Flashing

A thin continuous piece of sheet metal or other waterproof material installed to prevent the passage of water into a structure from a joint or angle. For example, roof flashing is placed around objects that protrude from the roof of a building (such as chimneys and pipes, or the edges of other roofs) to deflect water away from seams or joints. Flashing is usually made of a metal such as copper, zinc alloy, aluminium, painted galvanized steel, stainless steel or copper-clad lead.