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Asetback, in the specific sense of astep-back, is a step-like form of awall or other building frontage, also termed a recession or recessed story.[1] Step-backs lower the building'scenter of mass, making it more stable. A setback as a minimum one-bay indent across all stories is called a recessedbay or recess and is the more common exterior form of analcove.
Upper stories forming a step-back may form abelvedere – and in residential use are considered thepenthouse. If part of the roof, then they are aloft orattic/garret.
Setbacks were used by people to increase the height ofmasonry structures by distributing gravity loads produced bybuilding materials such as clay, stone, or brick. This was achieved by regularly reducing the footprint of each level located successively farther from the ground. Setbacks also allowed the natural erosion to occur without compromising the structural integrity of the building. The most prominent example of a setback technique is thestep pyramids ofMesopotamia andAncient Egypt, such as theTeppe Sialk ziggurat or thePyramid of Djoser.
For centuries, setbacks were a structural necessity for virtually all multi-level load-bearingmasonry buildings and structures.[2] Asarchitects learned how to turn setbacks into an architectural feature, most setbacks were however less pronounced than in step pyramids and often skillfully masked by richornamentation.
The introduction of asteel frame structural system in the late 19th century eliminated the need for structural setbacks. The use of a frame building technology combined with conveniences such aselevators and motorizedwater pumps influenced the physical growth and density of buildings in largecities. Driven by the desire to maximize the usable floor area, some developers avoided the use of setbacks, creating in many instances a range of fire safety and health hazards. Thus, the 38-story[3]Equitable Building, constructed inNew York in 1915, produced a huge shadow, said to "cast a noonday shadow four blocks long",[3] which effectively deprived neighboring properties of sunlight. It resulted in the1916 Zoning Resolution, which gave New York City's skyscrapers their typical setbacks and soaring designs.
Today manyjurisdictions rely onurban planning regulations, such aszoning ordinances, which use setbacks to make sure that streets and yards are provided more open space and adequate light and air. For example, in high density districts, such asManhattan inNew York, front walls of buildings at thestreet line may be limited to a specified height or number of stories. This height is also called base height.[4] Above that height, the buildings are required to set back behind a theoretical inclined plane, calledsky exposure plane, which cannot be penetrated by the building's exterior wall. For the same reason, setbacks may also be used in lower density districts to limit the height of perimeter walls above which a building must have a pitched roof or be set back before rising to the permitted height.[5]
In many cities, building setbacks add value to the interior real estate adjacent to the setback by creating usable exterior spaces. These setbackterraces are prized for the access they provide to fresh air,skyline views, and recreational uses such as gardening and outdoor dining. In addition, setbacks promote fire safety by spacing buildings and their protruding parts away from each other and allow for passage offirefighting apparatus between buildings.
In the United States, setback requirements vary amongmunicipalities. For example, the absence of sky exposure plane provisions inChicago's Zoning Code makes theChicago skyline quite different from the skyline of New York where construction of tall buildings was guided by the zoning ordinance since 1916. TheNew York City Zoning Ordinance also provided another kind of setback guideline, one that was intended to increase the amount of public space in the city. This was achieved by increasing the minimum setback at street level, creating in each instance an open space, often referred to asplaza, in front of the building.
