Vapor Permeance

Vapor permeance is the property of a material – and in our discussions this will be building materials – which permits the passage of water vapor through it. Today's guest is Jonathan Smegal of RDH Building Science Laboratories... Some materials have high vapor permeance which means they allow a lot of water vapor to pass and other materials have significantly less vapor permeance, so they block water vapor movement and these are called vapor barriers or vapor retarders."