Proper placement of the drip edge on through-wall flashing is a critical, yet often overlooked, detail in building envelope waterproofing. The drip edge is the leading edge of the flashing that projects outward from the wall face. Its primary function is to create a clean break in the water's surface tension, causing rainwater to drip harmlessly away from the wall below rather than running back down the masonry.

The key principle for location is that the drip edge must project far enough from the wall surface to prevent water from wrapping around the edge due to capillary action or wind. Industry standards, such as those from the Brick Industry Association, recommend a minimum projection of 1/2 inch (12.7 mm) from the face of the wall. This projection should also be sloped downward at a pitch of at least 1/4 inch per foot (1:48 slope) to ensure positive drainage. An integral drip edge, often formed by folding the metal flashing back on itself at a 45-degree angle or crimping a groove, helps break water adhesion. For example, a common practice is to use a "weep notch" or a continuous groove cut into the projecting metal.

Equally important is the vertical location within the wall assembly. Through-wall flashing must be placed directly over a continuous mortar joint, typically just above the foundation, above lintels over windows and doors, and below shelf angles at floor lines. The drip edge must not be buried in the mortar joint below. Instead, it should be fully exposed, hanging free to allow for unobstructed dripping. If the drip edge is even partially obstructed by a sealant bead or mortar droppings, water can bridge the gap and stain or damage the wall below. Always verify that the drip edge is clean, unobstructed, and properly sloped during installation. A well-placed drip edge is a simple but powerful defense against long-term moisture intrusion.