Radon Mitigation & Testing in Toronto

Health Canada recommends mitigation when the long-term average residential radon concentration exceeds 200 Bq/m³ (becquerels per cubic metre). The World Health Organization sets a tighter recommendation at 100 Bq/m³. Health Canada attributes 16% of all lung cancer deaths in Canada to residential radon — second only to smoking. Long-term testing of 91+ days, ideally over the heating season, is required for an accurate average.

Approximately 19% of GTA homes test above the Health Canada 200 Bq/m³ guideline per the Health Canada Cross-Canada Survey of Radon Concentrations in Homes — substantially higher than the 7% national average due to local shale and limestone bedrock. Cold-weather stack effect during Toronto's heating season concentrates radon entry through slab cracks, cold joints, plumbing penetrations, and uncovered sump pits.

Long-term alpha-track test 91+ days (Health Canada-recommended): $50–$150 DIY kit, $200–$400 with C-NRPP-certified professional placement and lab analysis. Continuous radon monitor (Airthings Wave Plus / Corentium): $250–$400. Professional pre-purchase short-term test (real-estate transactions): $300–$600. We recommend the 91+ day long-term test for any decision-making — short-term tests have too much variability.

Sub-slab depressurization mitigation system: $2,000–$4,500 typical residential. Includes slab coring, riser routing, fan installation (RadonAway RP145 or similar), exterior or attic discharge above roofline, slab sealing with radon-rated polyurethane sealant, sump cover, construction wrap, and post-mitigation verification test. Complex installations (finished basement riser concealment, multiple suction points, stone foundations): $4,500–$7,500. Pairing with basement finishing saves 25–40%.

Yes — for the mitigation system design and commissioning. Health Canada and most major Canadian insurers require C-NRPP (Canadian National Radon Proficiency Program) certification for the mitigation professional who designs the system and performs post-mitigation verification testing. RenoHouse does NOT hold C-NRPP certification in-house; we coordinate certified subcontractor partners (SafeAir Environmental, Radon Environmental Management, Take Action on Radon) for system design and verification. RenoHouse self-performs slab coring, construction wrap, and homeowner communication.

A 4-inch suction pit is cored through the basement slab into the gravel layer beneath. A sealed PVC riser pipe routes from the pit, through the basement, to a continuous-duty radon-rated fan (RadonAway RP145, Festa Fan-Tech) mounted in the attic or on the exterior wall above grade. The fan creates slight negative pressure under the slab, drawing radon-laden soil gas up and out the discharge stack above the roofline. All slab cracks, cold joints, plumbing penetrations, and the sump pit are sealed. Post-mitigation verification target: below 100 Bq/m³.

Effective January 1, 2025, the Ontario Building Code requires radon-resistant rough-ins for new residential construction: a continuous sub-slab gas-permeable layer (4 inches of clean stone), a sealed sub-slab vapour barrier (10-mil reinforced poly), and a capped 100mm vertical riser pipe from below the slab to above the roofline — ready for fan activation if post-occupancy testing exceeds 200 Bq/m³. Rough-in cost: $400–$800 incremental during framing. Activation if needed (fan + verification test): $800–$1,500.

Health Canada recommends every Canadian home test for radon at least once. Best time to start a long-term 91-day test: November through March, during the heating season when stack effect maximizes radon entry. Re-test after any major basement renovation, slab work, foundation repair, or HVAC change. Re-test 12–24 months after mitigation system commissioning to verify continued performance. We recommend testing BEFORE finishing a basement — retrofitting mitigation into a finished basement costs 1.5–2x more.

DIY long-term alpha-track test kits (Take Action on Radon, AccuStar, Radalink) are Health Canada-approved and produce reliable results when placed correctly: lowest occupied level of the home, minimum 50cm from exterior walls and floor, minimum 90cm above the floor, away from windows / vents / heat sources, in a normally occupied area for 91+ days. Mail to certified lab for analysis. For pre-purchase real estate transactions, a C-NRPP-certified measurement professional is typically required by lenders or buyers; we coordinate that referral.

Health Canada says mitigation is recommended above 200 Bq/m³ but acknowledges health benefits at lower thresholds. WHO recommends action above 100 Bq/m³. Between 100–200 Bq/m³ is a personal risk-tolerance decision: many homeowners mitigate at this level, especially for finished basements where children play, home offices, or rental units. Mitigation is the same cost ($2,000–$4,500) regardless of starting concentration — and post-mitigation results typically come in below 50 Bq/m³ regardless of pre-mitigation level.