ADU Builder & Home Additions in Costa Mesa, CA
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Last modified: 2026-09-24T00:00:00.000Z
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Image: Open-plan living room and kitchen with polished concrete floors
- Costa Mesa
Design · Permit · Build
ADUs & Additions in Costa Mesa
Detached ADUs, garage conversions and additions, from plans to move-in.
Book a Consultation Call 818-300-2393
Built for Costa Mesa Homes
A large share of the housing stock went up in the postwar boom of the 1950s and 1960s, which shapes many of the scopes we write: slab-on-grade with cast-iron or galvanized drain lines, undersized original electrical panels, and no room in the existing service for a pool heater, spa and outdoor kitchen without an upgrade.
Lots are generous by coastal-adjacent standards but shallow at the rear. Mature ficus and pepper roots complicate excavation more than the soil does.
Flat, regular postwar tract lots (the R1 zone minimum is 6,000 square feet) with a wide street frontage and a shallow but usable rear yard. Eastside parcels vary more, with some deeper original lots and mixed-era infill.
We are a design-build team, which means the people who draw your project are the people who build it. Design, engineering, permits and construction run through one project manager and our own crews, so nothing gets lost in a handoff between a salesperson and a subcontractor. We are licensed, bonded and insured, CSLB license #1119054 .
Permits in Costa Mesa: Building permits here are not issued by a community development department. They come from the Building Safety Division inside the Economic and Development Services Department, at 77 Fair Drive. Plan submittal, permit issuance and fee payment run through the city's TESSA portal, and a limited set of simple scopes qualify for the city's Insta-Permit program instead of full plan check.
Plan check appointments are scheduled by phone or email through the Building Safety counter. Pools, spas, additions and ADUs go through standard plan review, and the city publishes weekly issued-permit listings and a document search for pulling permit history on an existing property before scoping a remodel.
Permit details checked September 2026 against City of Costa Mesa . Rules change, so we confirm them again for your parcel.
What We Build
- Electrical service and subpanel upgrades
- Aging drain and supply line replacement
- Permit history research before scoping
- Detached ADUs, ground-up
- Garage conversions to living space
- Junior ADUs within the main house
- Room additions and bump-outs
- Second-story additions
- Full kitchens and bathrooms in the ADU
- Separate utility metering where required
- Private entries, patios and landscaping
- Plans, engineering and city submittals
- Title 24 energy compliance
Local Conditions
What to Know in Costa Mesa
These local conditions change the scope, the schedule and the budget.
01
A large share of the single-family housing stock dates from the postwar building boom of the 1950s and 1960s, so cast-iron and galvanized drain lines, undersized panels and original slab penetrations surface routinely once demolition starts.
02
Slab-on-grade construction over shallow footings means adding a pool, spa and outdoor kitchen usually forces a service upgrade and new subpanel rather than a simple tie-in.
03
Mature ficus, pepper and eucalyptus root systems planted decades ago frequently run under proposed shell and footing locations and complicate excavation more than the native soil does.
04
The city's Safety Element maps localized liquefaction potential in the northwest and western portions of the city, and peat deposits near the Santa Ana River and Upper Newport Bay, so deeper excavation there warrants a site-specific geotechnical assessment.
Areas we serve in Costa Mesa:Eastside Costa MesaMesa VerdeMesa del MarCollege ParkHalecrestHall of Fame
Investment
What It Costs in Costa Mesa
Real Southern California price ranges, not teaser numbers.
Detached ADU
$150,000 to $400,000+
What moves it: square footage, finish level, utility runs, and site access; garage conversions typically run well below a ground-up detached build
Garage conversion ADU
$80,000 to $180,000
What moves it: whether the existing slab and framing meet current code, how far utilities have to run, and the finish level of the kitchen and bathroom
Plans, drawings and permit management
$4,500 to $25,000+
What moves it: project type and size, whether structural engineering, Title 24 or a soils report is required, and how many jurisdictions or review bodies are involved
Your lot, access and finishes set the price. We walk the site, then show you where every dollar goes.
Get a line-item price for your Costa Mesa property
The Process
How We Work in Costa Mesa
01
Feasibility
We check lot size, setbacks, utilities and access to confirm what your property will actually support.
02
Design & 3D
Layout, elevations and finishes, modeled in 3D so you approve the unit before submittal.
