This section is from the book "The Carpenters' Guide", by Harvey Miller. Also available from Amazon: The carpenters' guide.

To find the number of base feet of a rafter is absolutely necessary in framing a roof. The base of a rafter is the number of horizontal feet to be spanned by the rafter. (See fig. 21.) It is advisable to draw the dimensions of the roof at 1/4" scale, and mark the rafters in, as shown in fig. 13.

Fig. 20

There are as many base feet in a common rafter of a Hip roof as there are number of feet in one-half the width of the building. (See fig. 21.) There are as many base feet in a common rafter of a gable roof as there are number of feet in half the width of the gable. (See fig. 22.) Or, there are as many horizontal feet from the plate to a perpendicular line of the ridge with any Rise to obtain the required pitch.

Fig. 21

Fig. 22

There are as many base feet in a Jack rafter as there are number of feet on the plate from the corner to the center of the rafter. (See fig. 21.)

There are as many base feet in a cripple rafter that extends from the valley to the hip as there are number of feet on the plate from the corner at the hip rafter to the center of the valley rafter, or from corner to angle. (See fig. 21.) The base of a cripple rafter that extends from the valley to the ridge of a gable roof is the number of feet on the ridge from the intersection of the valley and ridge. The rafters are set out on the ridge, 2', 4' and 6', and have respective base feet. (See fig. 21.)

Rule 1. There are as many base feet of 17" in a hip rafter as the number of feet in half the width of the building. (See fig. 21.)

Rule 2. In cases where the hip does not extend to the ridge, there are as many base feet in the hip rafter as there are feet on th plate at right angles to a plumb line of the intersection of the hip rafter.

There are as many base feet of 17" in a valley rafter as there are number of feet in half the width of the gable, or the number of feet at right angles from the plate to a perpendicular line of the ridge. (See fig. 21.)

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