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.
At the ridge of a roof where the two slopes meet there must be some special provision made for the proper finish of the roof covering, something for the shingling or slating to finish on as well as some adequate means of covering and making watertight the joint which occurs at this place. There is usually a ridge board, or ridgepole, which receives the rafters, and this piece may be cut off just at the ridge so that the rough roof boarding goes over it, or it may be made wider and may project up above the roof boarding, so that this boarding stops against it instead of going over it. The two different methods call for different kinds of ridge finish. The first is the most simple, and may be taken care of as shown in Fig. 287. Here, A is the ridge board, BB are the rafters, E is the roof boarding, C is the shingling, and D is the finish at the ridge, consisting of two pieces of board about 6 or 8 inches wide and 7/8 inch thick, which are nailed on top of the shingling to form a finish. In case the ridge board is carried up above the roof boarding, it is customary to make the ridge finish of galvanized iron or of copper or other metal. This may be done very simply, as shown in Fig. 288. Here the ridge board is extended above the roof boarding and around it is shaped a strip of galvanized iron or copper or zinc, which is continued down over the shingles of the roof so as to form a flashing. This makes a good ridge finish and one which is water-tight if it is properly put on. The galvanized iron should be flashed down over the shingles for a distance of at least 6 inches. It is not necessary that the ridge board should be extended above the roof boarding. The same result may be accomplished by nailing a separate piece of 2 X 4-inch or 2 X 5-inch scantling to the top of the shingles, running lengthwise of the roof, to form a ridge over which the metal may be shaped. This method may perhaps make a tighter job than the other.
Fig. 287. Simple Ridge Finish.
Fig. 288. Galvanized Iron Ridge Finish.