And this is how you figure out the pitch of the bastard hip/val. Say you have a 6/12 and a 9/12. Minus 6 from 9 you get 3 divide that in half add 1.5 to 6 you get 7.5 which is your hip/val rise/plumb cut.
Justin,
That doesn't work.
If you have a 6/12 and 9/12 Bastard Hip combination, the hip plumbcut angle will be 22.59° or 5 over 12 on the framing square or 7-1/16 over 17 on the framing square.
If you did what your saying on a 6/12 and 12/12 combination, the hip plumbcut angle will be 24.09° or 5-3/8 over 12 on the framing square or 7-5/8 over 17 on the framing square.
The way your saying the hip pitch would be 9 over 17 on the framing square.
12-6 = 6/2 = 3 + 6 = 9/17 (That's way off)
If you want to frame a bastard hip, close enough isn't good enough. You can get every angle you want to the exact degrees and they will help you with everything on the roof.
A 6/12 and 9/12 Bastard Hip combo gives you 56.31° in plan view on the 6/12 side and that would be the saw setting when you cut the plumbcut for the jack rafters. You will have 33.69° on the 9/12 side in plan view and that would be the saw setting on the 9/12 side.
A 6/12 and 12/12 combo would give you a 63.43° in plan view on the 6/12 side and 26.57° on the 12/12 side.
