![]() Cracking and blistering occurs and eventually water gets in. A flooded coat of bitumen is applied over the felts and gravel is embedded in the hot bitumen.Ī main reason for failure of these traditional roofs is ignorance or lack of maintenance where people or events cause the gravel to be moved or removed from the roof membrane, commonly called a built-up roof, thus exposing it to weather and sun. The mopping of bitumen is applied in two or more coats (usually three or four) as a hot liquid, heated in a kettle. Roof decking is usually of plywood, chipboard or oriented strand board (OSB, also known as Sterling board) of around 18 mm thickness, steel or concrete. The felt paper is in turn covered with a flood coat of bitumen (asphalt or tar) and then gravel to keep the sun's heat, ultraviolet light and weather off it and helps protect it from cracking or blistering and degradation. Traditionally most flat roofs in the western world make use of tar or asphalt more usually felt paper applied over roof decking to keep a building watertight. Occasionally, however, flat roofs are designed to collect water in a pool, usually for aesthetic purposes, or for rainwater buffering. Gutters on larger roofs usually lead water into the rainwater drainage system of any built up area. Gutters on smaller roofs often lead water directly onto the ground, or better, into a specially made soakaway. Water from some flat roofs such as on garden sheds sometimes flows freely off the edge of a roof, though gutter systems are of advantage in keeping both walls and foundations dry. Materials that cover flat roofs typically allow the water to run off from a slight inclination or camber into a gutter system. ( April 2018) ( Learn how and when to remove this template message)Īny sheet of material used to cover a flat or low-pitched roof is usually known as a membrane and the primary purpose of these membranes is to waterproof the roof area. Unsourced material may be challenged and removed. Please help improve this section by adding citations to reliable sources. The pitch of this type of roof is usually between 1 and 3 degrees depending upon sheet length. This gives the roof sheet very high water carrying capacity and allows the roof sheets to be more than 100 metres long in some cases. The roofs are usually clad with a deeper profile roof sheet (usually 40mm deep or greater). Īround the world, many modern commercial buildings have flat roofs. Flat roofs are characteristic of the Egyptian, Persian, and Arabian styles of architecture. ![]() In areas where the roof could become saturated by rain and leak, or where water soaked into the brickwork could freeze to ice and thus lead to 'blowing' (breaking up of the mortar/brickwork/concrete by the expansion of ice as it forms) these roofs are not suitable. In warmer climates, where there is less rainfall and freezing is unlikely to occur, many flat roofs are simply built of masonry or concrete and this is good at keeping out the heat of the sun and cheap and easy to build where timber is not readily available. įlat roofs exist all over the world, and each area has its own tradition or preference for materials used. ![]() The U.S.-based National Roofing Contractors Association defines a low-slope roof as having a slope of 3 in 12 (1:4) or less. Flat roofs, or "low-slope" roofs, are also commonly found on commercial buildings throughout the world. Flat roofs are an ancient form mostly used in arid climates and allow the roof space to be used as a living space or a living roof. The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. ( March 2012) ( Learn how and when to remove this template message)įlat roofs in Israel Flat roof in Los Angeles Flat roof in Warszawa Centralna railway station in Poland (1975)Ī flat roof is a roof which is almost level in contrast to the many types of sloped roofs. Statements consisting only of original research should be removed. Please improve it by verifying the claims made and adding inline citations. This article possibly contains original research.
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