9.25.5.2 — Position of Low Permeance Materials

(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, (a) the material has, (i) an air leakage characteristic less than 0.1 L/(s∙m2) at 75 Pa, and (ii) a water vapour permeance less than 60 ng/(Pa∙s∙m2) when measured in accordance with ASTM E96 / E96M “Water Vapor Transmission of Materials”, using the desiccant method (dry cup), and (b) the intended use of the interior space where the materials are installed will not result in high moisture generation. (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 9.23.16.2. need not comply with Sentence (1). (4) Sheet and panel-type materials need not comply with Sentence (1) where, (a) the material has, (i) a water vapour permeance not less than 30 ng/(Pa•s•m2), and (ii) a thermal resistance not less than 0.7 (m2•K)/W, and (b) the heating degree-days of the building location, in degrees Celsius, are less than 6 000.