To apply a drip edge, first remove the debris and dirt from the edges of the roof. Measure the roof edges, and use those measurements to cut the drip edge with metal snips. Lift the roof's shingles, and insert the top portion of the drip edge under them. Use a roofing nail to secure the drip edge every foot, and then replace the shingles. When starting a new piece of drip edge, overlap the two pieces to prevent any cracks.
Drip edges should be outfitted with an ice and water shield. This shield is a self-sealing membrane and, when applying it to the eaves, it is installed before replacing the roof's shingles. It comes in 3-foot rolls and has a backing to be peeled off one-half at a time. First stick the membrane on the drip edge, and fold it over the edge. Peel off the rest of the back, and stick it to the rest of the drip edge.
When applying the ice and water shield membrane to the rakes, install the membrane after removing the shingles and before laying the drip edge. Once the drip edge is in place, nail it down.
Drip edges are used to keep rainwater from running directly off the roof. Instead, it is routed to the gutters for proper dispersal. Additionally, it can prevent roof leaks by blocking rain blown by wind.