How Do I Choose the Right Contractor for ADU Construction?
Choose an ADU contractor who holds an active CSLB Class B license, has finished real ADU projects, knows your city's permit rules, and gives a written line-item estimate. Those four checks tell you almost everything you need to know before you sign.
Here is the plain truth. The builder you pick matters more than the floor plan you pick. An accessory dwelling unit in Orange County can cost $80,000 to $400,000 or more depending on the type of build. That is a lot of money to hand to the wrong person. We have built homes across South Orange County since 1991, and we have met many homeowners who hired on price alone and paid for it twice. So take ten minutes with this guide. It will help you hire with a clear head, whether you live in San Juan Capistrano or anywhere nearby.
Key Takeaways
Verify the contractor's license at cslb.ca.gov before anything else.
An ADU build needs a Class B General Building license.
Orange County ADUs cost about $80,000 to $400,000+.
California caps down payments at $1,000 or 10 percent.
Ask for two past ADU clients and call them both.
Why Your ADU Contractor Choice Matters So Much
Your contractor decides how close the build stays to your budget, your construction timeline, and local building codes.
An ADU is a full small home. Some people call it a granny flat, an in-law suite, or a backyard cottage. Whatever you call it, the unit needs a foundation, plumbing, electrical work, a kitchen, and a bathroom on one small footprint. A mistake on the sewer line or the slab costs serious money to fix after the fact. A careful general contractor spots those problems before the concrete pours. A careless one leaves them for you.
The money side matters too. A one-bedroom ADU in Orange County can rent for $1,700 to $3,200 a month. Good craftsmanship protects that rental income and your property value for years. Poor work eats both up in repairs. So give the hiring step the time it deserves.
Step 1: Check the License Before Anything Else
Verify the license yourself on the CSLB website, and look for an active Class B license, a bond, and workers' comp.
California makes this part simple. The Contractors State License Board (CSLB) keeps a free public record of every licensed builder in the state. Go to cslb.ca.gov, open the "Check a License" tool, and type in the contractor's license number or business name. You will see the license type, current status, expiration date, bond status, workers' comp coverage, and complaint history. The whole check takes about five minutes.
For ADU work, the license class matters. A Class B General Building license lets a contractor run the full ADU project, manage all the trades, and pull the building permit. A plumber or electrician license alone does not cover a complete build.
Here is what to look for on the CSLB page:
The workers' comp line protects you. If a worker gets hurt on your property and the builder carries no coverage, the medical bills can land on you. Liability insurance matters for the same reason. At ARC Construction, we hold CSLB license #1006389 with a Class B classification, and we show it to every client up front.
Step 2: Look for Real ADU Experience
Pick a contractor who has finished several ADU projects, not just kitchen and bathroom remodels.
ADU construction follows its own set of rules. Size limits, setbacks, parking, zoning, and utility connections all come into play, and a standard home remodel never touches most of them. A builder who only does bathrooms may do fine tile work, but the design and planning side of an ADU is new ground for them.
When you meet a builder, ask for:
Two or three completed projects you can see or ask about
A story about a job that hit a problem, and how the crew fixed it
Photos of work in progress, not just finished shots
The build types they know best
That last point matters because a garage conversion, an attached ADU, and a detached ADU are three different jobs with three different price tags. Some homeowners also look at a JADU or a prefab unit to save money. A good builder explains the trade-offs in plain words and helps you pick the one that fits your lot and your wallet.
Step 3: Test Their Local Permit Knowledge
A qualified ADU contractor knows your city's rules, the state ADU laws, and how to handle HOA approvals.
Each Orange County city treats ADUs a little differently. San Juan Capistrano, Mission Viejo, and Laguna Niguel each have their own takes on setbacks, height, and permit fees. A local builder already knows them. A builder from outside the area learns them on your time and your money.
State law sets the floor, and your contractor should know it well:
California rules let almost any homeowner build at least an 800 square foot ADU, no matter the lot size.
The state removed impact fees for ADUs under 750 square feet, which lowers the cost on smaller units.
A builder who knows these laws can speak up when a city asks for more than the law allows.
