Code Library › Volume 1 › Section 9.13 — Dampproofing, Waterproofing and
PART 9 — HOUSING AND SMALL BUILDINGSUpdated for the 2024 Ontario Building Code

9.13.2.6.Dampproofing of Floors-on-Ground

(1) Where dampproofing is installed below the floor, it shall consist of (a) polyethylene not less than 0.15 mm thick with joints lapped not less than 100 mm, (b) Type S roll roofing with joints lapped not less than 100 mm, or (c) rigid extruded/expanded polystyrene with sealed or shiplapped joints that has (i) sufficient compressive strength to support the floor assembly, and (ii) a water vapour permeance complying with Clause 9.13.2.2.(2)(a). (See Note A-9.13.2.6.(1)) (2) Where dampproofing is installed between a floor-on-ground and a finished floor, it shall consist of (a) rigid extruded/expanded polystyrene with sealed or shiplapped joints that has (i) sufficient compressive strength to support the floor assembly, and (ii) a water vapour permeance complying with Clause 9.13.2.2.(2)(b), or (b) polyethylene not less than 0.05 mm thick with joints lapped not less than 100 mm.
← Previous9.13.2.5. Moisture Protection for Interior Finishes (See NNext →9.13.2.7. Dampproofing of Preserved Wood Foundation Walls

Common questions about this part of the code

When is waterproofing required instead of dampproofing for a foundation in Ontario?What are the radon and soil gas control requirements for new houses in Ontario?Does foundation dampproofing go on the inside or outside of the wall in Ontario?

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Code text is reproduced for reference from the Ontario Building Code (O. Reg. 163/24, 2024 Building Code Compendium). This page is provided for general information and is not an official copy. Always verify requirements against the official Ontario Building Code and confirm with your local building department.