Vapour Permeability
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)
[edit] Related articles on Designing Buildings Wiki
Featured articles
Check out some of the best features and news from Designing Buildings as well as key stories from around the web.
Households living near new pylons to save on bills.
ECA warns growth must not outpace grid capacity or skills.
The role of the client and decision making
CIOB response to built environment professions call for evidence.
Construction's sustainability reporting revolution
Tracking upfront embodied carbon with digital tools.
ECA welcomes procurement reforms
Public spending must back British jobs and skills.
Campaigning for Edinburgh: the Cockburn Association 1875-2049
The role of the civic voice in protecting character. Book review.
CIOB photography competition is open for entries.
ECA Edmundson apprentice of the year award
Finalists announced.
Major new study exposes serious knowledge gaps.
Generating energy from internal light as well as sunshine.
ECA welcomes plans to strengthen subcontractor quality control.
Combining mid-career qualifications with experience broadens career opportunities.