A ledger is the board or framing member that secures a deck or porch to the structure. These framing members are vulnerable to moisture damage as debris and water often become trapped between the ledger and the wall leading to rot or decay.
One construction method used to address this problem is to space the ledger off-the-wall by installing metal washers or other appropriate material of sufficient thickness to allow water to flow behind the ledger and not get trapped. Another method is to install metal flashings that direct water over the top of the ledger and prevent it from being trapped. An uncommon, but effective method is to build the deck or structure freestanding adjacent to the structure, thereby requiring no penetration into the siding and eliminating the potential for leaks or moisture damage.