Figure 2-37.—Intersecting roof with unequal spans.formed by the intersecting ridges. Valley jack rafters runroofs, but they are quite rare and require special framingfrom the valley rafters to both ridges. Hip-valley cripplejack rafters are placed between the valley and hip rafters.An intersecting roof with unequal spans requires asupporting valley rafter to run from the inside cornerformed by the two sections of the building to the mainridge (fig. 2-37). A shortened valley rafter runs from theother inside comer of the building to the supportingvalley rafter. Like an intersecting roof with equal spans,one with unequal spans also requires valley jack raftersand hip-valley cripple jack rafters. In addition, a valleycripple jack rafter is placed between the supporting andshortened valley rafters. Note that the ridgeboard islower on the section with the shorter span.Valley RaftersValley rafters run at a 45° angle to the outside wallsof the building. This places them parallel 10 the hiprafters. Consequently, they are the same length as thehip rafters.A valley rafter follows the line of intersectionbetween a main-roof surface and a gable-roof additionor a gable-roof dormer surface. Most roofs havingvalley rafters are equal-pitch roofs, in which the pitchof the addition or dormer roof is the same as the pitchof the main roof. There are unequal-pitch valley-raftermethods.In the discussion of valley rafter layout, it isassumed that the roof is equal pitch. Also, the unit of runand unit of rise of an addition or dormer common rafterare assumed to be the same as the unit of run and rise ofa main-roof common rafter. In an equal-pitch roof, thevalley rafters always run at 45° to the building lines andthe ridge pieces.Figure 2-38 shows an equal-span framing situation,in which the span of the addition is the same as the spanof the main roof. Since the pitch of the addition roof isthe same as the pitch of the main roof, equal spans bringthe 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 byAB and AC in the diagram) is the hypotenuse of a righttriangle with the altitude and base equal to the total runof a common rafter in the main roof. The unit of run ofa valley rafter is therefore 16.97, the same as the unit ofrun for a hip rafter. It follows that figuring the length ofan equal-span valley rafter is the same as figuring thelength of an equal-pitch hip roof hip rafter.A valley rafter, however, does not require backingor dropping. The projection, if any, is figured just as itis for a hip rafter. Side cuts are laid out as they are for a2-26
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