Elgin & St. Thomas
Radon testing and mitigation in St. Thomas, Ontario
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. Here’s what’s known about radon in St. Thomas, and how to find out about your home.
- Region
- Elgin & St. Thomas
- Population
- about 43,000
- Public health
- Southwestern Public Health
- Local factors
- 4 reasons to test
Is radon a problem in St. Thomas?
Radon can exceed Health Canada’s 200 Bq/m³ guideline in any St. Thomas home. No published local data rules any neighbourhood in or out. Across Ontario, about 1 in 8 homes tested at or above the guideline in the 2024 national survey. Locally, cracking clay soils, century-home foundations and new airtight construction are reasons to test. A 91-day test is the only way to know your home’s level.
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. Old or new, both kinds of house deserve a radon test.
The ground under St. Thomas
The city sits on the Lake Erie lowland, on glacial lake clays and silts with sandier ridges, cut by Kettle Creek’s deep valley. The Kettle Point black shale runs beneath western Elgin. Clay slows soil gas but cracks in dry weather, and the gravel bed under every modern slab collects the gas right where it can get in.
St. Thomas’s homes
Railway-era homes near Talbot Street often have stone or early poured foundations with floor drains and sumps. Homes permitted under the 2024 Ontario Building Code include a radon rough-in, but it’s capped and passive until someone tests and adds a fan. Many St. Thomas homes built in the last decade predate that rule entirely.
What the data says
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)
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
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 results
Building a real radon picture for St. Thomas
Public radon data for Southern Ontario towns is thin. The national surveys tested only a handful of homes per area. So we’re building our own: anonymized long-term results from homes we test, published by area once there are at least 30, so no single home can be identified and small samples can’t mislead.
St. Thomas: collecting results. Already tested? Check your number and share it anonymously when you book.
Local factors
What can push radon up in St. Thomas
Not a prediction for any single home, just the reasons a test is worth it here.
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.
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.
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.
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.
Where we work
St. Thomas neighbourhoods and nearby communities
- Downtown & Talbot Street
- Pinafore Park area
- Lake Margaret
- North-end subdivisions
- Southwold
- Talbotville
- Union
- Shedden
Nearby: Radon in Port Stanley · Radon in Aylmer · Radon in London
How it works
From test to fix
- Book
Tell us about your St. Thomas home. We reply within one business day.
- Test for 91+ days
A certified technician places long-term detectors on your lowest lived-in floor. You get an early reading at 2 weeks.
- Get your result
Lab-verified average, explained against Health Canada’s guideline.
- Fix it if it’s high
A sub-slab system designed for your foundation, at a fixed price, with results guaranteed.
Questions
Radon in St. Thomas: FAQ
Is radon a problem in St. Thomas?
Radon can exceed Health Canada’s 200 Bq/m³ guideline in any St. Thomas home. No published local data rules any neighbourhood in or out. Across Ontario, about 1 in 8 homes tested at or above the guideline in the 2024 national survey. Locally, cracking clay soils, century-home foundations and new airtight construction are reasons to test. A 91-day test is the only way to know your home’s level.
Is my new St. Thomas home protected from radon?
If it was permitted under the 2024 Ontario Building Code, it should have a soil gas barrier and a capped rough-in pipe. That makes mitigation easier, but it doesn’t lower radon on its own. A long-term test after your first winter tells you whether to activate it.
Does Tarion cover radon in new St. Thomas homes?
Tarion’s new home warranty includes radon remediation, up to $50,000, if a long-term test (at least three months) shows levels above 200 Bq/m³ within seven years of possession. Contact your builder first. We can provide the certified test you’ll need.
Do you offer radon testing and mitigation in St. Thomas?
Yes. We test and mitigate homes throughout St. Thomas, including Downtown & Talbot Street, Pinafore Park area, Lake Margaret, North-end subdivisions, Southwold and nearby. Call (226) 271-4667 or book online.
Radon is fixable. First, know your number.
Serving St. Thomas, Port Stanley, Aylmer and London.