Span.

Tie-beam A.

King-post K.

Principal rafters P.

Braces B.

Purlins C.

Small rafters r.

feet.

inches.

inches.

inches.

indies.

inches

inches.

20

9 1/2

x

4

4

x

3

4

x

4

3 1/2

x

2

8

x

4 3/4

3 1/2

x

2

22

9 1/2

x

5

5

x

3

5

x

3

3 3/4

x

2 1/4

8 1/4

x

5

3 3/4

x

2

24

10 1/2

x

5

5

x

3 1/2

5

x

3 1/2

4

x

2 1/2

8 1/2

x

5

4

x

2

26

11 1/2

x

5

5

x

4

5

x

4 1/4

4 1/4

x

2 1/2

8 3/4

x

5

4 1/4

x

2

28

11 1/2

x

6

6

x

4

6

x

3 1/2

4 1/2

x

2 3/4

8 3/4

x

5 1/4

4 1/2

x

2

30

12 1/2

x

6

6

x

4 1/2

6

x

4

4 3/4

x

3

9

x

5 1/2

4 3/4

x

2

In this Table the trusses are supposed to be not more than 10 feet apart, the pitch of the roof about 27 degrees, the covering slate, and the timber Baltic pine. The timbers are marked with the letters A, K, P, B, C, and r, in the engraving.