2.6 : Cavity Drainage and Flashings in Masonry walls

Typically, a cavity wall consists of two wythes separated by a gap of at least 2 inches, which may contain insulation while still maintaining a minimum clear space of 1 inch to facilitate adequate drainage. Advanced methods like the insertion of a continuous drainage mat can further reduce this space while ensuring effective moisture expulsion.

Weep holes, strategically placed at the base of the cavity, are critical for draining accumulated water. These openings are created by leaving head joints open, often protected with screens to block pests. Flashings are implemented in two forms: external and internal. External flashings, including metal copings and counter flashings, protect vulnerable areas like parapets and intersections with flat roofs, preventing water ingress. Internal flashings are integrated during wall construction, positioned at potential water entry points like window heads and sills. These flashings catch and direct water toward the exterior via weep holes.

Materials for flashings vary, ranging from durable and expensive metals like copper and stainless steel to flexible, cost-effective options like asphaltic membranes and synthetic rubber. Given the complexity of replacing internal flashings and the relatively low cost of high-quality materials, the use of durable flashing materials is advisable to avoid future expenses related to water damage. Proper installation, including the overlapping and sealing of flashing sections, is vital for ensuring that all moisture is directed outwards.