How Do You Handle ADU Inheritance Fairly When One Sibling Gets the Property?

By Buz Artiano, BuildX | May 2026

Watch: 40% of Caregivers Pass First... Here's Why That Matters for Your Family

You want to build an ADU for your parents, but your siblings think it would be unfair for the parents to add hundreds of thousands of dollars of value to your land, when they are getting nothing. Your parents are caught in the middle of the whole thing because they don't know how to solve it, and the whole project is becoming more and more likely to fall apart. This isn't a construction problem, it's a family problem, and it prevents more ADUs from being built than zoning, septic, or financing issues combined.

My name is Buz Artiano, and I started BuildX. Since then we've built dozens of ADUs all over Massachusetts, but most of our builds have been around the South Shore and Plymouth County areas. We handle all the design, permitting, and construction ourselves, including dealing with septic evaluations, lot coverage constraints, and local bylaws and regulations. After years of walking people through these builds, we can tell you that at least 30 percent of the families who want to build an ADU never make it past the inheritance conversation. Projects die before they even start, we see it happen too often. We've had people ready to put down a deposit and get started, but then a couple weeks later when they call back, they tell us that the family just couldn't all get in agreement on everything so they would not be moving forward with the project.

This is why we are writing this article for you. We don't want to give you any legal advice, we just want to walk you through the conversations, the planning decisions, and the details on how to structure your estate that will help you move forward instead of falling apart. If your parents are thinking about building an ADU on your property and you have siblings, this is probably the most important thing you can read before you move forward.

Does the Sibling Hosting the ADU Get an Unfair Advantage?

Yes, if you're talking strictly dollar amounts. When your parents invest $300,000 to $400,000 to build an ADU on your property, your property value of course increases by that amount, or close to that amount anyway. If your parents have three children and a $1 million estate, that means $400,000 of that is now attached to your property. That leaves $600,000 for the rest of the estate, and if divided equally, your siblings are looking at a much smaller piece, which they are likely to be very unhappy about.

Trust us, it happens all the time. Let's do some math real quick. Parents sell their home for $1 million, then put $400,000 of that into an ADU on your property. That means there is now $600,000 left. If they split that evenly between the three of you, each one gets $200,000 from what's left. But if the ADU is on your property, you already received $400,000 in property value. The other two siblings are obviously going to see this as extremely unfair, and that's where the issues start.

Well here's the great news, this is a solvable problem, but it requires planning, honesty, and an estate attorney who understands and has experience with ADU families. But do not just ignore the subject, it will not go away, it will pop back up at the absolute worst time and cause all kinds of even bigger issues.

Do Your Siblings Need to Sign Off on the ADU?

No. Legally, your siblings don't have to approve your parents' decision to build an ADU on your property. As estate planning attorney Erin Nunes said:

That being said, just because you can go forward legally with buying in, doesn't mean that it's the right thing to do. Families who don't have this conversation and just go ahead and move forward without dealing with sibling concerns upfront will pay for it later. It can cause major problems with your sibling relationships, arguments over the parents' estate, or worse. You're not asking for permission, the goal is to make sure everyone understands the plan and why it's fair.

Your parents should be able to show that they had these conversations ahead of time, going into this decision seeing the full picture, and that they knew one child was receiving more in property value, but they adjusted their estate plan accordingly.

How Can Your Parents Offset the Property Value Increase?

The estate plan is the tool. Your parents' attorney will put together a strategy based on your family's finances and assets. It's very simple, if one child is receiving significant property value from the ADU investment, the estate plan adjusts so that other siblings get fair share through other assets.

Sometimes lawyers can allocate retirement funds or investment accounts to the other siblings, or adjust life insurance policies to benefit the non hosting siblings, or structuring a trust so that it accounts for the ADU value when everything is settled, and using the estate plan to document why things are being distributed the way they are.

The specific structure depends on what assets your parents have, how many siblings are involved, and how complicated the family situation is. A couple with two children and a simple estate will need a different plan than blended families. We have worked with families that have seven children between two previously married spouses, each with their own ideas about who gets what in the inheritance. The estate attorney will custom design a plan for your specific family situation.

