Question 29
Domain 3: Floor Construction and Supporting FramingWhat is the maximum span for a 2x10 floor joist at 16 inches on center using No. 2 Douglas Fir-Larch lumber in a living area?
Correct answer: B
Explanation
A 2x10 floor joist spaced 16 inches on center in a living area is sized from the span tables for No. 2 Douglas Fir-Larch. Those tables list the maximum span for that member as "16 feet 1 inch," which is why that is the allowable span for this condition.
Why each option is right or wrong
A. 14 feet 6 inches
B. 16 feet 1 inch
The allowable span is taken from the IRC span tables for floor joists, specifically the span table for Douglas Fir-Larch No. 2 lumber used in floor framing. For a 2x10 member spaced 16 inches on center and supporting a living area load, the table entry gives a maximum span of 16 feet 1 inch, which is the controlling value for this exact size, species, spacing, and use condition.
C. 17 feet 4 inches
D. 18 feet 8 inches