The plumb cut for the hip and valley uses 5" and 17" on the framing square, which is marked on the side of the rafter. This is the angle of the side cut which is marked on the top edge of the rafter. Use this number with 12" on the framing square to find the side cut. For a 5/12 roof pitch the side cut is 11.5". The angle of the side cut of the hip and valley rafters are also given on the rafter table. Shorten the hip by half the 45 degree horizontal thickness of the ridge. Multiply 17.69 times the decimal equivalent (.25 instead of 1/4, for example) of the run to get the distance from the center of the ridge to the outside of the wall line. For a 5/12 roof we look across at the 5 and find 17.69. In the third column of the rafter table (see my article: Rafter Tables on the Framing Square) on the framing square is the length of hip or valley rafter. Always make the hip from a board one size larger (in width) than the common rafters. A normal hip rafter, then, would be made out of a 2x8. For every 12" of run on a common rafter we have a hip or valley run of 17".Ī normal common rafter is usually made out of a 2圆. This is what we use on the framing square as our run for the hip, 17". Since the hip forms the diagonal of a square with a 12" run, the diagonal of this square measures 17". The length of the diagonal is the run of the hip rafter. The hip rafter is a diagonal of the square formed from the two common rafters and the two outside wall lines. When everything fits, nail on the rest of the common rafters and adjoining ceiling joists. Nail the common rafters flush on the ends of the ridge board and at 90 degrees to it in the center of the span. This is found by measuring the length of the building and subtracting the span and adding the thickness of the ridge board. The first thing to do is to layout the common rafters, so you need to know the length of the ridge board. If this is a long roof with hips on the ends, there will be common rafters in the center.
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