Spot the Violation

FramingDecksLevel 22018 IRC

Deck at the back of a rambler

End view of a new pressure-treated deck about 4 ft above the lawn, built against the back wall of a house below a patio door. The deck has no ledger: the joists stop about an inch short of the lap siding, which runs unbroken behind the deck. A doubled 2x10 beam sits on 6x6 posts about a foot out from the house wall, and a second beam on 6x6 posts sits about a foot in from the outer edge, with diagonal knee braces from the outer posts to the beam. The beams sit in galvanized post caps, and each post stands in a galvanized base on a concrete pier at the grass. A guard of 2x2 balusters with a flat top rail runs along the open sides.
New deck behind a one-story house, end view

The footings for this deck were inspected and approved at frost depth. What's wrong here?

  1. Nothing. This installation is compliant
  2. A deck built against a house must be bolted to it with a ledger
  3. The joint between the deck and the house wall must be flashed as required by R703.4
  4. Joists may not cantilever past a beam toward the house
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Show the answer and the code reference

The answer

Nothing is wrong. This is a freestanding deck: it stands on its own beams, posts and footings next to the house, so it needs no ledger and no ledger flashing.

Correct choice: 1. Nothing. This installation is compliant

R507.8 requires a deck that is supported by an exterior wall to be positively anchored for vertical and lateral loads, and it requires the deck to be self-supporting where that connection cannot be verified. This deck takes the second route: a doubled 2x10 beam on 6x6 posts about a foot from the house carries the inner end of the joists, so nothing hangs on the house band joist and the siding and weather barrier stay intact. The beams bear on top of the posts in post caps (R507.5.1, R507.5.2), the posts sit in manufactured bases on the inspected footings (R507.4.1), the joists cantilever about a foot past each beam (within R507.6), and the deck surface about 4 ft above grade has a 36 in. guard with balusters spaced under 4 in. (R312.1). Leaving a small gap at the wall keeps the deck from bearing on the siding.

How to fix it

No correction needed. Keep the deck clear of the siding so it does not bear on the house, and make sure the guard meets R312 (36 in. high and no opening that passes a 4 in. sphere) at final inspection.

Code references

  • 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 R507.4.1 — Deck post to deck footing connection

    Posts must bear on footings and be restrained against lateral displacement at the bottom, using manufactured connectors or at least 12 in. of post embedment in the surrounding soil or concrete pier.

    Drills citing R507.4.1

  • IRC 2018 R507.6 — Deck joists

    Deck joist spans follow Table R507.6, and a joist may cantilever past its beam no more than one-fourth of the joist span or the maximum cantilever in Table R507.6, whichever is less.

    Drills citing R507.6

  • IRC 2018 R312.1.1 — Where required

    Guards are required along open-sided walking surfaces, including floors, stairs, ramps and landings, that are more than 30 in. above the floor or grade below at any point within 36 in. horizontally of the open side. A deck surface is an open-sided walking surface.

    Drills citing R312.1.1

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 R507.1 is known. A deck this high still needs a building permit in Minnesota even though it is not attached to the house, because the permit exemption in Minn. Rules 1300.0120, subp. 4 covers only decks not more than 30 in. above grade. 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. The verifier moved the primary citation from R507.1 to R507.8 (Vertical and lateral supports) on the understanding that the 2018 reorganization of R507 moved the 2015 R507.1 attachment sentences (positive anchorage, no toenails, self-supporting where a connection cannot be verified) there. Confirm against the printed 2018 IRC, along with the R507.4.1 12 in. embedment alternative and the R507.6 cantilever limit (lesser of one-fourth of the joist span and the table value). The scene was redrawn so each cantilever is about 1 ft. The Minnesota permit statement relies on frame-mnbldg-001 and -003, which confirmed Minn. Rules 1300.0120, subp. 4 through search results.

Why the other choices are wrong

  • A deck built against a house must be bolted to it with a ledger. R507.8 lets a deck be self-supporting, and in fact requires that where a positive connection to the house cannot be verified. A freestanding deck on its own beams and footings needs no ledger.
  • The joint between the deck and the house wall must be flashed as required by R703.4. R703.4 requires flashing where a deck attaches to a wood-frame wall. Nothing attaches here: the siding and its weather barrier are unbroken behind the deck, so there is no penetration to flash.
  • Joists may not cantilever past a beam toward the house. R507.6 lets deck joists cantilever past a beam up to the lesser of one-fourth of the joist span and the Table R507.6 limit. These 2x10s overhang each beam by about a foot, well inside both, and the direction of the cantilever does not matter.
Code complianceLevel 2 · Journeyman#deck#freestanding#beam#posts#compliant#exterior

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