#1 ADU Contractor in Costa Mesa
Custom Builds by Horizon Remodeling
Horizon Construction & Remodeling Inc. builds accessory dwelling units and home additions throughout Costa Mesa, managing design, permitting through the City of Costa Mesa Building and Safety Division, budgeting, and material selection so the project stays on track from start to finish. Costa Mesa’s postwar tract stock, common across Mesa Verde, Mesa del Mar, and the Westside, often has room on the lot for a detached backyard unit or a conversion, while larger Eastside properties can support more substantial additions. We coordinate every trade involved so nothing falls through the cracks.
Services We Offer
How Our ADU Process Works
When it comes to enhancing your living space, room additions combined with Accessory Dwelling Unit (ADU) construction offer unparalleled versatility and value. These projects not only increase square footage but also provide additional living accommodations, whether for extended family, rental income, or work-from-home setups, making them a popular choice for homeowners seeking to maximize their property’s potential. According to California’s Department of Housing and Community Development, ADUs are a key solution to expanding housing options in urban and suburban neighborhoods.
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Finding the right adu contractor in Costa Mesa means understanding how state law and local process work together before a single wall goes up. Under California Government Code sections 66310 through 66342, as amended effective January 1, 2026, square footage is measured as interior livable space, and the City of Costa Mesa Building and Safety Division has 15 business days to determine whether your application is complete and 60 days to approve or deny it. Approval is ministerial, meaning no hearing and no discretionary design review stands between a complete submittal and a decision.
State law also sets hard floors that protect you regardless of where your parcel sits. A local agency cannot cap an ADU below 850 square feet of interior livable space, or 1,000 square feet for a unit with more than one bedroom. Side and rear setbacks cannot exceed four feet, owner-occupancy cannot be required, adding the unit cannot trigger a fire sprinkler retrofit on the main house, and there are no impact fees on units of 750 square feet or less.
Costa Mesa’s housing stock shapes what is actually possible on a given lot. The city built out rapidly after its 1953 incorporation, going from a semi-rural farming community of roughly 16,840 residents to a fully urban suburb within about thirty years. Most properties are single-story postwar tract houses on slabs, which affects utility routing and where a detached structure can sit. Eastside parcels tend to be larger and sometimes carry older or rebuilt homes, which opens different options than a compact Mesa Verde or Westside lot.
No unusual local overlay applies in Costa Mesa, so the state building code and any applicable association rules are what govern your project. We walk every parcel before drawing anything, checking setbacks, grade, equipment access, and how far utilities need to run, because those site conditions determine whether a garage conversion or a new detached build makes more practical sense for your property.
Other Remodeling Services We Offer
A modern kitchen adds functionality, comfort, and lasting value to your home. At Horizon Construction & Remodeling, our kitchen remodeling experts bring fresh ideas and professional project management tailored to your unique needs. From layout design to material selection, we prioritize delivering a high-standard kitchen that’s both beautiful and energy-efficient — enhancing the way you cook, gather, and live every day.
Whether you envision a classic Southern California pool or a fully customized backyard oasis, Horizon Construction & Remodeling delivers the highest level of quality and service. Our comprehensive pool design and remodeling services cover everything from layout and decking to built-in BBQs and final touches like landscaping. Let Horizon be your trusted partner in transforming your backyard into the perfect outdoor retreat.
If you are planning a complete bathroom remodel or simply want to change your tub, shower, update your plumbing fixtures, or make the space more efficient, our team at Horizon will help you through the process with expert advice, professional craftsmanship, and affordable options with beautiful results. Learn more about our bathroom remodeling services.
Transform your space with our expert interior work services. We offer a comprehensive range of solutions — from space planning and custom design to the selection of high-quality finishes and materials. Our team of experienced professionals works closely with you to create a space that’s both functional and stylish, tailored to your unique needs, goals, and budget. Whether you’re updating a single room or overhauling your entire interior, we bring precision, creativity, and craftsmanship to every project.
At Horizon, we believe your home is more than just four walls — it’s where life happens. It’s the place you relax, gather with family and friends, and create lasting memories. That’s why we offer a full range of exterior work services designed to elevate your outdoor living space. From patios and hardscaping to custom decks and exterior renovations, we help turn your vision into a dream yard that complements your lifestyle and enhances curb appeal.
At Horizon Construction & Remodeling, our expert team includes a dedicated design and planning division that works hand-in-hand with licensed architects and structural engineers. We take care of everything — from detailed plans and blueprints to securing city permits — so you don’t have to deal with delays or red tape. Our goal is to streamline the process and provide a fully approved set of documents that aligns with both your vision and city regulations, saving you time and stress.
Why Choose Horizon Remodeling As Your ADU Contractor in Costa Mesa ?
Horizon Construction and Remodeling is a licensed Class B general building contractor, bonded, with over 15 years of design-build work. Costa Mesa is a short drive from our Fullerton office, so projects here get the same hands-on attention as any local job. A detached ADU is essentially a small house placed on a lot that already has a primary residence: foundation, framing, roof, electrical service, plumbing, a kitchen, and a bathroom all have to come together as a coordinated whole.
