Your ADU builder will shape your budget, your timeline and how much you enjoy the process. Southern California has thousands of contractors who will say yes to an ADU. Far fewer have permitted and built dozens of them. Use this checklist to find the right one.
Step 1: Decide on a delivery model
- Design-build firm: one company handles design, engineering, permits and construction. You get a single point of responsibility, and it's often faster. Make sure design fees and the construction contract are clearly separated.
- Architect or designer plus a general contractor: more design control, and you can bid the construction. You coordinate more.
- Prefab company plus a site contractor: see our prefab ADU guide for the split-responsibility risk.
- Owner-builder: you can legally pull permits as an owner-builder in California. You take on the contractor's responsibilities, including employer obligations if you hire workers, and you face real risk if you sell soon after. Most people should hire a licensed contractor.
Step 2: The 15-point checklist
- An active CSLB license. Look it up at cslb.ca.gov. For ADUs, the typical classification is B (General Building). Make sure the name and address match. Our "CSLB License Verified" badge means we matched the business to a current license record, but check it yourself anyway.
- Workers' compensation and liability insurance. CSLB shows workers' comp status. Ask for a certificate of liability insurance naming you.
- Bond. Every license has a contractor's bond. It's small, so don't treat it as protection.
- ADU-specific experience. Ask how many ADUs they have permitted and finished in the last two years, and in your city.
- References and addresses. Ask to see a finished ADU and talk to a past client.
- Reviews. Read recent Google reviews for patterns about communication, schedule and change orders, not just stars. We rank by rating weighted by review count.
- A written, itemized bid that covers site work, utilities and allowances. Compare bids line by line.
- A clear scope of who handles design, engineering, the Title 24 report, permits, utility applications and final.
- A down payment within the legal limit. For home improvement contracts, California generally limits the down payment to 10% of the contract price or $1,000, whichever is less. Be wary of anyone asking for more up front.
- A progress-payment schedule tied to completed work, never ahead of it.
- A written change-order process with prices agreed before the work is done.
- A schedule with start and substantial-completion dates.
- Warranty terms for workmanship and manufacturer warranties.
- Lien protection. Understand California mechanics' liens. Ask for conditional and unconditional lien releases from subcontractors and suppliers as you pay.
- Communication. Who's your day-to-day contact? How often will you get updates?
Red flags
- Asking for large cash payments up front.
- Pressure to sign the same day.
- Suggesting you skip permits "to save time."
- A license that doesn't match the company name, or a license that's expired or suspended.
- A vague bid with lots of "TBD" lines.
- Guaranteeing a specific grant. CalHFA warns that anyone claiming they can get you its ADU grant is running a scam, and that grant is closed. See our financing page.
Questions to ask in the interview
- What's the most common surprise on ADUs in my city?
- How do you handle sewer and electrical panel issues?
- Can I use a pre-approved plan with you?
- How long did your last three permits take?
- Who supervises the job site daily?
How we rank builders
Our directory lists builders that Google Maps shows for "ADU builder" and "ADU contractor" searches in each city. We remove off-topic businesses, such as specialty trades and suppliers. We rank by Google rating weighted by review count. Featured spots are clearly labeled and don't change organic rankings.
Use filters to narrow your list
On each city page you can filter by:
- ADU specialist
- design-build
- garage conversions
- prefab or modular
- remodels and additions
- CSLB verified
- top rated
Start with ADU builders by city, or read about ADU types first.
Frequently asked questions
What license does an ADU builder need in California?
A contractor building an ADU typically needs a CSLB B (General Building) license. Verify any license at cslb.ca.gov.
Can I build my own ADU in California?
Yes. Owners can pull permits as owner-builders, but you take on the contractor's legal responsibilities, including employer obligations if you hire workers. Most homeowners hire a licensed contractor.
How much down payment can an ADU contractor ask for?
For home improvement contracts, California generally limits the down payment to 10% of the contract price or $1,000, whichever is less.
Is design-build better for ADUs?
Design-build gives you one point of responsibility and often a faster process. Hiring a separate architect gives you more design control. Both can work well.
How are builders ranked on this site?
By Google rating weighted by review count. Featured spots are labeled and do not affect organic rank.
This page is general information, not legal, tax or financial advice. Costs vary by property and builder. Images are AI-generated illustrations. Last updated November 2026.