Valley Rafters

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Figure 2-37.—Intersecting roof with unequal spans. formed by the intersecting ridges. Valley jack rafters run roofs, but they are quite rare and require special framing from the valley rafters to both ridges. Hip-valley cripple jack rafters are placed between the valley and hip rafters. An intersecting roof with unequal spans requires a supporting  valley  rafter  to  run  from  the  inside  corner formed by the two sections of the building to the main ridge (fig. 2-37). A shortened valley rafter runs from the other inside comer of the building to the supporting valley rafter. Like an intersecting roof with equal spans, one with unequal spans also requires valley jack rafters and  hip-valley  cripple  jack  rafters.  In  addition,  a  valley cripple jack rafter is placed between the supporting and shortened valley rafters. Note that the ridgeboard is lower on the section with the shorter span. Valley Rafters Valley rafters run at a 45° angle to the outside walls of the building. This places them parallel 10 the hip rafters. Consequently, they are the same length as the hip  rafters. A  valley  rafter  follows  the  line  of  intersection between a main-roof surface and a gable-roof addition or  a  gable-roof  dormer  surface.  Most  roofs  having valley rafters are equal-pitch roofs, in which the pitch of the addition or dormer roof is the same as the pitch of the main roof. There are unequal-pitch valley-rafter methods. In  the  discussion  of  valley  rafter  layout,  it  is assumed that the roof is equal pitch. Also, the unit of run and unit of rise of an addition or dormer common rafter are assumed to be the same as the unit of run and rise of a main-roof common rafter. In an equal-pitch roof, the valley rafters always run at 45° to the building lines and the  ridge  pieces. Figure 2-38 shows an equal-span framing situation, in which the span of the addition is the same as the span of the main roof. Since the pitch of the addition roof is the same as the pitch of the main roof, equal spans bring the ridge pieces to equal heights. Looking at the roof framing diagram in the figure, you can see the total run of a valley rafter (indicated by AB and AC in the diagram) is the hypotenuse of a right triangle with the altitude and base equal to the total run of a common rafter in the main roof. The unit of run of a valley rafter is therefore 16.97, the same as the unit of run for a hip rafter. It follows that figuring the length of an equal-span valley rafter is the same as figuring the length of an equal-pitch hip roof hip rafter. A valley rafter, however, does not require backing or dropping. The projection, if any, is figured just as it is for a hip rafter. Side cuts are laid out as they are for a 2-26

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