What is the maximum allowable span for a 2x8 floor joist (Grade 2 Douglas Fir) at 16" O.C. with 40 psf live load and 10 psf dead load according to Michigan Building Code span tables?
Correct Answer
A) 11 feet 10 inches
According to Michigan Building Code span tables, a 2x8 Grade 2 Douglas Fir floor joist at 16" O.C. with standard residential loading has a maximum span of 11 feet 10 inches.
Why This Is the Correct Answer
According to Michigan Building Code span tables, a 2x8 Grade 2 Douglas Fir floor joist at 16" O.C. with a total load of 50 psf (40 psf live + 10 psf dead) has a maximum allowable span of 11 feet 10 inches. This span limit ensures the joist meets deflection criteria (L/360 for live load) and stress requirements while maintaining structural integrity under standard residential loading conditions.
Why the Other Options Are Wrong
Option B: 13 feet 2 inches
13 feet 2 inches exceeds the safe span limit for a 2x8 Grade 2 Douglas Fir joist under the specified loading conditions. This span would result in excessive deflection and potentially unsafe stress levels that violate Michigan Building Code requirements for residential floor systems.
Option C: 14 feet 0 inches
14 feet 0 inches is significantly beyond the allowable span for this joist configuration. Such a span would cause dangerous deflection exceeding L/360 limits and stress levels that could lead to structural failure, making it non-compliant with Michigan Building Code safety standards.
Option D: 12 feet 6 inches
12 feet 6 inches exceeds the maximum allowable span of 11 feet 10 inches for a 2x8 Grade 2 Douglas Fir joist at 16" O.C. under 50 psf total load. While closer to the correct answer, this span still violates code requirements for deflection and stress limits.
Memory Technique
Remember '2x8 at 16 = 11-10' - A 2x8 joist at 16 inches on center spans just under 12 feet (11 feet 10 inches) for standard residential loads.
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