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Although roofers usually are trained to apply most kinds of roofing, they often specialize in either sheet membrane roofing or prepared roofing materials such as asphalt shingles, slate, or tile.
One kind of sheet membrane roofing is called built-up roofing. Built-up roofing, used on flat roofs, consists of roofing felt (fabric saturated in bitumen, a tar-like material) laid into hot bitumen. To prepare for putting on a built-up roof, roofers may apply a layer of insulation to the bare roof deck. Then they spread molten bitumen over the roof surface, lay down overlapping layers of roofing felt, and spread more hot bitumen over the felt, sealing the seams and making the roof watertight. They repeat this process several times to build up as many layers as desired. They then give the top a smooth finish or embed gravel in the top for a rough surface.
Single-ply roofing, a relatively new roofing method, uses a waterproof sheet membrane and employs any of several different types of chemical products. Some roofing consists of polymer-modified bituminous compounds that are rolled out in sheets on the building's insulation. The compound may be remelted on the roof by torch or hot anvil to fuse it to or embed it in hot bitumen in a manner similar to built-up roofing. Other single-ply roofing is made of rubber or plastic materials that can be sealed with contact adhesive cements, solvent welding, hot air welding, or other methods. Still another type of single-ply roofing consists of spray-in-place polyurethane foam with a polymeric coating. Roofers who apply these roofing systems must be trained in the application methods for each system. Many manufacturers of these systems require that roofers take special courses and receive certification before they are authorized to use the products.
To apply asphalt shingles, a very common roofing material on houses, roofers begin by cutting strips of roofing felt and tacking them down over the entire roof. They nail on horizontal rows of shingles, beginning at the low edge of the roof and working up. Sometimes they must cut shingles to fit around corners, vent pipes, and chimneys. Where two sections of roof meet, they nail or cement flashing, which consists of strips of metal or shingle that make the joints watertight.
Tile and slate shingles, which are more expensive types of residential roofing, are installed slightly differently. First, roofing felt is applied over the wood base. Next, the roofers punch holes in the slate or tile pieces so that nails can be inserted, or they embed the tiles in mortar. Each row of shingles overlaps the preceding row.
Metal roofing is applied by specially trained roofers or by sheet metal workers. One type of metal roof uses metal sections shaped like flat pans, soldered together for weatherproofing and attached by metal clips to the wood below. Another kind of metal roofing, called "standing seam roofing," has raised seams where the sections of sheet metal interlock.
Some roofers waterproof and damp-proof walls, swimming pools, tanks, and structures other than roofs. To prepare surfaces for waterproofing, workers smooth rough surfaces and roughen glazed surfaces. Then they brush or spray waterproofing material on the surface. Damp-proofing is done by spraying a coating of tar or asphalt onto interior or exterior surfaces to prevent the penetration of moisture.
The growing interest in "green" construction and more efficient use of natural resources has led some companies to incorporate landscape roofing systems to their buildings. With this type of roofing, roofers put a waterproof layer put down first and test to ensure it is leak free. They next place a roof barrier over it, and then layers of soil in which trees and grass are planted. The plants and greenery on the roof absorb the sun and keep buildings cool in the summer; they also handle storm water runoff.
Roofers use various hand tools in their work, including hammers, roofing knives, mops, pincers, caulking guns, rollers, welders, chalk lines, and cutters.