Flat roofs, with an incline of about 1/2 inch to the foot, should be covered with the flat-seam roof. The standing seam may be used on roofs with a pitch not less than 2 inches to the foot. The tin is laid upon the sheathing-boards without an intermediate layer of building-paper; in fact, tar paper should never be used. In cities building codes often require that tin roofs should be laid upon roofing felt 1/16 inch thick, placed over the sheathing-boards, but this is a fire precaution against burning brands which may drop upon the roof, for this felt cushion gives an air insulation, preventing the quick ignition of the decking below the tin.
In laying the flat-seam roof a number of sheets are fastened together to form a long strip of tin. The edges are bent over 1/2 inch, so that they can be interlocked with the next strip. The tin is fastened to the roof with tin cleats that lock into the seams of the sheets and are fastened at the other end with two 1-inch barbed-wire nails. These cleats are spaced about 8 inches apart. All the seams are flattened down, and solder well sweated into them, rosin being the only flux used.
Tin, approximately in thickness 30-gauge, U. S. Standard, is called IC, and recommended for the roof proper, while valleys and gutters should be lined with IX tin, approximately 27-gauge. It should be painted on both sides, before laying, with pure linseed-oil and red lead, or red oxide, Venetian red, or metallic brown. Two coats should be given to the exposed side and a third coat about a year later. Before the second coat is applied the first should have dried for at least two weeks.
The construction of the standing-seam roof is shown in the drawings to consist of long strips of tin, made of standard sheets fastened together with the flat and soldered seam, but the edges of the strips fastened to the next strip with the so-called standing seam, which must run parallel to the pitch of the roof. Cleats, spaced a foot apart, are used to fasten the tin to the sheathing-boards. One edge of the next strip is turned up 1 1/2 inches, and then over the top of the edge of the other strip. The cleat is locked in between the two. The upstanding seam is then turned down again upon itself, tightly locking the strips together.