Jack Rafters

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Figure  2-48.—Method  of  framing  gable  dormer  with  sidewalls. method of framing, the shortening allowance for the upper end of a valley rafter is one-half the 45° thickness of the inside member in the upper doubled header. There is  also  a  shortening  allowance  for  the  lower  end, consisting of one-half the 45° thickness of the inside member of the doubled common rafter. The figure also shows that each valley rafter has a double side cut at the upper and lower ends. Figure 2-48 shows a method of framing a gable dormer with sidewalls. As indicated in the framing diagram, the total run of a valley rafter is again the hypotenuse of a right triangle with the shorter sides each equal to the run of a common rafter in the dormer. You figure the lengths of the dormer corner posts and side studs just as you do the lengths of gable-end studs, and you lay off the lower end cutoff angle by setting the square to the cut of the main roof. Figure  2-49  shows  the  valley  rafter  shortening allowance for this method of framing a dormer with sidewalls. Figure 2-49.-Valley rafter shortening allowance for dormers with sidewalls. Figure 2-50.-Types of jack rafters. Jack Rafters A jack rafter is a part of a common rafter, shortened for framing a hip rafter, a valley rafter, or both. This means that, in an equal-pitch framing situation, the unit of rise of a jack rafter is always the same as the unit of rise of a common rafter. Figure 2-50 shows various types of jack rafters. A hip jack rafter extends from the top plate to a hip rafter. A vane y jack rafter extends from a valley rafter to a ridge. (Both are shown in fig. 2-51.) A cripple jack rafter does not contact either a top plate or a ridge. A 2-30

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