NEW LAW: Inlaw Apartments, 'Accessory Dwelling Units' now allowed by right in MA

Thinking of creating a multigenerational living space, or a rental unit to supplement your mortgage payment or take a bite out of your utility bills? The Commonwealth of Massachusetts, as part of the Affordable Homes Act, just made things a little easier, with new statewide rules for Accessory Dwelling Units, which allows ADUs by right in everywhere in Massachusetts (excluding Boston). This is all brand new as of February 2025, and I’m sure there’s a lot to be worked out before it’s fully understood, but I’m pretty excited about the idea of some kind of solution to help with housing affordability, literally in our own backyards.

I have a friend and real estate colleague who is working on an ADU for her father-in-law, so that he can live with them, but not quite with them, if you know what I mean. If you read one of my most popular stories, about my own multigenerational home search, you’ll see that I am a fan of separate kitchens, which I’m sure has helped my mother and I to stay on good terms in the 10 years we’ve now lived together (my mother’s granny kitchen, pictured above). You can read that story here: Considering Multi-Generational Living, an In-law or Accessory Apartment?

At the bottom of this story, you’ll see links to more information about Accessory Dwelling Units related to the new Affordable Homes Act, as well as a point in the right direction for your specific town, to learn more about their process. So, whether you’re thinking of finishing a basement or the space above your garage to create your own ADU, or maybe you would add onto your existing home, or build inside your existing footprint like we did–I hope this is a conversation starter for you. Or maybe you want a completely separate structure on your property–there are so many possibilities now!

As of February 2, 2025, ADUs (officially ‘Accessory Dwelling Units’, also referred to as inlaw apartments, accessory apartments and granny flats) will be legal on most single family lots across Massachusetts. Could this help with affordability, with the state’s housing shortage crisis? The Massachusetts Governor’s office estimates that this new law will help create more than 8,000 new ‘dwelling units’ over the next 10 years. If you’ve got family members who you’d like to bring in to your home (without actually bringing them IN to your home), an ADU might be for you. If you’d like to supplement your mortgage payment or utilities costs by having a tenant, an ADU might be for you. Princeton also recently adopted a Boarder Bylaw, which I find quite interesting because it allows homeowners to legally rent parts of their primary residence to two separate boarders (think traveling nurses looking for housing) to supplement their housing expenses. Here’s a link to the November 2024 Princeton Special Town Meeting Minutes detailing the voters’ decisions made on Bed and Breakfasts, Short Term Rentals and Boarders.

A big challenge, when it comes to ADUs, is even taking the generous changes in the law into account, in the smaller towns the individual septic system capacity of a property can play a significant role in the outcome, especially financially. The challenge if your home is served by a private septic system is that you might be limited on bedroom count because septic systems are sized by the number of bedrooms in a home. If you have a more modern septic system, hypothetically, you may be able to add capacity to that system. If you have an older or failed system, you may have to factor in the cost of design and replacement of your septic system. That is not a small budget line item, but as a realtor, I will say that a brand new septic system will add value to your property, and I believe having an accessory dwelling unit will as well. Things will be much simpler if a property is served by municipal sewer, but again, that’s not an option in some areas in the smaller towns, or at all in towns without municipal sewer. I’m on the Princeton Housing Implementation Committee, and we’ve heard from a few businesses that will build a detached ADU, from soup to nuts, streamlining the process significantly, according to their marketing.

My family spent a few years searching for a home with an ADU (it was just referred to an inlaw back when we were looking, back in 2013 – 2015). Keep in mind we were looking only in Westminster for 2 years (some homes are served by municipal sewer, but most are on private septic) and then finally, after finding nothing even close, we opened up our search to the Wachusett towns, and Princeton, where we ended up, has no municipal sewer at all. What did we run in to?

1. Homes with existing ADUs were VERY few and far between, and the few we did find had the accessory apartments either in dark basements or above garages with slanted ceilings. We had promised my parents they wouldn’t be an afterthought when we judged a home for suitability. One thing that I’m hopeful for with this law is that we’ll eventually start seeing homes for sale with built in features for multi-generational living.

