Aparapet is a barrier that is an upward extension of a wall at the edge of aroof,[1]terrace,balcony,walkway or otherstructure. The word derives from theItalianparapetto (parare 'to cover/defend' andpetto 'chest/breast'). Where extending above a roof, a parapet may simply be the portion of an exterior wall that continues above the edge line of the roof surface, or may be a continuation of a vertical feature beneath the roof such as afire wall orparty wall.[2] Parapets were originally used to defend buildings from military attack, but today they are primarily used asguard rails, to conceal rooftop equipment, reduce wind loads on the roof,[3] and to prevent the spread of fires.
Parapets may be plain,embattled, perforated or panelled,[1] which are not mutually exclusive terms.
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The Mirror Wall atSigiriya,Sri Lanka built between 477 and 495 AD is one of the few surviving protective parapet walls from antiquity. Built onto the side of Sigiriya Rock it ran for a distance of approximately 250 meters (270 yards) and provided protection from inclement weather. Only about 100 meters (110 yards) of this wall exists today, but brick debris and grooves on the rock face along the western side of the rock clearly show where the rest of this wall once stood.[4]
Parapets surrounding roofs are common inLondon. This dates from theBuilding Act 1707 which banned projecting wooden eaves in the cities ofWestminster andLondon as a fire risk.[citation needed] Instead an 18-inch brick parapet was required, with the roof set behind. This was continued in manyGeorgian houses, as it gave the appearance of a flat roof which accorded with the desire for classical proportions.
InShilpa Shastras, the ancient Indian science of sculpture, a parapet is known ashāra. It is optionally added while constructing a temple. Thehāra can be decorated with various miniature pavilions, according to theKāmikāgama.[5] In the Bible the Hebrews are obligated to build a parapet on the roof of their houses to prevent people falling (Deuteronomy 22:8).
Manyfirewalls are required to have a parapet, a portion of the wall extending above the roof. The parapet is required to be as fire resistant as the lower wall, and extend a distance prescribed by building code.
Parapets on bridges and otherhighway structures (such asretaining walls) prevent users from falling off where there is a drop.[6] They may also be meant to restrict views, to prevent rubbish passing below, and to act asnoise barriers.
Bridge parapets may be made from any material, butstructural steel,aluminium,timber andreinforced concrete are common. They may be of solid or framed construction.[6]
InEuropean standards, parapets are defined as a sub-category of "vehicle restraint systems" or "pedestrian restraint systems".
A parapetfortification (known as abreastwork when temporary) is a wall of stone, wood or earth on the outer edge of adefensive wall ortrench, which shelters the defenders.[7][8] In medievalcastles, they were oftencrenellated. In laterartillery forts, parapets tend to be higher and thicker. They could be provided withembrasures for the fort's guns to fire through, and abanquette or fire-step so that defending infantry could shoot over the top. The top of the parapet often slopes towards the enemy to enable the defenders to shoot downwards; this incline is called thesuperior talus.[9]
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