IRC R507.9

Deck Ledger Board Code Requirements

The single most failure-prone connection on any deck. Fastener types, spacing, flashing, prohibitions, and lateral load rules.

By Brian WilliamsPublished April 20, 2026Updated April 22, 2026

Why this matters: Improper ledger attachment is the leading cause of catastrophic deck collapses in the US. A failed ledger drops the entire deck at once, usually full of people. Get this one connection right and your deck stays up.

Approved Fastener Types

1/2" Lag Screws

The IRC baseline. Predrilled pilot holes required. Must penetrate into solid wood (house rim joist) by at least 3 inches after passing through the ledger, sheathing, and any airspace.

1/2" Through-Bolts

Stronger than lag screws. Bolt passes completely through the rim joist with a washer and nut on the inside. Used when inside access is available (unfinished basement behind the ledger).

Approved Structural Screws

Simpson SDWS, GRK RSS, FastenMaster LedgerLOK, and similar. Used per manufacturer-specified spacing patterns, which may differ from IRC lag-bolt tables. Faster install, no pre-drilling.

Never use regular nails or deck screws

Regular 16d framing nails, deck screws (#8 or #10), or drywall screws are NOT acceptable for ledger attachment. They lack the shear and withdrawal strength required. A deck attached with nails will pull free from the house, often with no warning. This is the single most common cause of deck collapse.

Fastener Spacing by Joist Span

Per IRC Table R507.9.1.3. Use two staggered rows with this center-to-center spacing along the ledger:

Joist Span	1/2" Lag (DFL/SP)	1/2" Lag (SPF/HF)	1/2" Bolt
Up to 6 ft	30"	30"	36"
6 to 8 ft	23"	23"	36"
8 to 10 ft	18"	18"	34"
10 to 12 ft	15"	15"	29"
12 to 14 ft	13"	13"	24"
14 to 16 ft	11"	11"	21"
16 to 18 ft	10"	10"	19"

DFL = Douglas Fir-Larch, SP = Southern Pine, SPF = Spruce-Pine-Fir, HF = Hem-Fir. Spacing assumes 40 PSF live + 10 PSF dead load. Stagger the two rows so no fastener is directly above another.

Flashing Requirements

Per IRC R507.9.1.4, continuous flashing is required at the ledger. Skip this step and water gets behind the ledger, rotting the house's rim joist within 5 to 10 years. Rotten rim joist = failed ledger attachment = collapsed deck.

Metal Z-flashing

• Galvanized steel, aluminum, or copper
• Top leg goes UNDER the house's WRB and siding
• Middle leg drops down the face of the ledger
• Bottom leg kicks out over the top of the ledger
• Continuous along the full length of the ledger

Self-adhering membrane

• Peel-and-stick butyl or rubberized asphalt
• Applied to house sheathing before ledger is installed
• Wraps up from the sheathing over the top of the ledger
• Lapped with the WRB above per manufacturer
• Easier than metal but requires clean application

The 1/2-inch drainage gap

Many builders leave a 1/2-inch air gap between the ledger and the siding (or install spacer washers between the ledger and the sheathing) to allow any water that does get behind to drain out. This is a belt-and-suspenders approach that complements flashing, not replaces it.

Prohibited Ledger Attachments

Brick or stone veneer

Veneer is not structural. It cannot carry deck load. Either remove the veneer to expose structural wall, or use a freestanding deck.

Cantilevered floor joists

Cantilevered bump-outs lack the load capacity of supported floor framing. Requires engineering.

SIP (structural insulated panel) walls

SIP walls have special connection requirements. Standard lag bolts do not develop full capacity. Use manufacturer-approved ledger connectors.

Stucco without sheathing

Stucco over metal lath on open studs offers no solid substrate. Remove stucco in ledger area and attach to structural framing.

Cantilevered rim joist

Same issue as cantilevered floor joists. No load capacity beyond the original design.

Engineered I-joist rim without reinforcement

The web of an I-joist is not designed for lag-bolt load transfer. Reinforce with an OSB ledger or an LVL rim board.

Lateral Load Connection

Lag bolts and through-bolts resist the deck pulling AWAY from the house, but not sliding or racking motion. IRC R507.9.2 requires a separate lateral load connection — typically hold-down hardware that ties the deck's floor framing to the house's floor framing.

Standard lateral load solution

Two Simpson DTT1Z or DTT2Z hold-downs (or equivalent)
One near each end of the ledger
Strap extends through the rim joist into the house floor framing
Bolted on both sides with the specified hardware
Provides minimum 1500 lb load capacity in tension

Frequently Asked Questions

What is a deck ledger board?

The ledger board is the horizontal 2x framing member bolted to the side of the house. Joists from the deck hang off the ledger, transferring the deck's load into the house's structure. The ledger-to-house connection is the single most failure-prone part of any attached deck.

Why does the ledger connection matter so much?

Ledger failure is the leading cause of catastrophic deck collapse in the US. The ledger carries half the weight of the deck (the house-side half). When it pulls away from the house, the entire deck falls. Most historic deck collapses have involved improper nailing to siding, missing flashing, or rotted rim joist behind the ledger.

Can I attach a ledger with nails?

No. IRC R507.9.1 requires 1/2-inch lag bolts or through-bolts for ledger attachment. Nails do not develop enough withdrawal strength and fail over time. Deck-screws rated for structural ledger use exist (Simpson SDWS, GRK RSS, FastenMaster LedgerLOK) and are also acceptable per manufacturer-specified patterns.

What is the fastener spacing?

IRC Table R507.9.1.3 gives spacing based on joist span and lumber size. Typical values: 1/2" lag bolts or through-bolts at 16" to 30" on center, in a staggered pattern, with at least two rows. Exact spacing depends on the joist span, so a deck with 10-foot joists needs tighter spacing than one with 6-foot joists.

What flashing do I need behind the ledger?

IRC R507.9.1.4 requires continuous flashing at the ledger. Two common methods: (1) metal Z-flashing integrated behind the siding, under the house's WRB (water-resistive barrier), extending out over the top of the ledger; or (2) self-adhering peel-and-stick membrane over the house sheathing and extending onto the ledger's top edge. Both need proper lapping with the WRB above. Failure to flash causes rim joist rot behind the ledger, which is how many 20-year-old decks collapse.

Can I attach a ledger to brick veneer?

No, not without engineering. IRC R507.9.1.5 prohibits ledger attachment to brick veneer or stone veneer because these are not structural. Options: (1) install a freestanding deck with its own beam parallel to the house, (2) have an engineer design an attachment that bypasses the veneer with long bolts into the structural studs behind, or (3) remove the veneer in the ledger area and attach directly to the sheathing and rim joist.

What about cantilevered floor joists?

Cannot attach a ledger directly to a cantilevered floor joist system without engineering. A cantilevered second-floor joist bay does not have the same load capacity as a supported bay. If your house has a cantilevered bump-out where you want to attach the deck, either build the deck freestanding or have a structural engineer evaluate the cantilever capacity.

What is lateral load connection?

IRC R507.9.2 requires a separate lateral load path between the deck and the house to resist horizontal forces (like a crowd moving in unison, wind on the deck railing). This is typically achieved with hold-down hardware (Simpson DTT or equivalent) installed through the deck joists and into the house floor framing. The hold-downs resist lateral movement that lag bolts alone cannot.