Radon in St. Thomas
St. Thomas is growing quickly, with new subdivisions spreading north and east of a downtown full of brick homes from the late 1800s and early 1900s.
St. Thomas radon guide
Radon in Elgin & St. Thomas
Radon testing and mitigation in Elgin & St. Thomas
Railway-city heritage homes, rapid new growth around St. Thomas, and Lake Erie shoreline cottages turned year-round.
Radon in Elgin & St. Thomas
Elgin County runs from the edge of London to the Lake Erie bluffs. St. Thomas is growing faster than it has in a century, with new subdivisions alongside its brick railway-era homes. Along the shore, Port Stanley, Port Bruce and Port Burwell mix cottages, converted seasonal homes and new builds. Inland, most of the county is farmland, with homes on private wells.
What’s under the ground
Elgin sits on the Lake Erie lowland: glacial lake clays and silts near the shore, sandier ground and moraine ridges inland, and the Kettle Point black shale band running under the western part of the county toward Lake Erie. Clay slows soil gas but cracks in dry summers. Sand and gravel move it freely.
The homes
St. Thomas has a large stock of older homes with stone and early concrete foundations. Its newest homes fall under the 2024 Ontario Building Code’s radon rough-in rules, but a rough-in is only a capped pipe. It does nothing until someone tests and adds a fan. On the lakeshore, winterized cottages on crawlspaces and patched slabs are a common reason we see a first-ever test come back high.
Public health: Southwestern Public Health.
What the data says
1 in 8
Ontario homes at or above Health Canada’s 200 Bq/m³ guideline in the 2024 Cross-Canada Survey, more than double the share found a decade earlier.Source: Cross-Canada Survey of Radon Exposure in the Residential Buildings of Urban and Rural Communities (2024)
+30%
Higher average radon exposure for rural residents than urban residents in a 2024 national study of 42,051 homes, mostly linked to drilled wells.Source: Goodarzi et al., Scientific Reports (2024) — rural communities and drilled-well annuli
~100
Roughly how many homes per health region the first national survey (2009–2011) could test. Too few to clear any neighbourhood, which is why public maps can’t tell you about your house.Source: Health Canada — Cross-Canada Survey of Radon Concentrations in Homes, Final Report (2012)
Local factors
Why Elgin homes should test
Clay plains
Dense clay slows soil gas, but it cracks in dry spells. Gas then follows the easiest route: the gravel backfill, weeping tile and utility trenches that lead straight to a basement.
Uranium-bearing shale nearby
Black shale is the most common uranium source rock in southern Ontario. The Kettle Point shale that runs under Lambton and western Middlesex and Elgin averages over 30 ppm uranium in Ontario Geological Survey drill core, roughly ten times a typical rock.
Rural homes on drilled wells
A 2024 national study of over 42,000 homes found rural residents were exposed to about 30% more radon than urban residents, with most of the gap linked to drilled wells. Researchers suspect gas travels up the gap around the well casing.
Century homes
Fieldstone, rubble and early concrete foundations, earth-floor cellars and open sumps give radon many ways in. Older doesn’t mean safer: these homes still need a test.
Cottages and crawlspaces
Lakeshore cottages converted to year-round homes often sit on crawlspaces, piers or patched slabs. Once winterized and heated, they can start pulling in soil gas they never did as summer places.
New, airtight construction
Canadian research shows newer homes have tended to test higher than older ones. Bigger, taller and tighter homes create a stronger stack effect that draws soil gas in through the slab.
Communities
Where we work in Elgin & St. Thomas
Questions
Radon in Elgin & St. Thomas: common questions
Do new homes in St. Thomas come with radon protection?
Homes permitted under the 2024 Ontario Building Code must include a soil gas barrier and a rough-in for a future sub-slab depressurization system. The rough-in is passive and capped. Health Canada and Tarion both rely on a long-term test after you move in to decide whether it needs to be activated.
My cottage in Port Stanley is now year-round. Should I test?
Yes, ideally during the first heating season after the conversion. Heating a closed-up building creates the stack effect that draws soil gas indoors, so a cottage that was fine in summer can test very differently in winter.
Book a radon test in Elgin & St. Thomas
C-NRPP certified testing and mitigation across St. Thomas, Port Stanley, Aylmer.