Most municipalities around the world include a variety of planning regulations in local ordinances, building codes, and zoning bylaws. They regulate land use characteristics and set out specific controls that outline a property's permitted activities as well as the height, density and location of any structure on the lot. In many cases, when a building is proposed for a particular site, it must be physically set back from streets, neighbouring structures, or other sensitive places. 

How zoning regulations can affect a building's profile, image via City of Toronto

Setbacks establish minimum distances from the property line for the placement of buildings, most commonly to avoid conflicts with adjacent structures. Setbacks may also be instituted to allow access for public utilities or for protection of nearby environmental assets like wetlands. Before the advent of the automobile, buildings often implemented very narrow setbacks or none at all. As people's travel distances lengthened, the space between buildings followed suit, leading to the large yards and driveways that typically characterize the suburban lifestyle. 

Setbacks, sometimes called step-backs, also refer to the step-like recessions in the profile of a building. Initially used as a method of maximizing the height of masonry structures, architectural setbacks in modern day applications are usually implemented for aesthetic purposes, or for more practical reasons such as the preservation of sunlight and fresh air.

1932 Manhattan shows the Zoning Resolution's impact, image by Gottscho-Schleisner Collection via Wikimedia Commons

In cities like Manhattan, structures built to the property line may only be allowed to rise a certain number of storeys. Beyond that height, they can be subject to setbacks that follow a theoretical inclined plane. The building would then not be permitted to pierce the resulting sky exposure plane. The 1916 Zoning Resolution adopted this thinking, which had substantial impact on the way buildings were formed, as the rule established strict limits in massing to prevent significant shadowing. In addition to providing space at ground level for public parks and plazas, setbacks can create unique building terraces for use as lounging and dining areas. 

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