Why Does the Family Conversation Kill So Many ADU Projects?

We've seen this happen more times than we can count. A couple comes to us all fired up about building an ADU. They have the land and the money, and they're motivated and ready to move forward. Their parents need a place to live, and they've got a great design. But then we tell them to go talk to their family before we move forward. Two weeks later they call us to tell us they won't be going forward with the build because the family can't get in agreement on things.

About 30 percent of the families that want to build an ADU with us never get past this stage. The project just dies, and it's not because of zoning problems, or septic costs, or financing issues. It's because someone in the family feels left out or screwed over.

What we have learned from building a lot of ADUs is that the family has to have this conversation early in the process if they want to succeed. Don't wait until the foundation is poured to bring up inheritance, and don't assume your siblings will be ok with it. You need to sit down, walk through the specific numbers, explain the reasoning, and give everyone a chance to get their questions answered. The families that skip that step are the ones we lose.

Because of this, this conversation is now a permanent part of our process. Before we will take a deposit from any family where the ADU involves a parent moving onto a child's property, we recommend they meet with an estate planning attorney and have the sibling conversation first. It's not our job to manage family dynamics, but it is our job to make sure families don't invest huge amounts of money and time into a project that is going to fall apart because everyone is not on the same page.

What About the Caregiver's Side of the Equation?

The sibling hosting the ADU is not just receiving property value, they're taking on a huge responsibility that is going to change everything for them on a daily basis. Their parents will have the right to come and go, invite people over, and live completely independently on their property. Their schedule, privacy, and household dynamic will change in a major way.

You could say that the caregiving sibling should get a larger share of the estate because they are providing proximity, support, and sometimes direct care that the other siblings are not responsible for. Sometimes families will put something in the estate plan that acknowledges the hosting sibling's extra effort and contribution, and that this affects them financially and personally, and the estate plan should show that.

The caregiving burden is very real and can be extremely stressful. Forty percent of caregivers pass away before the person they are caring for, usually because they stop prioritizing their own health. If one sibling is carrying that burden while others are not, the inheritance needs to account for that, for the physical and emotional toll it takes, it's about more than just money.

Is BuildX the Right Builder If Your Family Has Not Settled This Yet?

We're definitely not the right builder for every family, we'll be upfront about that. If your siblings are against the whole ADU project and your parents haven't talked to an estate attorney, our advice is to put the brakes on. We won't take a deposit from a family who isn't in agreement, because that project is highly likely to fail and cause huge regret and disappointment.

We've turned many families away to be honest. Not because their lot didn't work or their budget was too tight, but because the family was simply not ready to make the commitment. And yeah, maybe that costs us money in the short term, but it protects our reputation and, more importantly, it protects you from making a decision that your family is not fully prepared to make.

If you're in the middle of this conversation with your family and it's not going well, that's actually pretty normal. Most families need to take time to work through the emotions. An estate planning attorney who understands ADU families can be a big help and walk you through the process and find a way to structure things so that everyone is happy. We recommend having that conversation before you call any builder, including us.

What Happens When Blended Families Add Even More Complexity?

The inheritance fairness question gets a lot more complicated in blended families. When both spouses have children from previous marriages, all the children have different ideas about who will get what in the inheritance. It can cause a lot of issues if the parents build an ADU on one stepchild's property while the other spouse's children get nothing from that whole investment.

We are working with a couple right now that has seven children between them from prior marriages. Both spouses wanted to build an ADU so they could be near their family as they age. But an attorney had to help them figure out whose property to build on, and how that affected the inheritance of the other 6 children. It required very careful legal structuring and planning. But the good news is that these situations are common and they have solutions, but they require an estate plan that accounts for the blended family from the start.

If your family includes stepchildren, half-siblings, or children from other marriages, the estate planning conversation is an absolute must. It's the foundation that makes the ADU project possible.

Your Family Can Solve This Before It Becomes a Problem

The inheritance fairness question stops more ADU projects than most families expect. But it does not have to stop yours. The families who build successfully are the ones who address the sibling conversation early, engage an estate planning attorney, and document the plan so everyone understands the reasoning. The ADU is worth building, so talk to your family about it first, so that everything goes smoothly.