How to Design a Roof – Part 7
Deflections were not considered in compiling Table 5. Since there are hardly any stiff wallfinishing materials (for example, plaster) in common use today, deflections of only fractions of an inch would not be harmful to the building or the inhabitants.
For rafter lengths of less than 2’ increments use the higher span. That is, if you have a span of 10 feet 11 inches, use the span tables for 12 feet 0 inches.
Figure 14  12 foot ridge span 
Figure 15  16 foot ridge span 
Figure 16  Ridge beam members for plank and beam construction
Figure 17  Framing plan
Table 5 RidgeBeam Members For PlankandBeam Construction 

For Ridge Spans Of Either 12 feet or 16 feet 

L.L. of 20 psf 

Span of Rafter 
Ridge Span = 12' 0" 
Ridge Span = 16' 0" 

f = 1,200 
f = 1,500 
f = 1,200 
f = 1,500 

10' 
3/2 X 10 
4 X 10 
8 X 12 
6 X 12 
12' 
4 X 12 
4 X 12 
10 X 12 
4 X 16 
14' 
4 X 14 
4 X 12 
10 X 12 
8 X 12 
16' 
4 X 14 
6 X 10 
12 X 12 
10 X 12 
18' 
6 X 12 
4 X 14 
6 X 18 
10 X 12 
20' 
4 X 16 
4 X 14 
10 X 14 
6 X 18 
L.L. of 30 psf 

10' 
4 X 14 
4 X 12 
8 X 12 
6 X 12 
12' 
4 X 14 
6 X 10 
10 X 12 
4 X 16 
14' 
4 X 16 
4 X 14 
6 X 16 
10 X 12 
16' 
4 X 16 
4 X 14 
6 X 18 
10 X 12 
18' 
8 X 12 
4 X 16 
6 X 18 
6 X 16 
20' 
6 X 14 
4 X 16 
8 X 16 
6 X 18 
Part 1  Part 2  Part 3  Part 4  Part 5  Part 6  Part 8 