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One of the main purposes of a roof is to resist water. Two broad categories of roofs are flat and pitched. Flat roofs actually slope up to 10° or 15° but are built to resist intrusion from standing water. Pitched roofs are designed to shed water but not resist standing water intrusion which can occur during wind-driven rain or ice damming ...
Ventilation of the roof deck speeds the evaporation of water from leakage or condensation and removes heat which helps prevent ice dams and helps asphalt shingles last longer. Building codes in the U.S. specify ventilation rates as a minimum of 1 sq ft (0.093 m 2 ) of opening per 150 sq ft (14 m 2 ) (1:150) with a ratio of 1:300 in some ...
Flat roofs, or "low-slope" roofs, are also commonly found on commercial buildings throughout the world. 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. [2] Flat roofs exist all over the world, and each area has its own tradition or preference for materials used.
Mechanically seamed metal with concealed fasteners contains sealant in seams for use on very low sloped roofs, suitable for roofs of low pitch such as 0.5/12 to 3/12 pitch. Flat-seam metal with or without soldered seams. Steel coated with a coloured alloy of zinc and aluminium. Stone-coated metal roofing.
On low-slope asphalt roofs, ponding water allows the oil solvent components of the asphalt to leach out and evaporate, leaving the roof membrane brittle and susceptible to cracking and leaking in the ponding location. [1] The time taken for water to saturate a zone, usually from rainfall, causing a pond to form, is referred to as the "ponding ...
A flat roof includes pitches as low as 1 ⁄ 2:12 to 2:12 (1 in 24 to 1 in 6), which are barely capable of properly shedding water. Such low-slope roofs (up to 4:12 (1 in 3)) require special materials and techniques to avoid leaks. [4] Conventional describes pitches from 4:12 (1 in 3) to 9:12 (3 in 4). [4]
Bell-cast (sprocketed, flared): A roof with the shallow slope below the steeper slope at the eaves. Compare with bell roof. East Asian hip-and-gable roof; Mokoshi: A Japanese decorative pent roof; Pavilion roof : A low-pitched roof hipped equally on all sides and centered over a square or regular polygonal floor plan. [10]
In some cases, a cricket can be used to transition from one roof area to another. On low-slope and flat roofs with parapet walls, crickets are commonly used to divert water to the drainage, against or perpendicular to the main roof slope. The pitch of a cricket is sometimes the same as the rest of the roof, but not always. For Steep-slope roofs ...