This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Fig. 248 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 M. The corner posts extend 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 scantling 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 H 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 A'. The rafters of the main roof M 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 1 1/2 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 6X6 inches, and the braces, girts, and intermediate studding may be 3X4 inches or 4X6 inches.
Fig. 248. Section Through Frame of a Simple Cupola.