Fig. 19. Diagram Showing Relative Lengths of Run
for Hips and Common Rafters In Equal-Pitch Roofs.
Fig. 20. Method of Determining Run of Valley
for Additional Run in Common Rafter.
The same results may be obtained by the following method of figuring:
| As 12 : 17 | :: 6 | |
| 6 | ||
| 12) | 102 | |
| 8 | - 6 = 8½ | |
In [Fig. 19] is shown a 12-inch square, the diagonal m being 17 inches. By drawing lines from the base a b to cut the diagonal line, the part of the hip to correspond to that of the common rafter will be indicated on the line 17. In this figure it is shown that a 6-inch run on a b, which represents the run of a foot of a common rafter, will have a corresponding length of 8½ inches run on the line 17, which represents the plan line of the hip or valley in all equal-pitch roofs.
In the front gable, [Fig. 14], it is shown that the run of the common rafter is 10 feet 4 inches. To find the length of the common rafter, take 12 on blade and 9 on tongue, and step 10 times along the rafter timber; and for the fractional part of a foot (4 inches), proceed as was shown in [Fig. 16] for the rafter of the main roof; but in this case measure out square to the tongue of square No. 1, 4 inches instead of 6 inches.