What Should You Ask a Modular ADU Company Before Signing a Contract?

By Buz Artiano, BuildX | April 2026

Watch: The Hidden Costs of Modular ADUs (Before You Sign Anything)

Suppose you found a modular ADU company with a price that looks too good to pass up. The website says $120,000 to $150,000, the drawings look nice, and the salesman has answers to all your questions. But something doesn't feel right about it. You don't really know what questions to ask, and you do not want to sign a contract and then find out that the actual cost is double what they told you it would be. Your smartest instinct is to hesitate right now.

My name is Buz Artiano, and we have built dozens of ADU projects across the state of Massachusetts at BuildX, with most of our builds on the South Shore and Plymouth County. We can handle the design, all the permits, and construction in one place, and we work within the by-right ADU rules for Massachusetts, septic regulations and the city zoning requirements every day.

We are not telling you that buying a modular ADU is always the wrong choice. We just want to give you all the exact questions that make the difference between an honest modular company and one that is hiding the real cost. If the company you are talking to can answer every question on this list clearly and in writing, they may be a good choice. But if they can't, you should know that before you sign anything. We have also taken calls from families who signed a contract with a modular company and later found out that the price they advertised actually left out things. That situation is why this article exists.

What Is the Single Most Important Question to Ask Before Signing?

Be sure to ask for a complete written list of the cost between the advertised price and an ADU that is ready to move into on your property. That one request will give you more information about a modular company than anything else.

When a modular company gives you a price of $120,000 to $150,000, that price will only include a manufactured structure which is the walls, the roof, and a simple shell with a few interior finishes. That price almost never includes all the work necessary for you to be able to live in the structure on your property. The difference between the price you have been quoted and the real installed cost is where families get a surprise, and these questions are being asked to show this difference.

We have seen that this difference can add $100,000 to $200,000 or more to the final cost of the module. When you add it all up, a $150,000 module then will cost $350,000 to $450,000 when it is installed. That is the same price range, or maybe sometimes higher, than an ADU that is custom-built and constructed on your property.

Does Your Price Include Site Preparation and Foundation?

You can't use your backyard for a parking lot. Before any ADU, whether it is a modular or one built on the property, can be set down, the ground has to be cleared, leveled and prepared. So be sure to ask the modular company if the necessary preparation of the site will be included in their price, and get the answer in writing.

Site preparation on average costs $10,000 to $30,000 and that cost depends on the slope of your lot, how many trees there are, if equipment can easily get in and the soil conditions. To put in a foundation will cost another $25,000 to $50,000 so these two things by themselves can add $35,000 to $80,000 to the cost of a modular home that you thought covered everything.

A modular unit does not skip any of these processes, but it does change the wording. You are still building a house and the foundation, grading, and site work on the property are exactly the same whether the walls are brought on a truck or get built on site. If your quote from a modular company doesn't have those costs included then that advertised price is not the real price at all.

Are Permits, Engineering, and Septic Included?

Every ADU in Massachusetts has to have permits and every property has to have engineering done. These two things are not optional, and they also are not without a cost. Be sure to ask the modular company if the quote they gave you includes all the costs of the permits, structural engineering, and a site survey that maps property lines and elevation.

The required permits and engineering will usually be $5,000 to $15,000. But if your property uses a septic system, Title V will decide what you have to do, and a newer or bigger septic system could cost $20,000 to $50,000. The connection for utilities, water, electric and possibly gas can add up to another $10,000 to $25,000 to the cost. These are costs that are there no matter what kind of structure is built. A modular unit doesn't get rid of them, it just takes them off of your original price quote.

Before you put any kind of ADU or modular on your lot, you will need to have a site survey done, and a perc test if you are using a septic system. Perc is short for percolation test, which measures how fast water drains down through your soil to decide the maximum capacity of your septic system. You must also have permits from the board of health, fire department, and building department. Ask the modular company who handles each of these, how much they will cost, and if those costs are included in their price quote.

What Finishes Are Included, and Is the Interior Move-In Ready?

Here is where the details will make the most difference. Many modular ADUs are sold as just a shell. When the structure gets there you will still need to buy flooring, cabinets, countertops, fixtures, and paint. So make sure you ask specifically: when this unit is delivered to my property, what work still has to be done before someone can live in it?

