A beautiful single-family home in Princeton with external secondary dwelling unit (right), accessible through its own side door. (Click to expand.)
Princeton planning and zoning has had unintended exclusionary outcomes, making it hard for local middle-class workers to live in town, and incentivizing car-dependency and traffic. In this series, we explore options for adding more walkable housing in Princeton to enable diversity and inclusivity, while maintaining and enhancing Princeton’s historic charm.
Accessory dwelling units are self-contained units in owner-occupied single-family homes. They can be internal, such as a converted basement; external, such as a second building or converted garage; or accommodated in an addition to the building. In some cases, they are ‘in-law units’ or ‘granny flats’, where an extra dwelling unit allows family to live on the same site with increased privacy and independence. However, it is equally valid to rent them to non-family members.
In recent years, accessory dwelling units (or ADUs) have been seen as a potential solution to adding housing in communities that are considered ‘built-out’. One phenomenon of the late 20th century has been a significant decline in the average number of occupants of each home. Allowing accessory dwellings helps reverse that trend, by allowing more than one household to share an existing lot. More ADUs in Princeton would increase housing opportunities, and in most cases, these housing opportunities would be at the lower end of the market, i.e. cheaper rental properties that are in the greatest demand. There are benefits to the homeowner as well, as extra rental income can help offset high property taxes.
Incentivizing new accessory dwellings would have minimal impact on Princeton’s historic charm. Internal ADUs, such as converted basements, are almost invisible, and even external secondary housing units can be extremely tasteful and do not add significantly to the overall impervious surface of a lot (as seen in the photo above).
Princeton already has a flat ordinance which can be used by homeowners to rent out accessory dwellings. Nonetheless, more flexibility, for example in terms of setback limits and parking minimums, could incentivize more homeowners to add ADUs, thereby increasing the supply of housing to middle-class workers. Another restriction which could be eliminated is the limit of only one ‘flat’ per property. It’s not obvious why two flats would be a big problem on large lots. There is probably the potential for several hundred additional housing units in Princeton through expanding the pool of ADUs.
Please leave your comments below…do you think incentivizing ADUs is a reasonable way to increase housing opportunity in Princeton? To what extent would it impact the historic charm of the town? What are the risks? Would you consider living in a converted garage or basement in Princeton, if one was available in your price range?
walkableprinceton 
Does this solution really help the middle class or does it just line the pockets of the already wealthy? It seems to me that property taxes on houses with ADU’s should be significantly increased, since they have to cover city services for 2 families, rather than one.
The system may provide more housing, but I don’t think it is the ideal solution – we need other solutions, too. A converted basement/garage seems like an ok option for a single person or a young couple, but for a family it seems inferior. Personally I’d rather not live in my landlord’s back pocket – I’d prefer a little more privacy. I think a an additional option is to alter planning regulations to allow higher density housing. For a start it is my understanding that in many places in Princeton zoning would not allow new housing to be built at the current density i.e. if the house was razed, then only a smaller one could be built. Bizarre! Talk about ‘changing the character of a neighborhood’!
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Hi Wow, I don’t think you need to worry about property taxes staying the same. I’m no expert on Princeton but where I live my property taxes definitely went up when I built my ADU, like they would for any other significant addition to my building. Also when I built my own ADU I had to pay “systems development charges” of many thousands of dollars to represent increased use of transit, parks, roads, etc.
In terms of who uses ADUs, you’re right, they seem best for small households — 1 or 2 people. I’m not sure anyone is claiming that ADUs are proper dwellings for larger families. On the other hand ADUs can be good for families if having the ADU allows extended families to stay together — for example if grandma lives in the ADU and helps take care of the kids sometimes.
The one place I share your skepticism is about the economics for the community. If ADUs are expensive to build, so that only well-established property owners can build them, and then are rented out for market rents, then the supply of housing has been increased, but economic justice hasn’t been served.
We don’t know yet who exactly is living in ADUs and what rents they are paying. If it turns out ADUs help create lower rents through informal support networks (such as grandma getting lower rent in exchange for childcare, or somebody getting lower rent in exchange for yardwork), then ADUs are doing something apartment blocks don’t do. But if they are merely real estate investments, well, that’s kind of no change at all.
Hopefully these questions will receive some research attention soon.
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