ADU companies in California: how to compare builders

We don't rank ADU companies, and this guide doesn't recommend any. Companies named below appear only as sources for published prices or as cautionary cases. If you want a starting list, our directory of verified ADU builders in San Diego includes only companies matched to an active state B license with a bond on file. That's a floor, not an endorsement.

Types of ADU companies

Design-build ADU companies

A design-build company owns the whole job. That cuts down on finger-pointing between a designer and a builder, and it usually means one number for the whole project. The trade-off is that you're choosing the builder before the design is finished, so you have less leverage to compare construction prices. Ask how the price can change between the design phase and the build contract, and what you keep if you walk away after design: you should get the plans you paid for.

Prefab ADU companies

A prefab company's headline price is often the unit alone. A modular unit must carry a state insignia of approval, but the foundation, trenching, crane and hookups on your lot are permitted and inspected by your city like any other job. Our guide to prefab ADUs in California covers the approvals and the costs outside the box price.

Custom ADU builder or general contractor

If you want a custom ADU, the usual route is a designer or architect first, then bids from general contractors on finished plans. California's architect law lets people without an architect's license prepare plans for conventional wood-frame single-family homes of up to two stories and the structures that go with them. For any part that departs from conventional framing, the building official must require plans or calculations stamped by a licensed architect or engineer. Bidding the same complete plans to several contractors gives you the cleanest price comparison you can get. Pre-approved plans are another shortcut; see pre-approved ADU plans in San Diego.

Checking an ADU construction company's license

The Contractors State License Board says B, General Building contractors can build or install ADUs, and a C-47 manufactured housing contractor can install an ADU that's a manufactured home. A B license covers projects that need at least two unrelated trades, which describes every ADU. A B-2 Residential Remodeling license is limited to existing homes, with no new electrical or plumbing systems, so it isn't enough for a new ADU.

Look the company up on the board's Instant License Check, or check a contractor's license on our site for San Diego County. Then confirm:

The name check matters most with companies that sell design, financing or a factory unit but hand the build to someone else. The license that counts belongs to whoever signs your construction contract. The board advises asking for the contractor's pocket license and photo ID, and confirming that the salesperson in your kitchen works for that licensee.

How to compare ADU companies

Bids for the same ADU can differ by tens of thousands of dollars because companies draw the line around “included” in different places. The state board recommends getting at least three bids and treats a bid far below the others as a red flag. Put each bid into one table like this before you compare totals:

One San Diego builder's published sitework costs show why the lines matter: a separate SDG&E meter at $10,500 to $15,000, a 2-to-4-foot slope at $10,000 to $20,000, retaining walls at $20,000 to $30,000 or more, a sewer pump around $5,000 and fire sprinklers at $5,000 to $10,000. A bid that leaves out three of those can look $50,000 cheaper and end up the same price or more.

What ADU companies publish on price

There's no official price list for ADUs. The best public numbers are what builders publish, and each one counts differently. These are sources, not recommendations.

Sources: Snap ADU's published prices, Lars Remodel's cost guide and Abodu's published pricing. For a fuller breakdown, see what an ADU costs in San Diego or run your numbers in the ADU cost calculator.

Deposits, contracts and payment schedules

The state treats ADU construction as a home improvement project, and that protects you no matter which type of company you hire.

• Deposit. A contractor can't take more than $1,000 or 10% of the price, whichever is less, and can't collect payment ahead of the work done.
• Written contract. The law requires the license number, the price, a description of the work and materials, start and finish dates, and a schedule of progress payments tied to specific work.
• Subcontractor list. Since 2026, a home improvement contractor must give you the names, contact details and license numbers of subcontractors on request.

Design fees are where companies most often ask for real money early. Pay a designer or architect for design work they've actually delivered, and get the plans. Be wary of a construction contract that bundles “design and permits” into a large first payment. Our guide on how to hire an ADU contractor walks through the board's sample payment schedule and how to collect lien releases.

When ADU companies fail

• Multitaskr (Chula Vista) closed in 2024. San Diego homeowners were left with loans in their names for unfinished ADUs. The state revoked its license in 2025.
• Anchored Tiny Homes (Fair Oaks) shut down in August 2024, leaving hundreds of customers with unbuilt units.
• Nonna Homes (Rancho Cordova) had its bond canceled and its license suspended in January 2026.

A contractor's $25,000 bond is shared by every claim against the company, which is little against an ADU contract worth hundreds of thousands. Your real protection is keeping payments behind the work, choosing your own lender, and noticing early warnings: crews that stop showing up, missed milestones, or requests to pay ahead “to lock in materials.”

Questions to ask every company

• “Which company signs the construction contract, and what's its license number?” Check that it's an active B.
• “Do you build with your own crews or subcontract the work?” Ask for the subcontractor list.
• “What does the price exclude?” Get the exclusions in writing: fees, trenching distance, meter, sprinklers, demolition.
• “What are the finish allowances?” Dollar amounts, not “standard.”
• “Who pulls the permit?” It should be the contractor, not you as owner-builder.
• “How many ADUs have you finished in my city, and can I talk to those owners?” Ask for addresses you can drive by.
• “Is every payment tied to a finished milestone?” Anything else is a reason to keep looking.

Before you sign, make sure the project fits the rules for your lot; see California ADU laws and ADU financing if you're borrowing.

Common questions