Best ADU Builders in Costa Mesa, CA
Compare vetted, CSLB license-verified ADU builders and ADU contractors in Costa Mesa. The average cost to build an ADU in Costa Mesa is $250–$400 per square foot. Top-rated builders include Acton ADU, ADU West Coast, Superior ADUs - ADU Builders Orange County.
Every builder below is CSLB license-verified, bonded, and insured — vetted before they ever reach a homeowner. Browse ratings and real reviews, compare starting prices, or let us match you with the best fit for your lot and budget. It's free; we're paid by the builders, not you.
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What kind of ADU are you planning?
ADU activity in Costa Mesa
ADU projects in Costa Mesa commonly budget $250-$400 per sq ft, or about $200,000-$320,000 for an 800 sq ft ADU, before site conditions, utility upgrades, and finish choices.
Showing 11 of 11 builders in Costa Mesa, CA
Last updated July 16, 2026
License VerifiedActon ADU
Serving Costa Mesa, CA · Campbell, CA
“We had a great experience working with Acton ADU on our ADU project, and I want to give a special shoutout to Sandro. Sandro was fantastic from start to finish—…”— N K
Pricing on request
A California general building contractor licensed since 1992, serving the LA market statewide.
License VerifiedADU West Coast
Serving Costa Mesa, CA · Seal Beach, CA
“Recently, I’ve had the opportunity to work with Cameron and the ADU West Coast team on a new home project. I am extremely impressed with their services that oth…”— Max “MaxMufc2018” T
Pricing on request
CSLB-verified B contractor in Seal Beach, CA.
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License VerifiedSuperior ADUs - ADU Builders Orange County
Serving Costa Mesa, CA · Irvine, CA
“Superior ADUs – A Top-Tier Experience from Start to Finish! I can't say enough great things about Superior ADUs! From the very first consultation to the final…”— Lisa Dumont
Pricing on request
CSLB-verified B contractor in Irvine, CA.
License VerifiedVilla Homes
Serving Costa Mesa, CA · San Francisco, CA
“Excellent job! The Villa crew from start to finish nothing short of professional. Foundation, home delivery, finish work etc top notch. I would recommend Vill…”— M Ferreira
Pricing on request
Tech-enabled prefab ADU builder delivering turnkey backyard homes across California.
Orange County Construction ADU Contractor
Serving Costa Mesa, CA · Anaheim, CA
“We purchased a Westminster, CA home that was a fixer upper with plans to fully renovate before moving in. Orange County Construction was recommended to us from…”— Daowyw Trosyao
Pricing on request
CSLB-verified B contractor in Anaheim, CA.
License VerifiedVision ADU
Serving Costa Mesa, CA · Anaheim, CA
“Jaime and his team are Amazing! Communication is key & all the plans with our ADU went smoothly. We will definitely be using their services again if any big pr…”— Ahide Calderon
Pricing on request
CSLB-verified B contractor in Anaheim, CA.
License VerifiedNestadu
Serving Costa Mesa, CA · Mill Valley, CA
“Nestadu did a great job on my backyard ADU. Their team was professional, and the final result looks fantastic—well-built and blends in nicely with my home. Pric…”— Stephen Reid
Pricing on request
Custom and prefab ADUs for California homeowners — design, permit, and build, turnkey.
License VerifiedWell Done Building & Design
Serving Costa Mesa, CA · Costa Mesa, CA
“My wife and I hired Zac and his team at Well Done for a home addition and full remodel, and to say the experience was pleasant would be an understatement. From…”— Chris Corsaro
Pricing on request
CSLB-verified B contractor in Costa Mesa, CA.
License VerifiedPelican ADU Builders
Serving Costa Mesa, CA · Irvine, CA
“Building our ADU was a game changer! The process was smoother than expected, thanks to a great contractor who handled permits and kept costs reasonable. It's…”— Norma Yarbrough
Pricing on request
CSLB-verified B contractor in Irvine, CA.
