What is the maximum span for 2"x6" #2 Douglas Fir rafters spaced 16" o.c. under a 50 psf snow load and a 20 psf dead load?

To determine the maximum span for 2"x6" #2 Douglas Fir rafters under specified loads, it is essential to understand how both the snow load and dead load impact the structural capability of the rafters. The building code typically provides span tables which detail how different wood sizes can support various loads based on their spacing and design values.

In this scenario, the total load acting on the rafters is the sum of the snow load and dead load, which totals 70 psf (50 psf snow load + 20 psf dead load). For 2"x6" Douglas Fir lumber, the allowable span is calculated using these load conditions. When evaluated against span tables or engineering standards for this lumber type, we find that rafters spaced 16" on center can effectively span up to 9'-2" under the cumulative load of 70 psf.

Choosing the correct option relies on comparing the total load with the specific structural capabilities established in span tables. Notably, while spans of 8'-0", 9'-8", and 10'-0" may present options, they either exceed structural recommendations or don't align with the calculated limits based on the given loading conditions. Therefore, the most accurate maximum span for 2