Behind-the-scenes look on what it takes to prepare, receive and connect a prefab accessory dwelling unit.

How to buy a modular home without getting burnt

Sales people make buying a modular home sound easy. However,  there are more moving parts involved than it looks like on the picture. Even though you might think that your ADU is just a small home, it is still a home – with all the details that go into a regular house: utilities, foundation, coordination of subs, waste management etc.

Prefab and modular are often used interchangeably, but they can have slightly different meanings.
Prefab refers to any type of housing built in a factory and then transported to its permanent location. There the builder will connnect it to the foundation and utilities.
Modular, on the other hand, typically refers to a specific type of prefab construction. The building is constructed using a series of modular units that the factory produces. Then then units get shipped to its permanent address and assembled on-site into one house. Modular ADUs are typically standardized. The ADUs are built to a set of specific dimensions and specifications. They can be combined in various configurations to create different types of buildings.
So, all modular units are prefab, but not all prefab units are modular.
A modular ADU (accessory dwelling unit) is a type of housing that is built off-site in a factory and then transported to the location where it will be used. Modular ADUs are often smaller in size than a traditional single-family home. They are designed to be used as a secondary dwelling on a property, in the backyard or as an addition to an existing home. They can also be used as a primary residence when one rents out the main house or for relatives, vacation home, rental unit or office. They are also known as “prefab” or “factory-built” housing.
Modular ADUs have become a popular option for homeowners and developers due to their speed of construction.
Modular houses are manufactured in factories or plants that are specifically designed for the mass production of housing units. These factories can be located anywhere in the world, but are most commonly found in the United States, Canada, and Europe.
In the United States, modular home manufacturers can be found in many states. The highest concentration is on the East Coast, particularly in states like Pennsylvania, New York, and Ohio. These states have a long history of manufacturing modular homes. The factories have a well-established supply chain of materials and labor.
In Canada, the provinces of Ontario and British Columbia are homes to modular home manufacturers. In Europe, the modular housing industry is well developed in Germany, Sweden and the UK. Eastern Europe is quickly catching up.
buying a modular home

How to buy a modular home without getting burnt

There is a number of things you need to be ready for.

First, construction is messy. It will be a hard hat zone for a while, even though this period is typically not longer than a month. Unless of course it rains just as you are ready to pour concrete. 

Second, site work is done by humans. Often coming from different background than yours. If there is something that causes you concern, please speak to their supervisor. More often than not, it is a matter of simple misunderstanding or cultural differences.

Considering current labor shortage in construction, we value each and every sub or crew member that comes to work on your property. Stay assured, we are all here to make you happy with your new home.

Looking for some control panel? We have mentioned the milestones in great detail in our previous post.

What is needed to make sure you could actually live in your modular home?

What your contractor is planning to do

Foundation for a modular ADU

Trenching for utilities. ADUs are built in backyards where people have done work previously. We often deal with existing drainage or irrigation lines. If it were a new development, we would use equipment. With limited backyard access or lots of pipes underground, we often have to dig manually.

forms for foundation

Work on foundation starts with rebars. It does not look pretty, but this is what calls for the first inspection with the local jurisdiction. The city is checking if we are sticking to the plans and if we are where we should be – with correct setbacks and distance from the main house. 

poured foundation

Forms are ready, let us pour. Probably, the loudest part of this type of construction. It takes half a day, but leaves your home grounded for years to come. The forms will come off in the next couple of days, and we are ready for the unit. This is most often also the time for site clean up and any extra soil haul off.

Ready for the unit? We need one more permit!

Next phase is more exciting.

poured foundation for modular ADU

Now that the foundation is ready, we have to wait for one more permit. Traffic control. Remember, your unit arrives on a vehicle. Then gets “craned in”. This typically means we need to stop the traffic on your street. So we apply to the city for the permit, and only when we get the green light – bring the unit in.

modular ADU on a crane

This is the part that regularly gets featured in social media, and seems the most exciting not only for you, but for your neighbors too. The crane is hard to miss, and “landing” a whole house is a sight to behold. Feels like magic every time, but for your construction team just one day in many.

For the construction crew, work is not complete yet. They need to build you the deck so that your could safely step in and out of the new house. All utilities need to be connected. Everything inside the unit needs to be checked for any transportation damages. 

Ask before you buy: quality control

Before you sign your contract with a modular builder – ask one question: How does quality control work? Who is it exactly who makes sure that you receive the unit that you have ordered in the quality that you expect? Who checks the quality of cabinet doors, the way the tile is done and all these little details that make up the impression of a well built house?

It is pretty much impossible to return a house once it is landed in your backyard.

Backyard home

Once the utilities are connected and the deck completed, then your contractor will call for the inspection. At this point the unit is completely functional. Washer and dryer, dishwasher and water heater, air conditioning unit – are all in working order. Time for the occupancy permit. And for some celebration. 


Building a modular ADU is not the same as building a modular main house.

If you are building a main house, the process is completely different from the ADU permitting.

There are design reviews, planning applications and only then building permit applications.


There are no State mandated 60 days for processing the permit. It can easily last a year. You have to go through planning approval first, only then through building approval process.


Your contract should include who is responsible for providing permit documentation.

You should not be paying for production until you see at least the State permit. Ideally, initial comments from the city/County.

Our feasibility reports are trusted by many modular builders.

Not sure if a modular home is for you?

We have more ways to build in our portfolio. Look at the image below – can you tell, if it is a custom built home, a modular one or built out of a home kit of prefabricated elements? There are different construction types of prefab ADUs

Tiny Home Designed in Finland

Ask before you pay: warranty

A modular home has been manufactured off site, this means the factory has issued the warranty. Make sure you know who to call in case of any questions.

Leave a Reply