To find a good ADU contractor in California, check the license on the CSLB website, ask to see ADUs they’ve finished and permitted in your city, and compare at least three itemized bids. Never pay more than $1,000 or 10% up front, whichever is less. And pick the lot before the builder: the property decides most of the cost.
I’m a realtor, not a builder. But my buyers bring me contractor bids on almost every deal, and I’ve seen what separates a smooth build from a stalled one. Here’s the vetting checklist I give them.
Start With the Lot, Not the Builder
Most people search “ADU builder near me” first. If you don’t own the property yet, that’s backwards. Alley access, utility distance, lot shape and the main house’s panel decide a big part of the bid before a contractor ever sees it. I cover what to look for in What Makes a Property Have ADU Potential and why it matters in ADU Realtor vs a Typical Agent.
With my buyers, the architect and builder conversations happen during escrow. An ADU architect prepares a feasibility report while inspections are still open, so you can walk away if the numbers don’t work.
The 10-Point ADU Contractor Checklist
- Active license. Look up the license number on the CSLB website. For a full ADU, you want a Class B general building contractor. Check that the name on the bid matches the license.
- Bond and insurance. The CSLB lookup shows the contractor bond and workers’ comp status. Ask for a certificate of general liability insurance too.
- Complaints and discipline. The same lookup shows any CSLB actions. A few online bad reviews are normal; a license suspension is not.
- Finished ADUs in your city. Ask for addresses of permitted, completed ADUs in your city, not just photos. Each city’s plan checkers work differently, and local experience saves weeks.
- References from recent clients. Ask about schedule, change orders and how problems were handled.
- Itemized bid. Line items for foundation, framing, utilities, electrical panel, solar, permits and finishes. A one-line price is a red flag.
- Legal payment schedule. Down payment capped at $1,000 or 10%, whichever is less, and progress payments tied to completed work. See CSLB’s ADU payment warning.
- Written change-order process. Every change priced and signed before work starts.
- Lien releases. Conditional and unconditional lien releases from subs and suppliers with each payment, using the forms in Civil Code § 8132 and the sections after it.
- Realistic schedule. A clear timeline for plans, permits, construction and utility hookups. Anyone promising a fully permitted detached ADU in three months is guessing.
CSLB also has a printable prescreening checklist and a sample home improvement contract you can compare bids against.
How to Compare ADU Bids
The lowest bid is usually the one leaving the most out. Line up every bid in the same format and check what each one includes:
| Item | Often left out of low bids |
|---|---|
| Plans, engineering, Title 24 report | Yes |
| City permit, school and impact fees | Yes |
| Sewer, water, gas and electric runs to the street | Yes |
| Main panel upgrade or subpanel | Yes |
| Solar (required on new detached ADUs) | Sometimes |
| Appliances, flooring and finish allowances | Allowances set too low |
| Landscaping, fencing, cleanup | Yes |
For reference, the 850-square-foot 2-bed, 2-bath I’m working on is about $300,000 all-in. If a bid comes in far below about $350 per square foot for a detached unit in OC, find out what’s missing. My full cost breakdown is in ADU Cost in Orange County and LA.
Design-Build vs Architect Plus Contractor
- Design-build firm: one company handles plans, permits and construction. One point of contact and a price earlier in the process, but fewer competing bids.
- Architect, then bid it out: you own the plans and can get three apples-to-apples bids. It takes longer, and you coordinate more.
- Prefab company: fixed unit price, but you may still need a local contractor for the foundation and utilities.
For a first ADU, design-build is usually simpler. For a second or third, many investors bid it out. The steps either way are in ADU Construction Process: Steps and Timeline.
Red Flags
- Asks for a large deposit or payment for permits before any work.
- Suggests skipping permits or “legalizing later.” Unpermitted units hurt appraisals and resale. See Does an Unpermitted ADU Add Value?
- License name doesn’t match the company on the bid.
- No completed ADUs in your city they can point to.
- Won’t put the schedule or change-order process in writing.
Line Up the Financing Before You Sign
Construction lenders review the contractor too. Many want a licensed contractor with ADU experience and a fixed-price contract before they’ll fund draws. Compare your options in How to Finance an ADU and see a real draw schedule in How ADU Construction Loans Work.
Frequently Asked Questions
What license does an ADU contractor need in California?
A Class B general building contractor license is standard for a full ADU. Verify it, along with the bond and insurance, on the CSLB website.
How much should I pay an ADU contractor up front?
No more than $1,000 or 10% of the contract price, whichever is less. Later payments should match work completed.
How many ADU bids should I get?
At least three, all itemized in the same format, so you can see what each one includes and leaves out.
Should I hire a contractor before I buy the property?
Talk to one during escrow, not before. Find the right lot first, then get a feasibility review and rough bid while you can still cancel.
Buy the Lot That Makes the Bid Work
I help buyers find properties where an ADU actually pencils, then connect them with ADU professionals during escrow so the build plan is in place before closing.
👉 Book a buyer ADU consult call to go through your options with Dylan
Prefer to talk now? Call Dylan Serna, ADU Realtor at 714-860-2868.
Dylan Serna | The ADU Realtor | eXp Realty | DRE #02217359
This post is general information, not legal or construction advice. Verify every contractor’s license and insurance directly with CSLB.
