Decks attach to houses at the ledger board, and that joint is a prime location for moisture accumulation that can cause rot and decay. Common aluminum flashing is no longer acceptable because it corrodes quickly when in contact with the new ACQ preservative treated exterior building materials. This vinyl flashing is acceptable for use in contact with ACQ pressure treated materials, and is conveniently pre-scored for standard sawn lumber (1-1/2 thick) deck ledger board. Just fold it to shape, tuck the 4-3/4 high top edge under the siding (for remodeling work) or under the house wrap for new construction. The flashing can be nailed in place on either vertical surface. Sold in 12 inch x 25 foot rolls. Made in USA.