What floor joist means
Floor joists are the horizontal framing members, set on edge in parallel rows, that hold up a floor.
Also called joist.
Where it matters on a carpentry job
Bouncy floors and cracked tile point to joists that are undersized, over spanned or notched. Sistering or adding a beam under them is a common fix that belongs in a separate quote from the finish work.
What the model code says
- Notches in solid lumber joists may not exceed one-sixth of the member's depth and may not sit in the middle third of the span. (IRC 2021, Chapter 5)
Check which code edition your building department enforces for floor 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.