There is one difference; the valley rafter at its seat must be framed as in Fig. 65 in order that the plumb line may come directly over the corner of the building. The ends of roof boards will rest upon the valley rafter at its center line, which line is in the same plane as that of the common rafters.
Like the hip rafter, the upper end may be laid out first, after which the rafter length is measured from this, the measurement being made along the middle of the back of the rafter, the top edge.
To lay out the cuts shown in Fig. 65-a, proceed as in laying out the end of a hip rafter, as described in Sec. 24, Fig. 63. In the case of an octagon the amount would be 5/12 of that used for the square, Fig. 65-b.
In Figs. 40 and 41 is shown a valley rafter framed thru to the ridge. This is done to give the valley support, for a valley, unlike a hip, is not self supporting when the jacks are attached. Against this valley rafter is framed a second valley rafter. The upper end of this second valley rafter is framed with a plumb cut such as would be given a hip or valley of the same rise and run; the end, however, is cut square across as in the case of a common rafter resting against a ridge.