In roofs of equal pitch, as illustrated in [Fig. 14], the steel square is all that is required if one properly understands how to handle it.
What is meant by a pitch of a roof, is the number of inches it rises to the foot of run.
Fig. 13. Method of Finding Relative Height of Hip
or Valley per Foot of Run to that of Common Rafter.
In [Fig. 15] is shown the steel square with figures representing the various pitches to the foot of run. For the ½-pitch roof, the figures as shown, from 12 on tongue to 12 on blade, are those to be used on the steel square for the common rafter; and for ⅜ pitch, the figures to be used on the square will be 12 and 9, as shown.
Fig. 14. Diagram to Illustrate Use of Steel Square
In Laying Out Timbers of Roofs of Equal Pitch.
To understand this figure, it is necessary only to keep in mind that the pitch of a roof is reckoned from the span. Since the run in each pitch as shown is 12 inches, the span is two times 12 inches, which equals 24 inches; hence, 12 on blade to represent the foot run, and 12 on tongue to represent the rise over ½ the span, will be the figures on the square for a ½-pitch roof.