Floor Joist Notching and Boring Limits (IRC R502.8.1)
The 'where can I notch or drill this floor joist' field check on the actual joist depth (sawn lumber): an end notch at the bearing may not exceed D/4; a top or bottom notch elsewhere is limited to D/6 deep and D/3 long and is not allowed in the middle third of the span; a bored hole may not exceed D/3 in diameter with its edge at least 2 in from the top and bottom and from any other hole or notch. A 2x10 (9.25 in) allows a 2.31 in end notch and a 3.08 in bore. ENGINEERED I-joists and trusses follow the manufacturer's hole chart only -- never field-notch a flange. Prescriptive IRC limits; a cantilever or heavily loaded joist may be tighter, and the AHJ-adopted code governs. A field check, not a stamped detail.
Formula and source
end_notch_max = D/4; notch_depth_max = D/6; notch_length_max = D/3; bore_dia_max = D/3; bore_edge_min = 2 in (D = actual joist depth).
IRC R502.8.1 sawn-lumber floor-joist notching and boring limits, by name; the fractions apply to the actual joist depth. The AHJ-adopted IRC edition governs.
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