Building & Renovating

Residential Construction Requirements for Radon Gas Mitigation

Radon is a colourless, odourless and tasteless gas that is formed naturally by the radioactive breakdown of uranium contained in soil and rock. Normally radon escapes from the ground into the air where it mixes with fresh air resulting in concentrations too low to be a health concern. However, when radon enters an enclosed space through cracks or openings in floors in contact with the ground, or through foundations, it can accumulate to higher concentrations.

According to Health Canada, long-term exposure to radon is linked to approximately 16% of lung cancer deaths in Canada and is the second leading cause of lung cancer after smoking. Canada’s radon guideline is currently 200 Bq/m³ (becquerels per cubic metre). The only way to determine if radon levels are within the guideline of 200 Bq/m³ is to carry out a test.

Residential construction requirements

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 requirements apply to the construction of new dwellings (including new laneway houses), and residential additions.

Radon Gas mitigation options

Building permit drawings shall clearly indicate details associated with one of the following three radon gas mitigation options in accordance with the Ontario Building Code (OBC). OBC Reference: Article, of Division B, and Supplementary Standard SB-9 “Requirements for Soil Gas Control”

  1. A 100 mm diameter grey PVC pipe rough-in, OBC Reference: Subsection 3.2., Sentences (1) through (5) of Supplementary Standard SB-9
  2. Minimum 150 mm granular material for a radius not less than 300 mm centered on the pipe, with the bottom of the pipe open to the granular,
  3. The upper end of the pipe shall be provided with a removable seal and labeled to indicate for “Radon Gas Removal Only”, and
  4. Mandatory radon gas testing (see “TESTING”). OBC Reference: Subsection 3.2., Sentence (6) of Supplementary Standard SB-9

Option 1 - Subfloor Depression Rough-in for Radon Gas Mitigation. Through the floor slab near centre or adjacent to an exterior wall and extending under the slab and terminating at or near the center.

  1. A soil gas barrier on the foundation walls (bituminous dampproofing), and OBC Reference: Sentence, of Division B
  2. Under the basement floor slab using 6 mil polyethylene lapped not less than 300 mm, and OBC Reference: Figures SB-9A or SB-9B of Supplementary Standard SB-9
  3. Sealing along the perimeter of the basement floor slab and at all penetrations using flexible sealant (polyurethane caulking).
    OBC Reference: Clause, of Division B, and Supplementary Standard SB-9

Option 2 - Radon Gas Barrier. Adding a 6 mil polyethylene to a solid or hollow foundation wall.Note: Care must be taken when installing 6 mil polyethylene since it is prone to puncture. Please ensure the 6 mil polyethylene is adequately protected.

  1. A soil gas barrier on the foundation walls (bituminous dampproofing), OBC Reference: Sentence, of Division B, and Figure SB-9A or SB-9B of Supplementary Standard SB-9
  2. Installation of a sub-slab depressurization system installed in accordance with Health Canada guideline “Reducing Radon Levels in Existing Homes: A Canadian Guide for Professional Contractors”,
  3. A properly labelled 100 mm grey PVC pipe shall be installed through the floor slab adjacent an exterior wall extending under the slab into a centrally located 150 mm thick bed of granular material, and OBC Reference: Subsection 3.2., Sentences (1)through (5) of Supplementary Standard SB-9
  4. Above the slab, 100 mm grey PVC piping shall be installed, extending either through the roof or the rim joist, and shall have a continuous duty centrifugal inline radon fan.

Option 3 - Active Subfloor Depressurization System. Installation of a radon exhaust fan.

For new construction and/or additions

Required inspections

The property owner or builder shall arrange for the following inspections:

  1. Installation of the rough-in soil gas pipe and granular material prior to pouring the basement slab.
  2. Installation of soil gas barrier on foundation wall (bituminous dampproofing) and under floor slab (6 mil polyethylene) prior to covering or pouring the basement slab.
  3. Sealing of the perimeter of the slab adjacent to the foundation wall and any slab penetrations (polyurethane caulking) prior to covering.
  4. Pipe cap and labelling and inline fan (where required) prior to occupancy.

Radon Gas testing

Depending on the radon gas mitigation option chosen by the builder, the building may be subject to mandatory radon gas testing.

It is the property owner’s responsibility to conduct radon gas testing and submit the results to the City of Hamilton at [email protected].

All radon testing will consist of long-term tests (minimum 91 days) completed during the winter season (October to April), when windows and doors are generally closed, and are recommended to be carried out by a Canadian National Radon Proficiency Program (C-NRPP) certified professional.

Where mandatory radon gas testing results come back above 200 Bq/m³ (becquerels per cubic metre), the property owner is to:

  1. Install an active subsoil depressurization system, OBC Reference: Subsection 3.2., Sentence (9) of Supplementary Standard SB-9
  2. Ensure any resultant decrease in soil temperature will not adversely affect the foundation - documentation to this affect is to be provided by a qualified person, and
  3. Submit test results indicating levels below 200 Bq/m³ to the City of Hamilton.

Health Canada recommends hiring a professional certified under the Canadian National Radon Proficiency Program (C-NRPP), as lowering radon levels in a home requires specific technical knowledge and skills to ensure the job is done properly.

Where to find a list of certified professionals? Contact the Canadian National Radon Proficiency Program (C-NRPP) at 1-855-722-6777, go to or email [email protected].

New homes - Tarion warranty

New homes in Ontario come with a new home warranty that is provided by the builder and backed by Tarion. The warranty covers radon gas levels exceeding 200 Bq/m³ in new homes for seven years from the date of occupancy.

Existing dwellings

Radon mitigation requirements do not apply to existing dwellings or retrofits for secondary dwelling units. If a homeowner wishes to conduct voluntary testing and mitigation, it is recommended they contact a Canadian National Radon Proficiency Program (C-NRPP) certified professional.

Contact us

Building Division
City Hall, 3rd floor
Phone: 905-546-2720
Email: [email protected]