Continuing the discussion from Student Discussion: The 2021 International Residential Code® (IRC®) Exam Study Course: Notches and Bored Holes in Floor Joists Notches at the top or bottom of a floor joist are limited to a maximum of 1/6 of the joist’s depth, and notches are not permitted anywhere within the middle third of the joist’s span. Notches located at the ends of the joist are allowed to be larger, up to a maximum of 1/4 of the joist depth, since the joist experiences less bending stress near its supports.
Bored holes in floor joists cannot exceed 1/3 of the joist’s depth, and they must maintain a minimum of 2 inches of clearance from both the top and bottom edges of the joist. Bored holes must also be located at least 2 inches away from any notch in the same joist. These limitations exist to prevent excessive weakening of the joist, since removing too much material — or removing it in the wrong location — can significantly reduce the joist’s load-carrying capacity and lead to sagging, cracking, or structural failure over time.