The lack of flashing above a ledger is a very upsetting situation. When it comes to water damage turning to rot in wood materials, getting wet is not the problem…it’s not being able to dry that creates havoc. In the case of the ledger sans flashing, the ledger is the visible part, but that part can also dry. While everything may appear okay from a view of the ledger, the framing of your home may be rotting apart. This condition can cause significant damage to the home that can rival the cost of the new deck.
If you're rebuilding your deck, then without any question, it’s time to pull that ledger and see what has not been seen in years. Any damage to the home should be promptly and properly repaired before construction of the new deck with a flashed ledger begins. If the deck appears to have life left in it, and the lacking flashing was discovered during an annual inspection (recommended), then some repair should be on your to do list. Though it will take some dismantling, and perhaps a replacement deck board or stick of siding, following the recommended practices for installed ledger flashing based on your exterior cladding is the best approach. If you’re just trying to buy a few years until a new deck can be built, some tubes of high-quality silicone caulk, and whatever other tricks it takes to divert water to the face of the ledger, can buy you some time. It all depends on what damage is already done.