2. We looked at homes with first floor master bedrooms (we could call them master bedrooms back then), that we could add on to in order to give my parents additional space, and the much needed second kitchen. Our struggle with this category of homes for sale was finding a house that would still be big enough for our family (at that point we had only three teenagers at home) because we would lose one of the bedrooms to grandma and grandpa.

3. We looked at homes with newer septic systems to see if adding on to an existing septic while also adding on to the house might be an option. Every home we looked at in this category became too expensive in that we’d have to make major septic modifications to be able to increase the bedroom count, and having the full cost of the addition.

4. Finally, after almost 3 years, I actually knocked on a few doors, believe it or not (if you know me, you know that door knocking is not my thing). What doors did I knock on, and what did this look like? “Hello, my name is Jen and I’m looking for a home for my family that either has an inlaw apartment or is large enough that an inlaw apartment might be possible. It appears your home might be large enough to accomplish that. Is there any chance you’re considering selling?” “No? Ok, bye.”. I only did that a couple times, and it wasn’t very comfortable, to be honest.

What mistakes did we make, or almost make?
We had several near-misses, and still now we drive by certain houses and one of us will note ‘remember when we accidentally almost bought that house?’. We almost bought a house on such a dangerous curve (can’t do much about location), it was a home from 1790, with a new addition in place that could be converted to the inlaw. The issue with this home was that we’d be the owners but the inlaws would have a nice new space and we’d have original drafty windows, low ceilings and no closets on the second floor. Good thing the water quality tests came back high in arsenic twice, as we clearly dodged a bullet on that one. We toured houses where we’d have to remind my stepfather to be careful, don’t trip, etc. If a home has this type of issue and it’s not fixable, this isn’t the house to buy when you’re looking to bring in someone with mobility issues.

If I’m being honest, a big mistake was my inflexibility in that I thought I knew, and could hold out for, the exact layout I was looking for. This did not work, and it did not work in spades. I needed to be more realistic in that if a house checked off enough of my boxes, we needed to seriously consider it.

Finally, one day my husband and youngest daughter went to an open house without me. It was an XL existing single family with a failed septic. A dream come true after having been living in my teenage bedroom in Templeton for years at that point. But nope, I wasn’t having it. It was too big, too expensive, and being a very angular contemporary home, did not sing to me at all. Not buying this house, I truly believe, would have been the biggest mistake of my life, because the possibilities it had fit our family situation to a T at that time, then years later it was a fantastic spot to Covid in place, and now that the kids are adults, we’ve got room for anyone who is saving for a house, between college and career, between college and more college, etc. And I definitely wasn’t buying this house. My advice to anyone embarking on this type of multi-generational adventure is to keep an open mind.

“What is an ADU? An Accessory Dwelling Unit (ADU) is a small residential living space located on the same lot as another home. ADUs can play a significant role in our housing crisis. The ADU policy recently signed by the Governor allows property owners to build an ADU without having to get special or discretionary approval from the local zoning board. ADUs can be internal within an existing primary residence, like converting a basement into an apartment, attached to a primary residence as a new construction addition, or completely detached, like a cottage or converted detached garage in a backyard. The Affordable Homes Act amends the definition of “Accessory Dwelling Unit” under Section 1A of Chapter 40A of the General Laws to clarify that the maximum size of an ADU is no more than half of the gross floor area of the principal dwelling, or 900 square feet, whichever is smaller. The definition was also amended to prohibit owner-occupancy requirements and unreasonably restricting the creation or rental of an ADU.

