CSLB General Building (B)Framing and CarpentryMedium
A roof truss package originally designed for 16-inch on-center spacing is field-adjusted by the framing crew to 24-inch on-center spacing to save material. What additional change is required to maintain proper roof sheathing performance?
- AThe truss top chord size must be reduced to offset the wider spacing
- BThe roof sheathing must be a thicker panel with a higher span rating to span the greater distance between trusses
- CNo change is needed since truss spacing does not affect sheathing requirements
- DThe sheathing nailing pattern must be reduced to compensate for wider spacing
Show answer & explanationAnswer & explanation
Correct answer: B. The roof sheathing must be a thicker panel with a higher span rating to span the greater distance between trusses
Roof sheathing panels are engineered with span ratings that specify the maximum allowable support spacing. Increasing truss spacing from 16 to 24 inches on-center exceeds many panels' rated span, requiring a thicker panel (or one rated for 24-inch spans) to safely support roof loads without excessive deflection.
Why the other options are wrong
- A. Reducing chord size would weaken the truss further, worsening structural performance.
- C. Incorrect—sheathing span ratings are directly tied to support spacing.
- D. Reducing nailing would decrease shear capacity, not compensate for span issues.
Sheathing Span Rating
A rating printed on structural panels indicating the maximum on-center support spacing for roof or floor applications.
- Span rating shown as two numbers (e.g., 24/16)
- Wider truss/joist spacing requires higher-rated panels
- Using undersized panels risks sagging or failure
Memory trick: Wider gaps need stronger bridges—thicker panels span farther.