Location of airtight barrier I'm curious about locating the airtight barrier - why on the outside? Especially if modelling is suggesting a potential moisture risk, even if potentially solved with the use of the 1.1 perm rating building paper on the inside.
Posted: 02:14 pm on April 27th 2016
air barrier Thanks for your reply, Martin. It makes me curious rather than nervous! The moisture risk was noted in the article. Curious because I'm not familiar with the standard practice in that part of the US, nor the local climate conditions. it is standard practice in the UK and EU to locate the air barrier on the inside of the thermal envelope to prevent internal moist air passing into/through the insulation. The outside of a wall assembly is often taped also but for wind-tightness (not airtightness) to prevent thermal bypass.
Posted: 09:03 am on April 28th 2016
air tight vs wind tight I get where you are coming from, Martin, I think. It is perhaps rather a subtle distinction between air tight and wind tight, mixed up even more by not specifically identifying if the airtight layer is also the vapour control layer. In this case, I guess the kraft paper is acting as a vapour control layer? (Excuse my ignorance as we don't use the term kraft paper in the UK.) Otherwise, internal air-bourne moisture entering the assembly can reach the cold side of the insulation and could cause condensation. 475 have a useful article on this which aligns with typical UK / EU practice: https://foursevenfive.com/an-interior-air-barrier-does-it-better/
Posted: 02:14 pm on April 28th 2016