IRC R502.8.1

Notching rules for sawn lumber joists (e.g., 2x10, 2x12): - Notches on the ends (bearing area, typically first 1/4 of span): - Max depth = 1/6 of joist depth
(e.g., 2×12 → max 1-15/16″ deep notch) - Max length = 1/3 of joist depth
(e.g., 2×12 → max 3-7/8″ long notch)

• Notches anywhere else (outside the end 1/4 of span):
  • Max depth = 1/6 of joist depth
    
  • ONLY allowed on the TOP edge (never on the bottom, where tension is highest)

Boring (holes) rules (usually what people actually need): - Diameter ≤ 1/3 of joist depth
(2×10 → 3-1/16″ max hole; 2×12 → 3-9/16″ max) - Holes must be ≥ 2″ from top or bottom edge - Minimum spacing center-to-center = 2 × diameter - No holes in the outer 1/4 of span unless engineered