CSLB General Building (B)Framing and CarpentryMedium
A framing contractor is installing blocking between floor joists to provide lateral support and prevent twisting. The floor joists are 2x10s spaced 16 inches on center. If the joist span is 14 feet, what is the minimum number of rows of blocking required by code for this span?
- AOne row
- BTwo rows
- CThree rows
- DNone
Show answer & explanationAnswer & explanation
Correct answer: A. One row
For joist spans exceeding 12 feet, building codes typically require at least one row of blocking or bridging at the mid-span to prevent joist rotation and improve load distribution. Since 14 feet exceeds 12 feet, one row is required.
Why the other options are wrong
- B. Two rows would be required for longer spans, typically over 24 feet, or if the span was divided into thirds.
- C. Three rows would be excessive for a 14-foot span and not typically required by code.
- D. Blocking is required for spans exceeding 12 feet to prevent joist rotation.
Floor Joist Blocking Requirements
Code-mandated installation of solid blocking or bridging between floor joists to provide lateral support, prevent twisting, and distribute loads, especially for longer spans.
- Required for joist spans exceeding 12 feet.
- Installed at mid-span or at third points for very long spans.
- Helps prevent joist rotation and improves floor stiffness.
Memory trick: Long spans need blocks, short spans don't get knocks.