External Vapour Permeable Air Barrier

[warby]

Is this a better solution to achieving Air Tightness, i.e. establishing air tightness on the external face of the timberframe? I have no affiliation to this company. This is an extract from their website:

This product is Wraptite-SA, the only self-adhering vapour permeable air barrier certified by the BBA, was installed as part of the OSB panel construction of the home. The use of Wraptite-SA in the construction makes a significant contribution to a building’s thermal performance by preventing lateral air movement. It also provides high vapour permeability in a continuously sealed, self-adhered, airtight membrane.

Unlike internal air barriers, which can be complex and costly to install due to the need to accommodate building services such as electrical, lighting, heating and drainage systems, Wraptite-SA was applied externally, quickly and easily to the OSB boards in continuous pieces

[IanR]

While it's unconventional in the UK, an airtight layer on the outside can be made to work. But I would say it needs to be done with a proven wall and roof build up. If not then at the very least a full condensation risk analysis should be completed.

 

I assume the makers of Wraptite-SA can suggest some appropriate wall build ups?

 

Touchwood have the Airtight layer on the outside for their Passivhaus build-up and have gone to some lengths to mitigate any potential risks.

http://www.touchwoodhomes.co.uk/index.php/en/renewable/how-does-your-wall-build-up-provide-a-vcl-vapor-control-layer

 

The benefit of doing this is a simpler airtight layer, with fewer penetrations and avoiding the need for a service gap on the inside of external walls.