Can My Town Override the Massachusetts ADU Law or Make It Harder to Get a Permit?

By Buz Artiano, BuildX | May 2026

Watch: Why ADUs Are the Housing Solution Massachusetts Needs Now

You read the headlines. Massachusetts just passed an ADU law that says homeowners have the right to build an ADU on their property. But then you called your town hall, and everything changed. The building department wanted extra reviews and the planning board requires that all the landowners next to your property be notified about the ADU. The board of health needs a separate septic system, even though your existing system is big enough to handle the ADU. The state says you can build but it sounds like your town is telling you that you can't. That difference between what the law says and the laws in your own town is a frustration that faces Massachusetts homeowners right now.

My name is Buz Artiano, and I am the founder of BuildX. We've built dozens of ADU projects across Massachusetts, mostly around the South Shore and Plymouth County areas. We are the only team you need, we handle design, permitting, and construction. So we see every phase of a project from the first site visit up until you move in. We deal with septic constraints, zoning issues, and the state's new ADU laws. That front-line experience has taught us exactly where towns will dispute the state ADU law, what they can legally require, and what goes over the line.

This article will tell you the specific ways Massachusetts towns are making it harder to get a permit for an ADU, which of those rules are legal under the Affordable Homes Act, and what you can do when your town adds requirements that the state never intended. This is where you should start if you are trying to figure out whether your town is going by the rules.

Can My Town Actually Block My ADU Under the State Law?

The short answer is no. The Affordable Homes Act says that every town in Massachusetts must allow at least one ADU on any property that has a single family home. Towns can't pass local laws that ban ADUs, and they can't make someone get a special permit for a standard ADU that meets the size requirements of the state. The state minimum allows an ADU of up to 900 square feet or 50% of the main home's total floor area, whichever is less. You can review the full requirements at mass.gov.

However, the term by-right does not mean there are no rules. Towns still enforce the Massachusetts building code, Title V septic regulations, and their own requirements for setbacks, height, and lot coverage. The law prevents towns from banning ADUs altogether but it doesn't stop towns from enforcing existing health and safety regulations on ADU projects. The difference between those rules causes most of the friction.

If your town tells you that ADUs are not allowed, that isn't true under state law. If your town tells you that your specific project needs to meet certain site plan, septic, or setback rules, that may be true. The difference matters, and understanding it will decide how you deal with the permit process.

Where Are Towns Pushing Back on ADU Permits?

The points of contention we see with our projects fall into several expected categories. Not all of them are unlawful, some are legal for the town to regulate. Others seem like they are just deliberate attempts to discourage homeowners from building.

Planning board review and abutter notification. Some towns make ADU applicants go before the planning board and let all adjoining property owners know before a building permit will be given. We have seen this in Duxbury, where our projects have to get approval from the planning board first, and then we file for the building permit. The town lets all the abutters know about the project. All of that takes time and brings in comments from the public that seems at odds with the idea of by-right permitting.

Mandatory separate septic systems. We have also seen towns that require a completely separate septic system for the ADU, even if the existing system for the main house has enough capacity to deal with additional bedrooms. That requirement can add $40,000 to $60,000 to the cost of the project and sometimes will make the project too expensive to build. The state regulations say towns can't have that kind of requirement, but individual boards of health and town utilities are in what one housing policy researcher called "a bit of a gray area."

Subjective design review criteria. In Cohasset, for instance, larger ADUs have to go through a process with the planning board that has no written rules for approval. The decision is left up to whatever the board decides. When issuing a permit depends on whether a board member likes the look of your project instead of if it meets the outlined rules, then the process isn't really working as by-right permitting.

Informal pressure and overreach. We have been in town board Zoom meetings where a member of the board said they had driven by the applicant's house, counted the cars in the driveway, and wanted to know how many people were living there. That sort of question based on surveillance of the property shouldn't be allowed in the permit process for an ADU. That board member should have taken themselves out of the process.

What Can My Town Legally Require for an ADU Permit?

There are several parts of the ADU construction that towns have legal authority over. If you understand which parts those are, you can understand the difference between those requirements that you must follow and those that are just bureaucratic overreach.

Following building codes is not negotiable. Your ADU must meet the Massachusetts building code for structural integrity, fire safety, exits, the height of the ceiling, and accessibility. These are state-level standards that you must follow no matter what town you are building in. Your town's building inspector enforces these requirements, and that enforcement is completely reasonable.

