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For a cavity wall to function properly, water that collects on flashing must be able to drain through weep holes to the exterior of the building. If weep holes do not function properly, water collecting in the cavity can infiltrate to the building's interior. For proper drainage cavity walls must be detailed correctly and constructed to keep the cavity clear of mortar droppings and prevent weep hole blockage. The most common types of weep holes are open head joints, louvered vents, rope wicks, tubes, cellular vents, or a combination of these. TYPES OF WEEP HOLES Open head joints: Unmortared head joints, spaced at regular intervals at the base of the cavity, are highly effective and are the easiest type of weep hole to construct. Louvered vents: Louvered aluminum or plastic vents sometimes are used in conjunction with open head joints to keep insects out of the cavity. Rope wicks: Cotton sash cord also is commonly used for weeps. The cotton fibers have a wicking effect that draws moisture from the cavity to the exterior of the building. Tubes: One-quarter-inch-diameter plastic or metal tubing, cut slightly longer that the thickness of the wythe, is mortared in place as the course immediately above the flashing is laid. Cellular vents: Plastic cellular vents consist of many small, adjacent passageways bonded together in one unit. The cross section is similar to that of a honeycomb. PREVENT MORTAR BUILDUP The best way to assure proper drainage of water is to maintain a cavity that is free of mortar droppings. This requires good workmanship and construction.