The most critical concern while installing the ledger board should be how to prevent water from entering the seams into the house. You will have to install flashing also known as a drip edge to act as a barrier to keep water out. If water can penetrate into the house framing it can result in severe mold, decay, and overall serious and expensive damage. After you have cut the siding but before you install the ledger board you must apply your flashing. To install flashing you will need to tuck 2-3” under the house siding before bending the material over the top of the ledger board. You may have to remove nails in the siding to allow the flashing into place. Make sure the flashing runs the entire length of the ledger board.
Once the flashing is in place behind the siding you can install the ledger board underneath. Afterwards you can use a wood block and a hammer to bend the flashing over the ledger board to form the drip edge. Use silicone caulking to seal the end butt joints and any places where water might intrude. Make sure that you overlap and seal any seams with 6-10” of overlap and that you never allow the flashing to become punctured by nail and screw holes. In areas where there will be significant amounts of rain and snow you may want to line the house wall with a bituminous house wrap like Tyvek before installing the flashing for an extra layer of protection. Some Deck builders also install a layer of flashing to the bottom of the ledger board. This is not required but offers an additional barrier for water that could flow into the house underneath the ledger board. Water it seems can get into anyplace that is not appropriately sealed.