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Newton 311 Services

Accessory Dwelling Units (ADU)

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This webpage has the relevant information regarding ADUs in Newton

What is an ADU?

An Accessory Dwelling Unit (ADU) is a smaller, self-contained residential unit located on the same lot as a primary residence, such as a single-family house or a small apartment building. ADUs are intended to be secondary to the primary residence and are sometimes referred to as in-law suites, granny flats, or accessory apartments. ADUs can be classified by their location:

Internal ADUs are located within the primary residence, such as in a basement or converted attic.
Detached ADUs are separate structures, such as carriage houses or converted garages.

What are the benefits to ADUs?

1. Diversify housing choices in the City while respecting the residential character and scale of existing neighborhoods

2. Provide a non-subsidized form of housing that is generally less expensive than similar rental units in multi-family buildings

3. Create more housing units with minimal adverse effects on Newton's Neighborhoods

4. Provide flexibility for families as their needs change over time and, in particular, provide options for seniors to be able to stay in their homes and for households with disabled persons

5. Preserve historic buildings, particularly historic carriage houses and barns.

ADU FAQs

Please click the plus button to the right to expand the question and read the answer.

Can I build an ADU on my property?

Do I have to live on the property where I want to put the ADU?

It depends, but generally no. However, there are a few exceptions in which the property owner must live on the property. These exceptions are:

If you choose to build a new detached ADU between 1,000 sf and 1,200 sf by-right (see ADU size questions).
If you seek a special permit for a larger ADU, the City Council may put on a condition requiring the owner occupancy.
If you have an ADU permitted prior to February 12, 2025 that does not meet the requirements for a by-right ADU under the current ordinance.

Can the ADU be sold separately from the principal residence?

Can I use the ADU as a short-term rental like Airbnb?

What size ADU can I build?

BY RIGHT

For new internal and detached ADUs they are allowed by right up to 1,000 sq ft or 50% of the total floor area of the primary residence, whichever is smaller. Only a building permit is required.

BY RIGHT WITH CERTAIN CONDITIONS

For an internal ADU where the main residence was issued a Certificate of Occupancy (CO) at least 4 years prior, they are allowed by right up to 1,200 sq ft or 50% of the total floor area of the primary residence, whichever is smaller.
For a detached ADU where the existing structure (garage, other kind of structure) in which the main residence was issued a Certificate of Occupancy (CO) at least 4 years prior OR the owner lives in either the main building or ADU, they are allowed by right up to 1,200 sq ft or 50% of the total floor area of the primary residence, whichever is smaller.

SPECIAL PERMIT REQUIRED BY CITY COUNCIL

For an internal ADU that is up to 1,200 sq ft in a dwelling that did not receive a Certificate of Occupancy (CO) at least 4 years prior.
For an external ADU that is up to 1,500 sq ft.

What are the height and setback requirements for an ADU?

Detached ADUs can be up to 2.5 stories or 36 feet. They must meet the setback requirements for a single family, detached home in that particular zoning district.
If a detached ADU is no taller than 1.5 stories and 22 feet, it must be at least 5 feet away from the side and back property lines. It also must follow the same front yard setback rules as a regular single-family home.
Detached ADUs are not subject to the 700 sq ft footprint limitation for other accessory buildings or garages.

I have an old carriage house; can I turn that into an ADU?

How do I know if my carriage house is historically significant so it can bypass the ADU size, height, and setback requirements?

You need to apply for a historical review through the Newton Historical Commission. If it is approved as historic, any outside changes to the building will also need to be reviewed. If your property is in a local historic district that particular historical district commission would do the review.
If your carriage house is not considered historic, you can still convert it to an ADU up to 1,200 sq ft, but it will need to follow all the regular rules for detached ADUs, like size, height, and setbacks from the property line.