Lookouts. Lookouts for the common rafters of a box-corniced house are usually part of the same stick as the rafter, if they do not require too long a stick to be practicable; but if an open cornice is to be built, the lookouts are generally sawed to some design, and the pitch ends of the rafters cut as shown in Fig. 21, the lookouts being spiked on as indicated. The length of the lookouts may be found by using the pitch and the base lines of the rafters, laying Bl. upon the base line, and sliding it until the figure upon Bl. denoting the horizontal projection of the lookout beyond the plate coincides with the pitch line, say 20", where a mark by the tongue upon the pitch line should be made, as shown at a in Fig. 74. The distance, or bridge measure, between a and b, is the length of the lookout on the line with the top of the rafter of which it is a continuation. To this must be added about a foot for spiking to the rafter.

The formula for finding the length of a lookout for a common rafter is as follows : -

L2 = horizontal projection of lookout. L3 = length of lookout. X = bridge measure.

Formula 13. L3 = X of L2 on Bl. as base line, and intersection of To. with pitch line.

Fig. 74. - To find the Length of the Lookout.

The mathematical formula for finding the length of the lookout is as follows: - A = rise of lookout.

Formula 14. L3 =