ADU Cities · Design-Build ADU Contractor
ADU Contractor in Southern California
One licensed contractor for your whole ADU — design, engineering, permits, and construction under a single contract. Detached ADUs, garage conversions, and attached or junior ADUs, built across Orange, Los Angeles, Riverside, San Bernardino, and San Diego counties.
Why Hire a Design-Build ADU Contractor
What an ADU Contractor Actually Does
An ADU contractor takes your project from a backyard idea to a legal, rentable home. That means confirming what your lot allows under California ADU law, designing the unit, engineering it, pulling permits with your city, and building it — foundation to final inspection.
Hiring separate designers, engineers, and builders is where ADU projects stall: plans the builder prices differently, permit corrections nobody owns, budgets that drift. As a design-build contractor, ADU Cities holds one contract and one point of accountability for all of it — and because our parent company, Mars Construction Industries, is a licensed general engineering and building contractor, the same team that designs your ADU also builds it.
- Licensed with the CSLB — verify us: License #1138550 (A General Engineering, B General Building)
- Feasibility first: lot, setbacks, utilities, and city rules checked before you spend on plans
- One written, itemized contract — design, permits, and build priced together
- Local permit experience in hundreds of California cities
ADU Construction Services
ADUs We Design and Build
Typically $250K–$450K
Detached ADUs
A brand-new backyard home with its own entrance, kitchen, and bath — the strongest rental income and property-value play. Most of our detached builds run 600–1,200 sq ft.
Detached ADU details →
Typically $100K–$200K
Garage Conversions
The fastest, most affordable route: your existing garage becomes a legal studio or one-bedroom home. The structure is already there, so permits and construction move quicker.
Garage conversion details →
Typically $180K–$300K
Attached & Junior ADUs
Attached ADUs share a wall with your home; junior ADUs (JADUs) convert up to 500 sq ft inside it. Ideal for family housing, caregivers, and a lower-cost second unit.
Attached ADU details →How It Works
Our ADU Process: Four Steps, One Contractor
Most ADU projects take about nine to twelve months from first sketch to final inspection. Here is how a project moves with ADU Cities — see the full ADU timeline for phase-by-phase timing.
Feasibility
We check your lot against state ADU law and your city’s rules — size, setbacks, utilities, and special cases like SB 9 lot splits — and give you straight numbers before design starts.
Design & Plans
Our design team drafts the floor plan, elevations, and engineering, sized to your budget and your lot — including details like fire sprinkler requirements that can change the price.
Permits
We submit and shepherd your plans through plan check. California law gives cities 60 days to respond to a complete ADU application. More in our permit process guide.
Build
Our own crews and licensed trade partners build it — foundation, framing, utilities, finishes — through final inspection and sign-off, ready for family or tenants.
Straight Numbers
What Does an ADU Contractor Charge in Southern California?
In 2026, most professionally built ADUs in Southern California land here: garage conversions $100,000–$200,000, attached ADUs $180,000–$300,000, and detached ADUs $250,000–$450,000. Staying under 750 sq ft typically waives $5,000–$15,000 in city impact fees — one of several places a contractor who knows the rules saves you real money.
Run your own numbers with our ADU cost estimator, or read the full Southern California ADU cost guide. Then weigh the return: ADUs commonly add 20–30% to a property’s value and rent for around $2,500 a month in much of Southern California.
Try the Cost Estimator
Know Before You Build
ADU Guides From Our Team
SB 9 Lot Splits
Split your lot and build up to four homes under California’s SB 9 — who qualifies and how the process works.
Read the SB 9 guide →Fire Sprinkler Rules
When does a California ADU need fire sprinklers? The answer depends on your main house — and it affects your budget.
Read the sprinkler guide →ADU Rental Income
What Southern California ADUs actually rent for, and how the income stacks up over five years of ownership.
See the rent math →Unincorporated LA County ADUs
County parcels permit differently than city lots — the county-vs-city rules, LA County’s free pre-approved plans, and the EPIC-LA path, explained.
Read the county guide →California ADU Handbook
The complete ADU reference — 500 topics and 1,000 homeowner questions on laws, costs, sizes, permits, and city rules, in one place.
Open the handbook →Service Areas
An ADU Contractor Near You
ADU Cities builds across five Southern California counties — Orange County, Los Angeles County, Riverside County, San Bernardino County, and San Diego County — with local ADU rules research for hundreds of California cities. Start with your city:
Common Questions
ADU Contractor FAQs
How do I choose an ADU contractor in California?
Verify the contractor’s CSLB license is active (you can check ours — #1138550, A General Engineering and B General Building), confirm they handle design and permits in-house or under one contract, ask for local ADU projects they’ve completed, and get a written, itemized bid. Avoid anyone who asks you to pull the permit in your own name as “owner-builder” on a project they’re running.
How much does it cost to build an ADU in Southern California?
Most 2026 projects land at $100,000–$200,000 for a garage conversion, $180,000–$300,000 for an attached ADU, and $250,000–$450,000 for a detached ADU. Your lot, city fees, and finishes move the number. Our ADU cost guide breaks down where the money goes.
How long does an ADU project take from start to finish?
About nine to twelve months for most projects: feasibility and design first, then permits (cities have 60 days to respond to a complete application under California law), then construction. Garage conversions are usually fastest. See our step-by-step ADU timeline.
Does the contractor handle permits, or do I?
With a design-build contractor like ADU Cities, we handle it: plans, engineering, city submittal, corrections, and inspections are all under our contract. Permitting is where unlicensed or out-of-area builders most often leave homeowners stuck.
Can I build an ADU on my property?
Most owners of single-family homes in California can. State law lets you build at least an 800 sq ft ADU on nearly any residential lot, and garage conversions get extra flexibility. Lot size, setbacks, and utilities decide the details — start with our free eligibility check and we’ll confirm what your lot allows.
Will my ADU need fire sprinklers?
Sometimes. California generally requires sprinklers in the ADU when the main house has them, and some cities and lot conditions add their own triggers. It can add thousands to a budget, so we confirm it during design. Our fire sprinkler guide explains the rules.
How much rent can an ADU earn?
Finished ADUs in much of Southern California rent for around $2,500 a month — roughly $30,000 a year — depending on size and neighborhood. Many owners also house family instead. We walk through real numbers in our ADU rental income guide.
Free Eligibility Check
Ready to Talk to an ADU Contractor?
Tell us about your property and we’ll confirm what you can build, what it should cost, and how long it takes — no obligation, and no pressure.
ADU Cities is the ADU design-build brand of Mars Construction Industries Corp · CSLB License #1138550 — A General Engineering, B General Building · Licensed & Insured
