to molded forms, such as ridge rolls, hips, finials, etc. Copper roofing is often "crimped", that is, the surface is covered by fine corrugations, which give a softer and more even appearance than the plain metal, and conceal the waviness which plain sheets may show. Slate Roofing. On roofs which pitch more than 5 inches to the foot, slates may be used. With a slate roofing the boarding should be matched and covered with tarred paper. On this surface the slates are laid in layers, beginning at the eaves with a double course and working upward to the ridge. The gaging of the courses is determined by the head cover, that is, the distance which the top of the slate is overlapped by the second slate above, Fig. 186. This lap should not be less than 3 inches. *3* Slates are usually 8×16 inches and 10×20 inches in size, and run from about to inch in thickness. They should be put on with tinned, galvanized, or copper nails, two to each slate, and care must be taken that the nails are driven in, not hard enough to crack the slates, and yet hard enough to prevent them from rattling. The nails should have large heads and be 3-penny or 4-penny nails. Where slates are cut, as against hips or valleys, care should be taken that each slate receives two nails. For thick slates the holes should be drilled and countersunk. First-class work requires that the slates, for a distance of 2 feet each side of valleys and above gutters, should be "rendered", that is, bedded in elastic cement, and the same precaution should be taken for the width of a foot at hips, ridges, and all vertical parts. If slating is to be used on roofs of very slight slope, the whole should be laid in cement. Fig. 186. Head Cover of Slates Slate Roofing on Flat Roofs. Flat composition roofs are often surfaced with slate in place of the final coat of gravel or slag, the process up to this point being the same as if a gravel finish were to be used. This produces a roof which may be freely walked upon and permits the removal of snow without injury, whereas a gravel coating is a protection mainly against the elements, and is not suitable for use unless further protected." Flashings. Valleys in slate roofs should be open valleys of metal at least 18 inches wide, often laid, like a tin roof, with the end joints locked and soldered and the edges securely nailed to the roof boarding. Tin, zinc, or copper may be used, but copper is to be preferred for valleys, as well as for all flashings. Where the slope of the roof changes or where dormers, chimneys, or other vertical parts cut the roof, wide aprons of metal should be set and turned up against the rising wall to be covered over by the wall covering, or by lead counter-flashings built into the brickwork. Gables are finished by continuous metal members, run at least 8 inches under the slates and tacked over the edge of the wooden finish, or cemented into grooves cut in stone copings, called reglets. Raggle Blocks. Special blocks made of terra cotta or hard clay and having a reglet cast in the back may be obtained for use at the roof level if it is not desired to flash the back of the wall, or for use as a coping in case the wall is to be covered, Fig. 187. The blocks are made to receive the roof composition, or metal cap flashings, as may be desired. tion is a great convenience where flashings have to be removed. Fig. 187. Section Showing Raggle Block for Holding Roof Composition or Metal Flashings This style of construc A good practice is to cap all flashings; that is, the metal which runs under the slates is turned up against the wall, and a separate piece of metal is wedged and cemented into the reglet and turned down over the other flashing to within half an inch of the roof. This method allows free movement to each piece of metal, which is necessary because of expansion and shrinkage. For the same reason it is much better to form the valleys and hips of sheets which are laid in with each course, lapped, and not locked and soldered. Various Methods of Laying. Slates are sometimes laid on strips of wood or battens without boarding, but this does not make so tight a roof. For fireproof roofs, however, it has been common to L secure the slates to small T-bars by bolts and then to plaster the underside, but a better way is to lay porous terra cotta blocks between the irons, to which the slates may be nailed or cemented. A method of slating which may be employed where absolute tightness is not required is one called half-slating, and consists in leaving between the sloping edges of each slate a space not exceeding half the width of the slate, Fig. 188. Qualities of Slate. In appearance, good slates should be of an even color without spots, and pre Fig. 188. Half-Slating Roof Covering sent a hard, straight grain, which should shine in certain lights with metallic, silken luster. They should be square and true, and free from warped or nicked edges, and neither too brittle nor too soft. Tiles. Tiles for roofing, although by no means a modern invention, have of late years come into more general use in this country. They are made in a variety of shapes, the general principle in all cases being that of a slab of baked clay, molded with an interlocking roll or rim. Tiles are laid on battens or on boarding, as described for slates, but instead of a double lap for tightness, the tightness of this roof depends upon the fitting of the tiles into each other. Some of the modern forms of tiles are shown in Fig. 189. With tiles should be used copper or zinc for valleys and flashings, but ridges and hips are generally formed by tiles of special patterns. Plain tiles have long been used in England and in most cases have been found after years of service to be in as good condition as when new. Tiles may be used on roofs which have a pitch of more than Fig. 189. Standard Shapes of Roof Tiling 22 degrees, but they need a free use of elastic cement, especially in valleys, hips, and ridges. In appearance, tiles should be of even color, free from fire checks but well-burned and nonabsorbent, of uniform size, and without blisters, cracks, or warped surfaces. Cement Tiles. A variety of roofing tiles is made of Portland cement reinforced with metal. These are molded in large sizes, approximately 2×4 feet, and when laid on steel ribs they present a surface on the underside which requires no further finish, and is suitable for warehouses, machine shops, and power houses where the roof has a reasonable pitch-usually not less than one-fifth of the whole span. For flat roofs which are to be used for observation or roofgarden purposes, there is a kind of hard tile called "promenade" tile, or quarry tile, which is laid in cement as a paving, and has been used with good results. These tiles, usually from 6×6 inches up to 12x12 inches if square, or in equivalent oblong shapes, should be hard burned and sound and solid in every particular. When well laid in Portland cement they form a pleasing and permanent roof. Asbestos Shingles. As a substitute for wood shingles, there are shingles made by molding asbestos fibers and Portland cement into a solid sheet under hydraulic or other extreme pressure. These shingles come in various shapes and colors, and are usually inch or inch thick; the latter are made with rough edges to resemble tiles or slate, but they are much lighter and tougher, allowing a lighter roof construction. The 3-inch shingles are less pleasing than the thicker ones as they present a surface extremely smooth and uniform in appearance; they are made in patterns which run to diagonal as well as horizontal lines on the roof. Selection having been made, the laying does not differ from the familiar construction of slate or tile covering, equal care being necessary to see that proper metal flashings are introduced in the portions especially exposed to rain or snow. Composition Roofing. 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 over wood consists, first, in covering the boarding with dry resin-sized felt with a lap of 2 inches, tacked only often enough to hold it in place. Over this are laid two 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 three layers of tarred felt are tacked, each lapped about 22 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, as a protection, a coat of clean, white gravel, completely covering the whole, Fig. 190. In the case of a composition roof laid over a concrete surface, the operations are the same except for the first mopping of pitch Fig. 190. Section Showing Layers of Composition Roofing on Board Sheeting directly upon the concrete, and the omission of the nailings which are required on a wooden roof, their place being taken by moppings of pitch. This composition of tar and gravel makes a very good roof, but it is suitable only for roofs with a grade up to 2 inch to the foot. If the roof is much steeper, the heavy coats of pitch will run in hot weather and, settling down, will gradually fill the gutters. A com |