Because Costa Mesa’s housing stock is largely postwar single-story tract construction on slabs, an ADU often occupies underused rear yard space those original builders left behind. Design-build matters here because the design decisions and the construction constraints are the same decisions, handled by one company that draws the plans, submits to the City of Costa Mesa Building and Safety Division, and builds the finished unit.
Where a homeowners association is involved, we prepare that submittal alongside the building permit application rather than treating it as an afterthought. We work throughout Costa Mesa, including Eastside, Westside, Mesa Verde, and Mesa del Mar.
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ADU Contractor Services in Costa Mesa
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ADU Contractor in Costa Mesa FAQ
What is an ADU and why should I build one?
An accessory dwelling unit is a secondary home built on your existing property, taking the form of a backyard cottage, a converted garage, or an in-law suite. Building one with Horizon Construction and Remodeling can add rental income, house a family member independently, or simply give you more usable space on lots across Costa Mesa, from Mesa Verde to the Eastside.
How much does it cost to build an ADU in California?
What an ADU costs in Costa Mesa depends on details no contractor can assess from a distance: the size and type of unit you want, whether you are converting existing space or building a detached structure from the ground up, how much site work and utility routing your lot requires, and the finish level you select. Those variables matter because they determine where the money actually goes. State law does give you some clear protections on cost, though. Any ADU with 750 square feet or less of interior livable space is exempt from impact fees. School fees only apply once the unit exceeds 500 square feet. Connection fees are capped for conversions and junior ADUs because state law does not classify those as a new residential use, and adding an ADU cannot force a fire sprinkler retrofit on your existing home.
Costa Mesa permits go through the City of Costa Mesa Building and Safety Division, and the governing rules are the building code and any applicable association rules, since no unusual local overlay applies here. On the Eastside, where lots tend to run larger and many homes have already been expanded, a detached unit is often straightforward to site. On the more compact postwar parcels common throughout Mesa Verde and the Westside, setback and utility placement require a closer look before anyone can quote honestly. We walk the property first, confirm the actual conditions, and then give you a fixed scope and price. One point worth stating plainly: the CalHFA ADU grant program is closed, its funding fully allocated, and the agency itself warns that any offer to help you obtain that grant is a scam.
Do I need permits for an ADU in Costa Mesa?
Yes, an ADU in Costa Mesa requires a building permit, but state law makes approval ministerial rather than discretionary, meaning no hearing or design review stands between you and a decision. The application goes to the City of Costa Mesa Building and Safety Division, which has 15 business days to confirm the submission is complete and 60 days to approve or deny it. A pre-approved plan can shorten that review to 30 days. We prepare and submit the full package and carry it through every inspection, so the permitting process stays off your plate.
How long does ADU construction take with Horizon Remodeling?
Most ADU construction projects take between 4 to 8 months from design to completion, depending on scope and permit approvals. Horizon Remodeling prioritizes efficient timelines while maintaining quality workmanship.
What types of ADUs can Horizon Remodeling build?
We specialize in building detached ADUs, attached ADUs, garage conversions, backyard cottages, and junior ADUs (JADUs). Our team can help you choose the right ADU style for your property and goals.
Can I build a detached ADU on my property in Costa Mesa?
Yes, if your property meets California zoning and space requirements. Horizon Remodeling will assess your site, secure the necessary permits, and build a fully detached ADU tailored to your preferences.
Is Horizon Remodeling licensed to build ADUs in my area?
Yes, Horizon Remodeling is fully licensed, bonded, and insured to build ADUs throughout Orange County and surrounding areas. We have over 18 years of experience delivering high-quality ADU projects.
What are the benefits of hiring Horizon Remodeling for my ADU project?
Horizon Construction & Remodeling Inc. handles ADU design, permitting through the City of Costa Mesa Building and Safety Division, and construction under one contract, managing the full process so your project meets building code requirements and stays on budget.
Does Horizon Remodeling handle ADU design and permitting?
Absolutely! Horizon Remodeling provides complete ADU design services, including architectural plans and 3D renderings. We also handle city permits and inspections, streamlining your project and reducing stress.
How do I get started on an ADU with Horizon Remodeling?
Ready to get started? Contact Horizon Construction & Remodeling Inc. for a free consultation, where we assess your Costa Mesa property, talk through your goals, and deliver a detailed estimate covering every phase of your ADU project.
Recent ADU and Garage Conversions
Three completed ADU and garage conversion projects from our Orange County portfolio. Every project below was built in San Clemente. Nothing loads from YouTube until you press play.
ADU project in San Clemente
ADU project in San Clemente
ADU project in San Clemente
Built by Horizon Construction & Remodeling, Inc. Licensed Class B general building contractor.
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Horizon is a licensed Class B general building contractor serving Costa Mesa and the surrounding Orange County communities.
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