What I-joist means
An I-joist is an engineered floor or roof joist shaped like the letter I, with solid wood or LVL flanges and an OSB web.
Also called TJI, engineered joist.
Where it matters on a carpentry job
I-joists span farther and stay straighter than lumber, but holes and notches must follow the maker's chart. Plumbers cutting through flanges is a classic failure; mark the rules on site.
What the model code says
- Cuts, notches and holes in I-joists are prohibited except as the manufacturer allows or a design professional considers. (IRC 2021, Chapter 5)
Check which code edition your building department enforces for I-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.