To cut rafters with the help of a framing square, you need to know the pitch of the roof and the roof span, then you need to mark the measurements on the lumber and cut it with a miter saw. Use the framing square to find the pitch of the roof; climb up, place the long part of the square parallel to the ground and mark the point at which the other arm of the square intersects the roof.Continue Reading
Roof pitch is written as a ratio of x to 12, where x is the number of inches the roof rises per 12 inches of horizontal distance. For example, a roof with a 3:12 pitch rises 3 inches over one foot. Use a tape measure to find the span of the roof from the outside of the wall to the opposite wall, and divide by two for the length of the rafter.
After getting the measurements, place the framing square on the board so the pitch number is on the inside edge of the board. Adjust the angle to put the 12 on the outside edge, and draw a line to mark the plumb cut. Consult the rafter table on the square to find out the length of the rafter, move the framing square to that point, and mark the heel cut. Remove half the thickness of the ridge board from the length of the plumb edge of the rafter.Learn more about Carpentry