Topic: Roof Framing

Finding the Hip Drop.

Dropping the hip is done so that the top of the hip rafter doesn't protrude past the top of the ridge. A quick way to determine this amount is to lay your square on a piece of plywood and trace out the triangle that represents the unit length of the hip/valley rafter. If you are working on an 8/12 pitch roof, then this would consist of 8" of rise and ~17" of run with the unit length connecting the lines. Measure in from the 17" side ½ the thickness of the ridge and mark the point. From this point scribe a line square to the run line. Measure the length of that line from the run line to where in intersects the unit length line. In your case it would be just about 3/8" long. This amount will be deducted from the H.A.P. and will therefore adjust the birds mouth cut.