An extract on #coinlinemurah
The elements in the design of a roof are:
The material of a roof may range from banana leaves, wheaten straw or seagrass to laminated glass, copper (see: copper roofing), aluminium sheeting and pre-cast concrete. In many parts of the world ceramic tiles have been the predominant roofing material for centuries, if not millennia. Other roofing materials include asphalt, coal tar pitch, EPDM rubber, Hypalon, polyurethane foam, PVC, slate, Teflon fabric, TPO, and wood shakes and shingles.
The construction of a roof is determined by its method of support and how the underneath space is bridged and whether or not the roof is pitched. The pitch is the angle at which the roof rises from its lowest to highest point. Most US domestic architecture, except in very dry regions, has roofs that are sloped, or pitched. Although modern construction elements such as drainpipes may remove the need for pitch, roofs are pitched for reasons of tradition and aesthetics. So the pitch is partly dependent upon stylistic factors, and partially to do with practicalities.
Some types of roofing, for example thatch, require a steep pitch in order to be waterproof and durable. Other types of roofing, for example pantiles, are unstable on a steeply pitched roof but provide excellent weather protection at a relatively low angle. In regions where there is little rain, an almost flat roof with a slight run-off provides adequate protection against an occasional downpour. Drainpipes also remove the need for a sloping roof.
A person that specializes in roof construction is called a roofer.
The durability of a roof is a matter of concern because the roof is often the least accessible part of a building for purposes of repair and renewal, while its damage or destruction can have serious effects.
Due to the maritime danger that Robben Island presents to shipping, Jan van Riebeeck, the first Dutch colonial administrator in Cape Town in the 1650s, ordered that huge bonfires were to be lit at night on top of Fire Hill, the highest point on the island (now Minto Hill). These were to warn VOC ships approaching the island.
In 1865 Robben Island lighthouse was completed on Minto Hill. The cylindrical masonry tower, which has an attached lightkeepers house at its base, is 18 metres (59 ft) high with a lantern gallery at the top. In 1938 the lamp was converted to electricity. The lighthouse utilises a flashing lantern instead of a revolving lamp; it shines for a duration of 5 seconds every seven seconds. The 46,000 candela beam flashes white light away from Table Bay. It is visible up to 24 nautical miles (28 mi). A secondary red light acts as a navigation aid for vessels sailing south southeast.