Besides the angles already mentioned, A F C Figure 3, shows the angle formed by the upper side of the rafter and the ridge piece, and the angle 13 E C, the angle which the top side of the hips makes with a vertical or plumbline; also the angle F A c shows the form of the heel of the common rafters, and E n C that of the hips.
Figure 5, is a diagram showing the length of the parts and angles concerned in the roof, in the same manner as above; but the plan of the building, or form of the wall•plate, is a quadrilateral, wIlielt has neither part of its opposite sides par allel; the method of executing the roof in this ease is to form a level on the top, from the top of the hips at the narrow end to the other extretnity, as otherwise the roof must either wind, or be brought to a ridge forming a line inclined to the horizon ; and either of the two last eases is very unsightly. But, that nothing should be wanting, the construction is given in the next figure.
Ptak 111.—Fiyare 6.—To lay out an irregular roof in ledgment, with all its Imams bevel upon the plan, so drat the ridge may be level when finished ; the plan and heiyht of the roof being given.
The length of the common and hip-rafters arc found as usual. From each side in the broadest end of the roof; through c and D, draw two lines parallel to the ridge-line draw lines from the centres and ends of the ',cants, perpen dicular to the ridge-line, and lay out the two sides of the roof 2 and 3, by making E n at 3 equal to x a in I, the of the longest common rafter, and c a in 3 equal to u & at A, and so on with all the other rafters.
To jind the winding (f this roof—Take y (6, half the base of the shortest rafter, and apply this to the base of the longest rafter from z to 1 ; then the distance from 1 to 2 shows the quantity of winding.
To lay the sides in windiny.—Lay a straight beam along the top ends of the rafters at E, that is, from c to E, and lay another beam along the line A B, parallel to it, to take the ends of the hip-rafters at xm and L, and the beams to be made out of Ns hiding at first. Raise the beam that lies from a to B, at the point B, to the distance 1 2 above the level ; which beam, being thus raised, will elevate all the ends of the rafters gradually, the same as they would be when in their places.
The same is to be understood of the other side n; the ends are laid down in the same manner as in making a triangle of any three dimensions.
In this example, the purlins are supposed to be framed into the sides of the rafters flush, so that the lop of the pur lins may be flush with the back of the rafters. The manner of' framing the dragon beams and diagonal ties, is shown at the angles.
Flute IV.—Figurc 7, shows the manner of framing a roof when the sides are square. The purlins are prepared to bridge over the rafters, which are notched out of the sides next to the back, in order to receive them.