Eliminating Single Family Zoning Isn't Enough
Across the country, there has been a somewhat successful move to end restrictive single family zoning. This move is a shift towards increasing housing affordability, and should be applauded: by rolling back historical inequities in access to housing, it can be both a practical win in creating more homes, as well as correcting for an often-explicitly racist history in the way zoning laws have been designed. Both Oregon and Minneapolis have made headlines recently for implementing policies of this nature.
In Cambridge, eliminating single family zoning without changing any other zoning requirements achieves relatively little direct impact because of how our zoning rules have been designed. Even on the few properties where such a policy change is effective, its primary impact would be on properties that are highly unlikely to be redeveloped for other reasons. Finally, while it may be a laudable goal to correct for some of our historical inequality, it is not sufficient to have any meaningful impact on the ability to build new housing targeted at those making below the area median wage.
The Limits of Single Family Zoning
Eliminating single family zoning in Cambridge is of low value on its own: it affects a relatively small number of parcels, and other zoning restrictions limit the number of units on the affected properties.
Of the 13,000 or so properties in Cambridge, only 978 are zoned solely for single family homes. Unlike in many other cities across the country, Cambridge’s land zoned explicitly for single family homes is narrowly scoped largely to a relatively small area near Harvard University. Prior to their recent change, Minneapolis had approximately 70% of their properties zoned only for single family construction; in Cambridge, that number is only 7%, one of the lowest in the country. This rate of single family zoning puts us below even New York City -- hardly a city known for its suburban feel.
Even if single family zoning were to be eliminated, other elements of zoning play a significant role in limiting the number of homes that can be built on such properties. Through the use of floor area ratios and lot size per unit limits, properties in the single-family zoned districts in Cambridge are required to be significantly less dense than other parts of town: they simply aren’t allowed to house as many people, even once you eliminate single family zoning. If there is to be a serious proposal which eliminates single family zoning, it needs to come along with a specific recommendation on what additional changes to building would be allowed: whether that be increased density (“floor area ratio”), or eliminating restrictions on number of dwelling units allowed based on the size of the lot. Without changing other restrictions, eliminating single family zoning would increase available zoned capacity in Cambridge’s residential districts by less than 3%, which would likely have only a minimal impact on creation of new homes.
Unlike many other cities, Cambridge has only a relatively small portion of the city zoned exclusively for single family housing -- just 7% of the City's parcels, below even the level seen in New York City.
Additional Limits on Redevelopment
Beyond the limitations on built form, our historical single family zones are home to many properties that are simply never likely to be redeveloped. This area covers many historical properties that have played a significant role in Cambridge’s history dating back to the Revolutionary War. A simple example is the homes along Tory Row on Brattle Street: this section of Brattle Street was referred to in 1913 as “not only one of the most beautiful but also one of the most historic streets in America.” A significant part of Cambridge's unique character it its history -- and we do what we can to ensure that history is preserved.
Cambridge’s historical preservation ordinances are designed to prevent modification to historically significant buildings. To that end, both demolition and modification have significant limitations placed on them in historical historical districts -- and almost all areas in Cambridge which are single family zoned are contained within both national and local historical preservation districts. A large number of buildings in these districts are simply part of Cambridge’s architectural history, and are likely to be preferably preserved: this makes significant redevelopment of those properties unlikely.
The intentionally limited density in these single-family zoned areas also results in them having access to fewer services. One example can be found in transit access: these areas tend to be further from access to subway lines, and have limited access to bus service, making them a poor design for potential residents who may not have access to cars. They are also deeply residential districts, which leaves them far from grocery stores, restaurants, and other amenity access which helps build thriving neighborhoods. Increasing density in these spaces could help increase the value of transportation -- but a broad rezoning of this area should be more thoughtful in taking into account the value of growing the amenities needed to create a walkable community as well.
The Henry Vassal House, at 94 Brattle Street, is one of the 7 houses that makes up Tory Row, in one of Cambridge's single family zoned districts.
Overall, the areas in Cambridge covered by single family zoning today are simply poorly situated for significant redevelopment without other changes: as the remaining suburban-style area of Cambridge containing many of its historical architectural sites, it is unreasonable to expect redevelopment of this area from eliminating single-family zoning alone.
Affordable Housing in Single Family Districts
In the context of affordable housing development, eliminating single family zoning without changing other limitations in allowed housing density would have no impact on the ability of affordable housing developers to take advantage of these properties. Without significant increases in the number of allowed units, the financial impact of eliminating single family zoning alone will not be anywhere near sufficient to achieve the scale necessary to make such purchases viable.
Affordable housing developers in the city have established that the effective cap on land price per unit for their developments is approximately $200,000: that is, if they purchase a property for redevelopment, they have to be able to build enough units on that property to lower the purchase cost to $200,000 per unit. If single family zoning were to be changed, without changing other zoning restrictions, almost all parcels would still be limited to just a small handful of units. Across the 978 single family zoned parcels in Cambridge, only 25 are sufficiently large to allow construction of a 5-unit apartment if single family zoning were removed; the median assessed value of those 25 properties is more than $8M, meaning the typical cost per unit would still be over $1M -- far out of the reach of both affordable developers and most market rate developers.
If single family zoning were eliminated, this parcel -- assessed at $3.2M -- would still only be legally allowed to hold 2 units due to other zoning restrictions, meaning a purchase price of $1.6M per unit.
These limitations mean that no single family parcel has the potential to be redeveloped by an affordable housing developer simply by eliminating single-family zoning. This is one of the reasons why the proposed 100% Affordable Housing Overlay combines changes a number of existing zoning limitations. Rather than simply eliminating single family zoning, the overlay combines a number of changes -- to allow floor area ratios, lot size per unit requirements, setbacks, and more. Under the combined changes proposed under the affordable housing overlay, nearly 75% of the properties in these single family zones become financially viable locations for developing a small affordable development.
It is clear that the majority of these properties are not appropriate for redevelopment under the affordable housing overlay. Many of these properties are historical; others are owned by universities or local schools, or act as architectural landmarks and local institutions. However, there is likely still room in the area to thoughtfully redevelop a small number of these properties under the guidelines of the affordable housing overlay -- and in that context, what matters is making a greater portion of properties financially viable so that when a good option does become available, the City or its non-profit partners can take advantage of it.
Eliminating Single Family Zoning Must Be Combined With Other Changes
Eliminating single family zoning is a worthwhile goal -- and one towards which Cambridge has already made significant progress. Doing so in combination with other zoning changes could lead to additional opportunities to create new homes for residents, which would help to generally increase affordability in the city. However, Cambridge’s limited number of single-family zoned parcels, and its other restrictive zoning elements, means that making this change alone is insufficient to have any meaningful effect -- and for our low to middle income families dependent on supportive housing, it would mean no change at all.
While eliminating single family zoning on its own will do nothing to increase the availability of affordable housing targeted at low-income families, the Affordable Housing Overlay would. By combining the elimination of single family zoning and removal of other restrictive zoning elements, the proposed Affordable Housing Overlay could open the door for thoughtful redevelopment of a small number of parcels anywhere in the city -- including in the single family zones that we have today.
Eliminating single family zoning isn't enough to make new affordable housing development possible -- but the Proposed Affordable Housing Overlay is.
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