What rim joist means
The rim joist is the board around the outside edge of a floor frame, capping the ends of the joists and sitting on the sill plate.
Also called band joist, rim board.
Where it matters on a carpentry job
Rim joists are a big air leak and a common insulation upgrade with foam. They are also where deck ledgers attach, so their condition matters to deck builders.
What the model code says
- Where rim joists provide lateral restraint, they are secured to the end of each joist with at least three 10d nails. (IRC 2021, Chapter 5)
Check which code edition your building department enforces for rim joist before you quote.
Work it out
- Free calculator: Framing calculator
- Tools, templates and guides: Free carpentry resources
Sources: 2021 International Residential Code, Chapter 5, Floors (ICC). Checked October 9, 2026.