One more local point. Many South Orange County neighborhoods have an HOA. Your builder should handle that approval paperwork, not pass it to you. We manage HOA and city approvals for our clients every week, and it saves them real time.
Step 4: Get a Clear Written Estimate
A proper ADU estimate lists every cost line by line, with a payment schedule tied to completed work.
Know the normal prices first, so an odd bid stands out. Here is what ADU builds usually cost in Orange County:
Per square footage, most builds land between $250 and $450, based on site conditions, size, and finishes.
A bid far below those ranges needs a hard look. Low bids tend to grow later through change orders, and by then the job is half done and you have few options.
A solid free estimate spells out:
Site work and foundation
Framing, roofing, plumbing, and electrical
Finishes like flooring, cabinetry, and countertops
Permit and city fees
A payment schedule tied to finished work
Keep this rule in mind too. California caps your down payment at $1,000 or 10 percent of the contract price, whichever is less. A builder who asks for half the money up front is breaking the rules, and that tells you plenty.
Step 5: Read Reviews and Call Past Clients
Check Google reviews for patterns, then call two past clients and ask about the timeline, the price, and the work.
Read the reviews, but read them the right way. Look for repeat complaints, not one upset post. Busy contractors pick up a bad review now and then. What matters is whether the same problem shows up again and again, and how the company responds. Strong customer satisfaction leaves a trail you can follow.
Then make two phone calls. Ask the contractor for two references and ring them both. Keep it short:
Did the job finish on time and within budget?
Did the final price match the contract?
Would you hire them again?
Ten minutes on the phone teaches you more than an hour of reading.
Step 6: Watch for These Red Flags
Avoid any contractor with no license number, a very low bid, a big cash deposit request, or loose talk about skipping permits.
Step back if you notice any of these:
No license number on the contract, truck, or business card
A bid far under every other bid
Pressure to sign today before "the price goes up"
A request for a large cash deposit
No written contract at all
Talk of skipping the building permit to save money
That last one costs you later. Unpermitted work becomes a code violation you must disclose when you sell the house. The permit fee is small next to that problem, and a failed inspection can stop a sale cold.
Step 7: Ask These Questions Before You Sign
Ask who pulls the permit, who runs the site, how change orders work, and what the warranty covers.
Sit down with your top pick and go through this list:
Who pulls the permit, you or me?
Who runs the job site and manages the subcontractors day to day?
How do you price and handle change orders?
What does the payment schedule look like?
How long will my build take, start to finish?
What does your warranty cover, and for how long?
A good builder answers all six in plain words, with clear communication and no dodging. Fuzzy answers mean you should keep looking.
Why Orange County Homeowners Trust ARC Construction
ARC Construction is a licensed, family-run general contractor that has served South Orange County since 1991.
Tony Carrieri learned the trade from his father, Vito, and his sons Matthew and Joe now build beside him. Three generations work under one name, and that name rides on every job. Here is what you get when you build your ADU with us:
30+ years of local experience – We have built and remodeled homes across South Orange County since 1991.
Fully licensed and insured – CSLB license #1006389, Class B General Building.
Full project handling – We design your ADU, pull the permits, manage HOA approvals, and build it with our own trusted crew.
Final walkthrough – We walk the finished unit with you at a final inspection before we call it done.
Free estimates – Clear pricing with no pressure and no surprise fees.
Local service area – We serve San Juan Capistrano, Ladera Ranch, Mission Viejo, San Clemente, Dana Point, and the towns around them.
FAQs
How much does an A2DU cost in Orange County?
Garage conversions start around $80,000, and detached new builds can pass $400,000. Size, site, and finishes set the final price.
How long does an ADU take to build?
Most projects take several months from design to move-in. City review, unit size, and site conditions all play a part.
Do I need a permit for an ADU?
Yes, every time. A licensed contractor pulls the building permit for you and keeps the build up to code compliance.
Can my contractor handle the HOA paperwork?
A good one should. ARC Construction manages HOA and city approvals for every ADU we build.
Final Thoughts
The right ADU contractor comes down to four things: a valid CSLB license, real ADU experience, local permit knowledge, and honest answers to your questions. Check all four before you sign. When you are ready to build, ARC Construction is here. Call (949) 710-5062 for a free estimate.
