5.4.1.1.

(1) Where a building component or assembly separates interior conditioned space from exterior space, interior space from the ground, or environmentally dissimilar interior spaces, the properties and position of the materials and components in those components or assemblies shall be such that they control air leakage or permit venting to the exterior so as to,

(a) provide acceptable conditions for the building occupants,

(b) maintain appropriate conditions for the intended use of the building,

(c) minimize the accumulation of condensation in and penetration of precipitation into the building component or assembly,

(d) control heat transfer to roofs where ice damming can occur, and

(e) not compromise the operation of building services.

(2) Except as provided in Sentence (3), an air barrier system shall be installed to provide the principal resistance to air leakage.

(3) An air barrier system is not required where it can be shown that uncontrolled air leakage will not adversely affect any of,

(a) the health or safety of building users,

(b) the intended use of the building, or

(c) the operation of building services.