TOWERS AND STEEPLES Towers are a very common feature in building construction, ranging in size from the small cupola used on barns to the high tapering spire which is the distinguishing mark of churches.
They have roofs of various shapes, some in the form of pyramids, with four, eight, or twelve sides, some of conical form, and others bell-shaped or having a slightly concave surface.
The construction of all these forms of towers is much the same, consisting of an arrangement of posts and braces, which becomes more elaborate as the tower or steeple becomes larger. The bracing is the most important consideration, because the towers will be exposed to the full force of the wind and must be designed to resist great strain.
Cupola. Fig. 24S shows a section through the frame of a simple cupola. It has posts A at each corner, which rest at the bottom on the sills B. The sills are supported on extra heavy collar beams C, which are very securely spiked to the rafters of the main roof 31. The corner posts tend clear up to the main plate D, which supports the rafters E of the cupola. There are hip rafters at the corner of the roof, which bear at the top against a piece F placed in the center of the roof. This ling extends above the roof surface far enough to receive some kind of metal finial which forms the finish at the extreme top of the cupola; and at the bottom it is firmly fastened to the tie G, which is cut in between the plates. The braces II stiffen the frames against the wind. Girts I are cut in between the corner posts and form the top and bottom of the slat frame opening R, besides tying the posts together. The sides of the opening for the slat frame are formed by the vertical studs K. The rafters of the main roof 11 are placed close up against the corner posts on the outside, and the posts may be spiked to them. The pieces 0 are of plank 2 inches thick, and are simply furring pieces placed at intervals of to 2 feet all around the cupola to give the desired shape to the bottom part. The size of the pieces will depend on the size of the cupola. The posts may be 4X4 inches or 6)(6 inches, and the braces, girts, and intermediate studding may be 3X 4 inches or 4X6 inches.
Miscellaneous Towers. Other towers are framed in a manner similar to that described for a cupola. There is always a base or drum, with posts at the corners and with the walls filled in with studding, which supports a plate at the top. The rafters forming the tower roof rest at the foot on this plate, and at the top they bear against a piece of scantling which is carried down into the body of the tower for a considerable distance and is there fastened to a tie passing between rafters on opposite sides. This is shown in Fig.
249. The tie A is securely nailed to the rafters at each end, and to a post in the mid dle. The post is cut so as to • have as many faces as the roof has sides, four for a square hip roof, eight for an octagon roof, and so on. Each face receives one of the hip rafters and the intermediate rafters are framed in between them. If the roof is conical or bell shape, as shown in the figure, the post at the top may be cylindrical in form. Although the roof shown is bell shaped the rafters are not cut to fit the curve. They are made straight and are filled out by furring pieces B. Pieces of plank C are cut in between the furring pieces, as shown, so as to give a nailing for the boarding, and they are cut to the shape of segments of circles, so as to form complete circles around the tower when they have been put in place. If a tower of this shape is to be built, having a number of faces and hips, the curve of the hip rafters will not be the same as the curve shown by a section .through one of the faces of the tower. In order to find the'true curve for the hip rafter, the same method is followed as was explained for hip rafters in an ogee roof over a hay window, using the principle that any line drawn in the roof surface parallel to the plate is horizontal throughout its length. By this means any number of points in the curve of the hip rafter may be obtained and the curve for the hip may be drawn through them. Thus a pattern for the hip rafter may be obtained.