Let Fig. 252 be a half section through a deck roof, supported by trusses with purlins located as indicated, and the trusses spaced 12 ft. on centres. The roof areas supported at the joints are computed precisely as in Example 1, except that the flat and sloping areas should be kept separate as they will probably have different weights per sq. ft.

Thus roof area at

joint 2

=

9' 10" x 12' = 118 sq. ft. sloping roof.

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joint 3

=

4' 11" x 12' = 59 sq. ft. sloping roof.

4' 6" + 1' x 12' = 66 sq. ft. flat roof.

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joint 4

=

9'3" X 12' = 111 sq. ft. flat roof.

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joint 5

=

9' 6" X 12' = 114 sq. ft. flat roof.

In figuring the area of deck supported at joint 3 one foot in width is added to allow for the projection beyond centre of purlin.