Flashing prevents water that runs down a wall from penetrating the joints between materials. Available types include standard galvanized and aluminum.

Varieties made for vinyl and metal sidings are sold by siding manufacturers. Specialty flashings and flashings made of copper are usually custom fabricated at sheet-metal shops.

Use only galvanized nails for galvanized flashing, aluminum nails for aluminum, and bronze nails for copper flashing. Combining differing metals can cause corrosive electrolysis that may weaken nails and stain siding.