What This Drawing Shows

This drawing is designed to show Valley, Zipper and Double-step jack rafters. Lengths are calculated with the hip offset to make both sides plane and the valley is centered. The drawing does not represent any specific span but only represents a typical span with an offset of a given size. Zipper jacks are shown even though they may not be needed on the offset they are being calculated for. The ridge direction may be the same as the offset but the calculated length will be the same in either case.

Zipper Length:

The Zipper Length is the length calculated for the zipper jack rafters and will all be the same.

Ridge to Valley Length:

The Ridge to Valley Length is the length calculated for the longest valley jack rafter or a valley jack rafter at the end of the ridge.

Double Step Jack Length:

The Double Step Jack Length is the length calculated for the jacks from a partial hip to valley if the valley jack hits the end of the ridge.

Bevel:

The Bevel is the saw cut bevel for the jack rafters where they contact the hip or valley rafter. Note: One thing to remember is that on a circular saw the degree of bevel is how many degrees from 90 degrees.