Deck Ledger Board Attachment: The Complete Fastening Rules

Jump to what you need

Why the Ledger Is Structurally Different from Every Other Deck Connection

A post on a footing is compression into soil. A joist on a beam is bearing on wood. The ledger is a fastener group into an existing structure. Withdrawal, shear, and the condition of the band joist all matter. If that group lets go, the deck drops away from the house — the classic residential deck collapse mode.

That is why ledger fastening is its own calculation. Beam span, footing size, and post spacing size the free-standing side of the deck. They do not attach it to the house. Size those with the beam span, footing, and post spacing calculators, then come back here for the house connection.

Two Staggered Rows on a Standard-Depth Ledger

On a 2x8 or deeper ledger (about 7.25" actual and up), fasteners go in two staggered rows — one toward the top edge, one toward the bottom, offset so you are not splitting the same grain line. A single row is a shallower-ledger / special-case layout. The calculator defaults to two rows for that reason.

Stagger spreads load into more of the band joist and keeps edge distance on both the ledger and the rim. Do not put both rows so close to the edges that you blow out the board, and do not line them up as a single perforated line down the middle.

End Distance, Edge Distance, and Where the First Fastener Goes

Keep a minimum 2" end distance from each end of the ledger. The calculator uses that 2" margin when it counts fasteners. Edge distance toward the top and bottom of the board still matters so you do not split the ledger or miss the band joist behind it.

The first and last fasteners in each row sit at that end margin. Everything between them follows the on-center spacing. If the last gap wants to run wider than the calculated spacing, add a fastener rather than stretching the last bay.

Flashing Is Not Optional — It Is How the Joint Stays Dry

Water that sits in the ledger-to-house joint is the number-one rot cause at this connection. Rotten band joist plus loaded fasteners is how ledgers walk off the house years later, not the day you hang them.

Z-flashing (or an equivalent one-piece flashing that kicks water out over the ledger and behind the siding above) keeps that joint from becoming a trough. Siding is cut so the flashing tucks up behind it. Do not caulk the top of the ledger as a substitute. Do not bury the ledger behind siding with no flashing path out.

Lateral Load Devices (IRC R507.9.2) — Brief, On Purpose

Vertical load is the lag/bolt group. Decks also try to pull away from the house. IRC R507.9.2 covers tension/hold-down devices for that lateral load. They are a separate hardware path from the spacing table — listed hold-downs, tension ties, or an approved alternative, installed per the manufacturer.

This page does not size those devices. If the inspector asks for lateral load connections, that is a listed-product install, not a denser lag pattern. Do not assume extra lags replace hold-downs.

What Hardware Is Actually Listed for This Connection

For the IRC prescriptive path, plan on 1/2" hot-dip-galvanized hex-head bolts or 1/2" hot-dip-galvanized lag screws. Carriage / cap-head bolts and ordinary deck screws are not permitted for attaching the ledger to the band joist.

Lag screws must fully penetrate through and beyond the inside face of the band joist. A lag that dies in sheathing or in the first inch of rim is not that connection. Through-bolts need a washer and nut on the inside face — which means you can reach it. Structural screws (Simpson SDWS, LedgerLOK, and similar) are an ICC-ES alternate path, not the IRC table itself. Walk that three-way choice in lag vs through-bolt vs structural screw.