CSLB General Building (B)Framing and CarpentryMedium
A framer is boring holes through the middle of 2x10 floor joists for plumbing pipe. According to standard framing limitations, what is the maximum allowable hole diameter as a fraction of the joist depth?
- A1/2 the joist depth
- B1/4 the joist depth
- C1/3 the joist depth
- D2/3 the joist depth
Show answer & explanationAnswer & explanation
Correct answer: C. 1/3 the joist depth
Standard framing rules (per IRC/CBC) limit bored holes in solid-sawn joists to a maximum diameter of 1/3 the joist depth, and holes must not be located within 2 inches of the top or bottom edge or within 2 inches of another hole or notch.
Why the other options are wrong
- A. 1/2 depth exceeds the allowable limit and would dangerously weaken the joist.
- B. 1/4 depth is overly conservative; code allows up to 1/3 depth.
- D. 2/3 depth is far beyond code allowance and would compromise structural integrity.
Joist Boring Limits
Holes bored through solid-sawn joists may not exceed 1/3 of the joist depth and must maintain 2 inches clearance from edges and other holes/notches.
- Max hole diameter = 1/3 depth
- 2-inch minimum edge clearance
- Notches limited to 1/6 depth, none in middle third
Memory trick: Third for the hole, sixth for the notch.