what are prefab ADU costs

What Is The Cost Of A Prefab ADU

What is the Cost of a Prefab ADU?

A prefabricated ADU – commonly known as Prefab ADU – is built in a factory and arrives at your home 90% complete. Because they are built off-site, you don’t have to worry about construction noises and disruptions around your home.

The demand for ADUs or Backyard Dwellings is exploding across California because of the housing crisis.  It is the best solution for anyone looking for more space to house family members, remote work, or rental income opportunities.

Adding an ADU to your backyard is less expensive than upgrading to a whole new home or buying an investment property. It is essential to know how much it will cost you – from installing the foundation to receiving the keys to your new accessory dwelling unit.

How Much Does a Prefab ADU Cost?

Figuring out the cost of a Backyard Dwelling  can be very confusing. The price difference between companies for apparently similar ADUs can be shocking.

You are probably also looking to hire an ADU contractor – how can you tell who delivers the best overall value?

A prefab ADU will cost $216,000 to $438,000, depending on the size of the unit and the quality of the materials to be used.

Why the Price Varies from Company to Company

Several Prefab ADU companies use low-end materials – similar to those used for building trailer home units. They also employ techniques that focus on price instead of durability.

At ADU DIGGS, providing quality to our clients is one of our topmost priorities. We employ the latest and most stringent uniform building standards given by the U.S. Department of Housing and Urban Development (HUD) code.

Our goal is to create durable, beautifully designed homes, and give you the best ADU experience. We use high-end materials and deliver quality designs and finishes. This enhances the look and increases your home’s value. 

Once installed, your ADU DIGGS Backyard Dwelling  will be virtually indistinguishable from a site-built unit! You get a feeling of luxury and you can remodel or add on whenever you like.

ADU DIGGS Prefab Vs. Site-built ADUs: Which Cost More?

Generally speaking, a prefab ADU is less expensive to build because of the centralized process for labor and materials. It is also a more environmentally friendly building process by reducing construction material waste and employee commute time. However, when all costs are taken into account, a prefab ADU winds up being about the same price as a quality traditional site-built ADU. With our Prefab ADU, most of the work is done off-site, so you can enjoy serenity when your ADU DIGGS home is being put together. The situation is contrary to a stick-built accessory dwelling unit, where everything happens right outside your back door, creating noise, dirt, loss of privacy for 5 – 8 months… or more.. 

ADU DIGGS is quick and easy. We are in and out of your hair in under 6 weeks. 

You hit the easy button when you work with us to build your dream Prefab ADU home. All you have to do is just tell us what you want, and we’ll help you take care of the rest. That is peace of mind.

costs of prefab ADU

DIGGS Prefab ADU Costs Breakdown

We designed our pricing to simplify your decision-making process and make the cost of owning a Prefab ADU more predictable and a lot less scary. Here is a  detailed breakdown of all items that make up the costs quoted in our base price.

Certified Architect-designed Site Plan

We have pre-approved Prefab ADU models designed by one of the city’s best local and certified architects. Upon request, we can modify your DIGGS ADU, which will usually increase the design fee.

Exterior and Interior Elevations and Finishes

You can trust our certified architect to do a perfect job on the inside and out. We designed four architectural looks to blend with your unique home. Our Casita, Cottage, Modern Farmhouse, and Mid Century Modern will blend in as if they were always meant to be in your backyard. Choose from three different interior finish packages to complete your look. Everything is included except for a refrigerator and washer/dryer.


Permitting fees can vary depending on your Prefab unit’s design and square footage. They range between $9,000 – $13,000, with an additional $2,348 for covenant fees. Our base price includes all of the basic permit fees- you’ll only pay for unusual permit requirements. Our models are already pre-approved by the State, all we need is local approval for the site and utility connections. Don’t worry- we take care of the entire process on your behalf!


Our engineers ensure that your ADU home is structurally sound and energy efficient- in fact they are OVER engineered to ensure the highest quality and durability. We hired the best engineers and their fees are included in our base price. 

Licensed Contractor

With us, you don’t have to go through the hassle of looking for a contractor yourself, as we partner with Rhino Construction- an amazing company with impeccable expertise and reputation.   –. The work scope would include basic site prep, laying the foundation, utility connections, installation, stitching, and clean-up.

Transportation and Delivery

The distance between the ADU factory and your home will influence the cost of your prefab unit. Our base price includes up to 900 miles from our factory – which covers most of LA and Ventura County.

We did not include the cost of the installation method because that is highly dependent on your unique site. It is 50% less expensive to use a forklift vs using a crane to install your ADU. We designed our units with a forklift in mind and we even have a pending patent on the method!

Mechanical Systems

Our base price includes solar energy system, plumbing, electricity, central heating, and central air conditioning.

Check out our turnkey services here

Site-specific Costs 

Here are a few common site-specific situations to note before starting development for your Prefab ADU:

  • Site Grading and Soil Prep: some homes need additional grading and soil prep before a proper foundation can be installed.
  • Demolition: includes tearing down existing structures, concrete work, and even rebuilding and repair. These are all additional costs you can’t overlook
  • Electric Service: your electric service may need to be upgraded 

The prefab process allows us to predict the cost of your building, and that is half the battle. We have decades of construction and development experience and we have your back. Talk about peace of mind! 

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