Accessory Dwelling Units
Accessory Dwelling Units (ADUs) were legalized in Massachusetts state-wide in 2024. According to state law, ADUs under 900 square feet are permitted "by right" but local laws still apply, including design restrictions. ADUs may be a standalone building, a garage with living space above it, an addition to the primary home or a converted section of that home.
While the name may be new, ADUs have a long historic tradition. Some families built small homes on their property to live in while they saved up to construct a bigger house, later using the small house as a source of rental income. Other ADUs are more obvious indicator of changing times: former carriage houses or repurposed attics that once housed multiple servants. Whatever you call them - granny flats, in-law suites, garden apartments - ADUs can be an appropriate addition even in historic districts.
The Secretary of the Interior's Standards for Historic Building Additions instruct that additions should be subordinate, sympathetic and harmonious in scale, proportion, colors and materials to the original building. They should not attempt to imply that the new structure was built at the same time as the original structure - you should be able to identify which is the "real" historic building. If possible, you should not be able to see the ADU from the public-facing sides of the building.
The glass-and-brick addition to this Colonial Revival house (right) was designed by Cunningham/Quill architects. It's mostly obscured from the street and it uses the same colored brick and multi-lite windows of the original structure while remaining subordinate.
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Converting existing outbuildings to ADUs is a popular choice in historic districts, but they may be considered contributing historic structures and come with their own design restrictions.
This carriage house in Brookline was modified by Landmark Services. The structure was required to visually incorporate the hayloft opening and the extra-wide barn door as a nod to its original purpose.
Many homeowners will need to build an entirely new structure for their ADU. Most of the existing designs are very modern, but may not suit your historic district requirements or personal tastes. Architects can design a custom build, but it can save money to use an existing design. We've found a few floor plans inspired by older building styles and are always looking for more. This yellow home was designed by Backyard ADUs.
Floor plans inspired by Victorian era homes
