the foregoing, metallic shingles of various decorative designs, imitating the appearance of the finely-finished terra cotta tiles, are in the United States much in vogue on steep roofs. In respect of fire- and storm-proof qualities, these have all the advantages pos sessed by terra-cotta tiles; they are in no wise inferior to the latter in attractive appearance, and in respect of durability and lightness are dis tinctly superior. Figure r3 GO/. 2) shows one of the forms of metallic roofing tiles in common use. These tiles have a thickened edge, which adds greatly to their appearance. When laid, they slightly overlap at the edges; so that the nail holes are covered. The usnal dimensions of these tiles are 5 x 5 or 6 x 6 inches.
the modes of roofing already mentioned, a support of boarding is absolutely necessary; Figure 13 (fii. 7) exhibits the method applied when corrugated sheets are used. Metal thus formed by rolling has much greater stiffness than ordinary metal, and can lie free over much larger spans. As the corrugations must run in the same direc tion as the roof gutter, it will be seen that the plan exhibited in the illus tration is suited only for purlin construction. The overlapping of the sheets, about inches, and the tongues for securing them, are shown on the Plate. Corrugated iron laid upon roofs in sheets should overlap about 23,1 inches along the sides and 4 inches along the ends, and about 6 inches is usually allowed for extension over the eaves. This substance offers an excellent and permanent protection.
A serious objection to simple iron roofing—known as " black iron "— is the very rapid condensation of the atmospheric moisture, which falls from the metal like drops of rain and is likely to injure the ceilings be neath; and this dang-er is not entirely removed by painting, although it can be prevented by plastering. This material is, however, very enduring, when kept thoroughly defended by paint composed of some mineral oxide, the sheets being overlapped and folded at the edges and placed upon sheet ing boards. Galvanized iron, which is much used, and which is very useful for roofing, is manufactured by applying a thin coating of zinc to both sides of the sheet of iron by immersing the latter in a bath of molten zinc.
Tin-plate Roofing.—The tin plate, also used extensively for roofs, is produced by covering iron sheets (in the same iiianner) with a coating of tin or of an alloy of tin and lead. The sheets of tin—or, rather, of iron faced with tin—are joined together in the shop, end to end, bv being bent over, hammered flat, and then soldered. 'When each sbeet is of the required length to reach from the eaves to the peak of the roof, it is, for convenience, turned into a roll and carried to the roof, where it is spread upon the sheeting boards and joined to the next length along the edges by bending, and for further security is fastened by cleats about IS inches apart. Terne, or sheet iron covered with a mixture of tin and lead instead of with tin, is frequently used for the same purpose, but is not so durable, although less expensive. The best plates of both tin and terne are made from char
coal-iron, which is tough and does not suffer from bending; iron made with coke is inferior in this respect. Tinned and leaded sheets of Bessemer and other steel are also used.
Zinc ana' Colofier Roofing.—Zinc, like tin, furnishes an excellent resist ant to the moisture and changes of the atmosphere. Zinc in sheets, laid like slates, is much employed in various parts of Europe, and proves very durable, as a thin film of white oxide collects upon it by exposure to the weather and increases its resistant poi.ver. Copper as roofing material is applied in sheets 5 feet in length by 2 feet in breadth, and is laid on boards, to which it is held by copper cleats.
Glass Roofing.—Glass is used for roofing only when light is to be ad mitted through the entire surface or by a skylight. The glass sheets, either of ordinary or of cast glass, are best laid upon bars of I-shape cross section, and are, as usual, glazed with putty. In skylights arrangement should be made to carry off by small inside gutters any leakage or con densed moisture gathering on the inside. In large roofs it is not desirable to trust to putty, and there are now introduced many different systems of glazing which, while aiming at freedom from leakage, permit the glass to expand and contract at the edges. For skylights from to LI inch in thickness a thick ground-glass is made i.yhich has the effect of preventing the full glare of the sun, and of diffusing the light over a much greater space below. Where skylights are glazed with clear or double-thick glass, it is used in lengths of froin 16 to 3o inches by a width of from 9. to 15 inches. A lap of at least r inches is recommended for the securing of all joints. Fluted glass (sheet-glass rolled so as to form flutes or corruga tions on both sides) is best suited for this purpose, as it secures privacy without obscuring light, while it is stronger than ground-g,lass. The Crystal Palace in Loudon affords an example on a large scale of complete, and at the same time original, roofing in fluted glass, a specimen being shown in Figure rd. („6/. 7).
Shed Iron for Exierior Finish and employment of cralvanized sheet iron for the exterior finish and ornamentation of buildinos has become very general in the United States, and by its use the most elaborate decorative effects are obtained. It is chiefly employed for cor nices and roof crestings, for which it is well adapted as a fireproof cover ing. It is also applied to the fronts of buildings, to columns, etc., in imi tation of wood, stone, or iron. Fig-ures 8 and 12 col. 2) show respectively the mode of attaching a sheet-iron cornice by braces extending through the masonry, and the appearance of a finished cornice. Figure to shows a roof cresting, and Figure 7 shows a capital of a column.