A parapet wall is a low wall that encloses a roof or provides a protective barrier at the edge of a terrace or bridge. They were originally used for defense but now serve to prevent accidents and fires. Different types of parapets include crenellated, pierced, paneled, and plain. Modern buildings require parapets for safety reasons, and fire codes mandate that they be at least 30 inches high and fire-resistant. Bridges also have parapets with handrails for pedestrian safety.
A parapet wall is a low wall, usually enclosing a roof, or protective barrier at the edge of a terrace or side of a bridge. In modern usage, one is constructed to provide a barrier to prevent people or objects from falling over the edge of the structure and to slow the spread of fire; in earlier times, these walls were built to offer some protection to defenders on the roofs of a structure, such as a castle or city wall, under attack.
There are several types of railings. One of the best known types is the crenelated parapet, or crenellation, which is crenellated, that is, it is constructed with alternating upper and lower parts. Defenders would use the high parts for protection, moving into the low sections just enough to fire their weapons. A pierced parapet is similar, but instead of being “notched” in appearance, the wall is pierced with various shapes, such as circles, trefoils, or four-leaf clovers, for both decorative and defensive purposes. Paneled walls have outward facing ornamental panels, often of carved stone. Plain parapet walls have none of the decoration or features of other parapets, but may have copings or even corbels, depending on their construction.
While parapets originated from the need for defensive construction atop structures, their use has continued to the present day, but they defend more against accident and fire than against attackers. In the evolution of the modern city, for example, what were once attractive features of detached houses have turned into dangers in densely populated areas. In the City of London, overhanging eaves on houses are considered a fire hazard and since 1707 roofs have been required by law to be enclosed within a parapet wall.
Most modern flat-roof buildings, residential or otherwise, include these walls at the edges as a matter of safety, both to prevent people from accidentally falling off the roof and to prevent accumulated debris from falling down and possibly injuring people below. Many modern fire codes also require that firewalls extend above the roofline of a structure a minimum of 30 inches (76.2 centimeters) and that the wall created be at least as fire resistant as the portion under the roof. On most bridges there are also walls of some kind, built for safety reasons. Where pedestrian crossing is the order of the day, the parapets of some bridges are even equipped with handrails.
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