Installation

Figure 2-58.-Method of framing a shed dormer. difference between the unit of rise of the dormer roof and the unit of rise of the main roof. Take the dormer shown in figure 2-59, for example. The height of the dormer end wall is 9 feet, or 108 inches. The unit of rise of the main roof is 8; the unit of rise of the dormer roof is 2 1/2; the difference is 5 1/2. The total run of a dormer rafter is therefore 108 divided by 5 1/2, or 19.63 feet. Knowing the total run and the unit of rise, you can figure the length of a dormer rafter by any of the methods already described. As indicated in figure 2-59, the inboard ends of the dormer rafters must be cut to fit the slope of the main roof. To get the angle of this cut, set the square on the rafter to the cut of the main roof, as shown in the bottom view of figure 2-59. Measure off the unit of rise of the dormer roof from the heel of the square along the tongue as indicated and make a mark at this point. Draw the cutoff line through this mark from the 12-inch mark. You figure the lengths of the sidewall studs on a shed dormer as follows: In the roof shown in figure 2-59, a dormer rafter raises 2 1/2 units for every 12 units of run. A main-roof common rafter rises 8 units for every 12 units of run. If the studs were spaced 12 inches OC, the length of the shortest stud (which is also the common difference of studs) would be the difference between 8 and 2 1/2 inches, or 5 1/2 inches. If the stud spacing is 16 inches, the length of the shortest stud is the value of x in the proportional equation 12:5 1/2::16:x, or 7 5/16 inches. The shortest stud, then, will be 7 5/16 inches long. To get the lower end cutoff angle for studs, set the square on the stud to the cut of the main Figure 2-59.-Shed dormer framing calculation. roof. To get the upper end cutoff angle, set the square to the cut of the dormer roof. INSTALLATION Rafter locations are laid out on wall plates and ridgeboards with matching lines and marked with X’s, as used to lay out stud and joist locations. For a gable roof, the rafter locations are laid out on the rafter plates first. The locations are then transferred to the ridge by matching the ridge against a rafter plate. Rafter Locations The rafter plate locations of the ridge-end common rafters in an equal-pitch hip roof measure one-half of the span (or the run of a main-roof common rafter) away from the building comers. These locations, plus the rafter plate locations of the rafters lying between the ridge-end common rafters, can be transferred to the ridge by matching the ridgeboads against the rafter plates. 2-35