How to Connect a Deck Ledger Flashing to a House

Install sheet flashing, before the ledger board, if you decide to use this method. Follow the instructions for the sheet flashing based on the manufacturer. The flashing needs to slide up under the bottom row of siding and will be held in place with an adhesive of some kind. Usually this is a peel-away membrane, but you can also use silicone caulking to adhere the flashing to the wall of the house.

Use lag screws to mount the ledger board to the side of the house on top of the sheet flashing. Use a drill to set the lag screws and level the board across the length. Mount it at the ends and also set screws at every stud that runs up the wall. Use at least three washers behind the ledger board to keep the board clear of the flashing and caulk around the screws with silicone caulking after the board is set. Set the board 1 inch plus the width of the deck planking below the door or 2 inches below the bottom row of siding.

Mount the ledger board in place under the bottom row of siding if you use Z-flashing. Allow the minimum spacing as recommended by the siding manufacturer, which is usually 2 inches of empty space between the bottom row of siding and the top of the ledger board or an inch plus the width of the deck boards below the door. You do not need to use spacers in this case; merely screw the board into the studs.

Wrap the top of the board with the Z-flashing. The upper part of the flashing slides under the bottom row of siding, and the other part of the flashing folds over the top of the ledger board and down over its face. Use silicone caulking to adhere the Z-flashing in place and press it firmly against the wall, under the siding and on top of the ledger board to ensure its bond.