Accessory Dwelling Units (ADUs) A Smart Housing Strategy in Massachusetts Now Allowed By Right in Massachusetts
In August 2024, Massachusetts passed the Affordable Homes Act, which, among other things, legalized Accessory Dwelling Units (ADUs) by right in the entire state.
Accessory Dwelling Units (ADUs) are self-contained housing units located on the same lot as a single-family home. These units may be found inside the main house (like a basement or attic conversion), attached (such as a new addition), or entirely separate (think garage conversion or backyard cottage).
This legislation went into effect on February 2, 2025.
Why ADUs are an Important Housing Tool for the OCPC Region?
What are ADU's?
What is the New State Law?
Implementation Tools and Local Support
EOHLC ADU Office Hours
What are ADU's?
Accessory Dwelling Units (ADUs) are self-contained housing units located on the same lot as a single-family home. These units may be found inside the main house (like a basement or attic conversion), attached (such as a new addition), or entirely separate (think garage conversion or backyard cottage).
What is the New State Law?
The new law sets clear boundaries on how municipalities can regulate Accessory Dwelling Units (ADUs). It mandates by-right approval (i.e., without discretionary approvals) for the first ADU on a property, prohibits requiring that the unit be occupied by the property owner, and limits the ability to impose additional parking requirements. However, local governments are still allowed to regulate the use of ADUs as short-term or vacation rentals.
The ADU law took effect on February 2, 2025 (read the final regulations). As a result, any local zoning rules that conflict with the provisions of M.G.L. c. 40A Section 3 may now be unenforceable. Applications for ADUs in single-family zoning districts that comply with the law’s definitions and requirements should be processed in accordance with state statute. Cities and towns are advised to examine their zoning bylaws and identify any provisions that no longer align with the updated law. (Source: EOHLC ADU FAQs: Accessory Dwelling Units (ADUs) – FAQs | Mass.gov)
Implementation Tools and Local Support
The Executive Office of Housing and Livable Communities (EOHLC) has issued final regulations under 760 CMR 71.00, effective January 31, 2025, to guide how ADUs are interpreted and permitted by municipalities.
EOHLC, in coordination with MAPC and the Massachusetts Housing Partnership, released a model ADU zoning bylaw and checklist to assist cities and towns in updating local ordinances efficiently.
Municipalities can apply for technical assistance or grant funding via the One Stop for Growth Program, which funds planning and zoning updates aligned with ADU policy goals.
How OCPC is Supporting Our Local Communities
OCPC is ready to assist member municipalities in interpreting the new ADU law and aligning local zoning codes accordingly. Our services include:
Reviewing and recommending necessary zoning updates.
Providing design and planning best practice guidance.
Supporting public engagement around ADU adoption.
Helping streamline permitting processes and forms.
EOHLC ADU Office Hours
The Executive Office of Housing and Livable Communities (EOHLC) is offering office hours to help municipal planners understand the Accessory Dwelling Unit (ADU) law and regulations, that became effective on February 2, 2025.
The office ours will be once a month on every second Wednesday, 3:00 – 4:30 p.m. Registration for any of the office hours is required.
To learn more about the office hours, the office hour dates, and to register, please visit the registration page
More Information
Every ADU built under this law must:
- Have a separate entrance, either directly from the outside or via an interior hall that meets building code standards.
- Not exceed 900 sq ft or half of the gross floor area of the primary dwelling.
- Fall within applicable local restrictions—such as setback, height, or short-term rental limits—that communities may still impose.
Municipalities are not permitted to require:
- Special permits or zoning board approval for ADU use or rental.
- Owner occupancy or familial relationship between residents.
- More than one parking space for ADUs located outside a half-mile of designated transit http://Read the Full Legislation
ADUs offer property owners a range of practical, personal, and financial benefits, including the ability to:
- Move into a smaller unit on their own lot while retaining ownership and staying in their neighborhood.
- Provide on-site housing for a caregiver or family member in need of support.
- Accommodate adult children or aging parents with privacy and proximity.
- Offset housing costs by renting out the ADU and supplementing their household income.
- ADUs promote smart growth by adding gentle density in walkable, already developed areas—reducing pressure to develop open or undeveloped land.
- Their small-scale results in minimal construction impacts and fit well within the existing neighborhood character.
- They rely on existing utility systems and infrastructure, which can reduce costs for towns and cities.
- Because ADUs are usually built and maintained by the homeowner, they tend to reflect a high level of care and integration with the main home and surrounding properties.
ADUs offer a host of benefits:
Expand Affordable Housing Options
- ADUs are significantly less costly to construct than building a new single-family home on a separate parcel, making them a viable option for individuals and families with low to moderate incomes.
- Homeowners can benefit financially by renting out an ADU, generating supplemental income.
- These smaller, independent units create affordable rental opportunities in neighborhoods where housing is often limited or expensive.
- ADUs support older adults who wish to stay in their neighborhood by allowing them to downsize into an ADU or rent it out for extra income.
- They also serve the changing needs of smaller households, such as empty nesters, young adults, or single individuals.
- ADUs facilitate close living arrangements for extended families, making it easier for aging parents or adult children to live nearby.
- By making use of existing residential lots, ADUs support compact, sustainable development and reduce the need for large-scale new construction.
State projections estimate that 8,000–10,000 ADUs may be constructed across the commonwealth within the next five years, thanks to streamlined permitting and standardized rules.
Mythbusting: Dispelling the Myths of ADUs
ADUs are little housing unit’s homeowners can add to their property to help a parent age in place, or to rent out to someone in need of affordable housing (two of the more common uses). Misconceptions or a misunderstanding of ADUs can cause people to worry about the potential impacts of ADUs on their neighborhood. We would like to dispel a few myths about these valuable housing resources:
Reality: Most ADUs are converted garages or backyard units, not visible to the public at large. ADUs are intended to be lived in by older family members or to be rented out, which means they need to be visually appealing. There’s a growing ADU movement, which means lots of design resources for those interested in building them. Here are some examples of ADU design. And here’s another page with examples of ADU design.
Reality: There is no evidence that ADUs cause parking problems. Most of those who use ADUs have fewer cars than people using larger, more land-intensive housing. ADUs tend to be dispersed, which is one of their great advantages, so their impact on any particular neighborhood is negligible. More readings (link): ADUs and Condos: Separating Ownership
Reality: ADUs benefit a wide swath of people, from recent college graduates to retirees looking to age in place, which is why the American Association of Retired Persons (AARP) “supports the wider availability of accessory dwelling units, or ADUs, as an affordable, accessible housing option for people of all ages.”
Reality: Many ADUs are modular, built off-site. Those built in the backyard won’t bring more noise than any other home remodeling project. And there really won’t be very many of them in a given neighborhood. In locations that have made much more permissive rules about ADUs, the number built in a particular place hasn’t bumped up much; they are scattered around and residents don’t really notice them. In Denver, which recently overhauled its code to encourage ADUs, only 33 ADU permits are issued per year on average. For context, Denver is a city of 715,000!
Resources
Executive Office of Housing and Livable Communities (EOHLC)
Accessory Dwelling Units (ADUs) FAQs (September 2024)
AARP Resources
All About Accessory Dwelling Units
ADU Model State Act and Local Ordinance
American Planning Association (APA) Resources
American Planning Association Accessory Dwelling Units
Staff Assistance
Senior Planner for Housing and Public Engagement
(774) 273-2372
