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Designing for Density: Accessory Dwelling Units

As cities and towns across Massachusetts begin the process of refining their zoning by-laws to encourage density and affordability, many municipalities have found accessory dwelling units to be a critical part of this effort. Accessory dwelling units are typically small, secondary dwelling units that are attached to existing single-family homes. However, they can also take the form of small, detached carriage houses in areas where detached ADU's are allowed.

Rochester Road Residence

ACA has experience with this new housing type on a couple of recent projects. Our Rochester Road residence in Newton incorporates space for a future accessory dwelling unit into a new construction single-family home. Providing space for a future ADU in the house creates challenges for access and egress, as well as the daylighting, HVAC systems, and electrical systems for the ADU. In addition, the architect must be creative in defining the basement, living, storage, and HVAC space for the main house, because it is somewhat constrained by the ADU.

Perry Street Residence: Main Stair (ADU Egress Below)

We have also planned an ADU for an existing home on Perry Street in Brookline, which is currently under construction. Older homes present many of the same challenges for ADU's as new construction. However, they often have the added challenges of existing basement slabs or foundation walls which need to be significantly modified or replaced to allow for entries and egress windows. This can add to the structural costs for a renovation of an older home, and the structural changes must be carefully studied to ensure project feasibility.

Overall, ADU's have many advantages. They can be great options for seniors who would like to age-in-place with their extended families, or for nannies who can also benefit from close proximity to the main house. The small footprints of ADU's ensure that they can can rented at an affordable price point, and incorporating an ADU can allow homeowners to reduce their monthly mortgage payments through the rental income. For this reason, they can be a great option for first-time homebuyers. On the whole, they provide many benefits which are worthy of consideration when designing a new home.

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