This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
85. Galvanized iron is iron coated with zinc, the object being to protect its surface from the rapid oxidation taking place when it is exposed to atmospheric influences. The zinc coating is applied to the plates while they are heated, the plates being previously prepared by cleaning and dipping in various chemical solutions, as sulphuric acid, and the salts of chloride of zinc, or sal ammoniac. The coating should be of uniform thickness and should cover the entire surface.
86. To test the quality of galvanized iron, make a double seam and mallet it down close; if it shows no fracture the iron is of a good quality. A more severe test is to again flatten out the joint or seam so made, without the material showing fracture. Samples may be tested for thickness of coating by greasing them and holding them over a gas jet with a pair of pliers; the amount of fusible metal flowing off will determine the character of each sample.
87. The ordinary sheets in use are from No. 16 to No.
88. Corrugated sheets may be placed on boards or applied direct to the rafters; flat sheets may be laid on boards, divided by wood rolls into panels. In either case, felt or paper should be placed under galvanized-iron roofing, to prevent sweating. The sheets should have a lap of at least 4 inches on the roof boards. Where the sheets abut against a fire wall, an edge a should be turned up about 6 inches, secured to the wall with wall hooks, and covered with an apron flashing b, secured as shown at (a), Fig. 71; otherwise, first lay a flashing c and carry the roofing over it and counterflash as shown in (b), Fig. 71.
89. Ridges should be finished by a ridge roll or cap, as shown in Fig. 72 (a), having an apron or wing b corrugated to suit the corrugations of the sheets, or, as indicated at (b), Fig. 72, a ridge board c having its lower face corrugated to match the sheets, may be attached to the roof and then covered with a plain cap d.
Hips should be finished as shown in Fig. 73, by cutting the iron sheet c to connect with the hip strip b and then covering the joint with a hip cap a.
Valleys should be formed of plain sheets of galvanized iron, from 18 to 24 inches wide, the ends being lapped at least 6 inches. Corrugated iron is cut to the proper angle and fitted over the valley, the sheets lapping for a distance of 6 inches over the edges. In fitting around chimneys, bulkheads, etc., the sheets on the lower side a and flanks b, Fig. 74, should abut against the chimney; a flashing should be turned up against the chimney 5 or 6 inches, as at c, and counterflashed, as at d. The tops of the two flashings are secured with wall hooks.
90. When used for siding, the sheets should have a lap of at least 1 inch at the ends and one corrugation at the edges of the sheets. The edge laps should be nailed every 6 inches, and the end laps in every other corrugation. If the metal is put on studding, the studs should be spaced to suit the width of the sheet used. If the height is greater than one sheet, a piece of studding should be put in horizontally, at the proper height, to take the end laps.
If applied to rafters without boards, the rafter must be spaced to suit the width of the sheets, and a piece of studding must be put in between each rafter where the sheets join at top and bottom, and also midway between, to prevent sagging.
Another method is to set the rafters to suit the width of the sheet and cover them with strong slats, bringing up the rafter edge with a piece of the same material.
91. In preparing the material for flat sheets laid with wood rolls, the sheets are riveted together, end to end, making a continuous sheet from eave to ridge; or each sheet may be laid with a lock seam, as described for copper roofs. The rivets should not be more than 1 inch apart.
The eaves gutter, or flashing, must be attached to the roof before laying the roof proper, and must lap the roof boards not less than 4 inches.
The wood rolls or strips a in Fig. 75 are attached to the sheathing, and spaced to suit the width of the sheets. Against a fire or parapet wall, a sheet b will be required, which will be counterflashed as at c. Clips 2 inches wide by 5 inches long should be attached to the edges of the rolls. The method of securing the sheets by the clips and rolls is shown in Fig. 76, in which a is the clip; b, the sheet; c, the lock; and d, the cap roll. The cap roll is slipped over the wood roll, the edges of the roll passing over the throating formed by the ends of the clips a, a, which thus hold it in place. The horizontal end joints are made with a single lock and are secured to the roof by clips, in the same manner as in the roofing.
02. The following table gives the amount of galvanized corrugated sheet iron required to lay one square: