Building Science-Perm

Builders in northern Minnesota have been using polyethylene sheeting on the warm in winter side of wall assemblies for years.  Beginning in the 1960’s, we were taught that the poly would stop vapor diffusion in building cavity, keeping walls dryer.  During the 1990’s and 2000’s, building scientists determined that only a small percentage of wall wetness comes from vapor diffusion.  So, how does moisture end up inside building assemblies in a northern climate?  Mostly by air leaks! Continue reading “Building Science-Perm”