How to Cut Compound Mitres on Roof Rafters

Roof rafters often require miter cuts, cuts at an angle other than 90 degrees. Occasionally a rafter needs two miter cuts, called a compound cut. The top end of a hip rafter rests against both the ridge board and a long common rafter. To fit comfortably between these two framing members, the hip rafter needs a miter cut on both sides of the board. Making these types of cuts involves some mathematical calculation but nothing especially complicated.

Level
Framing square
Board
Pencil
Circular saw

Instructions

- 1
  Place a level against the gable side of your roof at the top of the wall. Measure out 12 inches and make a mark. Place the level vertically against the roof and mark the distance from the wall to the sheathing. The combination of numbers gives you the roof pitch. For example, a roof that rises 6 inches for every 12 inches of horizontal run has a slope of 6 in 12.
- 2
  Set a framing square across one end of a rafter. Place the blade, or broad arm, on the bottom edge of the board so that the slope rise, 6 inches for example, shows at the edge. Position the tongue, or narrow edge, so that the number 17 shows at the top edge of the board. A hip rafter would cover the same span in 17 inches that a common rafter covers in 12 inches, so you would use 17 instead of 12 for the run.
- 3
  Draw lines on both sides of the framing square's tongue.
- 4
  Set a circular saw to cut at a 45-degree angle.
- 5
  Make the first cut from one side of the board. Make the second cut from the other side of the board.

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