It is not the purpose of the author in this part to describe other methods of roofing than by shingles, as he proposes to treat the subject, which is an important one, in another volume, but as porch roofs are very commonly covered with tin, a short description of such roofs may be serviceable here.
Before applying the tin all uneven edges of the boarding should be smoothed off and the boarding covered with at least one thickness of sheathing paper or dry (not tarred) felt, more to form a cushion than for any other purpose. If there are knot holes in the boarding they should be covered with pieces of heavy galvanized iron. The tin should be of one of the best brands (only those which have the trade mark stamped on each sheet should be used) and should be painted on the under side before laying.
Laying, - When tin is laid on a flat roof it is customary to use "flat seams," that is the four edges of the tin sheets are turned over so as to lock together, as shown in Fig. 178, and after fastening to the roof the seams are pounded flat and soldered, thus making one large sheet of tin covering the roof. Occasionally a double-lock seam is used, but for ordinary purposes the single lock shown is sufficient. The tin is usually laid in courses across the roof, using
2ox28-inch sheets, the side seams being made first, and the next course is locked to the one below it. Each course should be fastened to the roof at the top, the common method of fastening being to nail the sheets to the roof by short wire nails driven under the turned-over edge of the tin as shown at B.
This method of fastening, however, is objectionable, from the fact that it causes the tin to form in waves as it expands, and there is also some danger of the tin, when expanding, drawing the nails. A better method of fastening the sheets to the roof is by means of strips of tin about 1 ½x4 inches, called "cleats." These cleats are locked over the upper edge of the sheet about every 14 inches and then nailed to the roof, as shown at A; when the next sheet (above) is laid the cleat is concealed. These cleats permit the roofing to expand and rise some without straining the tin or drawing the nails, and are recommended for good work. For very large roofs, however, provision for expansion should be made by standing seams, but as these are not common on residences, except occasionally on pitch roofs, we will not describe them here.
After the sheets are all laid the seams are pounded down with a wooden mallet and all the joints well soldered. For soldering only rosin should be used as a flux, as acid, which is easier to use, is liable to destroy the tin. Before the roof is painted all rosin should be wiped or scraped off. The outer edges of the tin roofing should be turned over the upper edge of the wooden cornice and nailed about every 2 or 3 inches, or if it connects with a metal gutter the two should be locked and soldered together. Whenever a tin roof abuts against a wall or chimney the tin should be turned up a sufficient distance to prevent water from rising over it (at least 4 inches), and against a brick wall it should be counter flashed with sheet lead, as described in Section 134. When against wooden walls the roofing should be turned up against the boarding and the siding or shingles laid over it. The tin should also be turned up against all balcony posts (see Section 126) and the edges at the angles well soldered.
All tin roofs should be painted within a few days after they are laid, either with red lead in linseed oil or a good asphaltum paint.
Copper roofs are laid in the same way as tin roofs, and the above remarks apply as well to copper as to tin, except that it is not customary to paint copper roofing.