# How to Design a Roof – Part 7

Deflections were not considered in compiling Table 5. Since there are hardly any stiff wall-finishing 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 5Ridge-Beam Members For Plank-and-Beam 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 126 X 10 4 X 10 8 X 126 X 14 6 X 12 12' 4 X 12 3/2 X 10 6 X 10 4 X 12 10 X 12 4 X 16 14' 4 X 14 4 X 126 X 10 10 X 12 8 X 126 X 14 16' 4 X 148 X 10 6 X 10 12 X 126 X 18 10 X 12 18' 6 X 12 4 X 148 X 10 6 X 1810 X 14 10 X 126 X 16 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 126 X 16 4 X 16 14' 4 X 16 4 X 14 6 X 168 X 14 10 X 12 16' 4 X 166 X 14 4 X 14 6 X 18 10 X 126 X 16 18' 8 X 126 X 14 4 X 16 6 X 18 6 X 168 X 14 20' 6 X 14 4 X 16 8 X 16 6 X 18

Continued......

 Part 1 Part 2 Part 3 Part 4 Part 5 Part 6 Part 8