The Ontario Building Code | Protection of Interior Finish
9.20.13.9. Protection of interior Finish
(1) Except as provided in Sentence (3), where the interior finish of the exterior walls of a building is a type that may be damaged by moisture, exterior masonry walls, other than cavity wallsor walls that are protected for their full height by a roof of a carport or porch, shall be,
(a) parged on the interior surface, and
(b) covered with No. 15 breather-type asphalt-saturated paper conforming to CAN/cgsb-51.32-M, "Sheathing, Membrane, Breather Type", and shall be lapped not less than 100 mm at the joints.
(2) In situations described in Sentence (1), flashing shall be provided where water will accumulate, to lead it to the exterior.
(3) Where the insulationhttp://thehandyforce.com/insulation/" title ="Toronto home insulation">insulation effectively limits the passage of water vapour and is applied by a waterproof adhesive or by mortar directly to the masonry, the requirements for sheathing paper do not apply.
In Plain Language
Interior finish must be protected as set out in this article, addressing moisture that could migrate from a masonry wall assembly into the occupied interior space.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.