At the street line a building may rise to a multiple of the street’s width; above that it must stay behind a plane drawn from the centre of the street, stepping back as it rises.
street wall H₀ = k × street width (k = 1 … 2½) · above it, 1 m back for every 2k m up
The plane was meant to guarantee light and air in the streets below. Because it starts from the middle of the street, its slope depends only on the height multiple: in a “2 times” district the street wall may rise to twice the street width, and the plane then climbs 4 m for every metre of setback. Architects filled the envelope with a series of stepped tiers, and the stepped skyline of 1920s New York (the “wedding cake”) was the result.
Treat a tall office building as base, shaft and top: an open, accessible ground storey for shops and entrances; an indefinite stack of identical office floors expressed as one; and a distinct attic that closes the composition.
base (1–2 storeys) + shaft (n identical storeys) + attic
Over one quarter of the lot area, a tower may rise to any height, free of the setback planes.
tower footprint ≤ 25% of lot area · height unlimited
Lay the whole island out in a single rectangular grid regardless of the ground: avenues 100 ft wide running its length, cross streets 60 ft wide across it, and blocks 200 ft deep between them, the houses to be straight-sided and right-angled because such houses are cheapest to build and most convenient to live in.
avenue 100 ft (30 m) · street 60 ft (18 m) · block 200 ft (61 m) deep, 600–900 ft long
Divide the city into residence, business and unrestricted districts, and admit to each only the uses that belong there, so that lofts and factories cannot invade the shopping streets and houses.
Treat the largest mass the zoning law allows as a block to be sculpted: cut it into setbacks that give usable, well-lit floors, and gather the remaining height into a tower that ends in a crown.
Cite this page Chris Paton, “Setbacks behind a sloping plane”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/zoning-setback. Text, drawings and models licensed under CC BY-NC 4.0.