A treatise on architecture and building construction . of the example in Fig. 51 give the risefd as equal to one-half the span ha, which is the commonproportion of this form of roof; the pitch de should neverbe more than 30° from the horizontal, and the inclination e ashould not be less than 60°. In framing a gambrel roof it is always necessary to havea plate or curb at c h, as well as at a /, the rafters betweenthem being ciit to foot on a /, and to rest their plumb-cutagainst eh. The rafters between the ridge dg and thephite ch are cut in the same manner for ridge and plateas in an ordinary
A treatise on architecture and building construction . of the example in Fig. 51 give the risefd as equal to one-half the span ha, which is the commonproportion of this form of roof; the pitch de should neverbe more than 30° from the horizontal, and the inclination e ashould not be less than 60°. In framing a gambrel roof it is always necessary to havea plate or curb at c h, as well as at a /, the rafters betweenthem being ciit to foot on a /, and to rest their plumb-cutagainst eh. The rafters between the ridge dg and thephite ch are cut in the same manner for ridge and plateas in an ordinary gable roof, the plate ch being seciirelytied across the building to keep it from spreading imderthe thrust. 141. The Mansard roof, sometimes called a curb roof,is shown in Fig. 52, and, as will be seen, it resembles thegambrel roof in having a very flat top abed and verysteep sides adfe and dcgf. Its points of difference,however, are equally prominent; for, while the gambrelroof has its ends always enclosed with gables, the Mansard 9 CARPENTRY. 73. Fig. 52. roof is always the same on all sides, therein somewhatresembling the hip roof. The sides of the Mansard roof are generally, though notalways, curved, and aremuch more nearly perpen-dicular than the sides ofthe gambrel roof, as, inreality, these lower slopesof the Mansard are nothingmore than continuations ofthe side walls of the build-ing. In fact, the distin-guishing characteristics be-tween the gambrel and theMansard roofs may be saidto be that the former is anendeavor to make the inside of the roof appear like an upperstory, while the latter is an effort to make the outside ofthe upper story look like part of the roof. The relative pitch of the top and side slopes of a Mansard roof may be determined inseveral ways, one of which,known as Belidors method,is shown in Fig. 53. Upon the center Jl of aline a f, representing thespan of the roof, a semi-circle acdf is drawn andits circumference divided into five equal parts at
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