The Task Group on Radon Gas Mitigation continued reviewing items carried forward from the 2025 code cycle, beginning with public review comments on radon illustrations in the 2025 Part 9 Illustrated User’s Guide.

Members agreed that the full granular layer beneath the slab shown in the Illustrated Guide should be identified as the “gas-permeable layer,” while recognizing that alternative Code-compliant solutions remain available. Discussion focused on concerns that existing illustrations showing a capped pipe stub could lead to radon piping being capped in situations where a passive radon stack is required. The group reached consensus on revising the drawings to clearly distinguish between a sealed-cap arrangement permitted in certain Part 9 non-residential applications and passive stacks, which are required in all dwelling units.

Radon mitigation professionals also raised field concerns related to pipe placement, condensation within piping below the slab, pipe slope, and suction-point location. Staff noted that some proposed details are not currently Code requirements and would therefore need to proceed through the code-change process rather than be incorporated as guidance in the Illustrated User’s Guide.

The Task Group also reviewed a public review comment regarding condensation forming on a passive stack within the conditioned area of the home after activation with a fan, an issue identified by CHBA in its white paper on 2025 code changes which was submitted to the Prime Minister and NRC management. While the Code does not require activation of a passive stack, it does require space for a future fan if radon levels exceed 200 Bq/m³. CHBA maintained that the issue remains relevant and should be addressed prior to the adoption of the passive stack requirement. NRC Research indicated condensation should not occur on the exterior of the pipe under normal conditions based on their research findings in various regions across Canada. It was also noted it should not be an issue in homes with air conditioning and a balanced ventilation system. The group agreed to review existing NRC research before determining next steps.

The next meeting is scheduled for November 19.