How Much of Your Stuff Actually Fits When You Downsize Into a 900 Sq Ft ADU?

By Buz Artiano, BuildX | August 2026

Watch: Downsizing a Whole House Into 900 Square Feet, Who Actually Helps You Do That?

You have been in the same house for 35 years. The kids' rooms are still furnished. There's boxes in the attic that haven't been opened up since you put them there. Now your daughter has found a builder to build a 900 square foot ADU in her backyard for you. When you go to tour a finished ADU for the first time, all you can think is "where is all of my stuff supposed to go?"

My name is Buz Artiano, founder of BuildX. We've built dozens of ADUs all over Massachusetts, but most of our jobs have been on the South Shore and in Plymouth County. We do everything, that means design, permitting, and construction ourselves. Massachusetts allows one ADU by right on most single-family lots. All that means is that the town approves it without a discretionary special permit hearing. The size cap is 900 square feet. You can look at all the specific requirements at mass.gov. Local building code, health code, and dimensional rules all still apply however, and 900 square feet is the number most of our clients end up building.

That's why the storage question comes up on every tour, and the truth is that about one item in ten moves in with you. We would rather you hear that here, on paper, months before any construction starts so you know what to plan for and there are no surprises. We don't want you to be stuck in a position when you've already started the moving process and have a truck rented and still don't know what to do with your mother's china.

How Much of My Stuff Actually Makes It Into 900 Square Feet?

You'll be able to keep 10 to 20 percent of it. Moving a household from around 2,600 square feet into a 900 square foot ADU means that 80% of your stuff won't fit. Eight out of ten things have to go. On the larger houses we work with, it ends up being close to nine out of ten.

That ratio is the pattern that has shown itself based on all the families we've built ADUs for. You will see that it holds true when you start evaluating your own house. There is stuff everywhere. Family photos and albums. The collections of books or other things on the shelves. The mounted elk head. The toy race car collection or original Cabbage Patch dolls from the 1980s that somebody has kept for a long time. Every one of those things takes up space.

The number lands hard because nobody arrives at a tour having done the arithmetic. They arrive having done the emotional math, which says the ADU puts them close to the grandchildren and that is worth something. Both are true. The arithmetic still has to happen, and it is a far cheaper conversation now than in month three of a build calendar.

Why Does a 2,600 Square Foot House Not Fit Into 900?

You always have to get rid of more stuff than the reduction in square footage would suggest, and that catches people off guard. Going from 2,600 square feet to 900 square feet is about a 2/3 reduction in size. But you can't keep a third of your possessions. The limited space in an ADU has to be used for daily living first. So things you have in the spare bedroom, the basement, the linen closet, and the garage overflow that have been accumulating for 30 years don't have a place in the new ADU. Here is a chart that puts it simple and easy to understand at a glance.

An oversized crawl space adds a bit of extra storage, but it doesn't change the fact that you still have to sort through everything. On a 3,600 square foot house moving into an ADU with a six-foot-seven crawl space, people still end up having to reduce their belongings by about 80%. Crawl space is bulk storage stuff that you only access once or twice a year. Things like holiday storage and rarely used tools. It's not going to hold extra furniture, dish sets, or the closet stuff that you had in a big house. We design the crawl-space access and any shelving you'd like during the beginning in the design phase, because access height, hatch location, and stair placement are decided at framing. If you decide that you want stairs when we are four months in, that's a change order, which adds time and complication.

The other thing that helps is standing in the space. We do these home tours because the first thing someone says is that they don't know if they can live in 900 square feet. Square footage as just a number can be very misleading. A finished kitchen you can actually walk through is different. People who walk through a completed ADU tend to stop worrying so much about the number of square feet and start asking where the coat closet goes. That's the conversation that we want to have.

Where Do the Other Nine Out of Ten Things Go?

Every item in the house will go one of four directions. Knowing what they are before you start prevents things from stalling, because a stall is always because of indecision on an item. Michelle Sullivan and Nicole McCann of If the Shoe Fits, a South Shore personal assistance company, joined us on the show to describe how they deal with this issue room by room, and their process is what we see happen on our job sites. Options are:

• Keep it. It fits the floor plan and it's worth the space it takes up.
• Hand it down. If something is already earmarked for a grandchild or other family member, give it to them now rather than waiting until you're gone.
• Donate it. Call the extended family first to see if they want anything, whatever is left goes to charity. Animal shelters are always in need of linens and towels.
• Dispose of it. Some of it just needs to be thrown away. Pretending otherwise costs you extra space you don't have.

Handing things down to the family gets rid of a lot of volume. But it's important to remember that when you give something away, there are no conditions attached. Once it leaves, it belongs to the person you gave it to. If you don't fully understand this, you end up with items that technically moved locations, but are still taking up unnecessary space.

Something else that can help reduce a lot of volume is photographs and albums scanned into digital format. Once they are digital, more of the family can see them and they stop aging and getting ruined in a box. And just because an item hasn't been touched or used in years doesn't mean it has no value. Just because you haven't actually played with your baseball mitt from the second grade does not mean it is not important to you. The memory is still attached to the object whether you can see it or not, so it's not about whether it matters, it's about where it will go.

The Storage Unit Is the Only Destination With a Monthly Bill

There is a fifth option that families often try to go for when they are struggling with getting rid of things, and we always push back on this. A storage unit doesn't resolve anything. It only puts the sorting off and it adds another monthly bill that will likely be there for a very long time. A one-time sort through the house is permanent, you never have to worry about it again.

Short-term storage during a build is a little different, that's a pretty standard thing to do. Nicole McCann does this work professionally, and she told us on the show that her own family is using storage right now during their transition. The difference is that one is temporary and has an end date. If you rent a storage unit, set the date you will empty it before you sign the lease, and make sure every box inside it to one of the four destinations by that date. A unit with no end date is not storage or a solution. It's just another small house you're paying rent on.

Easy home delivery of things is part of why this is harder than it was many years ago. Things show up at the door every week and they don't get sorted as fast as they accumulate. If you want to get through this process easily, you have to stop things being delivered until you're settled in the ADU.

When Is 900 Square Feet the Wrong Answer for Your Family?

We build ADUs, so of course you expect us to tell you that a 900 square foot ADU works for everyone, and for most of the families we build for it does. But it's not right for everyone, and the way you know that is by using the test above.

If a walkthrough of the current house draws the conclusion that there's no way to downsize all your stuff by 80%, then a 900 square foot ADU isn't going to work. Some families are better off just building an addition to the main house or reconfiguring space they already have. We want you to know this upfront, not three months into a build and a garage nobody has started going through yet.

You also don't want to do things in the wrong order. If you think that sorting through the house is going to take a long time, start it with plenty of time before the build process. Building the ADU has a set schedule and timeframe. Sorting through a house does not, you never know for sure how long it's going to take.

Sort the House Before You Pour the Foundation

The decision in front of you was never whether 900 square feet is livable. Families live in it comfortably, and if you walk through a completed ADU you will see that it's comfortable. You have to decide whether you're able to get rid of one in ten items and send them to one of the four destinations we talked about in this article.

Make that call before you sign a build contract and the ADU becomes what it should be, which is a smaller house near people you love. Make it after, and the build calendar makes it for you.