CSLB General Building (B)Framing and CarpentryMedium
A framing crew is constructing a new residential deck that will be attached to the house. The deck joists are 2x8s spaced 16 inches on center and will cantilever 2 feet beyond the support beam. According to typical framing practices, what is the maximum recommended span for the 2x8 deck joists made from Douglas Fir-Larch No. 2, assuming a live load of 40 psf and a dead load of 10 psf?
- A9 feet 6 inches
- B10 feet 10 inches
- C12 feet 4 inches
- D8 feet 0 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 10 feet 10 inches
For 2x8 Douglas Fir-Larch No. 2 joists spaced 16 inches on center, supporting a typical deck load (40 psf live load, 10 psf dead load), the maximum recommended span is 10 feet 10 inches according to standard span tables. This accounts for both strength and deflection criteria.
Why the other options are wrong
- A. This span is less than the maximum allowed for 2x8 joists at 16 inches on center under these load conditions.
- C. This span exceeds the maximum recommended for 2x8 joists at 16 inches on center, which could lead to excessive deflection or structural failure.
- D. This span is significantly under-utilized for a 2x8 joist, suggesting an inefficient design.
Deck Joist Span Limits
The maximum allowable distance a deck joist can span between supports, determined by lumber species, grade, size, spacing, and applied loads, to ensure structural integrity and prevent excessive deflection.
- Based on span tables from building codes or lumber associations.
- Considers live load, dead load, lumber species, grade, and size.
- Deflection limits (L/360) often govern over strength for floor/deck joists.
Memory trick: Spanning a deck? Load, Lumber, Length are key!