Attach the Ledger and Protect the Ledger Remove the building’s trim and siding until it’s 1 foot above the top of where the ledger will sit. Cover the exposed sheathing with self-adhering waterproof membrane. Mark the exact location of the top of the ledger. Any step down to the finish decking, which sits atop the ledger, must be 4 to 7 3/4 inches below the door sill, according to code. Mark a level chalk line. Cut a 2-inch-wide, 1 1/2-inch-thick treated wood spacer for every 2 feet of ledger length. Align the top of each spacer with the chalk line and fasten with a 6d nail. Align the ledger with the tops of the spacers and nail it to the wall at each spacer with a 16d nail. Joints between ledger boards should fall on a spacer. Drill a 3 3/8-inch pilot hole through the ledger and into the house’s rim joist at each spacer, and follow a zigzag pattern. Insert a 1/2-inch lag screw in each hole and tighten it against a washer using an impact wrench or socket wrench.