Rain penetration is one of the oldest problems building owners have had to deal with, yet it still occurs all too frequently. The penetration of rain can not only damage interior finishes and materials, but it can also damage the structure of walls themselves.

One approach to controlling rain penetration, first introduced in the early 1960s, is the pressure-equalized rainscreen design. The theory of pressure-equalized cladding is that air flows into the cavity behind the exterior cladding equalizing the cavity pressure with the wind pressure and thus, minimizing the force (wind pressure) that causes most rain penetration. Previous research has shown that there is a time lag between the application of the wind load and pressure equalization in the cavity. As a result of this time lag, a pressure difference does occur across the exterior cladding. For the rainscreen concept to be effective, this time lag should be as short as possible. Therefore, when the performance of a rainscreen wall is examined, one of the primary factors considered is time to equalization; the longer the time to equalization, the more rain is likely to penetrate.

Another consideration is the load applied to the exterior cladding; the higher the load, the larger the driving force moving rain to the interior.