Following Title V septic regulations is also legitimate. If your property is on a septic system, the board of health has the authority to make certain that the system can handle the additional flow from a new ADU. What is not legal is making you add a separate system when the system already in place has enough capacity for the ADU too. The difference between the two is important. Your town can require proof of capacity, but making you put in an unnecessary new septic system goes beyond what the state law wanted.

Size requirements within the state's laws are allowed. Towns can have setback restrictions, height limits, and lot coverage maximums, but they can't use those standards as a way to prohibit building an ADU. If a town's setback requirements make it physically impossible to build an ADU on a normal town lot, the requirements might conflict with the state law's intent.

How Different Is the Permitting Process From Town to Town?

It is very different and that is not an exaggeration. The experience of getting a permit for a BuildX client in one town can be simple and completed in weeks. The same type of project in a town close by could take months and many board appearances.

Some towns have worked with the state law and made clear, simple processes for ADU applications. Others have added more requirements that slow down the process without any useful safety protections. Norwell now lets ADUs be up to 1,300 square feet. Plympton allows up to 1,200 square feet. Other towns are staying with the state limit of 900 square feet and treat every application like it needs more than normal examination.

We assess how a town handles the permit process before we give a quote for a project, because that will directly affect the timeline and total cost to build the ADU. When we walk into a town hall for the first time with an ADU application, we already know if that town has to do a planning board review, what their board of health expects for the documentation of the septic system and whether they have a history of adding conditions that go further than the state baseline. That information before getting a permit comes after having filed in dozens of Massachusetts towns. Most builders do not do that research beforehand. They give you a price, file the permit, and then find out that the town wants a separate septic system or a planning board hearing. And by that time, the homeowner is already locked in to a number that isn't reality. We build the city regulations into the project from the beginning, because surprises when you go to file a permit are the most costly kind.

The longest time to process a permit we have experienced was five months, and it involved a town that was dealing with its first ADU application. The whole reason for the delay was because of the septic. The septic system ended up being a political issue between the board of health and the building department. That project finally got approved, but the length of the timeline was a result of the town's process and had nothing to do with the construction of the ADU.

What Does California's Approach Tell Us About Where Massachusetts Is Headed?

California started making changes to its ADU laws years before Massachusetts and has data that our state does not. California started with giving 880 ADU permits per year in 2014 to more than 30,000 per year in 2024. That growth happened because the state methodically got rid of the same local barriers that Massachusetts homeowners are running up against right now.

California's approach is designed to be more preventative when it comes to local zoning. The state set a baseline that says every town must allow an ADU of at least 800 square feet with a setbacks of four to five feet, no matter what the local zoning says about lot coverage or density. There are no public hearings or design reviews. If the project meets objective criteria, the homeowner will get a permit. California's ADU guidebook is 55 pages long. Massachusetts's regulations at this time are five pages.

Massachusetts is building approximately one quarter of the ADUs that California builds on a per-capita basis. Roughly 550 ADUs were permitted through the first half of 2025, based on a survey by the Executive Office of Housing and Livable Communities, though not every municipality responded to that survey. The gap between where we are and where California is suggests that Massachusetts will eventually need to get more specific about what towns can and cannot require. The question is how quickly that happens.

Is Every Town Requirement a Problem?

No, and it would not be honest to say otherwise. Some local laws are there for lawful health and safety reasons. The capacity of the septic system affects the groundwater, and enforcing the building codes will protect the homeowners. The rules for a setback keeps neighbors safe and makes sure that emergency vehicles have access. These are not just obstacles put up by the government, they are standard safety measures.

The problem isn't that towns have authority, but that some towns keep that authority to do what that state laws were put in place to stop. And that is to make it impossible or at least very expensive for a homeowner to build an ADU. When a town requires a separate septic system on a property where the system already in place is proven to have enough capacity, that rule isn't about safety. It is about discouraging the project.

We are a design and build company, so we benefit when homeowners decide to go ahead with ADU projects. You should think about our point of view with that in mind. What we can give you is lots of experience with how dozens of towns actually handle ADU permits, what they make you provide, and where those requirements go over the line from reasonable into obstructive. That front-line knowledge is something most homeowners don't have access to until they are already well into the process.

Your Town Has Rules. Know Which Ones Actually Apply.

The Massachusetts ADU law gives you the right to build and your town can't take that right away. But the specific requirements that your town requires such as planning board review, rules for the septic, or standards for how big your ADU can be, will all influence how long the project takes and the cost and difficulty of it. Knowing those requirements before you decide on a design or a budget will be the difference between a project that moves forward smoothly and one that gets stalled at the permit stage.