How long does it take to build an ADU in Fullerton, CA?

It depends on the type of ADU and how complex the project is. A garage conversion wraps up faster than a new detached build starting from the foundation. Most projects run somewhere between four and twelve months from permit approval to final inspection. We give you a clear timeline before work starts and keep you updated throughout the entire process.

Do I need permits to build an ADU on my Fullerton property?

Yes, permits are required for all ADU construction in Fullerton. The City of Fullerton Building and Safety Division manages the permit process, which includes plan check review, structural inspections, and final sign-off. We handle the entire permitting process for you from the first submission through final approval. You won't be navigating city requirements on your own.

Can I convert my garage into an ADU in Fullerton?

Garage conversion ADUs are one of the most common projects we build across Southern California, and Fullerton is no exception. The city's ADU regulations have made garage conversions more accessible than before, and Fullerton has a solid stock of older homes with garages that convert well. We'll come take a look and give you an honest read on what your garage can become and what it would realistically cost.

Will building an ADU increase my property value in Fullerton?

Adding an accessory dwelling unit increases livable square footage on your property, which translates to a higher appraised value. A rental unit generating steady income also makes the property more attractive to future buyers. The exact figure depends on your market and the quality of the build, but across Southern California, ADU development has consistently shown strong returns.

Professional ADU Contractor in Santa Ana, CA

If you’ve been staring at your backyard, your garage, or that unused corner of your property thinking, “there’s got to be something I can do with this space,” you’re probably right.

The Santa Ana ADU Contractor Who Handles Everything

We’ve built 24 ADUs in four years across Southern California, and we’ll be honest with you: that number didn’t come from thin air. It came from showing up on time, keeping clients in the loop, and delivering work that looks and functions the way people imagined when they first called us.

Cornejos Builders handles every piece of the process, from design to final inspection, so you’re never left wondering what’s happening on your own property.

We work with all kinds of ADU projects. Detached ADUs, garage conversions, junior ADUs, second-story additions, granny flats, attached ADUs, bump-outs, home additions, porches and decks, and attached garages. If it can be built, we’ve probably built one like it nearby.

What keeps people coming back (and what keeps them referring their neighbors to us) is that we treat your home the way we’d want someone to treat ours.

Friendly, seasoned pros who communicate clearly and don’t disappear after the deposit clears. That’s the kind of team we set out to build, and that’s what you’re getting.

Alexsander Cornejo – Owner of Cornejo Builders

Hi, I’m Alexsander Cornejo, the owner and founder of Cornejo’s Builders. I started working in the remodeling and construction industry right out of high school, in 2009.

With Cornejo’s Builders, the goal is to give back to the city I grew up in. I want to send a message of hope and inspiration: any dream can be achieved, no matter where you come from, if you put in enough work and dedication.

ADU Work We're Proud to Show You In Santa Ana, CA

Browse our completed projects below and get a real sense of what we build. Every photo represents an actual home we worked on and an ADU that’s now adding value to a property just like yours.

60+ projects done

100+ of families helped

1:1 approach to your project

Unsure about choosing us? Request a quote to get to know us better! Let’s discuss your project. Or, call us at (562) 319-3178 now!

What Santa Ana Homeowners Are Saying About Our ADUs

Words on a webpage only go so far. Read through what our clients have actually said about working with us, and you’ll get a clearer picture of how we operate than any sales pitch could ever give you.

Chris

Rated 5 out of 5

Alexsander did an amazing job for me, I hired him for my project in Downey. He was very professional, clean, responsive and got the job done in a timely manner.

As problems came up during construction, he presented solutions right away.

He built from the ground a two-story apartment and converted a garage into an ADU. The cost of the construction was decent and the quality in material and labor was great.

I would hire him again and I have been looking for other projects to do with him already.

Yahritza Orellana

Rated 5 out of 5

Had a truly great experience with Alex. Cornejos builders just completed converting my crawlspace/basement into an ADU (studio with new bathroom and kitchen).

