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 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.
Fire Wall parapetsEdit
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. It is required to extend at least 30" above the roof. If the roof slopes at a rate of 2 in 12 or greater (16.7-percent slope), the parapet shall extend to the same height as any portion of the roof within a fire separation distance where protection of wall openings is required, but in no case shall the height be less than 30 inches (762 mm). Exterior walls that require to be fire protected are often required to have a parapet, but there are exceptions. *note* If the roofing material is combustible, it must stop 18" minimum from the top of the wall.
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.
In European standards, parapets are defined as a sub-category of "vehicle restraint systems" or "pedestrian restraint systems".
Parapets in FortificationEdit
In terms of fortification, a parapet (or breastwork) is a wall af 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.
- ↑ Ching, Francis D. K. (1995). A Visual Dictionary of Architecture. Van Nostrand Reinhold Company, ISBN 0-442-02462-2. p. 266
- ↑ "NC Building State Building Code: Building Code", page 90., January 2009
- ↑ Jefferis,Smith,Spence:"Commercial Materials & Construction Detailing", page 145.Thompson,December,2007
- ↑ http://www.castles-of-britain.com/castle38.htm
- ↑ http://www.palmerstonforts.org.uk/gloss.htm
- ↑ A New and Enlarged Military Dictionary, Charles James, Egerton Military Library 1810.
- This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.
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