Understanding vapor drive is a crucial part of designing effective building envelopes….
Vapor drive is the natural tendency for moisture vapor to diffuse from wetter areas to dryer areas.
In construction applications, vapor drive is beneficial when it helps dry damp materials, or detrimental when it causes condensation on moisture-sensitive areas. It is critical to understand how the transmission of water vapor through materials impacts the performance and integrity of wall assemblies.
Building scientists at Carlisle Coatings & Waterproofing have written a short guide describing basic concepts about vapor diffusion. In addition, the guide outlines ASTM E 96 test methods used for measuring water vapor permeance.