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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.

 

12' ridge span

Figure 14 - 12 foot ridge span

16' ridge span

Figure 15 - 16 foot ridge span

ridge beam members for plank and beam construction

Figure 16 - Ridge beam members for plank and beam construction

framing plan

Figure 17 - Framing plan

 

Table 5
Ridge-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 12
6 X 10

4 X 10

8 X 12
6 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 12
6 X 10

10 X 12

8 X 12
6 X 14

16'

4 X 14
8 X 10

6 X 10

12 X 12
6 X 18

10 X 12

18'

6 X 12

4 X 14
8 X 10

6 X 18
10 X 14

10 X 12
6 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 12
6 X 16

4 X 16

14'

4 X 16

4 X 14

6 X 16
8 X 14

10 X 12

16'

4 X 16
6 X 14

4 X 14

6 X 18

10 X 12
6 X 16

18'

8 X 12
6 X 14

4 X 16

6 X 18

6 X 16
8 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