My new house is being built with a deck and I noticed that the framer has fastened the ledger directly to the rim joist without any sort of waterproofing between. The sheathing which is Zip system doesn't cover the rim joist either, so it's truly ledger on joist.
When I asked him he said that because the deck will be waterproof (it's over the entry and is pitched and will be roofed before sleepers and decking) it will be flashed along with the remainder of the waterproofing and water will never get in. I would still have liked to see some flashing between the boards, but will it be watertight? I can't find any code that requires that he does it the way I would thing it should be done which is flashed behind and above the ledger.
Best Answer
You do not need water proofing in between the ledger and the rim joist, but the joint needs protected some how. Flashing, roofing membrane, etc. And what ever it is needs to go under the siding and over the ledger in a continuous fashion with no seams at the ledger. Tar paper is not enough. Metal, EPDM, etc is what is needed.