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ADU Cost in California

Author

the Team

Published

September 29, 2026

How Much Does an ADU Cost in California in 2026?

Building an ADU in California can cost anywhere from approximately $150,000 to $400,000 or more, depending on the size, location, construction method, site conditions, finishes, and what is included in the project.

The biggest mistake homeowners make is looking only at the advertised price of the home. An ADU project can also involve design, engineering, permits, foundation, site preparation, utilities, delivery, installation, and landscaping.

So when comparing ADU prices, it's important to look at the total project cost, not just the cost of the structure.


Manufactured ADU

What Does an ADU Cost in California?

There is no single price for an ADU because every property is different.
As a general 2026 planning range, California ADUs can fall into these broad categories:

garage

Garage Conversion

~$60,000–$150,000+

stick built

Detached Site-built ADU

~$150,000–$400,000+

Manufactured ADU

Manufactured ADU

Varies by model, site, and scope

These are planning ranges rather than quotes. A difficult property, premium finishes, extensive utility work, or complex foundation can increase the total significantly.
For this reason, cost per square foot should not be the only number you use when comparing ADUs.

What Is Included in the Cost of an ADU?

A complete ADU project may include:

- Architectural plans and design
- Engineering
- Permits and plan review
- Foundation
- Site preparation and excavation
- ADU construction
- Delivery and installation
- Water, sewer and electrical connections
- Interior finishes and appliances
- Landscaping and hardscape

Some builders include several of these items in their advertised price. Others charge them separately.

Always ask what is included before comparing two ADU quotes.

How Much Does a Manufactured ADU Cost?

Manufactured ADUs can have a different cost structure because much of the home is constructed in a controlled factory environment before being delivered to the property.

Backyard Home Company's published January 2025 pricing provides an example of this approach. Its manufactured housing plans ranged from approximately $172,900 for a one-bedroom, one-bath model to $279,900 for a 1,188-square-foot model. These are historical published prices, not guaranteed 2026 pricing.

TBHC's published cost breakdown included the manufactured home, plans, delivery, site preparation, excavation, installation, utility connections, and foundation, while landscaping, hardscape, septic and crane costs could be additional when required.

This illustrates an important point:
The price of the manufactured home is not necessarily the total cost of the ADU project.

What Factors Affect ADU Cost?

Several factors can change the final price of an ADU.

Size

Larger ADUs generally require more materials and construction, but smaller ADUs don't necessarily cost proportionally less because kitchens, bathrooms, utilities, and other systems are still required.

Property Conditions

Your lot can have a major impact on cost.

- Factors such as:
- Sloped terrain
- Difficult access
- Soil conditions
- Long utility runs
- Existing structures
- Drainage
- Excavation

can all increase the project budget.

Foundation

A detached ADU needs an appropriate foundation system.

For manufactured ADUs, the foundation is engineered specifically for the home and site. TBHC's installation process includes foundation construction, placement of the manufactured sections, utility connections and final inspection.

Finishes

Cabinetry, countertops, flooring, appliances, fixtures and other selections can also affect the final price.

Are Manufactured ADUs Less Expensive?

They can be, depending on the property and project scope.

Factory construction can provide efficiencies through controlled production, purchasing and reduced on-site construction.

Backyard Home Company's documentation identifies factors such as factory purchasing power, reduced exposure to weather delays and factory-controlled construction as potential cost advantages.

However, manufactured does not mean there are no site costs.

The home still needs to be delivered, installed, connected to utilities and placed on an appropriate foundation.

The best comparison is therefore the total cost of a manufactured ADU project versus the total cost of a site-built project.

Don't Forget Permits, Fees and Site Work

California ADU costs can also be affected by permitting and state regulations.

One important consideration is the 750-square-foot threshold. Under California's current ADU rules, ADUs of 750 square feet or less are exempt from certain local development impact fees, while larger ADUs may be subject to proportional fees.

Other project costs can include:

- Building permits
- Engineering
- Utility connections
- Foundation work
- Excavation
- Delivery
- Installation

This is why getting a property-specific evaluation is more useful than relying on a statewide average.

1. Your property and available space
2. The ADU size and floor plan
3. Access and site conditions
4. Utility connections
5. Foundation requirements
6. Engineering and permitting
7.Construction method
8. What is included and excluded from the quote

A detailed scope makes it much easier to compare proposals and avoid unexpected costs later.

How to Get an Accurate ADU Cost Estimate

Before starting your project, make sure your builder evaluates:

Planning an ADU in California?

The cost of an ADU depends on much more than the price of the home itself.

the Backyard Home Company helps California homeowners with manufactured ADUs from planning and engineering through permitting, foundation, delivery and installation.

If you're considering adding a backyard home to your property, we can help you understand the options and the costs involved.

Ready to Explore Your ADU Options?
Schedule a free consultation with Backyard Home Company.

Free Consultation

Got Questions?

We offer manufactured ADUs in multiple floor plans, sizes, and bedroom configurations designed for California residential properties.

Yes. Depending on the selected model, homeowners can choose from available finishes, colors, fixtures, and upgrade options.

Yes. The Backyard Home Company manages permitting, engineering, planning, and project coordination as part of its complete design-build process.

Yes. Every project includes professionally engineered foundation solutions designed specifically for the selected home and site conditions.

Visit our All Floor Plans page or Compare Models page to see available layouts side by side.

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