AMENDMENT DETAILS

  • The goal of this zoning amendment is to make it feasible to build car-free “missing middle” multifamily housing, like triple-deckers, townhouses, and fourplexes.

  • 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.

99 Fayerweather is the dark brown building in the center.

Background: Zoning Today


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.

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 read from the Dimensional Standards table of the zoning ordinance. Going through them one at a time, you 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.

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 sqft. 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.

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 a developer 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.


  • Maximum Floor Area Ratio: 1.25

  • Maximum height: 40'

  • Maximum stories: 3 above grade (unless special permit granted)

  • Maximum density: 1 unit per 500 sq. ft of lot area

  • Front setback: minimum 10' (unless neighboring lots have smaller setbacks)

  • Side setback: minimum 7'6" (or 5' if neighboring lot is significantly set back)

  • Rear setback: minimum 10'

  • Minimum private open space: 25%

  • Minimum parking: 0 spaces

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.


For example, if 99 Fayerweather St. were zoned for Residence N, it could be rebuilt almost exactly as it is, as a two-family house. But it could also 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/2BR units, providing lower costs as more units could be built on the same amount of land. In all of these scenarios, FAR still limits the building’s footprint, so the backyard is still present, and there are many opportunities for trees. (In almost every possible scenario on a lot this deep and narrow, for instance, either the front or rear setback would be significantly larger than the minimum requirement.) But in none of these scenarios is the developer required to sacrifice open space and provide free parking, adding more cars, more pollution, and more congestion to Cambridge.


“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