If a home’s siding is not protected, rain can penetrate joints or seams and lead to moisture damage. Flashing—usually made from galvanized steel, aluminum, or vinyl—prevents this.

Most flashing is sold along with siding. Specialized flashings, such as those made from copper, are generally fabricated by custom sheet-metal shops.

Fasteners should always match or complement the type of siding—galvanized nails for galvanized flashing, aluminum nails for aluminum, and bronze nails for copper. If, for example, galvanized nails were used with aluminum, electrolysis would occur, corroding the nails and staining the siding.