In the United States and Canada, they're often referred to as roofing contractors or roofing professionals. The most common roofing material in the United States is asphalt shingles. In the past, 3-tab shingles were used; nowadays, "architectural" or "dimensional" shingles are becoming very popular.
A simple rafter roof consists of rafters that the rafter foot rest on horizontal wall plates on top of each wall.The top ends of the rafters often meet at a ridge beam, but may butt directly to another rafter to form a pair of rafters called a couple. Depending on the roof covering material, either horizontal laths, battens, or purlins are fixed to the rafters; or boards, plywood, or oriented strand board form the roof deck (also called the sheeting or sheathing) to support the roof covering. Heavier under purlins or purlin plates are used to support longer rafter spans. Tie beams, which may also serve as ceiling joists, are typically connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength. The rafters, tie beams and plates serve to transmit the weight of the roof to the walls of the building.
Asphalt shingles is the most used roofing material in North America, making up as much as 75% of all steep slope roofs. This type of material is also gaining popularity in Europe due to lower installation costs. Asphalt shingles dominate North American residential roofing market, because they are about half the price of other materials.
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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