The first course of slates must be shorter than the ordinary slates by the amount of the gauge to which the slating is to be laid. The gauge of slating as of tiling is the length of slate (or tile) exposed to view in each course. For 20-inch slates laid to a lap of 3 inches, the gauge, as shown in Fig. 79, is 8 inches. The subsequent courses need no explanation.

All slates must be secured with nails, which may be 1 or 2 inches long. according to the thickness of the slates, and may be of copper, zinc, or "composition" (a mixture of copper, zinc, and tin). Iron nails, whether galvanized or not, should not be allowed, as they soon rust. Copper nails are used for the best work, but composition nails are also durable.

Rooflng-tiles are of several kinds, the most generally used being the "plain" (or "plane") tile, similar to those described in Chapter III (Drain-Pipes). of this Section, pp. 109-110. These are either simple oblongs or shaped on the lower edge, and are hung to wood laths by nibs formed on the tiles, or (in exposed situations) by copper or galvanized iron nails about 2 inches long. The usual colour is deep red, but other colours can be obtained - strawberry, blue, brindled, etc. - and semi-vitrified or glazed tiles are also made, and have the advantages of durability and imperviousness. Hips and valleys are formed by special tiles, as shown in Fig. 84, and wide tiles are inserted in the alternate courses of gables in order that the tiles may break joint. Roof-tiles are laid to gauges of 4, 3, or 3 inches, 54, 62, and 72 tiles respectively being required in every square yard. Tiles are heavier than slates, and as a rule more absorbent and more expensive; on the other hand, they are warmer. The Ruabon and Broseley tiles enjoy a good reputation.

A novel method of laying plain tiles on concrete or mortar, instead of on boards and felt, was introduced some years ago by Mr. Ralph Nevill, and has stood the test of experience. The first operation consists in nailing the plaster-laths to the underside of the common rafters, lest, if it were done afterwards, the concrete might suffer by the jarring. Single fir laths are then fixed with lath-hooks to the upper side of the rafters, and an eaves-lath or tilting-fillet is nailed along the eaves. Copper nails 2 inches long are then driven into the upper side of the rafters at distances of about 4 inches, and left projecting about an inch to furnish a key for the concrete, which is subsequently deposited to a thickness of about 1 inch. This concrete consists of one part of clean sharp sand, three parts of finely-sifted clean ashes or coke-breeze, and one part of a mixture of selenitic lime and Portland cement (3 to 1). The concrete must be laid in long strips, beginning at the eaves, and laying only so much as can be covered with tiles before it has become too hard. The surface must be trowelled fairly smooth, particular care being paid to the hips and valleys. After the concrete has been deposited for al>out 6 or 8 hours in the daytime, or about 10 or 12 at night, it will be ready to receive the tiles. The tiles may be gauged by means of chalk lines snapt on the concrete, and arc fixed by pressing two pins to each tile into the still moist concrete; "the thickness of concrete against chimneys, barge-boards, etc., should be slightly increased, so as to tilt the tiling; and throw off the water. As there will be no foothold on the roof, and all the tiles will be worked over, it will be necessary to sling a cradle over the ridge, resting on well-stuffed bags. To avoid returning over the tiles, it is important that the ridge should be fixed as the tiling is done."1

Fig. 84 Hip tiles and Valley tiles.

Fig. 84-Hip-tiles and Valley tiles.

Of special roofing-tiles there are numerous varieties. Pan-tiles are only used for farm-buildings and cheap work, hut several other varieties are suitable for good houses, such as the Broomhall tile, Major's, Taylor's, and others. Concrete roof-tiles have also been made, and a special diamond-shaped sort is now being introduced into this country after having achieved some measure of success abroad; its appearance, however, is most inartistic "Ridging*" is the name given to the materials used for covering the ridges of roofs. Blue and red ridge-tiles are now most generally used on account of their cheapness, but stone and slate ridging are also used; these should all be bedded and jointed with cement-mortar. Wood rolls covered with lead or zinc must also be mentioned. Fig. 85 shows a 2-inch wood roll with 1-inch neck, and a sheet of lead 24 inches wide dressed over the roll and down the slates about 7 inches on each side, and nailed to the wood roll with round-headed nails. The neck allows the lead to l>e dressed a little under the roll, and so be securely held to it. The end joints between two sheets of lead are simple laps of about 6 inches.

1 The Builder, Dec. 9. 1896.

Hips may be formed in tiled roofs by special tiles as already explained, and in slated roofs by A-shaped tiles or other material, or by wood rolls and lead, exactly as ridges. Frequently, however, the hips of slated roofs are formed by carefully cutting the slates to the requisite angle (known as "close bevel cutting"), and inserting at the angle in each course of slates a thin lead soaker (2 or 3 lbs. per sq. foot) cut to the proper shape and bent to the angle of the hip; this is the neatest method of forming hips.

Valleys in slated roofs are formed with 5 lbs. or 6 lbs. sheet-lead, about 18 inches wide, laid (with laps of from 3 to 6 inches at all joints) on boarding. In tiled roofs, curved valley-tiles may he used.

The dead weight of roofs varies considerably, but the table on p. 148 is approximately correct.

Eaves-troughs or gutters are still sometimes made of wood, but as a rule cast-iron is now preferred. Lighter gutters of galvanized wrought-iron and of zinc are also made, but are not as durable as cast-iron. Eaves-troughs should be securely fixed, either by being screwed to a fascia nailed to the end of the rafters, or by wrought-iron hangers nailed to the upper side of the rafters or boarding, and passing under the trough. Hangers are sometimes of ornamental appearance. In addition to screws or hangers, the gutters may be supported on stonework or on iron brackets. Stone cornices are sometimes hollowed and lined with lead to form eaves-gutters.