Backing An Octagon Hip Rafter. The backing of the hip rafters of polygonal roofs may be obtained by using the following formulas :-

Fig. 94. - A King-post Roof.

Fig. 95. - A King-Post And Finial.

B = backing.

R = ½ width of the house between parallel sides.

A = rise of the roof.

For an octagonal roof: -

Formula 35. B = A/4 on To., R on Bl. To. = B.

For a hexagonal roof: - Formula 36. B = A/3 on To., R on Bl. To. = B.

The backing frequently is omitted upon the roofs, and the hip rafters are treated as described in Topic 53, F, under the subtopic of backing.