Sonia Hirt and Zoning: The Roots of Urban Inequality in the USA

Zoning is the regulation that divides a city's land into zones and sets which uses, densities and heights are allowed in each, and it is also, according to the planner Sonia Hirt, the instrument that has contributed most to urban inequality in the United States. Hirt, a professor at the University of Georgia born in Bulgaria, compared American zoning with Europe's in Zoned in the USA: The Origins and Implications of American Land-Use Regulation (2014) and found an exception: only in the United States is there a land category reserved exclusively for the detached single-family house, and that category covers most of the country's urban territory.

From Germany to Euclid: the origin of American zoning

Hirt reconstructs the origin. Zoning arrived from Germany in the early twentieth century as a tool to separate industry from housing, but in the United States it became something different: an instrument to protect property values and the social homogeneity of neighbourhoods. The first comprehensive ordinance, New York's in 1916, and the Euclid v. Ambler ruling of 1926, which declared zoning constitutional, enshrined the idea that the apartment block was a parasite to be kept away from the single-family house. Since then, multi-family housing has been banned across most of the country's cities.

Spatial exceptionalism: the exclusive single-family zone

International comparison is the key to the book. In Germany, France, the United Kingdom, Sweden or Russia, residential zones admit a mix of housing types and compatible uses, shops, offices, facilities, and the single-family house has no exclusive category of its own. In the United States, the single-family zone bans everything else and occupies, according to the studies Hirt inspired, around three quarters of the residential land of cities such as Los Angeles, Seattle or Minneapolis. Hirt calls this spatial exceptionalism: a faith in the detached house with a garden as the moral way of living that the law turned into an obligation.

How zoning produces inequality and segregation

The consequences for inequality are direct. By banning apartments, duplexes and small homes on most of the land, zoning limits supply, raises housing costs and reserves the neighbourhoods with the best schools and services for those who can afford a large plot. Because that ability to pay is correlated with race, single-family zoning prolonged the segregation that racial covenants and mortgage redlining had established before they were outlawed. Hirt shows that an ordinance need not mention race to produce racial exclusion: setting minimum lot sizes is enough.

Minneapolis, Oregon, California: zoning reform

The book fed the reform movement. Minneapolis abolished exclusive single-family zoning citywide in 2018, allowing up to three homes per lot; Oregon did the same in 2019 for its medium and large cities; California in 2021 allowed single-family lots to be split in two and up to four units built. Early data show modest increases in supply and prices rising more slowly than in cities without reform, although the effect depends on accompanying affordable housing funding. Neighbourhood opposition, in the name of neighbourhood character, remains the main obstacle.

Hirt's contribution is to have shown that zoning is not a neutral technique but a cultural and political decision with distributive consequences. Her comparison leaves a question for any city, outside the United States too: which housing types and uses its rules prohibit, whom that prohibition protects and whom it leaves out. Changing a table of permitted uses can do more for affordability and integration than many housing programmes, and that change begins with understanding how the rule came to be what it is.