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.
For roofs of a pitch of | inch to the foot or less, a composition roofing, made of several thicknesses of paper coated with tar, and covered with gravel on top, may be used to advantage. The mode of constructing a composition roof will be to first cover the boarding, or, in case a fireproof roof, the smooth top of the concrete with dry resin-sized felt with a lap of two inches, tacked only often enough to hold it in place. Over this are laid three full thicknesses of tarred felt, each sheet lapping two-thirds of its width over the preceding one, and the whole covered with a uniform coat of pitch mopped on. Upon this coating, two layers of tarred felt are tacked, each lapped about twenty-two inches, and the whole mopped over and a thick coat of pitch flowed on. As the durability of the roof depends upon the paper, only the best should be used, and the pitch should not be so hot that it will destroy the life of the paper. Upon the final coat of pitch is spread immediately a coat of clean white gravel, completely covering the whole, as a protection. This composition of tar and gravel makes a very good roof, but is suitable only for roofs up to a grade of three-quarters inch to a foot.
Fig. 157. Shapes of Roof Tiles.
If much steeper, the heavy coat of tar will run in hot weather, and settling down, will gradually fill the gutters.
A composition of pulverized slate and asphalt, applied in layers with felting, has been placed upon the market, and is more adaptable to various pitches than tar and gravel.
The same precautions regarding the flashing of vulnerable parts will be needed in the laying of composition roofs that we have noted for slates or tiles, except in the case of the Plastic Slate roofing; here the composition itself is of such a nature that it may be applied with a trowel directly to the walls or copings against which the finish is made, and being of an elastic and adhesive nature, no great amount of metal flashing is needed.
The supervision of roofing work of all kinds deserves the closest attention. Nothing is more unsatisfactory than to find leaks in the roof of a new building, and the time spent in securing a first-class job will be well spent. Slates and tiles are easily broken, and unless discovered and brought to notice at once, will probably be overlooked by the contractor. Composition roofs are easily slighted, and when finished give little indication of defects.
Fig. 158. Copper Gutter.
Fig. 159. Lined Gutter.
The only safeguard is constant watchfulness, which is well repaid if the roofs prove satisfactory.