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What is the maximum allowable span for 2×10 floor joists spaced 16 inches on center using Southern Pine #2 grade lumber?

Correct Answer

B) 16 feet 2 inches

According to span tables, 2×10 Southern Pine #2 joists at 16" o.c. can span 16 feet 2 inches. Span tables account for deflection limits and load requirements for residential floor systems.

Answer Options
A
14 feet 6 inches
B
16 feet 2 inches
C
18 feet 0 inches
D
19 feet 6 inches

Why This Is the Correct Answer

Option B (16 feet 2 inches) is correct because it matches the standardized span table values for 2×10 Southern Pine #2 grade lumber at 16" on center spacing. These span tables are established by building codes and account for both live loads (40 psf) and dead loads (10 psf) typical in residential construction. The tables also incorporate deflection limits of L/360 for live loads to ensure structural integrity and occupant comfort.

Why the Other Options Are Wrong

Option A: 14 feet 6 inches

14 feet 6 inches is too conservative and represents a span that would be appropriate for a smaller joist size or lower grade lumber, not maximizing the structural capacity of 2×10 Southern Pine #2.

Option C: 18 feet 0 inches

18 feet 0 inches exceeds the safe span capacity for 2×10 Southern Pine #2 joists and would result in excessive deflection and potential structural failure under design loads.

Option D: 19 feet 6 inches

19 feet 6 inches is significantly beyond the allowable span and would create dangerous deflection issues and potential structural failure, requiring either larger joists or closer spacing.

Memory Technique

Use '2×10 at 16 o.c. spans 16+' - the joist depth (10) and spacing (16) both relate to the span being just over 16 feet.

Reference Hint

Florida Building Code, Chapter 5 - Floors, or IRC Table R502.3.1(1) - Floor Joist Spans for Common Lumber Species

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