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The Knowledge Centre provides CHBA members with access to information and resources. It is a growing resource that is currently focused on updating members about national building code information. Please note that this information is a benefit of your membership, and should not be shared beyond your company/organization.

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Radon in Homes

Radon in Homes

Tech Essentials

September 18, 2025

Radon in Homes

Radon is a naturally occurring radioactive gas produced during the breakdown of uranium in rocks and soil found across Canada. Radon escapes from the ground and gets into the air we breathe and can accumulate to high levels indoors. The radon concentration in a home depends on various factors including geology below a home and the ventilation and the airtightness of a home. According to Health Canada, radon is the second leading cause of lung cancer after smoking in Canada and it is recommended all homes be tested regardless of location.

What Can a Builder or Renovator do to Minimize the Ingress of Radon into Homes?

A builder’s goal should be to minimize radon ingress into new homes from the ground and to facilitate future radon mitigation in case testing by the homeowner finds the radon levels to be above the Canadian radon guideline level of 200 Becquerel per m³ (Bq/m3).

A renovator’s goal should be to inform the homeowner of the risk of radon ingress and recommend testing.  Ideally, before and after renovations that impact the slab or basement, the airtightness and ventilation of a home, any structural changes, or earthworks next to the home. Pre-renovation testing allows for mitigation strategies to be included in those renovations. After the renovations, homeowners should monitor that radon levels stay below the Canadian guideline.

Technical Concepts:

  • Post-Occupancy Testing (by the homeowner) determines radon levels in a home (Health Canada’s guideline level is less than 200 Bq/m3).
  • Below-Grade Soil Gas Barrier helps resist radon ingress and isolates the sub-slab space from the home (for example 6-mil polyethelyene).
  • Labelled Pipe Stub, Sealed with a Cap at the Top with bottom open to the building’s center below the slab allowing future connection to an active soil depressurization (ASD) system (see below).
  • Balanced Ventilation (for example HRV or ERV) can lower radon levels by dilution but can also increase levels if not maintained (clean filters, intakes etc).
  • Passive Stack is a pipe extending from the pipe stub to above the roof, with a top-end protected by a stainless-steel mesh, having limited offsets, and being insulated when passing through unheated areas (including above the roof in some regions).
  • Side Wall Vent extends from the pipe stub to the outside. Commonly used as radon mitigation in renovations (if used in new construction, has to be capped at the exterior until activated with a fan).

  • Active Soil Depressurization (ASD) System is a full radon mitigation system to keep indoor levels as low as possible all year where the passive stack or capped side wall vent needs to be upgraded by installing a properly sized fan that runs 24/7 to evacuate radon from the sub-slab space and vent it safely to the outdoors (the caped side wall vent becomes uncapped when upgrading to an ASD system).

What does the National Building Code (NBC) say about radon?

Since the 2010 edition, the NBC has required basic measures facilitating future radon mitigation –  gravel and a soil gas barrier below the basement slab sealed to the foundation, and a pipe stub open to the sub-slab space allowing connection to a future radon mitigation pipe – as well as sealed sump pits. A more performance-based approach also permits other material choices.

The 2025 NBC will require all new houses and Part 9 care homes to have a full-length passive radon stack to lower radon levels, installed prior to occupancy.  All overlapping joints in the polyethylene will also need to be sealed at overlaps and across the floor to wall joint at the foundation.

How do I know what the levels are in a home or my region?

The only way to know what the radon levels are in a home is to carry out post-occupancy testing and the levels can vary between two adjacent homes. The latest information on average radon levels in each region can be found in the 2024 Cross-Canada Radon Survey.  Some regions are known to have higher levels than others. 

Where can I find more information?

Best practice requirements for both new and existing homes can found in the 2024 versions of two standards published by the Canadian General Standards Board (CGSB)

Health Canada’s Technical information on radon includes

CHBA’s Renovators Manual, provides guidance on reducing radon ingress in chapter 14.6.

The Canadian National Radon Proficiency Program (C-NRPP) trains and certifies Radon Measurement & Mitigation Professionals and hosts a list of recommended consumer and professional measurement test devices. C-NRPP also offer courses aimed at builders and trades involved in new home construction.

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