Drip edge is metal border put along the edges of a roof to keep water from getting up under the shingles and down into the facing board (fascia), roof decking and rafters or trusses. It comes in varying widths, bent at a 90-degree angle so one face goes on the roof and the other side goes down the facing. It is nailed onto the roof after the roof decking and roofing felt have been put down, but before the shingles. On a roof on which a drip edge was not installed initially, it may be added by sliding one edge up under the shingles.
Nail drip edge starting at one corner of the roof. Overlap sections at least an inch on straight roof edges with the overlap in the direction of the prevailing wind. Overlap on rake or sloped edges from bottom to top, so water will not drain into the overlap. Ensure both sides are flush against the boards. Drive nails with a hammer about every 2 feet, starting at the corner.
Miter corners with tin snips. Cut angles about 45 degrees, but off just enough so that mitered ends overlap and are not flush. Miter just one end for better overlap; cut one piece square to the end of the roof and miter the overlap. Nail through the overlap to secure both pieces.
Overlap corners. Cut one piece of drip edge square on both edges to fit against the end of the roof. Cut the overlapping piece with the top edge to fit square against the end of the roof and the overhanging edge to fold around the corner. Slide the overlapping corner under the other overhanging piece of drip edge. Drive one nail through both top edge pieces to secure the corner.