Here's a framing square short cut for irregular roofs. I was reluctant to post this earlier as it is so limited in scope, but here goes. The following applies only to:
(1) Jack Rafter Side Cut Angles
(2) The angle of intercept of the Hip eave lines or Valley ridge lines in plan must be 90°
Say the intersecting pitches are Main pitch = 6/12 and Adjacent pitch = 10/12. To find the side cut for the 6/12 side, find value on the framing square given for 6/12 and multiply it by 6/10 (the ratio of the Main pitch/Adj. pitch ... if the runs are equal the ratio of the rises will suffice). Similarly, the side cut for the 10/12 side may be determined by multiplying the 10/12 value given on the framing square by 10/6 (Adj. pitch/Main pitch).
