• The goal of this zoning amendment is to make it feasible to build car-free “missing middle” multifamily housing (triple-deckers, townhouses, fourplexes) in ALL Cambridge residential neighborhoods.

  • Specifically, the amendment allows three-story buildings - with or without a driveway - to be built on up to 40% of the lot area on any neighborhood residential lot in Cambridge.

  • This zoning amendment also seeks to allow for modest additions and renovations to our existing homes as-of-right, rather than creating red tape and delays for such improvements

Background: Zoning Today

This colorful mosaic represents Cambridge's 60 different zoning districts. Five of those are residential-only districts, the remainder are commercial, industrial, office, or mixed-use districts. The five residential zones are graded as "A", "B" and "C" zones (light and darker yellow) "A" zones allow only single-family homes. "B" zones allow only single or two-family homes. "C" zones allow single, two-family and multi-family housing.

The vast majority of homes in Cambridge’s neighborhoods could not be built today, and are only allowed because they were constructed before the current zoning ordinances took effect. The zoning standards were imposed on existing neighborhoods to discourage further density, and to effectively ban apartments in much of Cambridge.

As a result, almost all Cambridge houses are non-conforming and owners are required to seek variances or special permits to build additions, add accessory apartments, or even add a porch or a window in many cases!. This is why most developers and wealthy home-owners hire lawyers to navigate the zoning process for them. "N" zoning is designed to legalize most existing homes so that owners can apply for building permits without facing the delays, costs or rejections of our current zoning policies.

When properties are re-developed - in the case of badly deteriorated houses ("tear-downs") or the occasional vacant lot, owners are held to the same low-density standards.

Proposal: Neighborhoods for All

The Missing Middle Housing Zoning Amendment has three main effects. It ends the ban on multifamily housing that exists in Residence A-1, A-2, and B zones. It removes minimum parking requirements in all residential zones, allowing for car-free units (while still allowing units with parking if an owner so chooses). And it increases dimensional standards, particularly FAR, to allow three-story buildings to sit on up to ~40% of a lot’s area. It accomplishes these effects by consolidating the neighborhood residential zones (A-1, A-2, B, C, and C-1) into a new zoning category, “Residence N” (for Neighborhood), with dimensional standards listed below.

These dimensional standards are designed to

  • bring the majority of pre-existing buildings in Cambridge into conformance, meaning that they can be redeveloped or renovated without the need for a variance or decreasing the number of units; and to

  • ensure that lots which aren’t yet built out have the opportunity to be developed responsibly, in accordance with our housing shortage and our climate crisis, rather than wastefully.

99 Fayerweather is the dark brown building in the center.

Example: Two-family home in "B" zone

Consider the example of 99 Fayerweather St., a fairly typical building on a block currently zoned for Residence B. It is a 3-story, 2-family building on a roughly 3800 sq. ft. lot, close to the median Cambridge neighborhood lot size (4000 sq. ft.). Those 3800 square feet contain a backyard, a front yard, a driveway, and the building itself, which has a roughly 1200 sq. ft. footprint.

The Residence B dimensional standards can be seen in the table above (or read from the Dimensional Standards table of the zoning ordinance).

Going through them one at a time, we can see all the ways that this building doesn't conform with current zoning:

  • Floor Area Ratio. In residence B, the maximum FAR is 0.5, meaning that since the lot area is 3800 sq. ft., only 0.5 * 3800 sq. ft. = 1900 sq. ft. of floor area can be built. However, counting the building footprint three times for each of the three stories, plus the porch and deck, the gross floor area of the building is about 4000 sq. ft. - far in excess of what is allowed!

  • Minimum Lot Area per Dwelling Unit (sometimes called "density"). Since this is a 3800 sq. ft. lot and the minimum lot area per dwelling unit is 2,500 sq. ft., if this building were rebuilt, it would only be allowed to have one dwelling unit instead of its current two.

  • Setbacks. The minimum front yard width is 15’, which this building complies with, and the minimum rear yard width is 25’, which this building might [note 1] comply with. But the side yards must be at least 7.5’ on each side, and while the left side driveway meets this requirement, the right side walkway does not, being only 5’ wide.

  • Maximum Height. The maximum allowed height is 35’, but this building is 37.7’ high. Although there are many 3-story buildings under 35’, most of them, like this one, fall in the 35’-to-40’ range. This is particularly true of triple-deckers, as fully building out the third story requires more height than a single attic room or two.

  • Open Space Percentage. The minimum required private open space in Residence B is 40% of lot area, with driveways and parking not counting as private open space. This building is right on the edge of meeting that requirement.

  • Parking Requirements. A different section of the zoning ordinance requires 1 off-street parking space per unit in almost all residential zones, including Residence B. However, this building has two units, and only one parking space (tandem spaces count as only “one space” [note 2]).

Left: 99 Fayerweather as it currently exists. Right: 99 Fayerweather as it could be rebuilt under today's zoning.

While all of these rules provide impediments to building housing, by far the most important restrictions are the parking requirements, the FAR cap, and the density cap. If you were to try to build a new two-family building on this lot today, to give each unit its own non-tandem parking space, you would have to transform substantial amounts of open space into concrete. In addition, because of FAR, you would have to cut the third story and significantly shrink the building footprint, in order to keep the gross floor area under 1900 sq ft. But even with those concessions, the building would still be illegal, because the minimum lot size per dwelling unit rules out two-family buildings entirely! You would just have to deprive one extra family of the opportunity to live in the neighborhood. Similar stories can be told for countless lots all over Cambridge.

Redevelopment Options

Under proposed "N" zoning--

Left: one additional unit in rear

Center: triple-decker or six-plex

Right: two single family houses

By contrast, under the Missing Middle Housing proposal, it could be rebuilt almost exactly as it is, as a two-family house. But it could also be enlarged, to add a generous (1,285 sf) unit behind the existing home. This is the most environmentally-friendly option, as it preserves the "embodied energy" of the existing structure. Or, it could be rebuilt as a triple-decker, with three large 1500 sq. ft. 3BR units, or as a six-plex of medium-sized 750 sq. ft. 1BR units, providing lower costs as more units could be built on the same amount of land. If it were redeveloped as is commonly done in Cambridge today, with free-standing single-family homes and parking, the developer would not be able to maximize the FAR and still meet the Open Space requirement.

“Missing middle” multifamily housing already exists all over Cambridge, to some extent, in every neighborhood; what we’re seeking is simply to make it legal to build more of it. Every neighborhood in Cambridge deserves to have more plentiful, more affordable, and more sustainable new housing. It’s time for Cambridge’s historic legacy of exclusionary “sprawl zoning” to be just that - history.

[note 1]: depending on how you read the “averaging rule” in section 5.24.4 (3)

[note 2]: see section 6.43.2