Metal Roofs. (A.) In recent years, steel roofs have come into use in different parts of the country. The standing-seam steel roof (Fig. 129, a) is well adapted for use upon barns and warehouses. If used upon a roof which has no long valleys, it may be laid rapidly by unskilled labor with a little oversight, and will give good satisfaction, though steel is soldered with the greatest difficulty.
Tin roofs may be laid by this method, and are to be preferred to the flat seam shown at d, as the roof may be repaired more easily, and expansion and contraction in different temperatures will not be so apt to break the metal.
Dealers who handle the standing seam roofing generally have a set of tools to lend with which to lay the roof. They are very simple in their operation, doing all the work of laying the roof except fitting and driving the nails.
Steel or tin roofs should be painted upon the under side before being laid; then if kept painted upon the outside, they usually prove satisfactory.
If a metal roof is nailed directly upon the boards of the roof, it will buckle, and in time crack, on account of the expansion and contraction; therefore roofing tacks, (Fig. 129, b), strips of tin or steel, are hooked over a standing seam, as at b, or a flat seam, as indicated by the dotted lines at c, to allow the roof to expand and contract, as the temperature changes.
Fig. 129. - Metal Roofs. a, standing scam; d, flat seam.
The boarding of a roof which is to be covered with metal, should be perfectly smooth; upon the best work the roof is covered with matched boards. Upon all roofs which are to receive metal, the boards should be thoroughly seasoned, and carefully nailed down, to prevent any future warping and twisting. All nailheads should be set below the surface of the wood, to prevent the frost from backing them out. If there are knotholes, they should be covered with tin, and there should be no places where a corner of the boarding is likely to bear against the under side of the metal. Under the roofing there should be laid one or more thicknesses of paper, which add much to the life of the roof. Do not use tarred paper, as the acids in it will destroy the metal. Some builders object to the use of paper under a metal roof, claiming that it holds moisture, but it is certainly the best practice to use it, because it furnishes a cushion which protects the roofing from the roughness of the roofing boards; this is more important than any possible condensation.
If the carpenter is responsible, he should see that the work is done properly by the tinsmith, and that the right grades of all materials are used; only high-grade metal is suitable for roofing.
(B.) Tin roofs are often laid with a flat seam, commonly known as a lock joint, which should be made as shown in Fig. 129, at c, and thoroughly fastened, not nailed through the tin into the roof, but through the cleats. These should be at the top of the sheet, which is usually 20" X 28", and should be placed between 12" and 14" apart. The seam should be well pounded down to make the joint as tight as possible.
In soldering, rosin should be used as a flux, but no acid, as it is apt to destroy the tin. No rosin should be left upon the tin, as it will prevent the paint from holding well.
After the tin roof is laid, a good plan is to leave it for a few days, as it will then take the paint better, and if it is exposed to a shower, no harm will be done; this does not mean that an exposure to a long rainy spell is recommended.
The workmen must be careful to leave no loose nails upon the roof while at work, for if stepped upon they may punch a hole through the roof.