a spandrel beam or a column. It can happen at the sill of a door or a window as a gasket or weatherstrip ages, wears, and begins to leak large volumes of air. Sometimes we just want to be double sure that a detail won't leak. In any of these cases, a simple upstand can serve to prevent wind pressure from pushing water through a horizontal joint, even if the joint is totally unsealed against air leakage. The required height of an upstand is determined by the maximum expected wind pressure. To find the wind pressure, find the design wind speed in the appropriate building code. Then determine the necessary height of upstand according to the accompanying table, interpolating as necessary.

1. A manufacturer of sliding glass doors recognizes that if the interior weatherstrip becomes sufficiendy worn with years of use, the rainscrcen action of the sill detail may become inoperative. A 2" (50 mm) upstand at the interior

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