Although radon gas exists everywhere, there is good news: The City is proactively addressing radon gas in new buildings and additions through the Radon Gas Mitigation Program, which came into effect on September 1, 2015.
This program applies to all building permits.
On this page
What is radon gas?
Radon is a colourless, odourless and tasteless radioactive gas that forms when uranium in soil, rock and water breaks down. Radon gas seeps into homes and buildings through cracks and holes in floors and foundations.
According to Health Canada, long-term exposure to radon is the second leading cause of lung cancer after smoking. Canada’s radon guideline is 200 becquerels per cubic metre (Bq/m3).
Radon gas in Guelph
According to the results from residential surveys completed by Health Canada in 2012, 18 per cent of the 131 randomly tested buildings within the City of Guelph exceed Canada’s recommended guideline for radon gas. Recent Health Canada surveys have also reported similar results.
Houses and Part 9 residential buildings – updated to 2024 Ontario Building Code
The following applies to building permits applied for after December 31, 2024.
As part of the changes introduced in the 2024 Building Code, all new Part 9 residential buildings (e.g. detached houses and Additional Dwelling Units (ADU’s), semi-detached dwellings, row townhouses, stacked townhouses, and multi-residential buildings) require a full active sub slab depressurization (ASD) system and a soil gas barrier under the floor slab.
This program also applies to additions that exceed 20 metres squared (m²) in building area.
Building permit drawings shall clearly indicate details associated with the full active sub slab depressurization system and soil gas barrier under the floor slab.
The ASD system pipe outlet shall be located to meet the minimum clearances noted in the table below.
| Locations | Required ASD pipe outlet minimum clearance |
|---|---|
| Clearance from a mechanical air supply inlet | 1.8 metres (5 feet 11 inches) |
| Clearance from a permanently closed window | 0.3 metres (12 inches) |
| Clearance from an openable window | 1 metre (3 feet 3 inches) |
| Clearance from a door that may be opened | 0.3 metres (12 inches) |
| Clearance from a door that has an openable window | 1 metre (3 feet 3 inches) |
| Clearance from outside corner | 0.3 metres (12 inches) |
| Clearance from inside corner (outlet of pipe shall not face inside corner) | 1 metre (3 feet 3 inches) |
| Clearance above paved sidewalk or paved driveway located on public property | 2.1 metres (6 feet 11 inches) |
| Clearance from a veranda, a porch, a deck, or a balcony | 0.3 metres (12 inches) |
| Vertical clearance above grade | 0.3 metres (12 inches) |
| Vertical clearance below soffits or from any attic venting component | 1 metre (3 feet 3 inches) |
| Horizontal clearance from an area below the discharge where there is a risk of injury from ice falling | 1 metre (3 feet 3 inches) |
| Horizontal clearance from the vertical line (from the ground to the roof) aligned with a gas relieve valve termination | 1 metre (3 feet 3 inches) |
| Vertical distance above roof surface or parapet | 0.3 metres (12 inches) |
Information for new homeowners
As a new homeowner, your home will be built in compliance with the radon gas mitigation requirements in the Ontario Building Code.
All new homes in Ontario come with a new home warranty that is provided by your builder and backed by Tarion. This warranty also covers excessive radon gas levels in new homes.
Radon gas testing
As part of the changes introduced in the 2024 Building Code, radon gas testing is no longer required for new Part 9 residential buildings including houses. Although new homes aren’t subject to mandatory testing, Health Canada recommends that all buildings be tested for radon gas.
Industrial, commercial, institutional (ICI) and Part 3 multi-residential buildings
The following applies to building permits applied for after December 31, 2024.
As part of the Radon Gas Mitigation Program, all new ICI and Part 3 multi-residential buildings shall be designed and constructed in accordance with the radon mitigation requirements in the Ontario Building Code. This program also applies to additions that exceed 50 metres squared (m²) in building area.
These requirements include:
- Sealing of walls (e.g. bituminous damproofing), roofs (e.g. suitable waterproofing membrane) and floors (e.g. 6 milimetre polyethylene sheet) that are in contact with the soil, including connections and any penetrations through them,
- Pipe rough-in only of an active soil depressurization system, including a 100 mm layer of clean coarse granular material applied evenly under the entire floor slab (19 milimetre clear stone or larger aggregate),
- Mandatory long-term testing (minimum 91 days during winter months), and
- Installation of a full active soil depressurization system if concentration levels measured by long-term testing exceed 200 Bq/m3.
