August 26, 2009

Drainage is widely accepted as one of the most effective measures for reducing moisture damage due to rain penetration. As a result, a significant proportion of residential and commercial cladding systems employ drainage as a rain control mechanism. Although drainage is effective, some water is always retained in the drainage space, either as droplets on the surface or absorbed and adsorbed to materials lining the drainage space. Previous ASHRAE-sponsored research has shown that ventilation behind the cladding can remove significant amounts of this retained moisture.