1. Except as provided in Sentences (2) to (4), sheet and panel-type materials incorporated into assemblies described in Article 9.25.1.1. shall conform to Article 9.25.5.2., where
   1. the material has
      1. an air leakage characteristic less than 0.1 L/(s·m2) at 75 Pa, and
      2. a water vapour permeance less than 60 ng/(Pa·s·m2) when measured in accordance with ASTM E 96/E 96M, "Water Vapor Transmission of Materials," using the desiccant method (dry cup) (see Note A-9.25.5.1.(1)(a)(ii)), and
   2. the intended use of the interior space where the materials are installed will not result in high moisture generation. (See Note A-9.25.5.1.(1).)
2. Where the intended use of the interior space will result in high moisture generation, the assembly shall be designed according to Part 5.
3. Wood-based sheathing materials not more than 12.5 mm thick and complying with Article 9.23.17.2. need not comply with Sentence (1). (See Note A-9.25.5.1.(3).)
4. Where a material has a water vapour permeance not less than 30 ng/(Pa·s·m2) and a thermal resistance not less than 0.7 (m2·K)/W and the heating degree-days of the building location are less than 6000, the assembly need not comply with Sentence (1).

1. Sheet and panel-type materials described in Article 9.25.5.1. shall be installed
   1. on the warm face of the assembly (see also Article 9.25.4.2.),
   2. at a location where the ratio between the total thermal resistance of all materials outboard of its innermost impermeable surface and the total thermal resistance of all materials inboard of that surface is not less than that required by Table 9.25.5.2., or
   3. outboard of an air space that is vented to the outdoors.
2. For walls, the air space described in Clause (1)(c) shall comply with Clause 9.27.2.2.(1)(a).

Table 9.25.5.2.
Ratio of Outboard to Inboard Thermal Resistance
Forming Part of Sentence 9.25.5.2.(1)

Notes to Table 9.25.5.2.:
(1) See Sentence 1.1.3.1.(1).