Gravel Roofs. Gravel roofs are used upon flat-roofed buildings. First it is necessary that there should be a smooth, tight roof upon which this is to be laid. There should be four thicknesses of roofing felt, laid with a lap of two thirds of the width, starting with one third of the first course of the second layer of felt at the eaves. All the layers after the first should be well mopped with pitch. The first should be laid dry, because, if laid in pitch, it will be cemented to the roof, and the shrinking of the roofing boards will be apt to break the paper.

The last layer should be nailed with 3d common nails, driven through tin disks about 30" apart. A thick coat of moderately hot pitch is then laid on, over which is spread clean, well screened gravel, which, if laid in cold weather, should be warmed thoroughly.

In flashing a gravel roof the felt is turned up from 4" to 6", and held to a brick wall by nails driven through wooden laths, or to wood with nails driven through disks of tin; the whole is carefully bedded in thick pitch, and thoroughly doped. Care should be used that pitch is not daubed where it is not needed.

There are many different kinds of patent roofings upon the market, many of which are perfectly satisfactory, but a carpenter cannot afford to risk his reputation by putting on anything which he does not know to be all right, and which has not stood a reasonable test of time.

Suggestive Exercises

81. What is meant by the term "to the weather"? How much of a shingle is usually laid to the weather? Why is a shingle not laid 6" to the weather? What should be in place before the shingles are laid? In what respect does the lowest course differ from those above? What is the usual method of laying the lowest course? What is the least a joint should be broken? What sized nails and how many should be driven to each shingle? Why not more? Describe the method of treatment and the laying of dry shingles. Describe and compare two methods of laying shingles. Is it always necessary to build a scaffold in order to reshingle a roof ? Describe and compare four different methods of hip shingling. Describe the common method of valley shingling. Describe a closed valley, and compare it with an open valley. How are tin shingles used in repairing leaks ? How should a large leak be repaired? Describe the special tool used in removing shingles from a roof.

82. What is meant by "flashing"? Describe and compare three methods of flashing a shingle roof. Why is it the best method to use counter flashings around chimneys? How should the upper edge of the flashing be fastened to a skylight frame? How should the counter flashings be fastened to a brick chimney? How is it usually done? How should the flashing be put on in places where snow might collect?

83. Describe the standing-seam roof. How should the under side of the metal be treated before being laid ? How should a tin roof be fastened to the roofing boards? How should roofing boards be laid? What should be their quality? How should nailheads be treated? How should knotholes be treated? Why is it advisable to paper a roof before putting on the roofing? What kind of paper should be avoided?

Describe a flat-seam roof. How should the roofing material be selected? How should a flat-seam roof be fastened? What should be used as a flux in soldering a tin roof ? Is it the best plan to paint a tin roof as soon as it is laid?

84. What is the least rise which a slate roof should have? What kind of nails should be avoided? What is the best kind to use ? What kind of nail is generally used? What is the best material for flashing a slate roof? What is ordinarily used?

85. When are gravel roofs laid? Describe the method of laying a gravel roof. How is a gravel roof flashed? What should be the attitude of the carpenter regarding patent roofings?