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59. The Roof Flange.—Case I. The Roof Having One Inclination.—The measurements usually given for a roof flange are the diameter of the pipe, and the pitch of the roof. The roof pitch is generally given as "so many inches to the foot." Figure 176 shows the rise and run of the roof line. If the job called for a roof pitch of 4 in. to 1 ft., the line marked run, Fig. 176, would measure 12 in. and the line marked rise would measure 4 in.

Pattern of Pipe.—An elevation is first drawn according to the dimensions given in Fig. 176. A profile is drawn above this view and is divided into equal spaces. Each division is numbered. Extension lines from each division of the profile are carried down to the roof line. A line of stretchout is drawn, and the spacing from the profile transferred to this line. The spaces are numbered to correspond. The measuring lines of the stretchout are drawn in. From each intersection of the miter (roof) line of Fig. 176, extension lines are carried over into the stretchout. Starting from point 1 of the profile, the extension lines should be traced downward to the miter line, and thence to a correspondingly numbered line in the stretchout, Fig. 177. In like manner all points of intersection can be located in the stretchout. A curved line passing through these points will give the miter cut of the pattern. An extension line drawn from the top of the roof flange elevation completes the pattern. A ½-inch lock is added to each side of the pattern and a ⅜-inch double edge to the miter cut in order to join the pipe to the apron by double seaming.

Opening in Apron.—Any straight line is drawn to serve as a line of stretchout, Fig. 178. The exact spacing between the intersections of the miter line is transferred to this line, and these spacings numbered to correspond. A measuring line is drawn through each point as shown in Fig. 178. Upon line 2 of Fig. 178, a distance equal to line a of Fig. 176 is set off. Similarly, line 3 would receive the length of line b from Fig. 176, line 4 would receive c, line 5 would receive d, and line 6 would receive e. These distances may now be transferred to the opposite side of the line of stretchout, since both parts of the opening are exactly equal. A curved line drawn through the points thus located will give the