Roof flashing is a thin material, usually galvanized steel, that professional roofers use to direct water away from critical areas of the roof, wherever the roof plane meets a vertical surface like a wall or a dormer. Flashing is installed to surround roof features, such as vents, chimneys, and skylights. Water should run down the side of the flashing and be directed to the shingles instead of finding its way into the roof deck.