ADU Size Limits in Arlington, MA
Find the maximum ADU size allowed in Arlington, Massachusetts. Includes square footage limits, height restrictions, lot coverage, and bedroom count.
ADU Regulations in Arlington
Arlington follows the Massachusetts state baseline under the Affordable Homes Act. This means all Massachusetts state-level ADU rights apply — including by-right approval, no owner occupancy requirement, and standardized size limits. Arlington may also have additional local regulations that supplement the state baseline.
Size Limits: Room for a Full Cottage
At 900 sq ft, Arlington allows enough space for a complete 2-bedroom accessory dwelling unit. This is well above the minimum needed for a comfortable living space and provides flexibility for a kitchen, bathroom, living area, and dedicated bedrooms.
Height and Stories
ADUs in Arlington are limited to 25 feet in height and 2 stories. This allows for a two-story design, which maximizes living space on a smaller building footprint — useful if your lot has tight setbacks.
Percentage-Based Size Limit
In addition to the absolute square footage limit, Arlington allows ADUs up to 50% of the principal dwelling's living area. For homeowners with larger homes, this percentage rule may allow a bigger ADU than the flat square footage cap.
Arlington ADU Rules at a Glance
Max Size
900 sq ft
% of Home
50%
Max Height
25 ft
Max Stories
2
Front Setback
25 ft
Side Setback
6 ft
Rear Setback
6 ft
Parking
1 space(s)
Approval
BY RIGHT
Owner Occupancy
Not required
Rental Allowed
Yes
Short-Term Rental
Not allowed
Arlington Building Department
Arlington Inspectional Services Department
51e Grove St, Arlington, MA 02476, USA
Phone: (781) 316-3390
Frequently Asked Questions
What is the maximum ADU size in Arlington, MA?
In Arlington, you can build an ADU up to 900 square feet or 50% of your home's living area, whichever is larger. With 900 sq ft, you have enough room for a full 2-bedroom cottage with a kitchen, bathroom, and living area. This is guaranteed by the Affordable Homes Act.
How tall can an ADU be in Arlington?
ADUs in Arlington can be up to 25 feet tall (2 stories maximum). This allows for a two-story design, which is useful for maximizing living space on a small footprint.
Is ADU size based on my home's size in Arlington?
Yes. In Arlington, your ADU can be up to 50% of your main home's living area or 900 sq ft, whichever is larger. This means larger homes can support larger ADUs.
What types of ADUs are allowed in Arlington?
Arlington allows detached, attached, conversion ADUs. With up to 900 sq ft allowed, a detached ADU gives you the most flexibility — enough for a full 2-bedroom cottage.
Can I add a bedroom to my ADU in Arlington?
With 900 sq ft allowed in Arlington, you can comfortably fit 2 bedrooms plus a kitchen, bathroom, and living area. All bedrooms must meet building code requirements for egress windows and minimum dimensions.
Where can I find all ADU regulations for Arlington?
Visit our complete ADU rules page for Arlington, MA for a full overview of zoning, permits, size limits, setbacks, parking, and costs. We cover all Massachusetts municipalities with data sourced from local ordinances and state law.
Check Your Address
See exactly what ADU rules apply to your specific property in Arlington.