The answer to 'what causes drip edge' is that drip edge is a metal flashing installed along the edges of a roof to help direct water away from the fascia and exterior walls of a home. Drip edge helps prevent water damage by ensuring that rainwater and snowmelt flows off the roof and away from the home's siding and foundation.
Drip edge is an important component of a properly installed roof system. It is typically made of aluminum, galvanized steel, or vinyl and is installed along the eaves and rakes (the sloped edges) of the roof. The drip edge extends slightly past the edge of the roof, creating a small overhang that allows water to drip off the roof rather than running down the fascia board or exterior walls.