Radon in new homes: the 2024 Ontario Building Code, rough-ins and Tarion

What the code now requires

Ontario’s 2024 Building Code (O. Reg. 163/24) brought radon protection into new house construction across the province. For houses and small buildings regulated under Part 9, the soil gas control requirements (Subsection 9.13.4 and Supplementary Standard SB-9) call for two things:

• A soil gas barrier in floors, walls and roofs in contact with the ground. Under slabs, this is commonly 6-mil polyethylene lapped and sealed, with sealed penetrations and perimeter, or an approved alternative.
• A rough-in for a future subfloor depressurization system: either a gas-permeable layer with an inlet and outlet, or clean granular material with a pipe. Municipal guidance describes the pipe as at least 100 mm (4 inches), capped, sealed and clearly labelled for radon use.

Requirements took effect in 2025. Your municipality’s building department enforces them through permits and inspections and can confirm which version of the code applied to a specific home.

What a rough-in does, and doesn’t do

A rough-in makes mitigation fast, cheap and tidy if it’s ever needed: there’s already a collection layer and a pipe through the slab. But on its own, a capped pipe doesn’t remove any radon. Some homes with a passive pipe open to the roof see a modest reduction, but the reliable fix is to add a fan, turning the rough-in into an active system.

The code doesn’t require builders to test. The test is up to the homeowner, and it’s the only way to know whether the rough-in needs to be activated.

Tarion and radon

Ontario’s new home warranty includes radon remediation coverage, up to $50,000, for the full seven-year warranty period, when radon exceeds Health Canada’s guideline of 200 Bq/m³. To substantiate a claim, you need a test spanning at least three months, using a C-NRPP certified professional or a C-NRPP listed device. Contact your builder first and give them the chance to address it; if that doesn’t resolve it, you can file a claim with Tarion.

Homes built before the new code

Most of Southern Ontario’s housing, including many homes built in the last decade, predates the radon rough-in requirement. These homes can be mitigated with a standard sub-slab system; it simply involves coring through the slab rather than uncapping an existing pipe.

Why new homes still need testing

Research from the University of Calgary found newer Canadian homes have tended to have higher radon than older ones, likely because they’re larger, taller and more airtight, which strengthens the stack effect. A soil gas barrier reduces entry, but seams, penetrations and the floor–wall joint can still leak. A test settles it.

For builders

Getting the rough-in right (continuous gas-permeable layer, sealed barrier, correctly placed and labelled pipe, a route to an exterior discharge) makes the difference between a 2-hour activation and a difficult retrofit years later. It also reduces warranty exposure. See our builder programs.

Common questions