A parapet is a wall-like barrier at the edge of a roof, terrace, balcony, or other structure. Where extending above a roof, it may simply be the portion of an exterior wall that continues above the line of the roof surface, or may be a continuation of a vertical feature beneath the roof such as a fire wall or party wall. Parapets were originally used to defend buildings from military attack, but today they are primarily used to prevent the spread of fires.
Elaborate parapets flank the gable of King's College Chapel, Cambridge. A decorative parapet rings the gabled roof of this British building, which serves as a public house. A modern parapet with electric lights functions as a guard rail along the BP Pedestrian Bridge in Chicago.
The word comes ultimately from the Italian parapetto (parare = to cover/defend and petto =breast). The German term Brustwehr has the same significance.
Parapets may be plain embattled, perforated or panelled, which are not mutually exclusive terms.
- Plain parapets are upward extensions of the wall, sometimes with a coping at the top and corbel below.
- Embattled parapets may be panelled, but are pierced, if not purely as stylistic device, for the discharge of defensive projectiles.
- Perforated parapets are pierced in various designs such as circles, trefoils, quatrefoils.
- Panelled parapets are ornamented by a series of panels, either oblong or square, and more or less enriched, but not perforated. These are common in the Decorated and Perpendicular periods.
Parapets surrounding roofs are extremely common in London. This dates from the Building Act of 1707 which banned projecting wooden eaves in the cities of Westminster and London as a fire risk. Instead an 18-inch brick parapet was required, with the roof set behind. This was continued in many Georgian houses, as it gave the appearance of a flat roof which accorded with the desire for classical proportions.
The Mosaic law also prescribed parapets for newly constructed houses as a safety measure ().
Fire wall parapets
Many firewalls 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 other highway structures (such as retaining walls) prevent users from falling off where there is a drop. They may also be meant to restrict views, to prevent rubbish passing below, and to act as noise barriers.
Bridge parapets may be made from any material, but structural steel, aluminium, timber and reinforced concrete are common. They may be of solid or framed construction.
In European standards, parapets are defined as a sub-category of "vehicle restraint systems" or "pedestrian restraint systems".
Parapets in fortification
In terms of fortification, a parapet (or breastwork) is a wall of stone, wood or earth on the outer edge of a defensive wall or trench, which shelters the defenders. In medieval castles, they were often crenellated. In later artillery forts, parapets tend to be higher and thicker. They could be provided with embrasures for the fort's guns to fire through, and a banquette 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 the superior talus.
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