A couple of weeks ago, Minneapolis passed legislation banning single-family zoning. Here’s what that means (boldface mine):

Opening up Minneapolis’ wealthiest, most exclusive districts to triplexes, the theory goes, will create new opportunities for people to move for schools or a job, provide a way for aging residents to downsize without leaving their neighborhoods, help ease the affordability crunch citywide, and stem the displacement of lower-income residents in gentrifying areas. Homeownership in Minneapolis diverges along racial lines, with minority groups’ rates lagging between 20 and 35 percentage points behind that of whites. More rental supply citywide, in addition to a new $40 million slice of the budget for affordable housing, is expected to help tenants find a foothold. The mayor, for what it’s worth, is a renter himself—maybe the first tenant-mayor in the history of a city where (like in most American cities) the majority of people live in rental housing.

In my own home city of D.C., significant swathes of the city have mandatory single-family zoning, including areas near Metro stations:

Yellow areas are single-family only zones, brown is all other; green is parkland.

Despite this success, there is a great deal of concern about how to make this national. Will every battle have to be city by city? It seems to me that the mortgage interest deduction offers an opportunity here. Simply, any single-family zoned property in a census tract not defined as rural (< 1,000 people/sq. mile) would not receive the mortgage interest tax deduction. This isn’t telling people what to do with their property, and no one is showing up to knock your house down. But there’s no reason why it should be illegal–and why that policy should be subsidized with federal dollars–to build a duplex or a triplex. Do what you what with the property–and buy what you want too–but if you’re contributing to the housing shortage, renters don’t need to subsidize that.