VAPOUR DIFFUSION AND CONDENSATION CONTROL IN HIGH-PERFORMANCE BUILDINGS
More stringent energy codes demand higher levels of insulation for external walls, and in many cases this means using exterior insulation, either as a substitute for traditional cavity insulation, or to supplement it. Additional insulation thickness and changes to the insulation location require additional consideration with regards to vapour diffusion and condensation control.
The varying vapour permeability of different insulation products, membranes, and other building materials adds complexity to wall assembly design.
Some insulation materials, like mineral wool and fibreglass are vapour permeable, while others, like XPS, polyisocyanurate, and closed-cell spray foam are relatively impermeable.
Energy codes are silent on this issue and building codes can be confusing in regard to the selection of exterior insulation and vapour diffusion control for walls. This article clarifies and provides guidance on vapour diffusion and condensation control in these new wall assemblies.