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Radon is a naturally occurring odourless and colourless gas that is produced by the radioactive decay of uranium. In outdoor air, radon is not harmful. However, radon can accumulate indoors to high concentrations and pose health risks (Health Canada, 2012). The World Health Organization recognized radon as the second leading cause of lung cancer after smoking. In Ontario, approximately 13% of lung cancer deaths are related to radon, which is an estimated 850 lung cancer deaths per year in the province (PHO, 2013). The Government of Canada Radon Guideline recommends that if the annual average indoor radon concentration in a home’s normal occupancy area is greater than 200 Becquerel’s per cubic metre (Bq/m3) then steps are necessary to decrease the radon level (Health Canada, 2007).

The Windsor-Essex County Health Unit (WECHU) began a 3-year Radon: Know Your Level study and awareness campaign in 2015. As a part of this campaign, home-owners of detached and semi-detached homes were recruited to determine indoor radon levels in the areas of Windsor-Essex County (WEC). This document is a summary report of data collected from 2017/2018 study.

Percentage of Homes Above the Canadian Guideline (≥200 Bq/m³)

Close to seven percent of homes in WEC had radon levels above 200 Bq/m³ (Table 1).  Essex County had a significantly greater proportion of homes with levels above the Canadian guideline (11.2 %) than compared to the City of Windsor (2.1%) (Figure 1). The lowest and highest radon levels observed were 14 and 529 Bq/m³. The distribution of levels is shown in Figure 2.

Average Indoor Radon Levels

The average indoor radon level for WEC from the 2017/2018 study results was 79.5 Bq/m³ (Table 2).  The towns of Kingsville, Essex and Leamington had average concentrations almost 15 Bq/ m3 higher than WEC; however, the small sample size in these municipalities made it difficult to determine significant differences.

Table 1. Percentage of Homes with Indoor Radon Levels ≥200 Bq/m³ and 95% Confidence Intervals by Area

*The percentage for Ontario was obtained from the Cross-Canada Survey of Radon Concentrations in Homes – Final Report (Health Canada, 2012).


% ≥200 Bq/m³

95% Confidence Interval (%)

Essex County


8.1 to 15.3



1.1 to 4.1

Windsor-Essex County


4.9 to 8.6




Figure 1. Percentage of Homes with Indoor Radon Levels ≥200 Bq/m³by Area.

Figure 2. Distribution of Radon Levels in Participating Homes

Table 2. Average Indoor Radon Level (Bq/m³) and 95% Confidence Intervals by Area


Average (Bq/m³)

95% Confidence Interval (Bq/m³)



73 to 104

Town of Essex


74.8 to 116.1



80.4 to 120.3



77.9 to 103.6



74.1 to 92.7



74.2 to 123.2



76.9 to 94.9

Essex County


84.1 to 95.9

City of Windsor


67 to 74.9

Windsor-Essex County


76.1 to 82.9

House Characteristics

House characteristics assessed in the survey identify which participating homes were more susceptible to higher indoor radon concentrations.

Homes built from 1981 to present had over two times higher indoor radon concentrations than homes built in 1920 or before (Figure 3).

The number of levels in a home, including the basement, was associated with higher average indoor radon concentrations. Homes with two levels (i.e. ranch style) had 31% higher average radon levels compared to three-level houses (including basement or crawlspace) (Figure 4).

Figure 3. Average Indoor Radon Levels by original year of home construction.

Figure 4. Average Indoor Radon Levels (Bq/m³) by number of house levels

Data Notes

  1. The estimates reported are based on radon test kit and geographic data obtained from 821 participants that met the study criteria and provided valid results.
  2. An estimate was deemed to be significantly different than another estimate if the 95% Confidence Intervals for the two estimates did not overlap.  The 95% Confidence Interval is the range within which we can be 95% certain that the true population estimate falls.
  3. Geometric averages were calculated (rather than arithmetic averages) since indoor radon levels follow a lognormal distribution rather than a normal distribution (World Health Organization, 2009).
  4. Multiple linear regression model with survey weights and log-transformed outcome was used to associate municipality, adjusted for house traits, to radon levels.
  5. Participants were restricted to owners of detached and semi-detached homes who were 18 years or older and did not plan on moving or undertaking major renovations in the six months after start of testing.  Participants were asked to conduct the test in the normal occupancy area of the lowest lived-in level of their home, for at least 91 days.
  6. A stratified sampling strategy with proportionate allocation of test kits was undertaken to ensure regional representation. This was done by ensuring that the proportion of test kits distributed in a municipality was proportional to the number of homes in that municipality to the total number of homes in WEC.


  1. Health Canada. (2007). Government of Canada Radon Guideline. Ottawa. Retrieved from
  2. Health Canada. (2012). Cross-Canada Survey of Radon Concentrations in Homes - Final Report. Ottawa. Retrieved from
  3. World Health Organization. (2009). WHO handbook on indoor radon: a public health perspective. Geneva. Retrieved from
  4. Public Health Ontario (PHO). (2013). Radon in Ontario. Toronto. Retrieved from

More Information

Radon Hotline: 519-258-2146 ext. 1454 or


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