Hiring an ADU Builder: How to Check a CSLB License.

An ADU is a real construction project. In California, the Contractors State License Board (CSLB) licenses the people who build it. A few checks before you sign can protect you from the most common problems.

LA ADU Guide is an information site. We are not a contractor and do not recommend or rate builders. This page explains the rules.

ADU work is home improvement work

CSLB says that "building an ADU is considered a home improvement project under the Contractors State License Law." That has real consequences for the contract and for how much you can pay up front.

Which license should the builder hold?

CSLB's ADU fact sheet (revised November 2025) says:

• B, General Building Contractors can build or install ADUs. They are licensed to manage projects with two or more unrelated trades and can subcontract specialty work.
• C-47, General Manufactured Housing Contractors can install an ADU if it is a manufactured home built off site.
• Other C specialty licenses (electrician, plumber, roofer) "cannot generally manage a full ADU build" but can be hired by the builder for specific trades.

If someone who holds only a specialty license offers to run your whole ADU, ask CSLB or your building department about it before signing.

How to check a license

1. Go to the CSLB website, cslb.ca.gov, and use the license check. You can also call CSLB at 800-321-CSLB (2752).
2. Search by license number or business name.
3. Confirm the license is active and the class matches the work.
4. Match the name on the license to the name on the contract and the person you are dealing with.
5. Look for any disciplinary notes or complaints on the record.

CSLB also suggests that you ask to see the contractor's pocket license and insurance, and request references from similar jobs.

Get several bids

CSLB advises getting at least three bids "to become familiar with the differences between how costs can be estimated." Make sure each bid covers the same scope so you can compare. For cost context, see ADU cost in Los Angeles.

The written contract

A written home improvement contract is required. CSLB says to get one that includes:

• Scope of work
• Project timeline
• Payment schedule
• Materials and finishes
• The contractor's license number
• Notice of cancellation rights

Verbal agreements, in CSLB's words, offer "little to no legal protection if a dispute arises." If something was discussed but is not written down, add it before you sign. Get all change orders in writing.

Right to cancel

CSLB says you have three days from signing to cancel a contract, five days if you are 65 or older, and seven days in disaster zones.

Down payment and progress payments

Under Business and Professions Code section 7159, a down payment may not exceed $1,000 or 10 percent of the contract price, whichever is less. CSLB's 2024 ADU payments release says the same, and CSLB's ADU fact sheet shortens it to "the down payment cannot exceed $1,000." For a contract under $10,000, the 10 percent cap is the lower one.

On progress payments, CSLB says they "must reflect the actual work completed or materials delivered." Its advice:

• Never let payments get ahead of the work.
• Document every payment and get receipts.
• Do not pay a contractor for plans unless you know they have paid for them first. Ask for an accounting, or contact the designer to confirm.
• Check permit costs with your building department. Permits must be pulled through your local city or county.

CSLB's fact sheet includes this sample schedule for illustration, not as a requirement: 5 percent mobilization, 10 percent demolition and site prep, 10 percent foundation, 15 percent framing, 15 percent rough mechanical, electrical and plumbing, 15 percent roof and exterior wrap, 10 percent insulation and drywall, 10 percent flooring, tile and cabinets, 5 percent finish work, 3 percent final inspection, and 2 percent at completion of the punch list.

Licenses and payments at a glance

CSLB's sample payment schedule, for illustration only:

Permits and who pulls them

Ask who will pull the permit and in whose name. A licensed contractor normally does. See the ADU permit process in Los Angeles. Also confirm who is handling underground utilities for plumbing and electrical.

Red flags

CSLB warns against "unlicensed individuals offering cash deals or vague estimates." Other warning signs:

• A large deposit request.
• Pressure to sign the same day.
• No written contract, or a contract missing the license number.
• A builder who will not let you check the license.
• Payments requested for work not yet done.

Financing note

If you are borrowing for the build, your lender may have its own payment schedule. See ADU financing options. The CSLB payment limits still apply to the contract.

If something goes wrong

Contact CSLB at 800-321-CSLB (2752) or through its website. CSLB handles complaints about licensed contractors and about unlicensed work. For legal advice, talk to an attorney.

Questions to ask each builder

• How many ADUs have you built in my city, and can I see one?
• Which parts will you do yourself and which go to subcontractors?
• Who is responsible for utility work and for cleaning up the site?
• How are change orders priced and approved?
• What happens if the city asks for corrections or the design must change?
• How do you handle the final punch list before the last payment?

Write the answers into the contract. A good builder will not mind putting them on paper.

Checklist

• License is active and class B (or C-47 for a manufactured ADU).
• Name on license matches the contract.
• At least three comparable bids.
• References checked.
• Insurance seen.
• Written contract with every CSLB item above.
• Down payment no more than $1,000 or 10 percent of the contract price, whichever is less.
• Payments tied to completed work.
• Receipts kept for everything.