The Height of Cambridge’s Affordable Housing Overlay
One of the common misunderstandings about Cambridge’s proposed Affordable Housing Overlay is where it will allow buildings that are significantly taller than the built environment, and how tall those buildings can be. Other than a small number of parcels along Mass Ave. and Cambridge Street, there is no proposal to significantly expand available areas to develop buildings up to 80 feet tall, and there is no proposal to allow 8 story buildings above grade; buildings are limited to 7 stories.
The Affordable Housing Overlay zoning proposal is quite simple to read by municipal zoning standards: It uses existing zoning as a base, and allows heights specifically based on the existing base zoning. There are two classes of buildings allowed: 4 story buildings are allowed in most of the city, and a small number of properties will allow buildings up to 7 stories.
Where the District Dimensional Standards allow a maximum building height of 40 feet or less, an AHO Project shall contain no more than four Stories Above Grade and shall have a maximum height of 45 feet, as measured from existing Grade. For AHO Projects containing active non-residential uses on the ground floor, the maximum height may be increased to 50 feet but the number of Stories Above Grade shall not exceed four stories.
So, first we have the most typical class throughout the city: Projects can be 4 stories tall (45 feet above grade); or with first floor retail, they can be 50 feet tall (but are still limited to 4 stories above grade, including the retail). This is the case for 87% of the parcels in the city: because Cambridge is generally zoned for pretty low density city-wide, there’s relatively few parcels where you can develop above this height.
Where the District Dimensional Standards allow a maximum building height of more than 40 feet, an AHO Project shall contain no more than seven Stories Above Grade and shall have a maximum height of 80 feet, as measured from existing Grade, except that: Portions of buildings that are within 35 feet of a district whose District Dimensional Standards allow a maximum building height of 40 feet or less shall be reduced to a maximum of five Stories Above Grade and a maximum height of 60 feet, as measured from existing Grade, except where the building abuts a non-residential use.
For the few districts in the city — largely East Cambridge, MIT + Harvard, and some areas along Mass Ave — that allow maximum building heights of more than 40 feet, there is a higher standard set: buildings can be up to 80 feet tall. For most of these districts, this is already the case: for example, Central Square is already zoned for 80 feet, and has many buildings taller than that; most of MIT and Harvard are zoned C-3 and allow buildings up to 120 feet. In short, this change isn’t very significant.
Additionally: Portions of buildings that are within 35 feet of a lower zoned district are limited even further — to just 5 stories and 60 feet. This is, in fact, almost the entirety of taller zoning!
If you look carefully at the map of zoning areas in Cambridge, you’ll see that almost the entire city is zoned for lower heights: outside of the MIT and Harvard Campuses, and special development areas around Kendall Square, there is almost no area that does not abut a lower height zone.
(For a higher resolution version of the map, feel free to click through to a high-resolution original.)
There are a few takeaways to keep in mind here:
- There has been statements from some opponents that the Affordable Housing Overlay will allow 8 story buildings above grade. This is simply not true: The maximum under the overlay is 7 stories, and realistically, most buildings would likely be fewer, due to the 80 foot height limit.
- There is a belief that the proposed Affordable Housing Overlay would allow taller buildings along “transit corridors”. This is likely based on the simplification of Cambridge’s zoning law: the idea that ‘transit corridors’ are more densely zoned. As you can see from the map above, this is a confusing simplification; it is not accurate.
Instead of “transit corridors” generally, it makes more sense to talk about this directly as the affected streets. Setting aside the areas which are already zoned for heights at 80 feet or above, there are only 6.8% of the properties in Cambridge which are given new height availability above four stories. Making a map of just the properties which have an available height increase above the existing zoning, we see a map with even fewer properties highlighted:
These are clustered in a small number of areas:
- Fresh Pond Parkway, near Alewife.
- Northern Mass Avenue, past Harvard Square.
- Massachusetts Ave between Central Square and Harvard.
- Cambridge Street, east of Inman Square.
(High resolution map available here.)
There is no other significant concentration of 7 story height increases proposed (and even these properties are largely abutting other zones where they would be limited to 5 stories near residential abutters).
Since this appears to be a common misconception about the overlay, I wanted to help clarify: There is no proposal currently on the table which would allow new zoning for 7 story buildings along Huron Avenue, River Street or Western Avenue, or even Memorial Drive.
Instead, this increase in height is limited almost entirely to areas where buildings are already taller than 80 feet — either via zoning or via non-conforming buildings — meaning that the overlay simply matches the zoning code to most of the built environment.
Other than a small number of parcels along Mass Ave. and Cambridge Street, there is no proposal to significantly expand available areas to develop buildings up to 80 feet tall, and there is no proposal to allow 8 story buildings above grade. Most buildings would be 4 stories or fewer.
