The interior air barrier such as the polyethylene sheet or sealed sheathing should be detailed as the primary air barrier for this assembly. In addition to the interior air barrier, a secondary exterior air barrier such as the exterior vapour permeable sheathing membrane or sealed sheathing should be installed, to improve the overall assembly airtightness.

This double air barrier approach reduces the risk of air movement and condensation within the wall cavity, which increases the durability and thermal performance of the assembly. Note that the interior air barrier transition at the floor line requires careful attention to achieve continuity.