This mock-up was commissioned by the Township of Langley and developed in collaboration with the BCIT ZEB Learning Centre. We gratefully acknowledge the Township of Langley team for their guidance and support throughout the project, and the BCIT ZEB Learning Centre for designing and constructing the mock-up. The construction details shown in this mock-up are informed by NRCan’s LEEP program and the Net Zero Energy Wall Guides, which provide practical guidance for high-performance, energy-efficient building assemblies.
Can a Wall Have Two Air Barriers?
Yes. A wall can have more than one air barrier. In many assemblies, multiple materials can contribute to the air-barrier system. While one continuous and well-installed air barrier is usually sufficient, having two air barriers is not a building-science concern, as long as each layer is properly detailed and connected to maintain continuity.
Can a Wall Have Two Vapor Barriers?
No. Two vapor barriers should be avoided. A wall assembly must be able to dry in at least one direction, either toward the exterior, toward the interior, or both. A double vapor barrier can trap moisture within the assembly by limiting drying potential, increasing the risk of condensation, mold, and durability problems.
Air Barrier Approaches Shown in This Mock-Up
This mock-up shows examples of both interior and exterior air-barrier approaches. The intent is not to suggest that both are required. A project may use an interior approach, an exterior approach, or both together. The key is maintaining continuity and good detailing.