What is the law?
On August 6, 2024, Governor Healey signed the Affordable Homes Act into law (Chapter 150 of the Acts of 2024). Section 8 of the Affordable Homes Act amends the Zoning Act to allow ADUs up to 900 square feet to be built by right in single-family zoning districts. An Accessory Dwelling Unit, a self-contained housing unit, inclusive of sleeping, cooking and sanitary facilities on the same lot as a principal dwelling, subject to otherwise applicable dimensional and parking requirements, that: (i) maintains a separate entrance, either directly from the outside or through an entry hall or corridor shared with the principal dwelling sufficient to meet the requirements of the state building code for safe egress; (ii) is not larger in gross floor area than 1/2 the gross floor area of the principal dwelling or 900 square feet, whichever is smaller; and (iii) is subject to such additional restrictions as may be imposed by a municipality, including, but not limited to, additional size restrictions and restrictions or prohibitions on short-term rental, as defined in section 1 of chapter 64G; provided, however, that no municipality shall unreasonably restrict the creation or rental of an accessory dwelling unit that is not a short-term rental.

SECTION 8. Section 3 of said chapter 40A, as so appearing, is hereby amended by adding the following paragraph:-
No zoning ordinance or by-law shall prohibit, unreasonably restrict or require a special permit or other discretionary zoning approval for the use of land or structures for a single accessory dwelling unit, or the rental thereof, in a single-family residential zoning district; provided, that the use of land or structures for such accessory dwelling unit under this paragraph may be subject to reasonable regulations, including, but not limited to, 310 CMR 15.000 et seq., if applicable, site plan review, regulations concerning dimensional setbacks and the bulk and height of structures and may be subject to restrictions and prohibitions on short-term rental, as defined in section 1 of chapter 64G. The use of land or structures for an accessory dwelling unit under this paragraph shall not require owner occupancy of either the accessory dwelling unit or the principal dwelling; provided, that not more than 1 additional parking space shall be required for an accessory dwelling unit; and provided further, that no additional parking space shall be required for an accessory dwelling located not more than 0.5 miles from a commuter rail station, subway station, ferry terminal or bus station. For more than 1 accessory dwelling unit, or rental thereof, in a single-family residential zoning district there shall be a special permit for the use of land or structures for an accessory dwelling unit. The executive office of housing and livable communities may issue guidelines or promulgate regulations to administer this paragraph.” —Quoted sections from Mass.gov

I called around to several local towns to see what homeowners need to get started on their research for a potential accessory apartment on their property. Most said they were waiting for full wording to come down from the state. The links below will bring you to their most recent information by town. I’d suggest an informal appearance in front of the governing board (with permission first, of course), to talk through what you’re thinking of doing, so that if you DO decide to file an official application, you’re set up for success as much as possible.

Companies that focus on building ADUs
Backyard ADUs
MA Tiny Home

How to get started on your research in some local cities and towns
Pioneer Institute for Public Policy Research:
2004 compilation of Municipalities policies regarding Accessory Dwelling Units allowed by right or special permit.
Accessory Dwelling Units in MA
2025 Massachusetts Final Regulations for Accessory Dwelling Units
Home Modification Loan Program (HMLP)
Accessory Dwelling Units Officially Allowed Statewide

Ashburnham
Ashburnham Town Website
Ashburnham Planning Board
ADU Rules and Regulations

Ashby
Ashby Town Website
Ashby Planning Board
Ashby Permitting Guidebook
Ashby Zoning Board of Appeals Guide

Boylston
Boylston Town Website
Boylston Planning Board
Boylston Zoning Bylaws

Clinton
Clinton Town Website
Clinton Planning Board
Clinton Zoning Bylaws

Fitchburg
Fitchburg City Website
ADU Information (draft zoning amendment)

Gardner
Gardner City Website
Gardner Planning Board
Gardner Zoning

Holden
Holden Town Website
Holden Planning Board
Holden Zoning Board

Hubbardston
Hubbardston Town Website
Hubbardston Planning Board
Hubbardston Zoning Board
Hubbardston proposed changes to Accessory Dwelling Units

Lancaster
Lancaster Town Website
Lancaster Planning Board
Lancaster Zoning Bylaws

Leominster
Leominster City Website
Leominster Planning Board
Leominster Zoning Ordinance

Lunenburg
Lunenburg Town Website
Lunenburg Planning Board
Lunenburg Zoning Bylaws