3. The horizontal mullion of an aluminum curtain wall acts as a gutter to accumulate leakage if the seal between the glass and the glazing gasket is imperfect. Weep holes discharge this leakage back to the outdoors. A window of average width might have three weep holes distributed across its sill.

Wind can drive water back through a weep hole if there is not an adequate air barrier between the weep hole and the interior of the building. This possibility can be minimized by locating the weep hole in a sheltered location that is not likclv to become wet and by insert-

ing a baffle behind the weep hole. The baffle is made of a nondccaying, non-corroding open-celled material that allows water to filter out by gravity but that slows entering air currents enough so that they are unlikely to be able to move water through the opening. A typical baffle material is a nonwoven mat composed of stiff plastic filaments.

4. In detailing a rainscrcen panel system, it is important to design a three-dimensional system for draining the open joints. Especially crucial is the design of the intersections of the horizontal and vertical joints, which need to be detailed carefully for ease of assembly and for raintightness. Any cavity between the rainscreen panels and the air barrier wall must also be drained, using much the same detail as for a masonry cavity wall (detail 2, preceding). ■

Fibrous baffle

Weep holes-

Weep holes-

3. Weep holes in -horizontal Mullion

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