Ask where decks fail and the answer is almost always the same place: the ledger, the board that fastens the deck to the house. It carries half the deck’s load, it sits against the wall where rain runs down, and nobody sees it once the boards are on. In a Puget Sound climate, how that joint is flashed decides whether the framing outlasts the boards on top of it.
What the ledger does
A deck attached to a house hangs one side of its framing on a ledger bolted to the house’s rim joist. The joists hang from the ledger in metal hangers, and the ledger hands their load to the house. If the ledger or the rim joist behind it softens, the fasteners lose their grip and the deck can pull away from the house, and it tends to happen when the deck is most loaded. That is why every deck inspection starts at the ledger.
Why it rots here
Water does the damage, and not much of it is needed. Rain runs down the siding, reaches the top of the ledger and stops. Without flashing it soaks into the gap between ledger and house, wets the sheathing and the rim joist, and stays there, because that gap never sees sun or wind. Many older decks were fastened straight through the siding with no flashing at all; on a thirty-year-old deck, rot in the rim joist and ledger is one of the first things we find when the boards come up.
What a correct ledger detail looks like
- Siding off where the ledger goes. The ledger bears on the house framing, never on siding, and never on brick or stone veneer, which cannot carry it.
- A membrane on the sheathing. Self-adhered flashing membrane behind the ledger, lapped so water runs out over it, not behind it.
- Structural fasteners. Through-bolts or structural screws in the pattern the code or the engineer sets, into a sound rim joist. Nails are not a ledger connection.
- Room to drain. Spacers between ledger and wall, so water that gets behind can run out and the wood can dry.
- Cap flashing on top. Metal flashing over the ledger, tucked up under the house wrap and siding above, so the water running down the wall is carried over the ledger instead of into it.
- Tape on the wood. Butyl joist tape over the ledger and every joist and beam top, so water coming through the board gaps is not held against the framing.
The residential code Washington adopts requires flashing where a deck attaches to a wood-framed wall; the order of the layers is what makes it work. It is the same detail on every deck we build, cedar or composite.
Checking your own deck
Most of the warning signs can be seen from under the deck with a flashlight and a screwdriver:
- Dark streaks or stains on the siding or foundation just below the deck.
- Wood at the ledger or rim joist that a screwdriver sinks into.
- Rust streaks at the fasteners, or nails and no bolts at all.
- A gap opening between the ledger and the house.
- Joist hangers that are rusted through, bent or missing nails.
- Water stains on a ceiling or wall inside, near where the deck attaches.
Any one of these is a reason for a closer look. Two or more usually mean the ledger has to come off.
Repair or replace?
If the ledger and rim joist are sound, re-flashing during a resurface is a modest job. If the rim joist behind it has rotted, the repair is to the house as well as the deck, and it has to be done before anything goes back on. When the ledger, several joists and the posts all need work, a deck replacement on new framing usually costs little more than the repairs. Repair or Replace an Old Deck? walks through how to decide, and Deck Maintenance in a Wet Climate covers the yearly check.
Much of our work in Renton and other neighborhoods of older homes starts right here. If you are not sure what you are looking at, send photos of the ledger and the underside of the deck with the quote form, and we will tell you whether it needs an inspection.