Question 33
Domain 3: Floor Construction and Supporting FramingWhat is the minimum required dimension for floor joist notching — specifically, the minimum distance from the edge of the support to a notch in the top or bottom of a joist?
Correct answer: C
Explanation
Floor joist notching is limited because notches reduce the member’s load-carrying capacity. The rule states that a notch in the top or bottom of a joist cannot exceed "1/3 the depth of the joist," which sets the maximum allowable notch size at the support edge.
Why each option is right or wrong
A. The notch cannot exceed 1/6 the depth of the joist
B. The notch cannot exceed 1/4 the depth of the joist
C. The notch cannot exceed 1/3 the depth of the joist
IRC Section R502.8.1 limits notches in floor joists at the ends of the member: a notch at the top or bottom at the support may not exceed one-third of the joist depth. In practical terms, if the joist is 9 1/2 inches deep, the maximum notch depth at that location is 3 1/6 inches; anything larger violates the code because it removes too much section at the bearing point.
D. The notch cannot exceed 1/2 the depth of the joist