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Zoning is the term for rules that cities put in place to determine what kinds of buildings can be built where. It can be complex and technical, but it’s a force that shapes the places we live, and it often determines how a city grows and thrives — or doesn’t. Tight zoning can block the creation of sufficient housing, which leads to the skyrocketing prices we’ve seen in recent years. It can also create huge negative impacts for economic inequality, racial segregation, and the environment. That’s why Somerville YIMBY and other pro-housing groups have focused on it so closely.

Zoning and Segregation

Zoning laws can help cities guide their development in positive ways, and keep noxious industries away from homes and commerce, but the first zoning laws in the US were created to promote segregation. They achieved that mostly by keeping apartments and multifamily homes away from single-family homes. This worked because people of color were often shut out of mortgage lending, meaning that a neighborhood of owner-occupied houses was almost by definition entirely white. Federal lending policies that gave better ratings to all-white neighborhoods and restrictive covenants prohibiting future owners from selling to nonwhite people reinforced that segregation. To learn more about zoning’s role in creating and perpetuating segregation, read Richard Rothstein’s book The Color of Law.

Zoning and Economic Inequality

In the US, access to clean air, good schools and good jobs is closely tied to where you live, and wealthy communities that prohibit the creation of sufficient housing — and enough variety of housing types — are effectively pricing out lower-income families. Requiring big homes on big lots effectively requires building only the most-expensive housing types.

Zoning and the Environment

Zoning that prohibits construction of dense, multifamily buildings isn’t just racist. It’s also bad for the environment: the EPA notes that sprawling development patterns create a lot of harmful emissions, and that “infill” development is a great way to reduce carbon emissions, because density is more efficient and reduces the amount of time people spend driving.

What’s Good Zoning?

A good zoning code is easy to understand, broadly permissive, and reduces the need for special permits and complex approval processes.

Keeping things simple and allowing construction without special permits (“by right”) is especially important because complex codes and requirements for special or discretionary permits also make it harder and more expensive to build anything:

  • A complex zoning code requires specialized knowledge, which means hiring insiders or expensive specialists
  • Delays and uncertainty raise prices and reduce the amount of housing created
  • A discretionary permitting process leaves the door to favoritism or even outright corruption

California, especially in the San Francisco Bay Area, is emblematic of the danger of well-intentioned but counter-productive permit and process requirements, but similar issues play out in the Boston area and in many other high-cost cities.

Zoning in Somerville

In Somerville and many other places in the US, zoning got a lot stricter over the course of the 20th century, making existing buildings “nonconforming” — that is, they couldn’t be re-built under current rules. In 2016, a group of researchers pointed out that the Somerville zoning rules prohibited the construction of nearly every home that already existed. Fortunately, the city wrote an entirely new zoning code, passed in 2019, that is easier to understand and work with.

Somerville’s new zoning code is what is called a “form-based” code: it focuses most on the overall shape and size of buildings in each of the various districts.

You can find complete details at, but the most common districts in the city are:

  • Neighborhood Residence: Mostly 1–2 family residential buildings.
  • Urban Residence: Mostly multifamily residential buildings, with some corner stores and small retail.
  • Midrise 3, 4, and 5: 3-5 story buildings, mostly commercial. Large apartment buildings allowed by special permit.
  • Commercial Core 3, 4, and 5: 3-5 story commercial buildings.
  • High Rise: Tall buildings.

We also have overlay districts, which modify the base rules for specific reasons, ranging from flood risks to special development areas like Assembly Square. One of our favorites is the Affordable Housing Overlay (AHO), which allows more height and faster permitting for projects where every home is affordable. For more information about the exact definition of affordability and how we achieve it in Somerville, see “What exactly do we mean by Affordable Housing?”

Improving Somerville Zoning

Somerville YIMBY is broadly in agreement with our city’s current zoning code, but there are some changes we’d like to see.

Neighborhood Residence

Our least-dense district is far better than the “single-family only” rules seen in other cities. But it could be better:

  • It should allow accessory dwelling units (“in-law apartments”) with far fewer restrictions.
    • Today, homeowners are allowed to add a third unit to a two-family building only if the new apartment is part of the city’s affordable housing program.
    • The result has been very little new housing created at any price.
  • It should allow three-family buildings like our iconic triple-deckers with far fewer restrictions.

Midrise Districts

Code currently requires special permits to build apartments; this use should be allowed without special permits. These permits have generally been granted, but there’s not a really good reason to require them at all.

Parking Requirements

Zoning codes in other cities require that new buildings include a lot of off-street parking, which raises costs and encourages people to drive. Somerville’s code is better than most, because it doesn’t require nearly as much, and actually sets a maximum amount of parking for construction near transit. We’d like to see a few tweaks to the parking rules to encourage less parking construction citywide, on the general principle that space dedicated to cars is space we can’t dedicate to people. Obviously we’re not going to immediately get rid of all cars, but we shouldn’t be building extra parking and other infrastructure that will focus our future growth around cars.

Map Changes

There are also a number of places we’d like to see streets or blocks moved to a denser category. In fact, we’d like to see increases in allowable density throughout the city, but in particular:

  • Prospect Hill: The area between Union Square and Gilman Square is mostly Neighborhood Residence, but its proximity to two new Green Line stations and the high school suggest that it should be Urban Residence.
  • Davis Square: Most of the center of Davis Square is zoned for Midrise 3. Something so close to the Red Line deserves Commercial Core or Midrise 6, with surrounding residential neighborhoods zoned for Urban Residence. This is especially important as an equity issue, because the eastern parts of the city have seen far more upzoning, and Davis Square shouldn’t be exempt from development.
  • Areas surrounding the new Green Line Extension stops: Many areas near new Green Line stops are currently zoned for Neighborhood Residence and Urban Residence, but really ought to be allowed to grow to 4 to 6 stories high.