ADU Rules in Millis, MA
Millis follows the Massachusetts state baseline with local regulations.
State Baseline Only
This page uses Massachusetts state baseline rules. Local setbacks, height limits, and other dimensional standards may vary. Contact your local building department for specifics.
State Baseline: Affordable Homes Act
Up to 900 sq ft or 50% of principal dwelling (whichever is smaller). By-right approval statewide.
Zoning Districts
RES — Default Residential
Default residential zone (state baseline only — specific district not yet researched)
| Type | Approval | Max Size | Height | Parking | Owner Occ. |
|---|---|---|---|---|---|
| Detached ADU | By Right | 900 sq ft | — | 1 space | No |
| Attached ADU | By Right | 900 sq ft | — | 1 space | No |
| Interior Conversion | By Right | 900 sq ft | — | None | No |
Building Department
Explore ADU Topics in Millis
ADU Zoning in Millis, MA
ADU Permit Process in Millis, MA
ADU Costs in Millis, MA
ADU Size Limits in Millis, MA
ADU Setback Requirements in Millis, MA
ADU Parking Requirements in Millis, MA
ADU Types Explained in Millis, MA
ADU Financing in Millis, MA
ADU Timeline in Millis, MA
ADU Property Value Impact in Millis, MA
ADU Rental Income in Millis, MA
Frequently Asked Questions
Are ADUs allowed by right in Millis, MA?
Yes. ADUs in Millis are approved by right — you submit your plans to the building department and receive a building permit without a public hearing or special permit process. This is guaranteed by the Affordable Homes Act.
What types of ADUs can I build in Millis?
Millis allows detached, attached, conversion ADUs. With up to 900 sq ft allowed, a detached ADU gives you the most flexibility for a full living space.
Do I need to live on the property to build an ADU in Millis?
No. Millis does not require owner occupancy — this is a right guaranteed by the Affordable Homes Act. You can rent both your main home and the ADU, making this a pure investment property if you choose.
How big can I build an ADU in Millis, MA?
In Millis, 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.
Does Millis have historic district rules for ADUs?
Yes. Millis has historically significant areas including Kingsbury Grist Mill Medfield Ma, Medway Historical Society, Millis Historic Train Station, Millis Historical Commission, Prospect Heights Historic District (Milford, Massachusetts). If your property is in or near a historic district, your ADU design may require review by the local historical commission for architectural compatibility. This can affect timelines and design choices.
Can I rent out my ADU in Millis?
Yes, long-term rentals are allowed for ADUs in Millis. However, short-term rentals (like Airbnb) are not currently allowed for ADUs.
How accurate is the ADU data for Millis?
The information on this page reflects Massachusetts state baseline rules under the Affordable Homes Act. Millis may have additional local requirements that differ from the state baseline. We recommend confirming with your local building department before starting your project.