Tags: #buildingdesign #buildingenclosures #buildingenvelopes #buildingmaterials #buildingproducts #buildingscience #materialsscience #waterresistance

This visualization demonstrates moisture diffusion against steep thermal gradients. Two different strategies, same quality performance.

I’m using the same assemblies previously described as XiA and XiB. One has its sheathing & WRB inboard of the insulation (XiA) and the other has those components outboard of the insulation (XiB). Both assemblies are configured with 1-perm WRBs. The cavity is free of insulation and I’ve omitted an interior vapor retarder. Heat and moisture fluxes were applied to both sides of the assembly with the following conditions: 0F, 70% on the exterior side, and 70F, 40% on the interior side. This time-dependent simulation reflects a period of 7 days. 

As we all know, heat and moisture are coupled. The fate of moisture is determined by its temperature gradient as well as its vapor pressure gradient.