As additional dwelling units (ADUs) have become more popular, manufacturers around the world have started to produce prefab structures designed to serve the same purpose. Many of these come with enticing price points that are, at face value, significantly lower than the cost of building an ADU from scratch. 

However, those advertised prices don’t tell the whole story. Prefab structures also have significant downsides worth taking into consideration when deciding whether or not to buy one. In the following article, we get into some of the most important of those considerations to help you understand the true cost and realities of buying a prefab.

There’s More To the Cost of an ADU Than the Sticker Price

When you search for “prefab ADU” online, you’ll find many options with attractive prices that may pique your interest. If you’ve already spoken to an ADU contractor, these prices are likely lower than what you’ve been quoted – making the prefab route seem like a more cost-effective option.

However, there are many more costs that go into building a complete, fully-functional ADU than simply the structure itself. While the quote you get from an ADU builder typically reflects the total cost of a finished structure, the price you find online for a prefab doesn’t. Some of the additional costs include:

  • Shipping: Getting a prefab structure from the factory to your site can add thousands of dollars to your cost immediately. The more assembled the prefab you buy is, the more it will cost to ship.
  • Installation: No matter how complete the structure you buy is, it still needs to be installed at the site. That requires construction labor that doesn’t come cheap. Installing a prefab ADU will add several thousand more dollars to the project.
  • Finishing: Most of the prefab structures you’ll find online are essentially shells of a building, and don’t include much, if any, interior finishes. That means you’ll need to buy and install things like flooring, counters, and sometimes even walls, windows, and doors. These finishing materials are often some of the most expensive components of an ADU build when added together. Installing them requires more costly labor as well.
  • Site work: Building an ADU, whether from scratch or using a prefab, requires site preparation. This includes things such as grading, building a foundation, and laying down electrical, water, and sewer or septic lines. Prepping a site for a structure is another expensive part of the building process that isn’t reflected in the advertised price online.
  • Infrastructure: To serve as an actual ADU, your structure must provide an independent living space. That means including a bathroom and kitchen, which both require plumbing. It also means wiring your structure for electricity and sometimes internet connectivity. Adding this infrastructure is a considerable expense and is often cheaper to do before the structure is fully built.

Installing a Prefab Can Require Much More Site Work

When you work with an ADU builder to design a structure from the ground up, they will take the properties of your site into consideration. This allows them to find the most cost-effective way to prepare your site for installation.

When you buy a prefab ADU, on the other hand, a builder will have to work the site around the existing structure. This can often be more labor-intensive and therefore, expensive, than when your site and the structure are considered together from the beginning.

Furthermore, a custom-built ADU will utilize your site to support your structure in the best way possible. This helps ensure that it is stable and durable. A prefab structure is often only a “pretty good” fit at best.

an excavator doing site work for a prefab adu

Prefab Structures Often Use Cheaper Materials

Prefab ADUs often have lower price points because they use cheaper materials to cut down on costs. Since you typically buy these structures over the internet, you won’t find out what the quality of materials are until your unit arrives.

Cheaper materials may look similar to the higher-quality ones an ADU contractor is likely to use, but they are often inferior in several different ways. They aren’t likely to be as durable, and therefore will require more upkeep or need replacing after a while. 

They may also not function as well as higher-quality materials. Cheaper windows, for example, don’t offer the same insulation as better ones. Lower-quality doors may not fit exactly right. Poor-quality roofs can be prone to leaking and can allow water to damage the rest of your structure.

You Have To Take What You Get With a Prefab Structure

Working with an ADU builder gives you the opportunity to customize your building to suit your needs and preferences. During the design stage, you can often change the placement of interior walls or amenities to your liking.

With a prefab ADU, you’re stuck with what comes from the factory unless you want to add the time, effort, and expense of making changes to the existing structure. You’ll have to live with the choices of whoever designed the structure. This means you’re likely to end up with something that’s close to what you want, but not exactly what you want. When you’re spending the money to build an ADU, settling for something rather than getting what you really want can lead to years of disappointment.

For Most People, a Custom-Built ADU Is The Best Choice

It’s possible that going with a prefab ADU can save you a little money over working with a builder. But that’s not even always the case. When you add up all the additional costs of installing and finishing your in-law suite, it can easily come out to be the more expensive option. If the factory uses cheap materials for your unit, it may not be long before you have to spend even more to fix or replace things.

When you work with an experienced, reputable ADU contractor, you can get exactly what you want and be sure of the quality of the materials and craftsmanship. At Feel Love Homes, we are a full-service ADU contractor, which means we take care of more than just designing and building your unit. We also assist our clients with time-consuming and often confusing or frustrating parts of the process such as getting the right permits, ensuring compliance with local codes and regulations, and even finding financing for your build.

Advertisements for prefab ADUs can draw you in with attractive initial prices, while not taking into account the actual costs and realities of getting a project to completion. The prices and photos you see on the internet often deliver far less than they promise at a much higher price than advertised.