The Radon Gas Mitigation Task Group met to review actions arising, consider revised Terms of Reference, and discuss future work priorities. Codes Canada confirmed that errors identified in radon diagrams within the 2020 Part 9 Illustrated Guide cannot be corrected in the existing publication but will be addressed in the forthcoming 2025 Part 9 Illustrated User’s Guide.

The revised Terms of Reference, developed in response to direction from the Canadian Board for Harmonized Construction Codes (CBHCC), organize the work into phases. Phase 1 focuses on alterations to existing buildings, while topics such as alternate passive mitigation options, the effectiveness of polyethylene air barriers (6 mil poly), and crawl-space drainage issues have been deferred to Phase 2. CHBA questioned the rationale for this reprioritization and emphasized that important industry concerns should remain visible and continue to be tracked.

The task group reviewed several future work items that were drawn from public review comments. Members supported further consideration of lighter crawl-space ground-cover ballast materials, such as plywood, in crawlspaces where granular material may be impractical which was based on CHBA's public review comment. Alternate approaches (tape) for sealing below-grade membrane (penetrations were also identified as worthwhile but were generally assigned to Phase 2. The task group agreed to seek additional evidence from APCHQ regarding potential passive-stack damage caused by structural shrinkage and to determine whether existing provisions for piping expansion adequately address radon stacks or whether explicit National Building Code language is needed.

The group rejected make-up air as a radon-control strategy because it would not reliably prevent radon entry and could increase heating demand, but did agree to clarify the “gas-permeable layer” (where air can move) terminology under Phase 1 as it has created confusion in the field. Other important topics flagged in public review comments including condensation risks from fan-activated passive stacks (item #7 in the "list of future work/research items" found in the agenda package), and the impact of increased airtightness requirements on radon (item #14 in the "list of future work/research items" found in the agenda package) will be considered at future meetings. 

See below for the agenda package and please contact Jack.Mantyla@chba.ca for any questions.