In wood frame construction, what is the maximum spacing for 2×10 floor joists spanning 14 feet in a residential application using Southern Pine lumber?
Correct Answer
B) 16 inches on center
According to span tables, 2×10 Southern Pine joists can span 14 feet when spaced 16 inches on center under typical residential loading. Closer spacing would be acceptable but not necessary, while wider spacing would exceed the allowable span.
Why This Is the Correct Answer
According to standard span tables for Southern Pine lumber, 2×10 joists can safely span 14 feet when spaced 16 inches on center under typical residential live loads (40 psf) and dead loads (10 psf). This spacing provides adequate structural support while being economical. The span tables are based on deflection limits (L/360 for live load) and bending stress requirements that ensure the floor system meets code requirements.
Why the Other Options Are Wrong
Option A: 12 inches on center
While 12 inches on center spacing would be structurally adequate and allow for longer spans, it's unnecessarily close spacing for a 14-foot span with 2×10 joists, making it over-designed and uneconomical.
Option C: 19.2 inches on center
At 19.2 inches on center, 2×10 Southern Pine joists would exceed the maximum allowable span for 14 feet, potentially causing excessive deflection and failing to meet code requirements for residential floor systems.
Option D: 24 inches on center
24 inches on center spacing significantly exceeds the structural capacity for 2×10 joists spanning 14 feet, resulting in dangerous deflection and potential structural failure under normal residential loads.
Memory Technique
Remember '2×10 at 16 for 14' - the numbers flow nicely and represent a common residential application that balances structural adequacy with economy.
Reference Hint
Florida Building Code Chapter 5 - Wood Frame Construction, or IRC Table R502.3.1(1) Floor Joist Spans for Common Lumber Species
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