While many residential structures have a sloping roof, many commercial and multi-family structures utilize a flat roofing system. Just as sloping roofs are constructed out of different types of material, flat roofs are fabricated out of a diverse range of materials. The different flat roof material types range from asphalt roll roofing all the way to vegetated green roofs.
Asphalt Roll Roofing
Asphalt roll roofing is a type of flat roof material that has been in use since the 1890s. This type of roofing typically is composed of a layer of asphalt-saturated or fiberglass based felts that are layered on top with roof felt affixed by nails or cold asphalt cement, usually coated with a grainy mineral topping. This type of roofing usually lasts around 10 years.
Thermoset, Thermoplastic and Modified Bitumen
Thermoset, thermoplastic and modified bitumen are materials that are found in single-ply membrane flat roofs. These single-ply materials are applied through chemical or mechanical means and are secured by ballast that is usually composed of gravel or aggregate. Roofs constructed of this type of material usually last between 10 to 20 years, depending on the material and conditions.
This type of flat roof material falls under two basic classifications, structural and non-structural. The difference between structural and non-structural metal roofing is that structural metal roofing is affixed directly to wooden strips of board needing no solid support underneath it. Whereas non-structural metal roofing has to have solid decking underneath, which is usually plywood, OSB, or a metal roof deck. Many metal roof systems have manufacturers' guarantees that range from 20 to 50 years.
Vegetated (Green) Roof
Flat roofs composed of soil and vegetative cover use a membrane of thermoset or thermoplastic that is overlaid with the soil and greenery. This type of flat roof material offers protection to the underlying membrane from UV rays; however, the underlying membrane needs to be immune to root intrusion. Environmentalists believe that this type of roof lowers buildings energy consumption and some also favor this type of roof material for its ability to absorb rainfall, lowering urban storm water runoff.
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