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.
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.
There are four main types of roofers: shinglers, who primarily install shingles, shakes, tiles, and other nail-on products on roofs with 5:12 pitches or above; metal roofers, who focus on metal panels; single-ply or "flat" roofers, who focus on roofs such as single-ply or foam roofs; and "hot" roofers, who work using tar-based products. It is not uncommon, however, for companies to have their roofers service multiple styles and types of roofing; and certain manufactures will allow only pre-approved installers, thus making these four roofer types limiting. As per the application areas, roofing contractors can be categorized as Industrial or commercial roofers, Factory Shed roofers, Residential Roofers, Commercial roofers. Based on the types of the materials, roofing can be classified as terrace roofing, metal roofing, polycarbonate roofing, steel roofing, PVC roofing, skylight roofing. Pre-engineered companies installs roofing.
Depending on the region, other commonly applied roofing materials installed by roofers include concrete tiles, clay tiles, natural or synthetic slate, single-ply (primarily EPDM rubber, PVC, or TPO), rubber shingles (made from recycled tires), glass, metal panels or shingles, wood shakes or shingles, liquid-applied, hot asphalt/rubber, foam, thatch, and solar tiles. "Living roof" systems, or rooftop landscapes, have become increasingly common in recent years in both residential and commercial applications.