With the completion of the exterior masonry of a building will come, in most cases, the covering in, as practically nothing further than the rough work of flooring can be done inside until the work is protected from the weather by a roof.

Fig. 153. Drip of Cornice Stone.

Fig. 153. Drip of Cornice Stone.

For the roof covering, a variety of materials may be used, common among which may be mentioned tin, copper, slate, tiles, and for flat roofs, tar and gravel composition, besides many patented preparations of paper and tar which may be used for temporary roofs. Tin Roofs. The cheapest, and at the same time the least satisfactory of permanent roofing materials is probably tin. This may be used on steep roofs or on comparatively flat roofs, the least inclination advisable being § inch to the foot. The boarding under a tin roof should be smoothly matched and covered with dry sheathing paper, and any holes in the boarding should be filled up. The sheets of tin for a flat roof are prepared by turning the edges over so as to lock with the edge of the next sheet as shown at A, Fig. 154, and they should be painted on the under side and allowed to dry before laying. The usual method of laying is to run the sheets in courses across the roof, each course being nailed at the top with short wire nails under the lap of the tin. This method of fastening should not be permitted in a roof of any extent, as the rigid nailing of each sheet will give the roof a wavy appearance when the metal expands, and the wrenching of the tin will often draw out the nails or tear the tin from the heads. When this occurs, the great mass of tin will rattle against the roof, besides being exposed to the danger of leaking. The proper way to secure the tin is by the use of strips of tin called cleats, cut about 1 1/2 X 4 inches. These cleats should be locked over the turned edge of the sheet and nailed to the roof, being concealed by the next sheet added. These cleats should be used about every fourteen inches along the upper edge and the side of the sheet of tin, and they will allow the roof to expand without drawing the nails or destroying the tin.

When the roof has been covered, the seams are all pounded down and carefully soldered, making a continuous covering.

Against chimneys, dormers, or other openings in the roof, the tin should be turned up at least four inches to be capped by vertical flashings of lead or zinc, with gable ends carried out and tacked over the edge of the mouldings and finish. Connections should be made with metal gutters and finish by locking and soldering.

Fig. l54. Seams in Tin Roof.

Fig. l54. Seams in Tin Roof.

For large and steep roofs of tin, greater allowance must be made for the expansion, and this is done by means of standing seams, IS, which are formed by locking together vertically the sloping seams of the roof, the horizontal seams being flat. To do this the sheets of tin are locked and soldered together into strips running up the roof, and these strips are turned up and locked together without soldering, held in place by cleats. When finished, the seam should be about an inch in height.

Standing seams are often used for effect, and a still stronger appearance may be given by ribs of wood over which the tin is locked. The tinning of a roof should be carefully watched to see that tin of the required quality is used, that the cleats are put in as described, and that acid is not used in soldering. Only resin should be allowed as a flux for soldering, as acid, which is more easily used, will injure the tin. The standard sizes of roofing plates are 14 X 20 inches and 20 X 28 inches; and they are made in two thicknesses marked I C and I X, the former weighing 8 oz. to the square foot and the latter ten ounces. The lighter brand is more extensively used, but for first-class work and flashings, nothing but I X tin should be used. Imperfect sheets, called "wasters," are put upon the market, and are packed in boxes marked I C W or I X W according to the thickness, so that where perfect plates, called "prime," are called for, the super-intendent should reject any boxes marked "W." The best grades of tin are now sold with the name of the brand and the weight stamped on every sheet, and this should be noted for first-class work. It is worth remembering that the smaller sheets will make a stronger and better roof than the larger, and for a steep roof with standing seams the sheets should be laid with the narrow way for the width between the sloping seams, as this gives more chance for expansion. Tin roofs should not be painted until the rain has had a chance to wash the tin clean of grease, and all traces of resin should be removed.

Tin roofs, while under construction, should be kept clean, and rubbish never be allowed to collect, as nails and other hard substances are liable to cause perforations of the tin if stepped on by careless workmen. If tin is used for covering of a fireproof roof, the top filling should be of porous terra cotta which will receive the nails, and an even surface should be secured by smoothly plastering the surface of the terra cotta with hard cement. Steep fireproof roofs are often made by using hollow terra cotta tiles between T-irons, which may be treated in the same way.

Copper Roofing

The methods of laying copper roofing differ very little from those described for tin, except that the sheets of copper are much larger and therefore lend themselves more easily to moulded forms such as ridge rolls, hips, finials, etc. Copper roofing is often "crimped," that is, the surface is covered by fine corrugations which present a softer and more even appearance than the plain metal, and conceal the wavy appearance which plain sheets will acquire.