Figure 2-35.-Backing or dropping a hip rafter.
the top edge of the hip rafters. Dropping means to
deepen the birds-mouth so as to bring the top edge of
the hip rafter down to the upper ends of the jacks. The
amount of drop is taken on the heel plumb line (fig. 2-34,
The backing or drop required is calculated, as
shown in figure 2-34, view B. Set the framing square to
the cut of the rafter (8 inches and 17 inches) on the upper
edge, and measure off one-half the thickness of the rafter
from the edge along the blade. A line drawn through this
mark and parallel to the edge (view C) indicates the
bevel angle if the rafter is to be backed. The
perpendicular distance between the line and the edge of
the rafter is the amount of the drop. This represents the
amount the depth of the hip rafter birds-mouth should
exceed the depth of
the common rafter birds-mouth
An intersecting roof, also known as a combination
roof, consists of two or more sections sloping in
different directions. A valley is formed where the
different sections come together.
The two sections of an intersecting roof mayor may
not be the same width. If they are the same width, the
roof is said to have equal spans. If they are not the same
width, the roof is said to have unequal spans.
In a roof with equal spans, the height (total rise) is
the same for both ridges (fig. 2-36). That is, both
sections are the same width, and the ridgeboards are the
same height. A pair of valley rafters is placed where the
slopes of the roof meet to form a valley between the two
sections. These rafters go from the inside corners
formed by the two sections of the building to the corners
Figure 2-36.-Intersecting roof with equal spans.