The layer in an enclosure assembly that controls the passage of liquid water even after long or continuous exposure to moisture. More formally, the water control layer is the continuous layer (comprised of one of several materials and formed into planes to form a three dimensional boundary) that is designed, installed, or acts to form the rainwater boundary. In face-sealed perfect barrier systems, this is the exterior-most face of the enclosure. In concealed barrier perfect barrier systems it is a plane concealed behind the exterior face. In drained systems the water control layer is the drainage plane behind the drainage gap or drainage layer. In storage reservoir systems the rain penetration control is typically the innermost storage mass layer.

Variants: Rainwater Control Layer, Rain Penetration Control Layer

Special note: there is currently not an adequate performance metric or series of performance metrics for water control layers. Anyone interested in this issue is invited to contact Joe Lstiburek at