The Brick Institute of America (BIA) says, "A masonry cavity wall, properly designed and built, is totally resistant to rain penetration through the wall assembly." This article looks in-depth at each component of a cavity wall. OUTER WYTHE Both wythes can be load-bearing, but usually the outer wythe is nonload-bearing. INNER WYTHE The inner wythe may be clay brick, structural clay tile, or concrete masonry. CAVITY Construct the cavity between 2 and 4 1/2 inches wide. Leave the cavity as an air space or place insulation in it. METAL TIES In a cavity wall, both wythes must act together in resisting wind loads and other lateral forces. This usually is accomplished by connecting the wythes with corrosion resistant metal ties. FLASHING Install flashing at the bottom of the cavity and wherever the cavity is interrupted. WEEP HOLES Place weep holes in the outer wythe immediately above the flashing. MORTAR JOINTS For cavity walls, BIA recommends using Type S mortar where the wind exceeds 80 mph and Type N elsewhere. INSULATION Inside the cavity, you can install rigid board insulation or granular fills, such as water-repellent vermiculite or silicone-treated perlite.