drip edge

A drip edge is a strip of sheet metal, usually aluminum or galvanized steel, installed at the boundary between roofing and walls to redirect water away from the building structure. Its defining feature is a downward-pointing lip or hem at its outer edge, which breaks the surface tension of water and causes it to drop cleanly rather than run back along the underside of the material. Without it, water clings to the underside of fascia boards, gutters, and wall trim, soaking into wood and creating rot and mold damage behind the wall.

Drip edges come in several standard profiles. The most common is the L-shaped or angle piece, bent to fit the edge of a roof deck, with a small outward curl at the lower edge. Some versions feature a hemmed or turned lip that extends 0.5 to 1 inch beyond the bent corner, creating the actual break point for water. Widths typically range from 2 to 3 inches on the roof face. Material thickness is usually 0.024 to 0.032 inches for aluminum, slightly heavier for galvanized steel. The bend radius and lip design are critical: too sharp an angle and the metal will crack; too gentle, and water still creeps back.

Installation happens at the eaves and gables, typically before shingles or other roofing material goes down. Nailing height and spacing matter because fasteners themselves can become water entry points if placed incorrectly. Roofers install drip edge along the rake edge (sloped end) of the roof to manage water running down the sides, and along the eave edge where gutters are present. In gutterless installations, the drip edge is the only defense against water soaking the fascia and rim board.

Common failures and causes

Water damage often points to missing or undersized drip edge. In older buildings, drip edge is frequently absent entirely; modern building codes now require it. When present but failing, the problem is usually undersizing: an edge that doesn't project far enough, or a lip that is too small to break water flow reliably. Installation errors, such as placing drip edge under the first course of shingles instead of over it, eliminate its ability to channel water into the gutter. Improper fastening or corrosion perforation in galvanized steel also compromise performance.

The term comes directly from its function: it is the edge that causes water to drip, rather than flow or seep. In the building trades, it is sometimes called a drip flashing or eave trim, though drip edge is the standard term in most of North America. It is an unglamorous component but a critical one; the difference between a building that stays dry for decades and one that rots behind the walls often comes down to whether drip edge was installed correctly and whether it was sized for the expected water flow and wind-driven rain in the local climate.