Newton, Massachusetts’ Accessory Dwelling Unit (ADU) Rules

What you need to know:

Newton updated its zoning bylaw in 2017 and now allows both space conversion and detached ADUs. However, the design requirements and exceptions to their standard rules are extensive. Getting an approval to build a backyard home in Newton will be an arduous process.

Type of Permit Required:

Living Space Conversion:

Conversion of space within an existing home can be done with only a building permit.

Additions and Detached:

Both new additions, conversion of existing detached structures and newly constructed detached structures require a Special Permit.

Other ADU Rules:

Rules for both space conversations and detached:

• Ownership of the ADU and primary home cannot be split.

• An Accessory Apartment can be added to single-family and two-family homes.

• The owner must occupy either the ADU or primary home.

• The max number of people living in both the ADU and primary home cannot exceed the max number for the original primary dwelling. In other words, the total number people living on the property cannot be increased by the ADU.

• The primary home must be at least 4 years old.

• Short term rentals are not allowed. The minimum rental term is 30 days.

• No additional parking is required. However, if additional spots are added they must be screened.

• The owner must file a sworn certification stating they are following the rules annually.

Rules for space conversion:

• The ADU cannot be larger than 1/3 of the “Habitable Space” of the primary home or 1000 SF, whichever is less. A special permit can be granted to allow up to 40% and 1200 SF.

• The ADU cannot be less than 250 SF.

• Modifications to the exterior must matched the existing home. The specifically includes:

  • Siding

  • Roof pitch

  • Trim

  • windows

• Exterior staircases must be hidden or designed to compliment the existing home.

• New entrances facing the street can only be added with a special permit.

Rules for detached ADUs

• The ADU cannot be larger than 40% of the “Habitable Space” of the primary home or 1200 SF, whichever is less. A further special permit can be granted to build up to 1500 SF.

• The ADU’s design must match the character and architecture of the primary home.

• The new structure must be at least 6 feet from the primary home.

• ADUs must follow the setbacks for the primary home.

• ADUs are subject to dimensional requirements of Section 3.4.3, Accessory Buildings

• If a “historically significant” structure is being converted it must be 15’ from the primary home AND go through an additional review process by the Historical Commission. The review is necessary regardless of exterior modifications.

See the full Zoning Ordinance here: Zoning Ordinance Section 6.7.1 Accessory Apartments