What Home Buyers Should Know About Accessory Dwelling Units

Learn about accessory dwelling units in Massachusetts and why prospective home buyers should understand how these secondary units might affect their property.    

Originally referred to as "servant's quarters," these units have evolved over time into "mother-in-law houses," garage apartments, and detached secondary living spaces. In essence, accessory dwelling units are additional residences located on a primary residential property. They are also known as accessory apartments, guest apartments, family apartments, or in-law apartments.

The following is the transcript of the video above about what Massachusetts home buyers should know about accessory dwelling units. 

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An accessory dwelling unit (ADU) is not a new concept. Accessory dwelling units have been around in some form in the United States for nearly as long as housing. 

Once known as "servant's quarters," they morphed over the years into "mother-in-law houses," garage apartments, and detached secondary living units. The simplest definition is that accessory dwelling units are secondary dwellings on a primary residential property. Some also call an ADU an accessory apartment, guest apartment, family apartment, or in-law apartment. 

For a time, accessory dwelling units fell out of fashion. In recent years, they have come back into focus as an effective avenue for homeowners to increase the value or utility of their property and expand affordable housing stock. 

Massachusetts Governor Maura Healey signed a $5.16 billion housing bond bill on Tuesday, August 6, 2024. A key provision allows accessory dwelling units by right in single-family zoned neighborhoods statewide. These units can be basement and attic apartments, home additions, or small detached dwellings on the property. 

There are still rules and regulations, but the new law allows more flexibility and options. 

Local governments can impose reasonable regulations, such as, but not limited to, site plan review, dimensional setbacks, restrictions on the bulk and height of structures, and restrictions on and prohibition of short-term rental accessory dwelling units.

There are three key points relative to the new statewide ADU regulations home buyers should know. 

1. Accessory dwelling units can be up to 900 square feet or half the size of the primary home, whichever is smaller. Homeowners are not required to obtain a special permit for one ADU.

2. ADU occupants are not required to be related to the property owner, which is a typical local zoning restriction. An owner does not have to occupy the property, another often-seen restriction. The accessory dwelling may require one parking space per unit; however, the law does not require any parking spaces if the unit is within one-half mile of a commuter rail station, subway station, ferry terminal, or bus station.

3. Local laws on short-term rentals, such as Airbnb, still apply, but municipalities cannot unreasonably restrict accessory dwelling units.

The new provisions in the bill supersede any inconsistent local bylaws or ordinances already in existence; however, the ADU provision will not be in effect until February 2, 2025, 180 days after the Act became law.

Whether a homebuyer is looking for a property with an existing ADU or is considering building one in the future, it's essential to understand available options and how regulations might impact your home-buying decisions.