Sudbury, ON repair guide
Radon and Wet Basements in Sudbury: What the Canadian Shield Does to the Room Under Your House
Greater Sudbury is built on the Canadian Shield, and the Shield is under every basement in the city: blasted out to make room for the house, seeping water along its fractures, and giving off radon, the radioactive gas from the decay of uranium in bedrock that is the second-leading cause of lung cancer in Canada. Health Canada’s and Public Health Sudbury’s surveys have found elevated radon in a large share of Sudbury homes, more than in most Ontario cities. This guide covers how to test for radon and what mitigation involves, how to tell sewer backup from groundwater in a Sudbury basement, what the drainage fixes do, and who to hire in a city where the nearest big-city contractor is four hours away.
By Michael, founder, fixmystuff.ca · Reviewed and updated 2026-09-11 · About 7–10 minutes
Radon: test first
Radon enters a house through cracks in the slab, the gap around the sewer pipe, sump pits, and the fractured rock a Sudbury basement sits on, and it accumulates in the lowest level. You cannot see or smell it; the only way to know is to test. Health Canada recommends a long-term test of at least three months over the heating season, using a kit from a hardware store, the Lung Association or a certified professional; Public Health Sudbury and Districts has run awareness campaigns and kit programs because the regional numbers are high. The guideline for action is 200 becquerels per cubic metre, and Sudbury homes have tested at many times that.
If the result is above the guideline, a mitigator certified by the Canadian National Radon Proficiency Program installs a sub-slab depressurization system, a sealed pipe and fan that draws gas from under the slab and vents it above the roof. On fractured rock, a mitigator may need more than one suction point, and a post-mitigation test proves the result.
| Result | What Health Canada recommends | What it usually involves in Sudbury |
|---|---|---|
| Below 200 Bq/m³ | No action; retest every few years or after renovations | A new test kit |
| 200 to 600 Bq/m³ | Mitigate within two years | Sub-slab depressurization by a certified mitigator |
| Above 600 Bq/m³ | Mitigate within one year | Depressurization, sealing, possibly more than one suction point on rock |
| Basement on fractured rock, any level | Test; sealing alone rarely works | Mitigator assesses the slab and rock |
Wet basements on rock
Water on the Shield does not soak in; it runs along the rock surface and down the fractures until it finds the hole blasted for your basement, and then it finds the wall. Groundwater arrives at the wall-floor joint and through cracks in the melt and after rain; sewer backup arrives at the floor drain during a storm in the older serviced neighbourhoods and smells like sewage. Photograph where the water first appeared and when.
The drainage fix is a perimeter drain that works, a sump with a battery backup, and, where the lot allows, exterior grading and drainage that keep water from running toward the house along the rock. If a radon system is installed, the sump pit gets a gasketed lid, which a mitigator will fit; the two jobs should be planned together.
- Radon test result and date
- Where water appears and when
- Foundation type and whether it sits on or in rock
- Camera inspection of the lateral if drains are slow
- Sump pit sealed if a radon system is installed
Sewers, septic and who owns which pipe
In Sudbury’s serviced areas, from the core to New Sudbury, the South End and Lively, the City of Greater Sudbury owns the sanitary and storm sewers beyond your property line and the water supply; the lateral on your property is yours, and a camera inspection with a locate tells you which side a fault is on. Outlying communities from Capreol to Whitefish are largely on septic systems and wells, regulated under Ontario’s Building Code and Wells Regulation. A backwater valve on the sanitary lateral is the fix for sewer backup in the serviced areas; the City has offered protective plumbing programs at times, so check the current page.
Who to hire in the north
Radon mitigation is not a licensed trade in Ontario; look for C-NRPP certification, which is what Health Canada recognizes, and ask for a post-mitigation test. Sudbury has certified mitigators of its own, which matters because a contractor from the south adds four hours of driving to every visit. Waterproofing is unlicensed too; ask for liability insurance and a WSIB clearance and for examples of work on rock foundations. Plumbing work needs a licensed plumber and a City permit for layout changes. Consumer Protection Ontario’s rules on written contracts apply.
Questions to ask before booking
- Are you C-NRPP certified and based in the north, and will you do a post-mitigation test?
- On fractured rock, how many suction points will the system need?
- Will the sump pit be sealed for radon, and does the sump quote include a battery backup?
- Will you camera the lateral and give me the recording and locate?
- Can I see your liability certificate and WSIB clearance?
Frequently asked questions
Is radon a problem in Sudbury?
Yes, more than in most Ontario cities. The Canadian Shield’s bedrock gives off radon, and surveys by Health Canada and Public Health Sudbury have found elevated levels in a large share of homes. Test with a long-term kit over the winter.
What does radon mitigation involve on rock?
A certified mitigator installs a sub-slab depressurization system, a sealed pipe and fan that vents gas from under the slab above the roof. On fractured rock it may need more than one suction point. Ask for a post-mitigation test.
Why does my Sudbury basement get wet in the melt?
Water on the Shield runs along the rock surface and down the fractures to the hole blasted for your basement. A perimeter drain that works, a sealed sump with backup, and grading that keeps water away from the house are the fixes.
Who owns the sewers in Sudbury?
The City of Greater Sudbury owns the sanitary and storm sewers beyond your property line in the serviced areas; the lateral on your property is yours. Outlying communities are on septic and wells.
Nearby communities
Sudbury’s certified radon mitigators and waterproofers serve the whole northeast, from North Bay to Timmins and Sault Ste. Marie, where the Shield and the radon are the same. Contractors from the south add hours of driving to every visit.
Browsing more broadly? Start from the Sudbury repair hub for every local guide in one place.
Sources and further reading
- Health Canada: radonGuideline, testing and mitigation guidance.
- Public Health Sudbury and Districts: radonRegional survey results and test kit programs.
- Canadian National Radon Proficiency ProgramFind a certified radon measurement or mitigation professional.
- City of Greater Sudbury: water and wastewaterSewer responsibility and any protective plumbing program.
Prices, programs, and acceptance rules can change. Check each source and obtain a written local quote before deciding.