Deterrmine the minimum size (do not consider 2×4`s) and length of a rafter according to span tables and the supplemental design values for joists and rafters.
A. Wood-Fb = 1000 PSI: E=1,500,000 PSI
B. Roof:
1. Rise is 3″ in 12″
2. Live load is 30 PSF + dead load of
20 PSF
3. Limited deflection: space in inches
divided by 240
C. Rafter spacing: 24″ on center
D. Structure:
1. Single story residence
2. 23`-8″ wide measured from outside to
outside of the 4″ stud exterior walls.
3. The opposing rafeers meet at the ridge
at the midpoint of the 23`-8″ dimension
and span the distance to the exterior
plates.
4. Ceiling joists are spaced at 24″ on
center
Assume that the rafter is plumb cut at the ouside of the plate. What is the minimum length of material you would have to purchase?