- Project plans
- Project activities
- Legislation and standards
- Industry context
- Specialist wikis
Last edited 16 May 2022
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
Will you need it ? after June 15 and the new Part O ?
Create an account and write the first of many articles.
CIAT commentary after the first meeting.
Who is to blame?
Research recommends focussing on portfolio success rather than project success.
The revised standard for mapping underground utilities.
Cross-industry steering group seeks support in delivery.
Help us update process pieces from your field.
APM report explores existing practice.
COVID-19 and the importance of mental wellbeing.
As Professionally Qualified Person (PQP).
In order of relevance and with industry responses.
Raising awareness of the impacts of loneliness.
The list is growing, and in more ways than one.
We shouldn’t build new, If we can’t maintain what's built.
Timber Accelerator Hub phase 1 report