During typical winter months, vapor diffusion to the exterior is the main mode of moisture exchange in a “dry” wall, while in a “moist” wall, the forces of surface diffusion are simultaneously working to move moisture to the interior. The “wet” wall is dominated by forces of capillary conduction moving excess moisture to drier areas and components. The directions of moisture movement for these exchange mechanisms may be opposed, depending on variables such as RH, pressure/temperature differentials, and the amounts and sources of moisture and vapor.