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

9.13.2.5.Moisture Protection for Interior Finishes (See Note A-9.13.2.5.)

(1) The interior surface of foundation walls below ground level shall be protected by means that minimize the ingress of moisture from the foundation wall into interior spaces, where (a) a separate interior finish is applied to a concrete or unit masonry wall that is in contact with the soil, or (b) wood members are placed in contact with such walls for the installation of insulation or finish. (2) Except as provided in Sentence (3), where the protection of interior finishes required in Sentence (1) consists of membranes or coatings, (a) the membrane or coating shall extend from the basement floor surface up to the highest extent of the interior insulation or finish, but not higher than the exterior finished ground level, and (b) no membrane or coating with a permeance less than 170 ng/(Pa×s×m2) shall be applied to the interior surface of the foundation wall above ground level between the insulation and the foundation wall. (3) Where insulation functions as both moisture protection for interior finishes and as a vapour barrier in accordance with Subsection 9.25.4., it shall be applied over the entire interior surface of the foundation wall.
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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.