Take 12 on the blade and 9 on the tongue, and step 13 times along the rafter timber. This will give the length of rafter for 13 feet of run. In this example, however, there is another 6 inches of run to cover. For this additional length, take 6 inches on the blade (it being ½ a foot run) for run, and take ½ of 9 on the tongue (which is 4½ inches), and step one time. This, in addition to what has already been found by stepping 13 times with 12 and 9, will give the full length of the rafter.
Fig. 18. Method of Laying Out Hips and Rafters
for Roofs or Various Pitches over Square Corner.
The square with 12 on blade and 9 on tongue will give the heel and plumb cuts.
Another method of finding the length of rafter for the 6 inches is shown in [Fig. 16], where the square is shown applied to the rafter timber for the plumb cut. Square No. 1 is shown applied with 12 on blade and 9 on tongue for the length of the 13 feet. Square from this cut, measure 6 inches, the additional inches in the run; and to this point move the square, holding it on the side of the rafter timber with 12 on blade and 9 on tongue, as for a full foot run.
It will be observed that this method is easily adapted to find any fractional part of a foot in the length of rafters.
In the front gable, [Fig. 14], the fractional part of a foot is 4 inches to be added to 10 feet of run; therefore, in that case, the line shown measured to 6 inches in [Fig. 16] would measure only 4 inches for the front gable.