5.4.1.1.Required Resistance to Air Leakage (Note A-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 the penetration of precipitation into the building component or
        assembly,
    (d) control heat transfer to roofs where ice damming can occur,
    (e) minimize the ingress of airborne radon and other soil gases from the ground with an aim to controlling the indoor
        concentrations of these gases to an acceptable level, and
    (f) not compromise the operation of building services.

    (2) Except as provided in Sentence (7), an air barrier system shall be designed and constructed to provide the principal
    resistance to air leakage to meet the requirements of Sentence (1).

    (3) The air barrier system shall incorporate air barrier assemblies that meet the appropriate Performance Class as
    defined in Table 5.4.1.1. (See Note A-5.4.1.1.(3))

                                                                  Table 5.4.1.1.
                                         Maximum Air Leakage Rates for Air Barrier Assemblies
                                    Forming Part of Sentences 5.4.1.1.(3) and (6) and 5.4.1.2.(1) and (2)

                         Performance Class                                    Maximum Air Leakage Rate, L / (s × m2), at a Pressure Differential of 75 Pa
                                1                                                                                0.05
                                2                                                                                0.10
                                3                                                                                0.15
                                4                                                                                0.20
                                5                                                                                0.50

    (4) The air barrier system shall be designed and constructed to be continuous
    (a) across construction, control and expansion joints,
    (b) across junctions between different air barrier assemblies, and
    (c) around penetrations through air barrier assemblies.
    (See Note A-5.4.1.1.(4))

    (5) The structural design of air barrier assemblies, including junctions between air barrier assemblies, subject to air
    pressure loads shall comply with Article 5.1.4.1. and Subsection 5.2.2.

    (6) The maximum air leakage rates specified in Table 5.4.1.1. are permitted to be increased where it can be shown that
    the higher rate will not adversely affect any of
    (a) the health or safety of the building users,
    (b) the intended use of the building, or
    (c) the operation of building services.

    (7) 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.
    (See Note A-5.4.1.1.(7))

This provision includes a table — formatting is preserved from the source; refer to the official code for the authoritative layout.

Next →5.4.1.2. Air Barrier Assemblies

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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.