Spot the Violation

FramingDecksLevel 12018 IRC

New deck ledger below a patio door

Looking up from the lawn at a new deck frame below a patio door, before decking. A green pressure-treated 2x10 ledger runs along the house wall under a galvanized Z-flashing that is tucked up under the lap siding. Pressure-treated 2x10 joists come straight out from the ledger toward the camera, each in a galvanized face-mount hanger with a nail head in every hole. The face of the ledger between the hangers is dotted with small round nail heads in loose clusters; the board shows the slit pattern of incised treated lumber. A white dryer vent hood sits on the siding below the ledger.
New deck frame below a patio door, before decking

What's wrong here?

  1. The ledger is fastened to the house with nails only, with no 1/2 in. lag screws or through-bolts
  2. The ledger must be at least a 2x12 when it carries joist hangers
  3. Metal Z-flashing is not allowed against treated lumber; only a self-adhered membrane may be used
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

The deck ledger is held to the house band joist with nails only; there are no 1/2 in. lag screws or through-bolts.

Correct choice: 1. The ledger is fastened to the house with nails only, with no 1/2 in. lag screws or through-bolts

A ledger-supported deck hangs half its load on the ledger-to-band-joist connection, and nails loaded sideways and in withdrawal let go over time as the wood dries, cycles and corrodes. Ledger failure is the classic way decks collapse with a crowd on them. R507.9.1.3 requires hot-dip galvanized or stainless 1/2 in. lag screws or through-bolts installed at the spacing in Table R507.9.1.3(1) and the edge distances in Table R507.9.1.3(2), and R507.8 says deck attachment to the house may not be made with toenails or nails subject to withdrawal. The hangers, flashing and ledger size here are fine; the ledger is simply not fastened.

How to fix it

Before the decking goes on, add hot-dip galvanized or stainless 1/2 in. lag screws or through-bolts with washers in the staggered two-row pattern from Table R507.9.1.3(1) (spacing set by joist span), keeping the edge distances in Table R507.9.1.3(2), or use a listed proprietary ledger screw per its evaluation report. Pre-drill lag screws, and confirm the house band joist is solid sawn or LVL that can take them.

Code references

  • IRC 2018 R507.9.1.3 — Ledger to band joist details

    Fasteners for a deck ledger connection in accordance with Table R507.9.1.3(1) (1/2 in. lag screws or 1/2 in. bolts at on-center spacings based on joist span) must be hot-dipped galvanized or stainless steel and installed per Table R507.9.1.3(2) and the related figures for spacing and edge distances.

    Drills citing R507.9.1.3

  • IRC 2018 R507.8 — Vertical and lateral supports

    Where a deck is supported by attachment to an exterior wall, it must be positively anchored to the primary structure and designed for both vertical and lateral loads, and the attachment may not be made with toenails or nails subject to withdrawal. Where a positive connection to the primary building structure cannot be verified during inspection, the deck must be self-supporting.

    Drills citing R507.8

  • IRC 2018 R507.9.1.1 — Ledger details

    Deck ledgers must be at least 2x8 nominal, of pressure-preservative-treated or approved naturally durable lumber, may not carry concentrated loads from beams or girders, and may not be supported on stone or masonry veneer.

    Drills citing R507.9.1.1

2024 IRC:not yet checked Confidence: low

Minnesota

MN adopts this rule as writtenConfidence: medium

Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). No Minnesota amendment to R507.9.1.3 is known. DLI is adopting the 2024 IRC as the next edition; see the 2024 IRC note.

About the Minnesota Residential Code

Citation under review. Verified from the verifier's knowledge of the 2018 IRC; code text could not be fetched and web search was exhausted. The verifier moved the 'no toenails or nails subject to withdrawal' citation from R507.1 to R507.8 (Vertical and lateral supports), on the understanding that the 2018 reorganization of R507 moved that 2015 R507.1 sentence there. Confirm R507.8 against the printed 2018 IRC, and confirm the R507.9.1.3 heading reads 'Ledger to band joist details'.

Why the other choices are wrong

  • The ledger must be at least a 2x12 when it carries joist hangers. R507.9.1.1 sets the minimum deck ledger at 2x8 nominal; a 2x10 ledger is fine as long as it is fastened per Table R507.9.1.3(1).
  • Metal Z-flashing is not allowed against treated lumber; only a self-adhered membrane may be used. R507.2.4 permits corrosion-resistant metal flashing at least 0.019 in. thick or an approved nonmetallic material; galvanized Z-flashing over the ledger is a standard, accepted detail.
  • Nothing. This installation is compliant. Nails do not count as a ledger connection. The IRC prescribes 1/2 in. lag screws or bolts at tabulated spacing, and R507.8 says the attachment may not rely on nails subject to withdrawal.
Safety hazardLevel 1 · Apprentice#deck#ledger#lag screws#nails#exterior

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