• Vapour barriers must have a permeance no more than 60 ng/(Pa*s*m²)
• If the intended use of an area will produce substantially higher moisture levels during the heating season, the assemblies need to be engineered.

9.25.4.2.(1) Vapour barriers shall have a permeance not greater than 60 ng/(Pa*s*m²) measured in accordance with ASTM E 96/E 96M, "Water Vapor Transmission of Materials," using the desiccant method (dry cup).

9.25.4.2.(2) Where the intended use of the interior space will result in high moisture generation, the assembly shall be designed according to Part 5.