Spot the Violation

FramingDecksLevel 22018 IRC

Ledger and joists ready for decking

View from a ladder looking down at a deck frame where it meets the house, below a patio door. Gray lap siding has been cut back above a green pressure-treated 2x10 ledger, leaving a strip of white house wrap, printed with pale blue HOUSE WRAP lettering, showing between the bottom of the siding and the top edge of the ledger. The ledger face carries 1/2 in. lag screws with washers in a staggered pattern, and pressure-treated joists run toward the camera in galvanized face-mount hangers with every hole nailed. A yellow 4 ft level lies across two joists, and the foundation wall and lawn show about 3 ft below, between the joists. Blue-capped staples hold the house wrap. HOUSE WRAP HOUSE WRAP HOUSE WRAP HOUSE WRAP HOUSE WRAP HOUSE WRAP HOUSE WRAP
Deck frame at the house wall, ready for decking

What's wrong here?

  1. The ledger has no flashing; the top edge butts bare house wrap with nothing lapped over it
  2. The lag screws are staggered; they must be in one straight row along the center of the ledger
  3. The ledger must be held 1/2 in. off the wall on spacers so water can drain behind it
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

The ledger was installed with no flashing: the siding stops above it and the top edge of the ledger sits against bare house wrap, so water running down the wall goes behind the ledger.

Correct choice: 1. The ledger has no flashing; the top edge butts bare house wrap with nothing lapped over it

R703.4 requires approved corrosion-resistant flashing, applied shingle-fashion, where exterior porches, decks or stairs attach to a wall or floor assembly of wood-frame construction, so water is kept out of the wall and off the framing. Without it, every rain runs down the siding, onto the top of the ledger and behind it, where the house band joist and the ledger fasteners rot and corrode out of sight. That is how a properly lagged ledger fails ten years later. R507.2.4 sets the material: corrosion-resistant metal at least 0.019 in. thick or an approved nonmetallic flashing compatible with the wall and the deck. The lags, hangers and ledger size shown are fine.

How to fix it

Before decking, install flashing that laps shingle-fashion: a self-adhered membrane or metal flashing tucked up under the house wrap and siding, over the top of the ledger and down its face (a Z or L flashing with a drip edge is common). Tape or cut the wrap so the upper layer laps over the flashing, then bring the siding or trim down over the flashing's vertical leg.

Code references

  • IRC 2018 R703.4 — Flashing

    Approved corrosion-resistant flashing must be applied shingle-fashion to keep water out of the wall cavity and off structural framing, and must be installed at listed locations, including where exterior porches, decks or stairs attach to a wall or floor assembly of wood-frame construction.

    Drills citing R703.4

  • IRC 2018 R507.2.4 — Flashing

    Deck flashing must be corrosion-resistant metal of at least 0.019 in. nominal thickness or an approved nonmetallic material compatible with the substrate of the structure and the decking materials.

    Drills citing R507.2.4

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 R703.4 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. R703.4 item 5 (flashing where exterior porches, decks or stairs attach to a wall or floor assembly of wood-frame construction) and the staggered two-row ledger fastener pattern are well established. Confirm only that the deck flashing material rule (0.019 in. corrosion-resistant metal or approved nonmetallic) is numbered R507.2.4 in the 2018 IRC.

Why the other choices are wrong

  • The lag screws are staggered; they must be in one straight row along the center of the ledger. The IRC ledger figures show the fasteners staggered in two rows, with the edge distances in Table R507.9.1.3(2); a single center row is not the prescriptive pattern.
  • The ledger must be held 1/2 in. off the wall on spacers so water can drain behind it. Spacers are an optional drainage detail some builders use; the IRC requires flashing at the deck-to-wall joint (R703.4), not a gap.
  • Nothing. This installation is compliant. Everything else is right, but water running down the siding lands on the open top of the ledger and gets behind it into the house band joist, which R703.4 requires flashing to prevent.
Safety hazardLevel 2 · Journeyman#deck#ledger#flashing#house wrap#exterior

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