How to Install a Drip Edge to an Existing Roof

Choose a corner of the roof on which to begin attaching the drip edge. Measure two inches from the end of a piece of drip edge and cut the front lip with tin snips. Bend the drip edge at the cut to form a 90-degree angle.

Position the drip edge so the 90-degree angle wraps around the chosen corner. Slide the drip edge under the shingles and position it so it is flush against the roof edge.

Lift the shingles, one at a time, and drive roofing nails through the drip edge. Space the nails approximately 2 feet apart along the length of the drip edge. Install additional nails where the drip edge overlaps or wraps around corners. Make sure the nails are far enough up the drip edge that the shingles cover the nail heads.

Continue sliding sections of the drip edge under the shingles, overlapping the sections by one inch. Cut the lip of the drip edge at each corner and wrap it around the corners to create a continuous edge around the perimeter of the roof.

Cut the face of the drip edge with tin snips and bend it to fit around the roof peaks. Joining different sections at the peaks can leave gaps that water will penetrate.

Overlap the drip edge with the higher section on top, on roof edges that are not horizontal. Overlapping with the lower section on top can allow water to run behind the drip edge on sloped surfaces.