- Project plans
- Project activities
- Legislation and standards
- Industry context
- Specialist wikis
Last edited 15 Jan 2021
Vapour permeability, or "Breathability" in a building refers to the ease with which water vapour passes through building elements. Building elements where vapour permeability is poorly designed can result in condensation, leading to unhealthy living environments and degradation of fabric.
Vapour permeability can be expressed in several ways:
- vapour resistivity of a material, measured in GNs/kgm (giga Newton seconds per kilogram metre) or MNs/gm (mega Newton seconds per gram metre)
- vapour resistance for a given thickness of material, in GNs/kg or MNs/g
- vapour resistance factor, also known as th µ-value, which is the resistivity of a material relative to that of still air. It is a factor, and has no units.
- "perms", short for permeability, used commonly in North America, measured in grains/(ft2 ·h·inHg)
 Related articles on Designing Buildings Wiki
Featured articles and news
Proactive wellbeing measures for construction and engineering sectors.
Duty holders are responsible for creating emergency plans.
Saint Michael’s Kirkyard - a Presbyterian Valhalla. Book review.
Facing the impact of the COVID and the internet.
Preparing for the return of employees.
Using rainscreen walls to address energy efficiency.
Integrity of fire product marketing - post-Grenfell - addressed.
Data measurement and carbon reduction efforts.
Actuate UK issues stark warning.
Department for Levelling Up, Housing and Communities replaces MHCLG.
Protecting heritage from disasters. Book review.