In the search to house its booming population, Boston is looking everywhere. Given their preexisting density and relative stability, established residential neigh­bor­hoods typically have not been targeted for large-scale solutions to our 53,000-unit deficit. Recently, however, the city’s Department of Neighborhood Development has spearheaded efforts to tackle the shortage at a much finer grain. New proposals would allow the formerly forbidden Accessory Dwelling Units (ADUs), more commonly known as “granny flats” or “in-law” apartments, in existing owner-occupied one- to three-family buildings in select neighborhoods. The plan, which follows those in many other cities including Portland, Oregon; San Francisco; and, more recently, Cambridge, Massachusetts, wisely recognizes that Boston’s housing crisis cannot be solved through the creation of new developments alone: The city must also find ways to evolve its 19th-century residential fabric to meet the needs of its 21st-century occupants.

Like much of our zoning code, the prohibition against ADUs traces back to a mid-20th-century bias toward the nuclear family as the ideal unit of cohabitation. More-nuanced living arrangements that might have included the extra “half” unit for Grandma on the third floor, for example, did not fit the mold of inflexible zoning codes or public expectations about what constitutes a “family.” Today’s Boston is noticeably more socially complex and accepting. These additional units can provide the flexibility to support a growing population as well as a more diverse and vulnerable one.

Consider not only the elderly but also recent college graduates who cannot afford their own apartments, an adult child with mental disabilities, young parents willing to exchange housing for child care, a young couple in need of a small, affordable apartment, or empty nesters seeking to downsize in place. These scenarios are not typically supported by new luxury construction in former industrial areas or downtown. Allowing homeowners more freedom to adapt their existing homes to changing needs can promote long-term occupancy and neighborhood stability.

As the city proceeds cautiously, it will no doubt encounter the usual resistance to any form of densification, including concerns about parking, traffic, displacement, and change of neighborhood character. Beyond that, acceptance will require a more fundamental shift in our relationship with our neighbors and how we negotiate the balance of public and private in the intimate space between residential dwellings. What does it mean, for instance, for a unit to have its front door in the backyard? Our zoning code has for decades safeguarded a very traditional and uniquely American ideal of how and where residential occupation presents itself to the public, where front doors are located, and the distance to the property next door. Accessory Dwelling Units will challenge those norms by occupying the remaining layers of underused space in backyards, attics, and garages, and create new kinds of overlap between new kinds of neighbors.

In a city that tends to resist change, acceptance of ADUs will require time but ultimately could result in richer and more inclusive forms of residential life. Alone, ADUs will not provide the raw numbers of units the city so desperately needs, but they can help. More important, they can set the stage for long-term preservation and adaptation of sensitive neighborhoods that continue to struggle with the pressures of Boston’s extra­ordinary growth.

Kyle Nelson is an illustrator and art director at Stoltze Design.