radon for a building type was multiplied by the percentage of properties reported to create the weighted mean radon. The weighted geometric means were summed across the property types to get a weighted geometric mean for each community type. This process was repeated for community types to determine the overall geometric mean radon for each region of Canada. Finally, the regional geometric mean radon was weighted by region to determine Canada’s overall geometric mean radon. This weighting process was repeated.

TABLES OF RADON DATA BY CANADIAN CENSUS DIVISIONS

We obtained at least 25 long-term residential radon test outcomes for 58.4% (171 of the 293) individual Canadian census divisions. We obtained between 1 to 24 long-term residential radon test outcomes for another 37.2% (109 of the 293) census divisions.

Acknowledging that all areas of Canada are important to report on if possible, we clustered those census divisions with 1-24 readings together with other census divisions that directly border them, so that the pooled outcomes for a minimal geographic area can be based on a minimum of 25 long term radon readings. Doing this allows us to report useful information in a way that reduces the chance of over, or under-estimating residential radon levels due to insufficient data points within a single census division and is a strategy that has been used before in this context.

Including clustered group and single census divisions, we report on 183 geographic units encompassing 94.9% (278/293) of Canadian census divisions. The geometric mean number of radon tests per census division or per census division cluster is 109.

We emphasize that all areas of Canada will benefit from new radon testing as well as the acquisition of any existing data from potential future partners, and that individual census divisions with fewer than 25 radon test readings (i.e. any currently reported within a cluster) are areas of priority to update in near-future versions of this report.

We did not have access to any long-term residential radon test outcomes for 4.4% (13 of the 293) census divisions and had insufficient data (<4 readings) for two census divisions that could not be clustered as they were bordered by areas with no data. This group of census divisions is over-represented by those in more northern, less populated regions of Canada.

These census divisions should be considered high-priority areas for immediate radon test data collection, as well as the acquisition of any existing data from potential future partners. They will be areas of highest priority to update in near-future versions of this report.

Disclaimer: Some tables and charts are only viewable by downloading the report below

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