One of the first steps in developing the patterns for trimming the angles of a mansard roof is to obtain a representation of the true face of the roof. In other words, inasmuch as the surface of the roof has a slant equal to that shown in the profile of the return, the length of the hip is other than is shown in the elevation, and this difference in dimensions extends in a proportionate degree to the lines of the various parts forming the finish. Not only are the vertical and oblique dimensions different, but, as the result of this, the angle at A is different from that shown in a normal elevation. Hence, it is of the greatest importance to obtain a "true face" or elevation of the roof as it would appear if swung into a vertical position, which may be accomplished as follows:

In Fig. 285, let A E F C be the elevation of a mansard roof as ordinarily drawn, and let A1 G be the profile showing the pitch drawn in line with the elevation. Set the dividers to the length A1 G, and from A1 as center, strike the arc G G1, letting G1 fall in a vertical line from A'. From G1 draw a line parallel to the face of the elevation, as shown by G1 C, and from the several points in the hip finish, as shown by C and K, drop lines vertically, cutting G1 C1 in the points C1 and K1 as shown. From these points carry lines to corresponding points in the upper line of the elevation, as shown by C A and K1 h.Then A C1 F1 E represents the pattern of the surface shown by A G F E of the elevation. In cases where the whole hight of the roof cannot be put into the drawing for use, as above described, the same result may be accomplished by assuming any point as far from A as the size of the drawing will permit, as B, and treating the part between A and B as though it were the whole. That is, from A, in a vertical line, set off AB1, equal to A B. From B1 draw the horizontal line, as shown by B1 B3, and from B drop a vertical line cutting this line, as shown, in the point B3 By inspection of the engraving it will be seen that the point B3 falls in the line A C1 obtained in the previous operation, thus demonstrating that the latter method of obtaining the angle by which to proportion the several parts results the same as the method first described, and therefore may be used when more convenient.

Fig. 285. - The Plain Surfaces of a Mansard Roof Developed.