Why Did a Family Walk Away From Their Modular ADU Deposit?

By Buz Artiano, BuildX | July 2026

Watch: Modular vs. Site-Built ADU Real Cost Comparison in Massachusetts

You have seen an ad for an ADU that starts at $120,000. When you compare that to a custom build, that seems really cheap. And if you are trying to build a place for a parent, a returning child, or rental income without draining all your savings, that $120,000 starts looking really good. Most people have the same worry that they are at risk of overpaying a custom builder for something you can get from a factory for half the price. You need to find out for sure before you sign anything or put down a deposit, because the modular sticker price and the total cost to install the modular are two very different things.

My name is Buz Artiano, founder of BuildX. We've built dozens of ADUs all over Massachusetts, but most of our projects have been on the South Shore and in Plymouth County. We handle all the design, permitting, and construction ourselves, which means we have priced out a lot of site prep, foundation, septic, and permitting to know exactly what that advertised price isn't showing you. We've also met with people who came to us after they'd already put a deposit down on a modular unit and the deal had gone sideways. One of those stories is why we recorded the video above and wrote this article.

What you need to know is that modular ADUs are not cheaper. They are just priced differently, and that's why they can make the sticker price look so low. The document that ruined the entire plan for this family is called a site-readiness invoice. And modular companies only send you that invoice once you've paid them a deposit. What you need to ask every company before you ever write a check is what the total price is, not the price of the structure itself that's being advertised.

Why Did That Family Walk Away From Their Deposit?

They came to us after spending about three months dealing with a prefab company. They had already paid a deposit, scheduled the delivery, and were just waiting for it to arrive. Then they got the site-readiness invoice. It listed the site prep, the foundation, the permits, the utility hookups, and the finish work, and it added another $180,000 on top of the $165,000 they had already agreed to. They really thought they were getting a great deal. But once they added everything up, the modular ADU would cost more than building a custom ADU with us from the start, so they lost their deposit and cancelled their order because they didn't want to spend a ton of money for a lesser product.

We are keeping this family anonymous on purpose. We are not going to name them, their town, or the modular company they were working with, for privacy reasons. But it doesn't matter who they were or who the company was. What's important is the pattern that repeats itself over and over. You are lured in by a low sticker price, you commit and put down real money, and the total price shows up after it's too late to get your money back.

What Is a Site Readiness Invoice, and Why Does It Land After You Pay?

A site-readiness invoice is the bill for everything the building itself doesn't include. It includes preparing the land, building a foundation for the box to sit on, pulling the permits, connecting the utilities, and finishing the interior so it's actually ready to be lived in. When a modular company quotes $120,000 or $150,000, they are selling you just the structure. That's for the walls and roof, just the basic shell, and sometimes some really basic interior finishes. The shell is just the enclosed box itself, not a finished, move-in-ready home. Your yard will have to be cleared, graded, and prepped. If you're on septic, you will probably have to expand or replace it. The unit also has to have a foundation to sit on, and you still have to pull all the permits from the town, and water, electric, and sometimes gas still have to be run to the building. None of that stuff is on the advertised sticker price.

Here's why they send you that site readiness invoice only after you've paid a deposit. The sticker price is basic and easy to advertise, so it leads the sale. The site work is the part that depends entirely on your specific property, and they never price it out until after you've committed to the unit. By the time you know how much it's really going to cost, you've been working with the company for three months and you've already paid the deposit. There's one more important thing that everybody needs to know. When the modular unit shows up, you pay for it in full before they will set it on your foundation. So a lot of times you pay for the entire thing right then and there on top of that surprise site readiness bill.

We do things exactly the opposite. Before we give anyone a price, we send a survey to map the property lines and elevation, we test the soil on septic properties, and we price out the foundation, utilities, and permitting for what your lot specifically requires. We do that first because you need a price you can count on, it doesn't count if it changes after the fact. The whole reason that site-readiness invoice shocks people so much is that it was never part of the price they agreed to. We make sure it is, no surprises.

How Does a $150,000 Module Become $350,000 to $450,000 Installed?

The numbers we are about to talk about are not a quote for that family's project or for yours. They're just the general estimates we work from in Massachusetts. The range your property fits in will depend on its slope, soil, access, and whether it's on town sewer or if it has a septic. That's the reason that two similar ADUs on two different lots can have very different site bills. That being said, here's how that advertised price turns into the total.

• Site prep to clear, grade, and get the lot ready: $10,000 to $30,000.
• Foundation: $25,000 to $50,000.
• Permits and engineering (which every ADU and every site requires): $5,000 to $15,000.
• Septic or sewer connection just depends on what your property needs: $20,000 to $50,000.
• Utility connections for water, electric, and possibly gas: $10,000 to $25,000.

Add all that to the sticker price of the modular ADU and you end up with a $150,000 module box that really costs $350,000 to $450,000 when it's installed. That's the same price range as a custom, site-built ADU, and actually sometimes even higher. The family in the video did all the math and got to the same conclusion, so they just left their deposit behind and cancelled the order.

Does a Modular Unit Actually Skip the Permits and Site Work?

People believe this because they are led to think that a modular unit is a shortcut around the most expensive and time consuming parts of building. That is absolutely not true. Before any ADU can be installed, modular or site-built, you need a site survey to map the property lines and elevation. On a septic lot you need a perc test, which measures how fast the soil drains and lets you know what septic system your property can support. You'll probably need engineering for the foundation and utilities. And you need permits from every town department like the board of health, the fire department, and the building department. A modular unit doesn't skip any of these steps. They just word things differently in their sales pitch. You are still building a house on your land, and your land and the people who issue your permits don't care whether the house shows up on a truck or if you build it from scratch.

Massachusetts now lets all homeowners add one ADU by right under the Affordable Homes Act, but by right does not mean permit-free or review-free. Every ADU still has to have all the same local permits and engineering. And if you have a septic system, it still has to get a full Title V review at the board of health before anything can be installed. You can check all of the requirements at mass.gov.

That's the whole reason the site-readiness invoice even exists. All the same site work is still there, a modular quote just leaves it off the sticker so the first number you see looks a lot more enticing.

When Does Modular Actually Make Sense?

Just because we build site-built ADUs doesn't mean we're necessarily always going to steer you toward that option. There are times where the modular options should be considered. If your property is somewhere that's very remote and qualified local builders are hard to reach, a factory-built unit that is delivered can solve some real problems. And if strict scheduling matters more to you than choosing your own finishes, layout, and details, modular gives you a kind of assembly-line certainty that you won't get from a custom build. Modular homes are not there to trick you. For the right property and the right needs, it is a legitimate way to build.

But just remember, they're not automatically cheaper. The family in the video didn't make a mistake just because they chose a modular home. The only mistake was not comparing totals side by side. If they had compared the modular total, which is the unit plus the full site-readiness invoice, to a custom quote up front, they would have seen the price ranges were about the same and they would have kept their deposit. The decision is not modular versus custom. You have to compare sticker price versus total price, and you can only do that by pricing the whole thing before you commit.

What to Get in Writing Before You Put Down a Deposit

The one thing you can do to effectively protect yourself is to make sure you get the full site-readiness cost in writing before you put down a deposit. Tell them you don't want the sticker price, you want the total, including site prep, foundation, permits, utilities, and finish work, priced for your specific property. Then compare that to a custom build quote, which is one price that includes permits to paint with no separate bill later. If you compare total to total, you won't be surprised by an invoice after you've handed over your money. We hope that all of this will keep you from repeating the mistake that cost one family their deposit.