Center girder in a basement
What's wrong here?
- Nothing. This installation is compliant
- Joists that meet over a girder must be continuous or butted end to end in line, not offset side by side
- Each joist needs a joist hanger where it lands on the girder
- Lapped joists must overlap at least 12 in.
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: 1. 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 R502.6.1IRC 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
Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). 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 CodeWhy the other choices are wrong
- 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.
- 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.