Stair-Building and the Steel Square / A Manual of Practical Instruction in the Art of Stair-Building and Hand-Railing, and the Manifold Uses of the Steel Square

by Fred. T. Hodgson; Morris Williams

Fig. 38. Laying Out Timbers of Roof Shown in Fig. 36,
by Projecting Slope of Roof into Horizontal Plane.

The length of the rafter for the front wing, which has a run of 6 feet and a rise of 12 feet, may be obtained by placing the rule as shown in [Fig. 37] from 6 on blade to 12 on tongue, which will give a length of 13½ inches. If the scale be considered as one inch to a foot, this will equal 13 feet 6 inches, which will be the exact length of a common rafter rising 24 inches to the foot run and having a run of 6 feet.

It will be observed that the plan lines of the valleys in this figure in respect to one another deviate from forming a right angle. In equal-pitch roofs the plan lines are always at right angles to each other, and therefore the diagonal of 12 and 12, which is 17 inches, will be the relative foot run of valleys and hips in equal-pitch roofs.

In [Fig. 36] is shown how to find the figures to use on the square for valleys and hips when deviating from the right angle. A line is drawn at a distance of 12 inches from the plate and parallel to it, cutting the valley in m as shown. The part of the valley from m to the plate will measure 13½ inches, which is the figure that is to be used on the square to obtain the length and cuts of the valleys.

Fig. 39. Method of Finding Length and Cuts
of Octagon Hips Intersecting a Roof.

It will be observed that this equals the length of the common rafter as found by the square and rule in [Fig. 37]. In that figure is shown 12 on tongue and 6 on blade. The 12 here represents the rise, and the 6 the run of the front roof. If the 12 be taken to represent the run of the main roof, and the 6 to represent the run of the front roof, then, the diagonal 13½ will indicate the length of the seat of the valley for 12 feet of run, and therefore for one foot it will be 13½ inches. Now, by taking 13½ on the blade for run, and 12 inches on the tongue for rise, and stepping along the valley rafter timber 12 times, the length of the valley will be found. The blade will give the heel cut, and the tongue the plumb cut.