One question that reveals the answer faster than any other is this: does your price include the finished paint for the inside? Most modular units come with just a primer on the interior walls, which makes you wonder if they cannot even include paint, what else might be missing.

Even when modular companies do include finishes, they are many times low-quality materials. We are talking cheap laminate counters, trim that isn't natural wood, and ceilings as low as 6 feet 7 inches, sold as finishes in what will be your family's new home. So ask to see the list of finishes that will actually be installed, whether the trim is solid wood or MDF. Also ask about the height of the ceilings. These are not considered luxury upgrades. They are basic quality items that will either make your space feel like a home or just a temporary unit.

We always put nine-foot ceilings in our ADUs because we have seen what happens when families move into homes that have low ceilings. The room feels smaller than it is, the natural light coming in through the windows doesn't keep it bright enough, and within six months the family is talking about how the space feels smaller than it really is. The height of a ceiling isn't a cosmetic choice. It is a choice that determines how livable that home is and affects every day that a person spends in that space. When a modular company lists 6-foot-7 ceilings, that just means that it was built to ship more economically and not necessarily for the comfort of the people who will live in it.

What Are the Payment Terms, and When Is Full Payment Due?

This question catches most families by surprise. You need to ask the modular company: when do I pay for the unit, and what will happen if conditions of my site change after I have paid?

With most modular companies, you must pay for the unit completely before it will ever be put on the foundation, which means you will be giving the company $120,000 to $165,000 before the module has touched your property, before the site has been completely prepared, and before you will know what the final cost is going to actually be. That's a huge commitment of money and you will have no clout if problems come up during installation.

We have had families talk to us after they wasted three months working with a prefab company. They had put down a deposit, scheduled the delivery, and then got a separate invoice for getting the site ready: site prep, foundation, permits, utility hookups, and finish work that was another $180,000 on top of the $165,000 price of the unit itself. They thought they were getting a good deal but instead they ended up losing their deposit because the total cost was more than building an on-site ADU from the beginning.

It is important to get the payment schedule in writing. Find out what happens to your deposit if the total cost goes over your budget and ask if they will make provisions to change the order if the conditions of the site need extra work. If the company can't give you clear, written answers to all these questions, then that tells you everything you need to know.

Do You Have a Local Project Manager, and What Is Your Actual Service Area?

A modular ADU is not like a piece of furniture that just gets dropped off. It has to have coordinated installation, inspections, connections for utilities in place and follow-up work. So ask the company who will manage the project when it gets to the site and where that person's office is located.

Some modular companies do business in multiple states. Ask yourself if it is possible that the same company can work on a project in Maine and also handle one in Chatham at the same time. That is just not a realistic option. A company that works across a large region like that can't give the on-site presence your project requires.

Massachusetts has some of the most difficult to understand building codes in the United States. Your builder needs to understand the energy code, the stretch code, and all the Title V septic rules. Ask the modular company if they have a team of local people that deal with inspections, compliance with all codes, and municipal coordination in your particular town. And if they say they have someone that flies in or that they are subcontracting everything locally, you are basically in charge of your own construction project instead of buying a finished home.

Is a Modular ADU Ever the Right Choice?

We build custom ADUs on your site so naturally we think those are your best option. But we also believe that an informed buyer that has all the information will make a better decision than an uninformed one, no matter which direction they decide to go.

If a modular company can answer every question that we've talked about in this article in a way you can understand and in writing, and with a fully itemized total cost that includes site prep, foundation, permits, septic, utilities, and finished interiors, then their product should be on your shortlist. The issue isn't the modular idea itself. The real problem is that the pricing can make a $350,000 project seem like only a $150,000 purchase.

If you are comparing builders and the modular company gives you just one line-item price while another builder gives you a price that includes everything from permits to paint and a livable finished home, you can't compare those two numbers until you put both of them into the same format. These questions are what gets you there.

Your Shortlist Starts with the Right Questions

The questions in this article are not meant to eliminate modular companies. We want you to ask them to eliminate unpleasant surprises. An honest builder, modular or custom, will welcome these questions because they have nothing to hide. The companies that struggle with them are the ones that are using a gap between their advertised price and your final cost.

Ask every question and get each answer in writing. Then compare the real numbers.