Spot the Violation

FramingFloor framingLevel 22018 IRC

Center girder in a basement

Looking up at an unfinished basement ceiling toward a built-up three-ply 2x10 girder that runs across the room on an adjustable steel column. Floor joists from both sides meet over the girder side by side: the near joists run across the top of the girder and end just past its far face, and the far joists end just in front of its near face, so each pair overlaps across the whole girder with nail heads showing in the overlap. Full-depth blocks fill the bays between the pairs above the girder. A galvanized supply trunk hangs beyond the girder, a small window sits in the far foundation wall, and in the foreground a porcelain lampholder is mounted beside a joist, fed by a yellow cable stapled along the joist. S-P-FNo.2 KD-HT
Unfinished basement ceiling at the center girder

What's wrong here?

  1. Lapped joists must overlap at least 12 in.
  2. Joists that meet over a girder must be continuous or butted end to end in line, not offset side by side
  3. Each joist needs a joist hanger where it lands on the girder
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

Nothing is wrong: the joists lap over the girder by well over 3 in., are face-nailed together at each lap, and bear on the full width of the girder.

Correct choice: 4. Nothing. This installation is compliant

R502.6.1 lets joists framing from opposite sides of a bearing support lap instead of running continuous, as long as they overlap at least 3 in. and are nailed together with at least three 10d face nails. Here each pair overlaps by about 7-1/2 in. (the 4-1/2 in. girder plus about 1-1/2 in. of overhang on each side), with three nails in each lap, and each joist bears on the full 4-1/2 in. width of the girder, three times the 1-1/2 in. minimum on wood in R502.6. The side-by-side offset is simply what a lap looks like. Full-depth blocks between the pairs over the girder keep the joists from rolling.

How to fix it

None needed. Keep laps at 3 in. or more with at least three 10d face nails. Where joists butt end to end over a support instead, R502.6.1 requires a wood or metal splice at least as strong as the nailed lap.

Code references

  • IRC 2018 R502.6.1 — Floor systems

    Joists framing from opposite sides over a bearing support must lap at least 3 in. and be nailed together with at least three 10d face nails. A wood or metal splice at least as strong as the nailed lap is also permitted.

    Drills citing R502.6.1

  • IRC 2018 R502.6 — Bearing

    The ends of each joist, beam or girder must have at least 1-1/2 in. of bearing on wood or metal or at least 3 in. on masonry or concrete, or be supported by approved joist hangers.

    Drills citing R502.6

2024 IRC:same rule and number. Search results quoting the current IRC text give the same 3 in. lap and three 10d face nails, with the splice alternative, under R502.6.1. Not checked line by line against the printed 2024 IRC. Confidence: medium

Minnesota

MN adopts this rule as writtenConfidence: medium

No Minnesota amendment to R502.6.1 is known. DLI is adopting the 2024 IRC as the next edition; see the 2024 IRC note.

About the Minnesota Residential Code

Why the other choices are wrong

  • Lapped joists must overlap at least 12 in. R502.6.1 requires a lap of only 3 in. with at least three 10d face nails; these overlap about 7-1/2 in.
  • Joists that meet over a girder must be continuous or butted end to end in line, not offset side by side. R502.6.1 specifically allows joists framing from opposite sides of a support to lap side by side, so the 1-1/2 in. offset is normal.
  • Each joist needs a joist hanger where it lands on the girder. Hangers are only one of the options in R502.6; a joist may instead bear at least 1-1/2 in. on wood, and these bear on the full 4-1/2 in. width of the girder.
Code complianceLevel 2 · Journeyman#floor joist#lap#girder#bearing#basement#calibration

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