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Dropping The Hip
The seat cut of the birdsmouth is raised so that the top edge of
the hip, where the hip intersects the building line, matches
the top edge of the common rafters. The raising of the seat cut is
called
dropping the hip. Figure 8 shows the layout for dropping the hip. Mark
the height of the commons along the first plumb line extending
from
working point 2. The height of the commons is the distance from the top
edge of the common rafter to
the peak of the birdsmouth. Draw a second plumb line
where the wall plate intercepts the side of the hip. The distance
between the plumb lines will be 1/2 of the hip rafter
thickness measured at 90 degrees to the plumb line.
Mark the height of the commons along the second plumb line.
Draw a seat cut line at the bottom edge of the new height of the
commons
line. Extend it to the first plumb line
and the edge of the hip rafter. If the hip rafter at the
building corner is not going to be exposed, cut out the birdsmouth as
shown by the cutting lines in figure 8,
