Accessory Dwelling Units (ADUs)

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In the spring of 2021 Town Meeting adopted an Accessory Dwelling Unit (ADU) policy in its Zoning Bylaw, allowing attached or detached units of no more than 900 square feet, provided that the ADU or the primary residence is initially occupied by the property owner or a family member of the property owner.

Read below frequently asked questions.

On August 6, 2024, Governor Healey signed the Affordable Homes Act into law (Chapter 150 of the Acts of 2024). Section 8 of the Affordable Homes Act amends the Zoning Act to allow ADUs up to 900 square feet to be built by right in single-family zoning districts without an owner-occupancy requirement.

This law will take effect on February 2, 2025 and Arlington is in the process of reviewing its zoning to identify provisions that are not consistent with state law. For more information on changes to the state's Accessory Dwelling Unit zoning provisions, please visit https://www.mass.gov/info-details/accessory-dwelling-units

What is an Accessory Dwelling Unit (ADU)?

What is the purpose of an ADU?

Promoting the use of accessory dwelling units as a means of providing Arlington property owners with an opportunity to age in place, to create independent living space for elderly, disabled or other family or household members, to downsize or to earn supplemental income from investing in their properties.
Helping Arlington residents to conserve and grow their own property values.
Encouraging housing for persons of all income levels and ages.
Encouraging an orderly expansion of the tax base without detracting from the existing character of the affected neighborhoods.

Where are ADUs allowed?

What size ADU is allowed?

How long have ADUs been allowed in Arlington?

Do ADUs need to be attached to the principal structure?

ADUs can be attached or detached units. This means an ADU can be added to an existing home, or constructed in a separate structure on the same lot. A detached unit could be a new building, or conversion of an existing building, such as a garage. Constructing an attached ADU on an existing 2-family dwelling is likely to trigger additional building code requirements in effect for 3-family dwellings, such as fire suppression sprinklers, low voltage interconnected fire alarm systems, and Construction Control by a Registered Design Professional.

Can an ADU be sold separately?

Does the owner need to live in the ADU when constructed?

Where can I find additional information about ADUs?