Why does the City require it?
Radon is a natural gas from uranium in soil and rock that can build up indoors. The City quotes Health Canada: long-term exposure is linked to about 16% of lung cancer deaths in Canada, and Canada's guideline is 200 Bq/m³. Its rule: All building permit applications for new construction, and additions to, low-rise residential buildings in the City of Hamilton are required to incorporate radon gas mitigation construction requirements in compliance with the Ontario Building Code.
These apply to new dwellings (including new laneway houses), and residential additions
(City of Hamilton, Radon Gas Mitigation, read November 5, 2026).
What are the two options?
| Option 1: rough-in | Option 2: active system | |
|---|---|---|
| Under the slab | At least 100 mm of granular material, 6 mil polyethylene lapped at least 300 mm | A 100 mm bed of granular material in the centre |
| The pipe | A 100 mm grey PVC pipe, sealed and labelled "Radon Gas Removal Only" | A 100 mm grey PVC pipe through the slab, up through the roof or rim joist |
| The fan | Not installed; the pipe is ready for one | A continuous duty inline radon fan |
| Foundation walls | A soil gas barrier (bituminous dampproofing) | A soil gas barrier (bituminous dampproofing) |
| Sealing | The slab perimeter and every penetration, with flexible sealant | As the Building Code requires |
Both from the City's radon page (City of Hamilton, Radon Gas Mitigation, read November 5, 2026), which cites Building Code Article 9.13.4.2 of Division B and Supplementary Standard SB-9.
When is it inspected?
Before the basement slab is poured. The City's inspection list has a radon inspection Prior to pouring of the concrete floor slab
, checking the sub-soil pipes, the depressurization rough-in and the air barrier (City of Hamilton, Building Inspections, read November 5, 2026). The full list is in the inspections on a build.
Does it apply to an addition with no basement?
The City applies the requirement to residential additions, and the Building Code rules are about floors in contact with the ground, so any addition with a slab or crawl space gets it on the drawings. The only way to know an existing home's level is a test, the City notes. Basement work in an existing house is covered on the renovations page.