Program overview
A full overview of the Radon Mitigation Program from design through to occupancy is outlined in a comprehensive flow diagram. The diagram details the building permit application process, required site inspections, submission of documentation, testing, and permit close-out. We encourage you to refer to this diagram throughout the project.
To provide further guidance, a letter with supporting attachments was issued to Architects, Professional Engineers, ICI Contractors and other stakeholders on November 4, 2015.
To obtain a copy of the flow diagram and letter, please contact Patrick Andres, Technical Lead Resource Conservation at 519-837-5615 extension 3478 or [email protected].
Building permit applications
All permit applications for new buildings, and for additions that exceed 50 metres square (m²) in building area, will need to include a complete copy of the City of Guelph Radon Mitigation Certification Form. The notes provided on the back of this form indicate the design professionals that are permitted to take responsibility for the radon mitigation measures.
Building permit drawings must clearly indicate all aspects of the required radon mitigation measures.
If applicable, designers intending to submit with alternative design solutions must include all relevant documentation with the permit application. This includes a signed letter stating that the Level of Performance delivered will meet or exceed that required in the Ontario Building Code and/or EPA/625/R-92/016 document and shall list the standard and/or guideline that was used. Designers will be notified if a formal “Application for an Alternative Solution” is required after the permit application has been reviewed.
Inspections
Prior to the start of construction, Contractors are encouraged to schedule an initial meeting with the Resource Conservation Inspector by booking an inspection through the Guelph Permit and Application System. Please allow 48 hours’ notice for inspections. The Inspector will meet with the Contractor onsite to discuss the radon mitigation measures that are proposed for the project, outline the overall inspection and testing process, and review when to book inspections.
The Radon Gas Mitigation Program requires up to five City inspections for each project. The construction milestones and inspection process is outlined in the flow diagram highlighted under the “Program Overview” section of this page.
After all radon mitigation measures have been installed, the individual(s) taking responsibility is required to submit a General Review letter to the City inspector confirming that the installation complies with the design.
Radon gas testing
After construction is complete, a long-term radon concentration test (minimum 91 days) must be completed during the heating season as recommended by Health Canada, when windows and doors are generally closed. All testing must be carried out by a C-NRPP certified “Radon Measurement Professional”.
Before the building permit can be closed, a radon analysis certificate showing that the radon concentration level does not exceed 200 Bq/m3 must be submitted to the Inspector.
For a complete directory of C-NRPP certified professionals, please visit the Canadian – National Radon Proficiency Program website.
For additional information regarding the Radon Gas Mitigation Program as it applies to industrial, commercial, institutional & non-low-rise multi-unit residential buildings, please contact Patrick Andres, Technical Lead Resource Conservation at 519-837-5615 extension 3478 or [email protected].
Part 9 non-residential buildings
The following applies to building permits applied for after December 31, 2024.
As part of the Radon Gas Mitigation Program, all new Part 9 non-residential buildings may be designed and constructed in accordance with the radon mitigation requirements in the Ontario Building Code for either new houses and Part 9 residential buildings OR for new ICI and Part 3 multi-residential buildings. This program also applies to additions that exceed 50 metres squared (m²) in building area.
Existing buildings
The Ontario Building Code regulates new construction only and does not contain retrofit requirements for radon gas. The program is only able to address radon gas mitigation in new construction.
Regardless of the age or location of a building, Health Canada recommends that all homes and other buildings be tested for radon gas. Remedial measures should be undertaken when the average annual radon concentration level exceeds 200 Bq/m3.
It is recommended that radon testing be carried out by a certified Radon Measurement Professional, and radon mitigation be carried out by a certified Radon Mitigation Professional. Find a certified radon professional.
For more information
If you have questions or concerns about the health effects of radon gas, or to learn more about testing and mitigation options, contact Wellington-Dufferin-Guelph Public Health or Health Canada.
Wellington-Dufferin-Guelph Public Health
1-800-265-7293 extension 4753
[email protected]
wdgpublichealth.ca
Health Canada
613-946-6384 or 613-948-3232
[email protected]
healthcanada.gc.ca/radon
Building Services
519-837-5615
[email protected]
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