7.2.42 Describe how to determine the permeability of building materials

  • Also called permeance
  • Water vapour or air permeance are determined in the lab and recorded in tables, may be included in product data.
  • Water vapour: Perms (imperial) or ng/(Pa-s-m²) (metric), 1 Perm maximum for barriers
  • Air: l/s-m² @ 75 Pa, 0.02 minimum for barriers