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.
Condensation within the roof space is much more of a problem today due to: much less fortuitous ventilation due to tighter building envelopes with high performance windows and door and no chimneys leading. This tighter envelope means the air temperature in buildings has risen, the warmer the air in the building is, the more water vapour the air can carry.
The roofing material is primarily designed to shed water. The covering is also a major element of the architecture so roofing materials come in a wide variety of colors and textures. The primary roof covering on houses in North America are asphalt shingles, but some have other types of roof shingles or metal roofs. Tile and thatch roofs are more common in Europe than North America. Some roofing materials help reduce air conditioning costs in hot climates by being designed to reflect light.
A roofer, roof mechanic, or roofing contractor is a construction worker who specializes in roof construction. Roofers replace, repair, and install the roofs of buildings, using a variety of materials, including shingles, bitumen, and metal. Roofing work can be physically demanding because it involves heavy lifting, as well as climbing, bending, and kneeling, often in extreme weather conditions.
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