The Ontario Building Code | Required Barrier to Air Leakage
9.25.3.1. Required Barrier to Air Leakage
(1) wall, ceiling and floor assemblies that separate conditioned spaces from unconditioned spaces or from the ground shall be constructed so as to include an air barrier system that will provide a continuous barrier to air leakage,
(a) from the interior of the building into wall, floor, attic or roof spaces sufficient to prevent excessive moisture condensation in such spaces during the heating season, and
(b) from the exterior inward sufficient to prevent moisture condensation on the room side during the heating season.
(2) The continuity of the air barrier system shall extend throughout the basement.
In Plain Language
A continuous air barrier is required to control air leakage through the building envelope, as set out in this article, since uncontrolled air leakage wastes energy and can carry moisture into wall assemblies.
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.