With continual improvements in steel girders, these became the major structural support for large roofs, and eventually for ordinary houses as well. Another form of girder is the reinforced concrete beam, in which metal rods are encased in concrete, giving it greater strength under tension.
In Europe, slate and tile roofs are very popular. Many slate roofs in Europe are over 100 years old, and typically require minimal maintenance / repairs.
The construction of a roof is determined by its method of support and how the underneath space is bridged and whether or not the roof is pitched. The pitch is the angle at which the roof rises from its lowest to highest point. Most US domestic architecture, except in very dry regions, has roofs that are sloped, or pitched. Although modern construction elements such as drainpipes may remove the need for pitch, roofs are pitched for reasons of tradition and aesthetics. So the pitch is partly dependent upon stylistic factors, and partially to do with practicalities.
In the United States, regulation of the roofing trade is left up to individual states. Some states leave roofing regulation up to county-level and municipal-level jurisdictions. In California, for example, the California Contractors State License Board licenses and monitors roofing contractors. Unlicensed contracting of projects worth over a set threshold may result in stiff fines or even time in prison. In Oklahoma roofers are required to meet insurance and roofing license guidelines. Roofers are also required to show their license number on their marketing material.
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