License VerifiedSo Cal Casitas and Adu's Inc
Serving Costa Mesa, CA · Irvine, CA
“Great company to work with when considering an ADU! Excellent !!”— Kimberly Bayles
Pricing on request
CSLB-verified B contractor in Irvine, CA.
License VerifiedCustom ADU Builder
Serving Costa Mesa, CA · Fullerton, CA
“I had an excellent experience working with Custom ADU Builder. From start to finish the project was smooth and professional. Dennis was incredibly responsive -…”— Cecilia Lacuesta
Pricing on request
CSLB-verified B contractor in Fullerton, CA.
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Frequently Asked Questions
- How much does it cost to build an ADU in Costa Mesa, CA?
- In Costa Mesa, ADUs typically run $250–$400 per square foot all-in. A detached 800 sq ft unit commonly lands between $230k and $340k depending on finishes, site conditions, and utility connections. Garage conversions are the most affordable path, often under $180k.
- How long does it take to build an ADU in Costa Mesa?
- Plan to budget 6–12 months end to end. California law caps ADU plan check at 60 days for compliant designs, and construction usually takes 4–8 months after permits are issued.
- Do I need a permit to build an ADU in Costa Mesa?
- Yes. All ADUs require a building permit, but California mandates ministerial (non-discretionary) approval for compliant units, so there's no public hearing or design review. Your builder typically pulls the permit on your behalf.
- How do I choose a builder in Costa Mesa?
- Confirm the contractor holds an active CSLB license, is bonded and insured, and has built ADUs in Costa Mesa specifically. Every builder in this directory is license-verified. Use "Get a Quote" to be matched with the best fit for your lot and budget.
ADU costs in Costa Mesa: city vs. metro vs. state
Building an ADU in Costa Mesa runs roughly $250–$400 per square foot all-in. Here's how the city benchmarks against the broader metro and statewide averages.
| Area | Avg. cost / sq ft | Typical 800 sq ft ADU |
|---|---|---|
| Costa Mesa | $250–$400 | $200,000–$320,000 |
| Costa Mesa metro | ~$320 | ~$256,000 |
| California (CA) | ~$330 | ~$264,000 |
Cost by ADU type in Costa Mesa
| ADU type | Typical size | Project cost | Timeline |
|---|---|---|---|
| Detached ADU | 600–1,200 sq ft | $180,000–$420,000 | 8–12 months |
| Attached ADU | 400–800 sq ft | $140,000–$300,000 | 6–10 months |
| Garage Conversion | 400–600 sq ft | $90,000–$180,000 | 4–7 months |
| JADU (Junior ADU) | ≤ 500 sq ft | $60,000–$140,000 | 3–6 months |
ADU rules & permits in Costa Mesa, CA
Local ADU permitting in Costa Mesa follows California state ADU law, which caps plan-check at 60 days for compliant units. Confirm setbacks, height, and parking rules with the local building department.
| Jurisdiction | Permit timeline | Permit fees | Notes |
|---|---|---|---|
| Costa Mesa (independent city) | 60 days max by CA statute | Set by local ordinance | Permits are issued by the Costa Mesa building department, not the City of Los Angeles |
| Statewide (CA) | 60 days max by statute | Varies | Ministerial approval; owner-occupancy requirement waived through 2030 |
Financing your ADU in Costa Mesa
Common ADU funding paths include renovation and construction loans, a HELOC, or a cash-out refinance. ADU-specific lenders underwrite against after-build value, which often unlocks more than a standard HELOC.
Construction / renovation loan
Funds released in draws as the build hits milestones; underwritten against after-build value.
HELOC / home equity
Borrow against existing equity. Fast to set up if you have 20%+ equity.
Cash-out refinance
Replace your mortgage and pull equity as cash — best when rates are favorable.
ADU-specific lenders
RenoFi and similar lenders underwrite the projected value the ADU adds, often unlocking more.
Pre-ADU Checkup — $499 — Get finalized permits, a pre-ADU checklist, and an on-site feasibility visit. Homeowners save $1,000s by doing this before engaging a contractor.