Evolution of Wall Design for Controlling Rain Penetration

The penetration of rainwater through walls depends on the following combination of conditions: • the presence of water • openings in the assembly that permit water to enter • forces that can move water through the assembly. The control of rainwater penetration depends on being able to control any one or all of these conditions. Rain penetration creates problems ranging from damage to interior finishes and furnishings, to the growth of mold and mildew, to premature structural deterioration. Over time, rain penetration has been controlled in various ways ranging from massive masonry construction to pressureequalized rainscreen (PER) curtain-wall assemblies.