Zoning for accessory dwelling units

This article was posted to MetroWest Daily News.

For decades, housing experts and planners have been advocating for cities and towns allow for the owners of single family houses to add accessory dwelling units (ADUs) to their properties. The recommendation has been listed in most master plans and housing plans, going back decades. Yet only 37 out of 100 cities and towns in Greater Boston allow for ADUs to be put in and rented out.

Greater Boston needs much more housing, perhaps hundreds of thousands of new houses, apartments, and condos. The most conservative policy for adding more housing to neighborhoods, without changing the neighborhoods, is to allow ADUs. An ADU is a secondary apartment that can be rented out, on the property of an owner-occupied single family house — that appears from the street as a single family house, not a two-family.

ADUs are virtually invisible and highly dispersed across neighborhoods. The owners of ADUs live on the property, so the risk of neglect that people might associate with rental properties is minimal. The same goes for loud parties. (Which is not to say that it is fair to restrict other types of rental property.)

ADUs provide needed rental housing in residential neighborhoods, and the apartments tend to be relatively affordable for being modestly sized. The rents provide a stream of income for the homeowners. No new public investments in infrastructure are needed to serve the new housing. And the typical size limits on ADUs make teardowns for redevelopment less likely.

During a housing crisis, after concerted advocacy over a span of decades, far less than half of the cities and towns in Greater Boston allow for ADUs to be put in and rented out.

Another 31 municipalities also allow them, but only for occupancy by relatives of the homeowners, or caretakers, or the elderly; the units are supposed to be removed when the in-laws move out.

Many of the 37 municipalities highly restrict the houses eligible for ADUs. For example, Manchester allows ADUs, but only on exceptionally large lots, and only in houses built before 1984. In Dedham, ADUs can be added to houses where the lot is 10 percent bigger than the minimum lot size, but most of the houses in Dedham are on lots smaller than the zoning requires. Dedham has more than 6,000 single family houses, but the town receives only a few applications per year to add ADUs.

In Medfield, ADUs are allowed, in houses built before 1938 that have a minimum floor area of 2,000 square feet. In Weston, ADUs can be put into houses that have at least 3,000 square feet. In Belmont, ADUs are only allowed in detached historic structures, such as antique carriage houses.

Where allowed (as rentals or as in-law apartments), ADUs get permitted at very low rates, just 2.5 permits granted per year per municipality, due largely to the restrictive zoning.

If the region were to average five permits per municipality per year across 100 municipalities, over a ten year period, ADUs could provide five thousand apartments, dispersed among 538,000 single family houses. Less than one in a hundred houses would have an ADU, yet the new rentals would house thousands of people. Of course, this would not solve the housing crisis; it is merely the most conservative and incremental reform.

Every municipality should allow for ADUs to be added to owner-occupied single family houses and to be rented out. The zoning should not restrict ADUs only to old, large houses on large lots or to antique accessory buildings.

Municipalities are very gradually moving to liberalize zoning for ADUs. Revising zoning regulations is a long, labor-intensive process that involves holding hearings, drafting language, and securing two-thirds approval of the town meeting or city council. And it is not as if ADUs are the only item on a planning board’s agenda.

Under a proposal before the state legislature, town meetings and city councils could revise their zoning rules to allow ADUs — by majority vote, instead of the current two-thirds threshold. Such a reform would help a lot. Another option could be for the state directly to allow homeowners to add ADUs, and let local leaders direct their attention to more controversial housing decisions that demand long-term planning.

Amy Dain is a public policy researcher and consultant who wrote the report, “The State of Zoning for Multi-family Housing in Greater Boston” and “The State of Zoning for Accessory Dwelling Units.”

Public policy research: housing and land use, data use in public management, and environmental issues. Greater Boston. Instagram, Twitter: @amydain