For every 12" of common rafter run, there is 16.97" (17" approx.) of run for hip and valley rafters. Multiply the run in feet of the common rafter by 16.97" (17" is commonly used) to get the run of the hip or valley rafter.
Adjustments for the Top and Bottom Cuts
The cut mark will be made similar to the common rafter cut mark, except that the hip-val scale on the speed square will be used instead of the common scale to mark the line to cut. (See “Rafter Cut Length" and “Angle Cuts" earlier in this chapter)
If a framing square is used, apply the same procedure shown previously, except use 17" instead of 12" along the blade of the framing square.
These procedures assume a hip or valley corner of 90 degrees.
Hip Rafter Length (HRL) = Hip rafter length before adjustments (HRBA) — У diagonal thickness (DT) of rafter — thickness (T) of rafter (У thickness top and bottom combined).
HRL = HRBA — У DT — T
These figures are based on a 90-degree building
corner.
Valley Rafter Length = Valley rafter length before adjustment — % diagonal thickness of rafter.
(The % thickness factors cancel each other out.)
