The durability of a roof is a matter of concern because the roof is often the least accessible part of a building for purposes of repair and renewal, while its damage or destruction can have serious effects.
The material of a roof may range from banana leaves, wheaten straw or seagrass to laminated glass, copper (see: copper roofing), aluminium sheeting and pre-cast concrete. In many parts of the world ceramic tiles have been the predominant roofing material for centuries, if not millennia. Other roofing materials include asphalt, coal tar pitch, EPDM rubber, Hypalon, polyurethane foam, PVC, slate, Teflon fabric, TPO, and wood shakes and shingles.
Roof framing must be designed to hold up a structural load including what is called dead load, its own weight and the weight of the roof covering, and additional loading called the environmental load such as snow and wind. Flat roofs may also need to be designed for live loads if people can walk on them. In the United States, building codes specify the loads in pounds per square foot which vary by region. The load and span (distance between supports) defines the size and spacing of the rafters and trusses.
The supporting structure of a roof usually comprises beams that are long and of strong, fairly rigid material such as timber, and since the mid-19th century, cast iron or steel. In countries that use bamboo extensively, the flexibility of the material causes a distinctive curving line to the roof, characteristic of Oriental architecture.