What Happens to an ADU When Siblings Inherit the Property in Massachusetts?

By Buz Artiano, BuildX | April 2026

Watch: Bill Sims: What Builders Get Wrong About Real Estate Law | BuildX Podcast #24

Suppose you have decided to build an ADU for your mother. You have two siblings and your mother is paying for part or all of the building costs. You have a question that keeps coming to your mind however. What will happen to this property when my mom is gone? Will all the children in the family expect to get part of the proceeds? Could one of the children force your home to be sold? An ADU you build with the goal of keeping family together could become a problem in the future that tears it apart.

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. After years of building ADUs for multigenerational families, we can tell you that the inheritance question comes up in almost every single ADU project if there are siblings involved. It is one of the most common reasons families hesitate, and it is one of the problems that is most preventable in the whole ADU process.

This article will give you information about the specific legal problems that may come up when children inherit a property that has an ADU, and help you understand the difference between the two most common types of ownership. It will also outline the steps you can take now to prevent the chance of a forced sale, a fight in probate or a family disagreement later. The goal is to help you make one very important decision before you start building and that is how the property should be titled.

What Actually Happens to the ADU When a Parent Dies?

In the state of Massachusetts, an ADU does not transfer separately. It is considered to be attached to the real estate it is sitting on which means it's part of the property and is not an asset that stands alone. So when a parent dies, their ADU will go wherever the deed says the rest of property goes. Even if your mother paid $400,000 to $500,000 to build an ADU on your property, she does not own the ADU. You do. The structure is permanently attached to your land, and the deed controls it all.

This means that when your mother passes away, the money she has put into the ADU has been added to the value of your property. If she has other children, they might see the increase in the property value and ask where is my share of it? That question can be where the trouble starts.

The answer to that will depend on what the title of the property says. There are two main structures that decide what will happen next and they are joint tenancy and tenancy in common. The difference between these two structures will make the difference between an easy transfer and a probate fight.

What Is the Difference Between Joint Tenancy and Tenancy in Common?

These are the two most common ways property is held when more than only one person is listed on the deed. Each one has a very different outcome when someone dies.

Joint tenancy means that if one owner passes, that person's investment in the property will go to the surviving owner without conditions. There isn't any probate and no will is involved. The surviving owner will get full ownership under the law. In a different situation where a mother and daughter are joint tenants, the daughter will get the entire property when the mother dies and the other children will not get anything from that property.

Tenancy in common works differently than that. If property is held this way, when one owner dies, their share does not pass to the other owner. Instead, it has to go into probate and the deceased person's will decides who it is passed on to. If there isn't a will, the property would be passed on under the state's legal rules in that situation. So if a mother had a 50 percent interest as a tenant in common and left her share to all three children equally, the daughter who lives in the house now co-owns the property with her two siblings.

That's when the numbers start to feel uneasy. The daughter owns her original 50 percent, which means that each of the other children now have about a 16 to 17 percent share, so they have a legal right to their share of the property's value, including the value of the ADU.

How Can Siblings Force a Sale of the Property?

When siblings inherit a share of a property and they want their money, the options are very limited. The daughter who lives in the house can either buy out her siblings or sell the property.

If the daughter is able to take on the mortgage and pay off her siblings, she then becomes the sole owner of the property. That means the other siblings sign over their share of the property. But one of the attorneys that we work with every day says that does not happen every day. Most people are not able to finance or pay cash for a buyout that can cost $200,000 to $500,000, especially on short notice.

If the daughter is unable to buy them out, the siblings can go to court and ask for a partition sale, which forces the property to go up for sale, even if the daughter doesn't want to sell it, there's nothing she can do, she can only negotiate the terms.

This is a very tragic and difficult situation to be in. You built this ADU to keep your mom close to you, and she lived next to you for years. And now, after she's gone, the property she helped build could be the reason you lose your home. We see it happen every day in our work with Massachusetts families. When the money comes out, it changes people.

How Do You Prevent a Sibling Inheritance Dispute Before You Build?

The one thing that you absolutely must do is figure out the best way to legally structure the ownership of the property before starting construction. This is not something you figure out after the ADU is built. You need to work with an attorney to get all of that handled before even applying for permits.

The most common solution is a revocable trust with defined beneficial interests. When you do it this way, the entire property is placed into a trust. Each family member receives a specific percentage of what is in that trust. The percentages don't have to match who has contributed the most financially. You can give 33 percent to the mom and 67 percent to the daughter, or 51 percent to the mother so she controls it, or any other way you want to splice it up.

