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Band joist: what it means on an inspection

Rafter Tie editorial teamUpdated 3 min read

A band joist, also called a rim joist, is the board that runs along the outside edge of a floor frame and closes the ends of the floor joists. It keeps the joists upright, ties them together and carries the load of the wall above down to the sill plate. Without it the joist ends would be open and unsupported.

A cutaway of a floor edge with a foundation wall, a sill plate on top, floor joist ends seen end-on, a highlighted band joist closing them at the edge, and a subfloor and wall plate above
The band joist closes the ends of the joists along the edge of the floor.
Use this diagram

How to check the band joist

  1. Find it. Look along the edge of the floor frame, above the sill plate. The board that runs the length of the edge, across the ends of every joist, is the band joist.
  2. Check that it closes the joists. It should run continuously along the edge and be fastened to the end of each joist, so the joists cannot roll over and the edge is closed.
  3. Check its bearing. It should sit on the sill plate or on the support below, not hang past it. The wall above bears on it through the subfloor, so it is a load path member.
  4. Look at the size. A band joist is usually the same depth as the joists. Where engineered rim board is used, it should be installed per the product instructions, because it is rated for load transfer.
  5. Watch for cuts. Holes and notches for pipes and ducts weaken the board, and it carries the wall above, so never assume a cut in a band joist is harmless because it is small. Engineered rim board follows its maker's rules for holes.

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Common mix-ups

  • Band joist versus floor joist. Floor joists run across the floor and carry its load to the beams and walls. The band joist runs along the edge and closes their ends.
  • Band joist versus header joist. At a floor opening such as a stairwell, short framing members called headers and trimmers frame the hole. They are not the band joist at the edge.
  • Band joist versus sill plate. The sill plate sits on the foundation. The band joist sits on the plate. They are stacked, and each has its own anchorage or connection rule.
  • Rim joist versus rim board. In everyday use these mean the same board. Rim board is also the name of an engineered product made for this location.

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Band joists on the B1

Band joists belong to floor construction, 14% of the B1. Expect questions that ask which member closes the joist ends or carries wall load at the edge of the floor, and some that combine it with a hole or notch in a framing member. The floor framing sections are in Chapter 5; use the chapter table of contents to find them in your edition.

Practice it

Pair this page with sill plate, which is the member below, fireblocking versus draftstopping, which covers closing the hidden space at the floor line, and notching and boring joists, which sets the limits for cutting framing. The IRC chapters guide shows where floor framing sits in the book, and the IRC terms glossary links the next term.

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