To lay out a pitch roof for an irregularly-shaped building so that it will look well and properly sustain itself and the pressures liable to come upon it requires some little experience. The method which the author has always followed in designing a pitch roof where the building is of irregular plan is to draw an outline plan of the walls of the building, and on this construct the greatest rectangle that will be contained within it. This rectangle can then be covered with a hip roof and the various projections subordinated to it.
Thus in Fig. 76 we have the outline of a building which is to be covered with a pitch roof. The greatest rectangle that can be drawn within these lines is indicated by the letters a, b, c, d. From the corners of this rectangle draw lines at 450 until they intersect, and join the two intersecting points. The 450 lines represent the hips of a roof, and the connecting line will be the plan of the ridge, and the length and position of these lines in the roof plan will be the same for any degree of inclination of the roof, provided all portions of the roof have the same pitch. Having obtained the lines of the main body of the roof we proceed to draw the roof lines of the various projections, first drawing them all for hip roofs and afterward erasing the hip lines and extending the ridge if a gable is preferred. The lines of the main hips below where the subordinate ridges intersect them, as at h and i, should also be eraced. If the width of a projection is so great that its ridge would come too high up on the main roof it can be roofed by a double gable, as at G G, or two three-quarter gables. The portion of the roof e between the gables will, of course, have a much less pitch than that of the gable roofs, but it can not usually be seen from the ground.
Should a deck be desired on the roof it can be indicated by drawing a rectangle,//, between the hip lines at any desired point above the subordinate ridges.
Although the roof plan shown in Fig. 76 is a comparatively simple one, the method used in laying it out can be extended to the most complicated plan, provided the plate is all on the same level. If
* part of the roof starts from a different level then the plan must be worked out in connection with the elevations.