Figure 2-58.-Method of framing a shed dormer.difference between the unit of rise of the dormer roofand the unit of rise of the main roof. Take the dormershown in figure 2-59, for example. The height of thedormer end wall is 9 feet, or 108 inches. The unit of riseof the main roof is 8; the unit of rise of the dormer roofis 2 1/2; the difference is 5 1/2. The total run of a dormerrafter is therefore 108 divided by 5 1/2, or 19.63 feet.Knowing the total run and the unit of rise, you can figurethe length of a dormer rafter by any of the methodsalready described.As indicated in figure 2-59, the inboard ends of thedormer rafters must be cut to fit the slope of the mainroof. To get the angle of this cut, set the square on therafter to the cut of the main roof, as shown in the bottomview of figure 2-59. Measure off the unit of rise of thedormer roof from the heel of the square along the tongueas indicated and make a mark at this point. Draw thecutoff line through this mark from the 12-inch mark.You figure the lengths of the sidewall studs on ashed dormer as follows: In the roof shown in figure 2-59,a dormer rafter raises 2 1/2 units for every 12 units ofrun. A main-roof common rafter rises 8 units for every12 units of run. If the studs were spaced 12 inches OC,the length of the shortest stud (which is also the commondifference of studs) would be the difference between8 and 2 1/2 inches, or 5 1/2 inches. If the stud spacingis 16 inches, the length of the shortest stud is the valueof x in the proportional equation 12:5 1/2::16:x,or 7 5/16 inches. The shortest stud, then, will be7 5/16 inches long. To get the lower end cutoff angle forstuds, set the square on the stud to the cut of the mainFigure 2-59.-Shed dormer framing calculation.roof. To get the upper end cutoff angle, set the square tothe cut of the dormer roof.INSTALLATIONRafter locations are laid out on wall plates andridgeboards with matching lines and marked with X’s,as used to lay out stud and joist locations. For a gableroof, the rafter locations are laid out on the rafter platesfirst. The locations are then transferred to the ridge bymatching the ridge against a rafter plate.Rafter LocationsThe rafter plate locations of the ridge-end commonrafters in an equal-pitch hip roof measure one-half of thespan (or the run of a main-roof common rafter) awayfrom the building comers. These locations, plus therafter plate locations of the rafters lying between theridge-end common rafters, can be transferred to theridge by matching the ridgeboads against the rafterplates.2-35