Quote:
Originally Posted by Mass_nerder
Not to be pendantic, but the air barrier is what keeps warm moist air from passing through the wall assembly and causing the majority or moisture problems. The vapor ######er just stops vapor diffusion, which is less of a problem (but still important!)
Additionally, the air barrier needs to be on the warm side of the insulation, as the dew point occurs somewhere within the insulation. For most residential construction, this means it needs to be between the gypsum and the insulation (although they really need to start building with the insulation on the exterior of the sheathing like commerical projects).
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I don't want to get into a long discussion about this but after reading your comment I feel the need to respond. You have it backwards. The Vapour Barrier need to be on the warm side of the insulation (cold climate dependant) and the air barrier can be pretty mush anywhere in the assembly. For low rise construction 6mil ploy usually acts as both, but once you exceed 4 storeys 6 mil poly cant handle the air pressure and other forms of air barrier must be used. Below is a short article that explains it somewhat.
https://www.ecohome.net/guides/2316/...apor-barriers/