Deck ledger flashing and lateral connection — how to attach a deck so it cannot rot or pull off
A rotted or under-fastened ledger is the #1 cause of deck collapses. Flash it in order — membrane behind the ledger, ledger through-bolted to the band joist, then cap flashing tucked behind the house wrap so each layer laps the one below — and add the lateral ties that resist pull-off.
What this diagram shows
A cross-section through the deck-to-house connection showing the correct waterproofing order, because a rotted ledger is the leading cause of deck collapses. First a self-adhered membrane goes on the wall sheathing behind the ledger; then the ledger is through-bolted to the house band joist with half-inch bolts staggered top and bottom; then a cap or Z-flashing is set over the top of the ledger and tucked behind the house wrap, so each layer laps over the one below and sheds water outward. Deck joists hang off the ledger face on joist hangers, and a lateral-load tension tie connects the deck framing back into the house floor to resist pull-off — two are required per deck under IRC R507.9.2.
Deck Calculator
Code-compliant deck framing, decking, footings, ledger, stairs & railing — built on 2021 IRC R507 and AWC DCA 6 tables. Free, no signup.
