Figure 2-38.-Equal-span intersecting roof.
Figure 2-40.-Equal pitch but unequal span framing.
Figure 2-39.-Ridge-end shortening allowance for equal-span
intersecting valley rafter.
hip rafter. The valley-rafter tail has a double side cut
(like the hip-rafter tail) but in the reverse direction. This
is because the tail cut on a valley rafter must form an
inside, rather than an outside, corner. As indicated in
figure 2-39, the ridge-end shortening allowance in this
framing situation amounts to one-half of the 45°
thickness of the ridge.
Figure 2-40 shows a framing situation in which the
span of the addition is shorter than the span of the main
roof. Since the pitch of the addition roof is the same as
the pitch of the main roof, the shorter span of the
addition brings the addition ridge down to a lower level
than that of the main-roof ridge.
There are two ways of framing an intersection of
this type. In the method shown in figure 2-40, a full-
length valley rafter (AD in the figure) is framed between
the top plate and the main-roof ridgeboard. A shorter
valley rafter (BC in the figure) is then framed to the
longer one. If you study the framing diagram, you can
see that the total run of the longer valley rafter is the
hypotenuse of a right triangle with the altitude and base
equal to the total run of a common rafter in the main
roof. The total run of the shorter valley rafter, on the
other hand, is the hypotenuse of a right triangle with the
altitude and base equal to the total run of a common
rafter in the addition. The total run of a common rafter
in the main roof is equal to one-half the span of the main
roof. The total run of a common rafter in the addition is
equal to one-half the span of the addition.
Knowing the total run of a valley rafter, or of any
rafter for that matter, you can always find the line length
by applying the bridge measure times the total run.