Sheet steel is a cheap roof covering; it is light and water tight and as it comes in large sheets it can be rapidly applied; it is suitable for roofs of any pitch, is lightning proof and has a low insurance rate. Sheet copper, sheet lead and sheet zinc have been used for roofing in special cases, but they are much more expensive than sheet steel.
Sheet steel roofing is annealed Bessemer steel of the best quality; a sample piece may be hammered into all kinds of shapes without cracking. Sheet iron is unsuitable for roofing since it is liable to break when bent and hammered to a flat joint. Sheet steel roofing should not be laid over tar paper or on wood containing acids, and it should have a coat of paint on top. Steel roofing sheets are made 96x28 ins. in size and will cover an area 93 1/2x24 ins. They must be laid over lath or sheathing, and if warm air comes into contact with the undersides of the sheets they should be protected by an anti-condensation lining of the construction used for corrugated iron roofing previously described, or by a lining of asbestos paper.
The weight of sheet steel roofing of the construction just described is about8o lbs. per 10x10 ft. square. At present prices the cost per square of No. 27 B. W. G. sheet steel painted red is $3.50, and of galvanized sheet steel is $5.90. These prices are for small lots; for car load lots the cost will be about 10% less. Graphite paint costs 25 cts. more per square than iron oxide paint. Table VIII. shows the weight per square foot of painted and galvanized steel roofing sheets of different gages. Roughly speaking, galvanized sheets weigh about 20 lbs. per 10x10 ft. square more than black or painted sheets.
Table VIII. Showing Weight in Lbs. per Square Foot of Steel Roofing Sheets of Different Gages.
B. W. G......Black ......
B. W. G......Galvanized . .
U. S. Standard, Black ......
U. S. Standard, Galvanized ..
Crimped roofing is laid directly on wood rafters or over sheathing, the latter construction being preferable, and is probably the least expensive metal roof covering available. It should have a pitch of at least 2 ins. to the foot. Crimped roofing weighs 83 lbs. per 10x10 ft. square painted, and its present cost for No. 2,7 B. W. G. is $3.10 per square painted and $5.50 per square galvanized. For car load lots 10% should be deducted from the above prices.
Steel roll roofing differs from steel sheet roofing by having the sheets of 8 ft. and 10 ft. length joined at the factory into a continuous piece some 50 ft. long. As the side joints must be made after the material is laid out on the roof this roofing is more suitable to roofs of small pitch, say 1 in. to the foot, than to steeper roofs. Steel roll roofing is easily handled and the cost of shipping is less than in the case of steel sheets which have to be boxed. Parrafined felt packing should be inserted in the joints. If desired the manufacturers will make steel roll roofing in any length required up to 150 ft. to suit the length of roof to be covered. This roofing weighs about 85 lbs. per 10x10 ft. square, and in sheets of No. 27 B. W. G. it costs $3.50 per square painted, and $5.90 per square galvanized. Steel roll roofing requires no ridge capping since the strips or rolls are continuous over the ridge. Generally the manufacturers of any kind of steel roofing having folded joints provide special tools for laying it.
Tin and terne plate roofing are generally used only for flat roofs or roofs with a small pitch. The plates come in 14x20-in. and 28x2o-in. sizes, and well laid plates of good quality should last 30 years. It is very important to the life of the covering that its joints should be well soldered and that there should be no travel on the roof. Tin and terne plates may be laid on sheathing or over old shingles. If the roof is quite flat all joints should be soldered, but when laid on sloping roofs the side joints may be folded and the cross or horizontal joints soldered. Some roofers lock all joints and fill the horizontal seams with lead. The sheets are fastened to the roof by cleats; if the side joints are soldered the cleats should be soldered in the joints. For sloping roofs it is often convenient to have a number of sheets jointed in the shop into strips of the right length to reach from the eaves to the ridge. After laying the plates should be painted with two coats of paint and they should be repainted about every two years afterward. To reduce the noise, tin or terne sheet roofing may be laid on a lining of tar paper.
The old method of preparing tin or terne plates was to immerse the sheet of iron or steel in a bath of tin or lead, a coating of which adhered to the plates when they were removed. The modern method of manufacture is to pass the sheets between rolls which are immersed in a bath of tin or lead, and thus by adjusting the rolls to secure a coating as thin or as thick as may be desired. The cost of the finished plate depends largely upon the thickness of the coating. Plates coated with lead are called ternes and are somewhat cheaper and less durable than tin plates. Terne plates are more generally used for roofing than tin plates. The best plates are made from charcoal iron, but Bessemer steel is also used. The thickness of sheets commonly employed are known as I C and I X, and correspond to No. 30 and No. 28 B. W. G., respectively.