TABLE XVI COMMON ROOF PITCHES à pitch is 12 on the hody and 4 on the tongue. 6 8 12 10 12 12 15 18 * Pitch 12 Fig. 100.-Finding Pitch. 177. To Find the Cuts for a Common Rafter. The cut at the top of the rafter is called the ridge cut or the plumb cut. The cut at the lower end of the rafter is called the bottom cut or heel cut. First, to find the plumb cut place the square as shown in the upper position of Fig. 101. Use 12 on the body and other figures on the tongue, depending upon the pitch of the roof. For example, if the rafter is to be set at one-third pitch use 12 on the body and 8 on the tongue as indicated in the table above. For pitches not given in the table multiply the pitch by 2, express as a proportion and solve for the tongue reading: Thus, for one-fifth pitch Next, to find the heel cut place the square as shown in the lower portion of Fig. 101. If the rafter is to extend beyond the plate, the square is again set so as to give the plumb cut indicated in the figure. The process is repeated . again for the end cut. 178. The Rafter Table. The rafter table found on the back of the body of rafter squares or framing squares is used to find the length of a common rafter for various pitches. This table is shown in Fig. 102. The graduations on the outside edge of the body are used in connection with the 2" 60 18 8485 60 PAT.JUN 5, 1900 100 table. These gradu a tions are in twelfths and the inches may be used 12 17 to represent either inches or feet while the twelfth marks represent either twelfths of a foot (inches) or twelfths of an inch. These figures on the edge when making use of the table correspond to the run of the rafter. To use the rafter table, look at the left end of the table to find the required pitch. Then under the mark on the outer edge which corresponds to the run of the rafter in feet will be found the required length in feet, inches and twelfths of an inch. Thus a rafter set at one-half pitch with a run of ten feet is 14' 1,8" long. Again a rafter set at quarter pitch with a run of 12 ft. is 13' 5" long. When the run is given in inches the length will be in inches. Thus, a rafter set at quarter pitch with a run of 8'' would be 811" +4 of 1a", which, neglecting the added fraction, is approximately 811". If the run is given in both feet and inches find each separately and add the lengths together. Example. What is the length of a common rafter set at one-third pitch with a run of 10 ft. 6 in.? 3 0 1 6 2 02 711 4 9 10 36 5 2 715 6 7 16 28 81 201 12 יין 61001 Fig. 102. For run of 10 ft. the rafter length is 12' 028 2 11 12 Total length 12'71" Ans. 12 Explanation. Looking for the run in feet, we first find that the length for a 10 ft. run will be 12' 0,3". Now finding the length for the run in inches we get 718", disregarding , the last figure in the table. Adding these figures together gives 12' 752" for the distance from the outer edge of the plate to the center of the ridge. For the actual length deduct one-half the thickness of the ridge and add sufficient for the extension. 179. Roof Framing. Up to this point we have taken up only the lengths and cuts for common rafters. Any roof which is framed for gables, hips and valleys will require rafters of various lengths having both plumb cuts and side cuts. Fig. 103 shows the framing for such a roof. The ridge board marked A is the piece at the center to which the rafters are nailed. The plate marked B is the board placed on top of the studs to which the foot of each rafter is secured. The common rafters, C, are those which set square against the ridge board and which have no side cut. Hip rafters are those marked D. Valley rafters are those marked E. Jack rafters, marked F, are those the upper end , of which set against the hip rafter. Cripple rafters--rafters having no foot-span the space between the ridge board and valley rafter or between hip and valley rafters. They are marked G in the illustration. 180. Length of Hip or Valley Rafters. The length of the hip rafter is the hypotenuse of a right-angled triangle, one side of which is the common rafter and the other side is the distance on the plate from the foot of the hip rafter to |