Ontario radon requirements for new construction
What your permit set must show
- 100mm exhaust pipe rough-in for sub-slab depressurization in all new ground-contact homes (basement, crawl space, and slab-on-grade).
- Gas-permeable granular layer below the slab or membrane to allow air movement toward the pipe.
- Full soil gas barrier (air barrier) with sealed edges to prevent soil gas entry into the living space.
- Applies to all Part 9 residential occupancies with ground contact.
- Active fan not required at construction; installed post-occupancy only if radon testing triggers action.
Common questions
Does every new Ontario home require this?
Yes, for all new ground-contact homes under the 2024 Ontario Building Code. This includes homes with basements, crawl spaces, and slab-on-grade foundations. The requirement applies to all Part 9 residential occupancies built under permits issued on or after January 1, 2025.
Is a powered fan required at construction?
No. The Ontario code requires a passive rough-in only. The rough-in includes the pipe, the granular layer, and the air barrier. A powered fan is added after occupancy if radon testing shows levels that warrant activation.
What does the plans examiner look for?
Plan reviewers check for the 100mm pipe shown on foundation drawings, a gas-permeable granular layer specified below the slab or membrane, and a sealed soil gas barrier. The Markham building department, for example, lists OBC 9.13.4 soil gas control as a standard plan-check item for new residential builds.
What warranty applies to these components?
Ontario's new home warranty program provides coverage periods of up to 7 years for certain building elements. Whether radon rough-in components fall under a given coverage band depends on your warranty terms, so check your warranty documentation.
Get this handled for your next permit
Upload your plans and get back permit-ready radon detail sheets, routing, and citations for Ontario in 2 to 3 business days.
Or take the free Ontario checklist
The same items plans examiners flag, in order. Free, no sign-up required.