What is the MAXIMUM allowable span for a 2 x 8 #2 spruce-pine-fir rafter at 16 inches oc? The roof live load is 20psf and dead load is 10psf. Assume the ceiling joist are not attached to the rafters.
13 feet 9 inches is the maximum allowable span for a 2 x 8 #2 spruce-pine-fir rafter at 16 inches oc.
This maximum span is determined by the combined live and dead loads, which in this case total 30 psf, and the structural properties of the lumber used. Adhering to building codes ensures safety and structural integrity under the specified loading conditions.
This option correctly represents the maximum allowable span for a 2 x 8 #2 spruce-pine-fir rafter under the given loading conditions. The calculations for both the live load of 20 psf and dead load of 10 psf confirm that this span is within safe limits for structural performance.
This choice exceeds the allowable span for the specified loads and lumber type. A span of 18 feet 2 inches would likely lead to excessive deflection and potential structural failure under the combined live and dead loads, violating building safety standards.
This option also surpasses the maximum allowable span. Similar to choice B, a span of 19 feet 5 inches would not provide sufficient structural integrity and would be unsafe given the intended loads on the rafters.
This choice is well beyond the maximum allowable span for the specified conditions. A span of 21 feet would increase the risk of significant structural issues, including failure to meet deflection requirements, thus making it unsuitable for safe construction under the given loads.
In summary, the maximum allowable span for a 2 x 8 #2 spruce-pine-fir rafter at 16 inches on center, given a roof live load of 20 psf and a dead load of 10 psf, is 13 feet 9 inches. This span maintains safety and structural integrity, while options B, C, and D all exceed the limits set by building codes, posing risks that should be avoided in construction practices.
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