NASCLA Accredited Commercial General ContractorWoodHard
A framing contractor is installing wood floor joists in a commercial building. The joists are 2x10s and span 14 feet. The building inspector observes that several joists have been notched in the top or bottom flange, away from the ends. What is the maximum allowable depth of a notch in the top or bottom of a wood structural floor joist, according to typical building codes like the IBC/IRC?
- ANotching is prohibited in the tension or compression flange.
- BNo more than 1/8th of the joist depth.
- CNo more than 1/4th of the joist depth.
- DNo more than 1/6th of the joist depth.
Show answer & explanationAnswer & explanation
Correct answer: D. No more than 1/6th of the joist depth.
According to IBC/IRC, notches in the top or bottom of joists are limited to a depth not exceeding 1/6th of the joist depth and are generally prohibited in the middle third of the span where bending stresses are highest. Notches significantly reduce the strength of the joist.
Why the other options are wrong
- A. While there are restrictions on location, notching is not entirely prohibited in the top or bottom flange, only limited in depth and location.
- B. This is too restrictive; 1/6th is typically allowed.
- C. This is generally too deep and would significantly weaken the joist.
Wood Joist Notching Limits
Maximum allowable dimensions and locations for notches in solid sawn wood joists as defined by building codes to maintain structural integrity.
- Notches reduce the cross-sectional area and strength of a joist.
- Location and depth are strictly regulated.
- Notches are generally prohibited in the middle third of the span where bending moments are highest.
Memory trick: Notches are tricky, 1/6th is the max, holes are 1/3rd, don't relax!