03
Plans & Permits
We prepare the full drawing set, handle engineering and Title 24, and manage the city submittal and corrections. In Costa Mesa that submittal goes to City of Costa Mesa Economic and Development Services Department, Building Safety Division.
04
Foundation & Framing
Site prep, foundation, framing and dry-in by our own crews.
05
Systems & Finishes
Electrical, plumbing, HVAC, insulation, then kitchen, bath and interior finishes.
06
Final Inspection
We pass final inspection, walk the unit with you and hand over the keys.
Questions
What Costa Mesa Homeowners Ask
Who issues the permits for this work in Costa Mesa?
City of Costa Mesa Economic and Development Services Department, Building Safety Division. Building permits here are not issued by a community development department. They come from the Building Safety Division inside the Economic and Development Services Department, at 77 Fair Drive.
Plan submittal, permit issuance and fee payment run through the city's TESSA portal, and a limited set of simple scopes qualify for the city's Insta-Permit program instead of full plan check. Plan check appointments are scheduled by phone or email through the Building Safety counter.
Pools, spas, additions and ADUs go through standard plan review, and the city publishes weekly issued-permit listings and a document search for pulling permit history on an existing property before scoping a remodel. We prepare the drawings, make the submittal and handle plan-check corrections ourselves, so you are not the one chasing plan check.
What makes building in Costa Mesa different?
Flat, regular postwar tract lots (the R1 zone minimum is 6,000 square feet) with a wide street frontage and a shallow but usable rear yard. Eastside parcels vary more, with some deeper original lots and mixed-era infill. One local condition that shapes the work: A large share of the single-family housing stock dates from the postwar building boom of the 1950s and 1960s, so cast-iron and galvanized drain lines, undersized panels and original slab penetrations surface routinely once demolition starts.
Which parts of Costa Mesa do you work in?
All of it, including Eastside Costa Mesa, Mesa Verde, Mesa del Mar and College Park. Our crews run every job out of our Cahuenga Pass base in Los Angeles, with our own people on site.
What does an ADU or addition cost in Costa Mesa?
Detached ADU: generally $150,000 to $400,000+ across Southern California. What moves it is square footage, finish level, utility runs, and site access; garage conversions typically run well below a ground-up detached build. We give line-item pricing after seeing the site rather than quoting a number over the phone.
How long does an ADU take start to finish?
Plan a realistic year. Design and engineering typically take one to three months, city plan check and corrections add several more, and construction usually runs four to eight months depending on size and site access.
Is a garage conversion cheaper than a detached ADU?
Usually yes, and often substantially, because the foundation, walls and roof already exist. The trade-offs are that you lose the garage, and older slabs and framing sometimes need upgrading to meet current code.
Can I rent the ADU out?
California ADU law is designed to allow long-term rental, and an ADU is one of the few ways to add rentable square footage to a single-family lot. Short-term rental rules vary by city, so confirm your local ordinance before counting on that income.
Do you handle the permits?
Yes. Plans, engineering, Title 24 and the city submittal are all handled in-house, including responding to plan-check corrections. That is a service we sell on its own, so it is not something we hand off.
More Services in Costa Mesa
Pool & Spa Remodeling in Costa Mesa Backyard & Outdoor Living in Costa Mesa Everything we build in Costa Mesa
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Planning Guides
Before You Build in Costa Mesa
Costs, materials and process notes from our own projects.
ADU Cost Breakdown by Size in Los Angeles A detached ADU in Los Angeles runs $150,000 to $400,000-plus. Here is the real cost broken down by unit size, with the soft costs, utility work and finish decisions that move the number. Read guide Garage Conversion to ADU: The Step-by-Step Build A garage conversion runs $80,000 to $180,000 in Southern California. Here is the real sequence, from slab testing and plan check to the raised floor, the mini-split and final sign-off. Read guide ADU Rental Income Math in the San Fernando Valley A one-bedroom ADU in the San Fernando Valley rents for roughly $2,100 to $2,900 a month. Here is the honest arithmetic on payback, carrying costs and what the unit adds to the property. Read guide Second Story Addition vs Building Out: Which Costs Less Building out runs $350 to $500 per square foot. Going up runs $450 to $700. Here is when the cheaper option is actually the wrong one, and what drives each number. Read guide
Planning an ADU in Costa Mesa?
Sit down with your project manager and get an accurate estimate. We call you back within one business day.
Book a Consultation 818-300-2393
Licensed, bonded & insured · CSLB license #1119054
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