Cambridge Civic Journal Forum

A few observations on density

Feb 16, 2021 (w/Feb 17 addition of S. Normandy Ave.) – Several years ago I was thinking about the past, present, and future of Central Square and decided to simply take a walk through the Square with a camera with as objective an eye as I could manage. The result of that walk was something I called "Completing the Square" – a little math joke tied to the main observation that regardless of any opinions about how tall or dense Central Square may be or should be, there were lots of missing teeth and locations which could be improved by the presence of some new or enhanced buildings. That was before the new Mass & Main complex (now Market Central) was built.

In a similar vein, a couple of days ago I had the notion to do something of a virtual walk (in my head) along some streets with which I am quite familiar just to imagine how they might change under the proposed "Missing Middle Housing" zoning proposal. In my opinion, most of these streets function pretty well as they are and many of them (in particular those now zoned as Res C-1) would be considered pretty dense by any reasonable standard. I downloaded the City’s Assessors Database (thank you Open Data Portal!) and painstakingly reassembled all the living area information from the many condominiums in order to recreate the total living area to go with the total land area for each respective lot. (This was like reassembling puzzle pieces in some cases.) I then calculated the FAR (floor-area-ratio) for all lots on 28 representative streets (somewhat alphabetically biased as I went through them).

Prior to calculating some statistics on each of these streets I decided to exclude a few anomalies such as parks (no housing will be going there under any zoning revisions), municipal parking lots, City buildings (like City Hall, the Annex, DPW, etc.) as well as some lots that are in zoning districts unaffected by the proposed "Missing Middle Housing" zoning proposal, e.g. the Central Square BB district.
[You can view the data for each of these streets here.]

The summary sheet is below. Since there are already some nonconforming lots with FAR even greater than what is proposed in the petition, the increases noted below actually understate the increases under full build-out. On the other hand, it’s not likely that anything close to full build-out would happen any time soon (if the petition were to prevail), so this should be viewed more as a measure of what could eventually happen as opposed to what will happen in the near future.

Note that even a relatively dense C-1 street like Cherry Street in The Port could see a 66% increase in density. Chalk Street (Res C) could see a 72% increase. Cornelius Way could have a 175% increase (that’s 2.75 times the current density). Near me, Antrim Street could go up 47%, Maple Ave. could go up 84%, and Lee Street could go up 50%. In the leafy western "suburbs", a Res B street like Appleton St. could go up 137% (2.37 times the current density) and Lakeview Ave. (a mix of Res A-1 and Res B) would nearly triple in density. In contrast, Berkshire St. in Wellington-Harrington might only rise 2%, so I suppose this is the ideal street by the "Missing Middle" standard.

It’s also worth noting that there’s really nothing in the petition that would in any way ensure that the chief beneficiaries would be middle class residents. The petition is primarily a vehicle for increasing densities and this could just as easily translate into larger homes for those who can afford them or the freedom to add on significant additions to existing homes. In other words, the "middle" part of the "missing middle" petition is missing.- RW

gross FAR = total living area divided by total land area
median FAR = median FAR of all lots on the street
max FAR = largest FAR for all lots on the street
min FAR = smallest FAR for all lots on the street (note that there may be vacant lots with FAR of 0)
MM factor = ratio of proposed "Missing Middle" FAR of 1.25 to current median FAR for street
MM increase = percent increase in FAR from current median FAR under full build-out