Figure 2-41.-Rafter table method.Suppose, for example, that the span of the addition inof the addition. Since one-half the span of the additionfigure 2-40 is 30 feet and that the unit of rise of acommon rafter in the addition is 9. The total run of theshorter valley rafter is:Referring to the unit length rafter table in figure2-41, you can see the bridge measure for a valley rafterin a roof with a common rafter unit of rise of 9 is 19.21.Since the unit of run of a valley rafter is 16.97, and thetotal run of this rafter is 21.21 feet, the line length mustbe the value of x in the proportional equation16.97:19.21::21.21:x, or 24.01 feet.An easier way to find the length of a valley rafter isto multiply the bridge measure by the number of feet inone-half the span of the roof. The length of the longervalley rafter in figure 2-40, for example, would be 19.21times one-half the span of the main roof. The length ofthe shorter valley rafter is 19.21 times one-half the spanFigure 2-42.-Long and short valley rafter shortening allowance.is 15 feet, the length of the shorter valley rafter is15 x 9.21 = 288.15 inches, or approximately 24.01 feet.Figure 2-42 shows the long and short valley raftershortening allowances. Note that the long valley rafterhas a single side cut for framing to the main-roof ridgepiece, whereas the short valley rafter is cut square forframing to the long valley rafter.Figure 2-43 shows another method of framing anequal-pitch unequal-span addition. In this method, theinboard end of the addition ridge is nailed to a piece thathangs from the main-roof ridge. As shown in theframing diagram, this method calls for two short valleyrafters (AB and AC), each of which extends from thetop plate to the addition ridge.Figure 2-43.-Another method of framing equal-pitch unequal-span intersection.2-28

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