The advantage of a revocable trust is that it can always be changed. Unlike an irrevocable trust, which is extremely difficult to make any changes to, a revocable trust gives the family freedom to change the ownership percentages as their circumstances change. But everybody has to agree to any changes that are made.

The trust also provides protection for the mom while she's still living. If the property needs to be mortgaged, sold, or changed, the mom has to give her consent. That means the daughter can't sell the property out from under her, can't take out a loan against it, and can't do anything that would risk the mom's living situation.

In our experience building ADUs here in Massachusetts, we've noticed that about 50 percent of the ADU process is all the family dynamics and legal processes, 25 percent is what we are actually going to build, and 25 percent is getting the permits. Those numbers surprise a lot of people, but they're true. We tell every client that they need a whole team to build this ADU. You need an attorney who understands trusts and estate planning, you need a builder, and you need a surveyor. All three have a role, and if you skip the attorney, you're creating a big problem that can come back in a bad way to haunt you in 10 years. We've seen plenty of families who skipped this step and they all regretted it. Dealing with the legal paperwork costs only a small part of the construction budget and it saves you from extremely difficult and expensive problems down the road.

What If Your Siblings Are in Completely Different Financial Situations?

This is another very common thing we see. One sibling is working as an investment banker in New York and doesn't need the money, another one isn't doing so well financially, and maybe a third sibling is somewhere in the middle. They're each going to have different expectations and be in different financial positions, and they're all going to feel differently about what to do with the family home.

The trust helps here because it forces the family to have these difficult conversations before everyone's emotions are running high. When everyone agrees on what their shared percentage will be while the parents are still alive and involved in the conversation, it makes it very straightforward after the parents are gone, there's no room for disagreement, it's cut and dry who gets what, and the trust document that everybody signed will back that up.

Without those documents, you're relying on people to not change their minds and going off of verbal agreements alone. The problem with verbal agreements is that they don't hold up in court, they crumble under financial pressure and the grief and stress from losing a parent. You have to have these conversations before the foundation is poured, not after the funeral.

Can Condominiumizing the ADU Protect Against Inheritance Disputes?

Condominiumization is an emerging strategy in Massachusetts that gives the family extra protection in situations like this. Under Massachusetts General Laws Chapter 183A, property owners can split up the lot so that the ADU and the main house are each on a legally separate lot. Which means they can be owned, financed, and sold independently.

If the ADU is condominiumized, the parent would own the unit separately and independently and it becomes part of their estate, it's no longer the daughter's property. The parent can leave it to whomever they choose, refinance it, or sell it. The daughter's home isn't at risk of being sold out from under her in any way. This makes the inheritance so much simpler because the ADU is a separate legal entity. You can review the Massachusetts condominium statute framework at malegislature.gov.

Doing it this way is pretty new for ADUs in Massachusetts. We're actively pursuing it with a few of our clients and we think it will become more common as families recognize the long-term benefits of having it set up this way. We strongly encourage families who are thinking about doing this to install separate utilities, separate septic systems, and separate electrical service from the start, because you will need all that in place in order to condominiumize it later.

Is Legal Structuring Always Necessary for an ADU?

No. If you're building an ADU on your own property, with your own money, and no siblings who will be inheriting a share of it, then there's no need for a trust of any kind, it's just a standard deed with you as the single owner.

The legal side of things gets complicated when multiple family members have a financial stake in the property, when a parent is paying for it, or when the property will eventually need to be split up between siblings. If none of those things apply to your situation, you can probably skip the whole estate planning lawyer meeting completely.

We also want to be clear about our role in all this. We are builders, not attorneys, but we make sure families are aware of these issues because we've seen what happens when they're ignored. But the legal work itself needs to be done by a qualified real estate attorney who practices in Massachusetts and understands trusts, estate planning, and property law. We recommend that all families consult with an attorney before signing a construction contract, and we're more than happy to connect you with attorneys we've worked with on other projects.

For families building an ADU under the Massachusetts Affordable Homes Act, the by-right regulations allow one ADU per single-family lot. However, building code, health code, and size requirements are still imposed by your town. Full details on the state ADU regulations are available at mass.gov.

Your Family Deserves a Plan That Outlasts the Build

When you build an ADU, it's part of your family's property for decades. The construction part only takes a few months, but the inheritance question will last a lot longer than that. Getting the ownership structure right before you build is the single most important decision in the entire ADU process. It costs less than a single phase of construction, and it prevents problems that no amount of money can fix after the fact.