Roofs cover buildings and protect their interiors against snow, rain, wind, temperature extremes, and strong sunlight. The earliest roofs were probably thatched with plant materials such as leaves, branches, or straw. With clay or a similar substance pressed into any open spaces, such a roof can provide good protection from the weather.
Roofs constructed on frameworks of thick branches or timbers allowed different roof designs to develop, including the flat and pitched, or sloping, forms that are in use today. When brick and stone began to be used in buildings, people could construct domes and vaults, which are roof forms based on arches.
Throughout most of history, flat roofs have been associated with dry climates, where drainage of water off the roof is seldom a concern. In the 19th century, new roofing and building materials made flat roofs an economical alternative to pitched roofs in somewhat wetter conditions, such as those in much of the United States. Today, flat or very slightly sloped roofs are common on commercial buildings and are also used on some residential buildings.
Pitched roofs in various forms have been used for many centuries, largely in climates where drainage is a concern. Most houses have pitched roofs due to rainfall, although in desert climates this style will become less common, as seen in adobe houses.
All roofs must keep out water. There are two basic types of roof covering that do this: separate shingles, or flat pieces of a waterproof material that are placed so that water cannot get through at the joints; and a continuous layer or sheet membrane of a material that is impermeable to water. Different kinds of roofing materials are appropriate for different kinds of roofs, and each material has its own method of application.
The occupation of roofer has developed along with the various kinds of modern roofing materials. Roofers today must know about how the elements in each roofing system are used, and how water, temperature, and humidity affect the roof. While asphalt shingle roofs on homes may require only relatively simple materials and application procedures, large commercial building roofs can involve complex preparation and layering of materials to produce the necessary protective covering.
The sheer complexity of the different types of roofs require a versatile mind, unless one is specializing in residential. The future of roofing will hold much promise in making homes more energy efficient and weather resistant.