A 2x10 Southern Pine joist spans 14 feet and supports a live load of 40 psf. According to span tables, what is the maximum allowable spacing for these joists?
Correct Answer
B) 16 inches on center
For a 14-foot span with 40 psf live load, 2x10 Southern Pine joists can typically be spaced 16 inches on center according to standard span tables. Closer spacing would be over-designed and wider spacing would exceed allowable deflection limits.
Why This Is the Correct Answer
According to standard span tables for Southern Pine lumber, 2x10 joists spanning 14 feet with a 40 psf live load can safely be spaced at 16 inches on center. This spacing provides adequate structural support while meeting deflection requirements (typically L/360 for live loads). The 16-inch spacing is a common standard that balances material efficiency with structural performance for residential floor systems.
Why the Other Options Are Wrong
Option A: 12 inches on center
12 inches on center would be over-designed for this application. While structurally safe, it uses more material than necessary and increases construction costs without providing additional benefit for the given load and span requirements.
Option C: 19.2 inches on center
19.2 inches on center exceeds the maximum allowable spacing for this span and load combination. This wider spacing would result in excessive deflection and potentially inadequate load-carrying capacity, failing to meet building code requirements.
Option D: 24 inches on center
24 inches on center is too wide for 2x10 joists at this span and load. This spacing would cause significant deflection issues and structural inadequacy, well beyond what span tables allow for residential floor systems.
Memory Technique
Think '16 is sweet sixteen' - the most common and balanced spacing for standard residential floor joists in typical applications
Reference Hint
Florida Building Code Chapter 5 - Wood Frame Construction, or IRC Table R502.3.1(1) for floor joist spans
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