In December, Minneapolis became the first American city to decide to eliminate single-family residential districts by permitting triplexes in all the city's residential zones.
Minneapolis is not alone in pursuing a change: Other cities — including Seattle and Portland — are contemplating more dense development in their single-family districts. Legislation in California has contemplated state pre-emption of local single-family zoning around train stations.
California also recently required the permitting of accessory dwelling units (i.e., "in-law" units) in most of the state's single-family districts.
All these efforts are controversial, but perhaps inevitable: In Minneapolis, 60 percent of the city's area was designated single-family residential. Many U.S. cities are similarly zoned. If cities want to address housing affordability, racial segregation or climate change in any meaningful way, the single-family district has got to give.
Receiving little attention, however, is the fact that changing the zoning does not ensure the end of the single-family district. Since the Industrial Revolution, this country has had two overlapping systems of land control: one public, implemented through zoning; and one private, implemented through the "restrictive covenant."
Until the Industrial Revolution, courts disfavored restrictive covenants. But rapidly increasing urbanism and industrialism needed a legal tool to control change. American courts responded by making restrictive covenants easier to use.
By the late 1860s, when Frederick Law Olmsted developed the Chicago suburb of Riverside, Ill., he utilized restrictive covenants to do work now typical of zoning, such as mandatory setbacks. By the early 20th century, whole cities — like Beverly Hills — and neighborhoods within cities — like Country Club in Kansas City, Mo. — were regulated solely by private restrictive covenants that, among their most controversial restrictions, forbade sale to African-Americans.
Racially restrictive covenants were made unenforceable by the Supreme Court's 1948 decision in Shelley vs. Kraemer. But by then, the public system of zoning, which took off after it was held constitutional in the Supreme Court's 1926 decision in Euclid vs. Ambler, provided a public alternative to the covenant.