What made the experience even more valuable was that the owner himself (Alex) came over for a consultation. Other companies just send their sales reps and most of the time they don’t even know anything.

Feeling important is always a positive I can’t wait to work with them again. I highly recommend them. You can tell Alex is passionate about what he does, his clients, and his company.

How Much Does an ADU Cost in Santa Ana, CA?

ADU construction in Santa Ana typically runs anywhere from $80,000 to $250,000, depending on size, scope, and how customized you want to go. Here are a few examples from our past work to give you a better feel:

New 735 sq. ft. Two-Story ADU in Alhambra, CA. This project included a new foundation, new plumbing, new electrical, new HVAC, Spanish-style finishes, custom kitchen cabinets, and separate utility connections. The total came out to $250,000, with architectural plans accounting for $15,000 of that.
New 535 sq. ft. ADU in Whittier, CA. This one featured central AC, an open concept kitchen and living room, custom bathroom tile, vinyl engineered flooring, and a level 5 drywall finish. Total: $150,000, with the custom kitchen cabinets and marble countertops coming in at $12,550.
New 798 sq. ft. ADU in Downey, CA. This project had vaulted ceilings, a smooth level 5 finish inside and out, smart home electrical, a curbless walk-in shower, and central AC. Final cost was $200,000, with bathroom tile at $8,000.

These numbers are based on past project estimates. Your project will vary depending on your specific property and goals. The best way to get an accurate number is to reach out with your details.

Five factors that affect ADU pricing:

The bigger the build, the more material and labor it takes. A 500 sq. ft. junior ADU and an 800 sq. ft. two-story ADU are very different scopes of work, and the pricing reflects that.

A garage conversion generally costs less than a fully detached ADU built from the ground up, because you’re starting with an existing structure. Detached ADUs require a new foundation, new utility connections, and more site work overall.

Standard finishes keep costs down. Custom cabinetry, premium tile, smart home features, and architectural details add up quickly, though they also tend to add the most to your property’s value.

Santa Ana has its own set of local regulations, and navigating those takes time and experience. Permit fees, plan check costs, and compliance requirements vary and can influence the overall project budget.

Grading, soil type, existing utility locations, and access to your yard space can all affect the cost of prep work before a single wall goes up. Properties with more complex site conditions require more work before construction even begins.

Your Budget and Timeline Are in Good Hands

We understand that budget concerns and construction timelines are usually the two things keeping homeowners up at night. We take both seriously.

An ADU that adds a rental unit to your property can generate steady income month after month. If a $150,000 build brings in $1,800 a month in rental income, that investment pays for itself in under seven years, and keeps paying you long after that. We price our work honestly and up front, with clear, transparent pricing and no hidden fees or vague estimates that balloon later.

Construction can feel overwhelming. We know that. But we’ve been doing this long enough to know how to build a realistic schedule and stick to it. We value your home and your yard space, we keep the site clean throughout the entire construction process, and we hit our deadlines consistently. You’ll always know where your project stands.

From First Call to Final Inspection, We Handle It

Most homeowners don’t want to become amateur project managers just to get an ADU built. We built our process so you don’t have to.

Collaborate

We sit down with you, map out your vision, and design a plan that fits your property and your budget.

Build

Our team manages permits, construction, subcontractors, and inspections so you can stay out of it.

Enjoy

You get the keys to a finished, beautiful ADU that’s ready to use from day one.

FAQs About ADU Contractor Services in Santa Ana, CA

Do I need a permit to build an ADU in Santa Ana?

Yes, and getting those permits handled correctly is one of the most important parts of the process. Santa Ana follows California state ADU law, which has made permitting significantly more accessible in recent years, but there are still local requirements to meet. We manage the entire permitting process on your behalf.

How long does it take to build an ADU in Santa Ana?

It depends on the type and size of the ADU, but most projects run anywhere from four to ten months from design to final inspection. Garage conversions tend to move faster than fully detached ADUs built from the ground up. We’ll give you a realistic timeline at the start of your project and keep you updated every step of the way.

Can I rent out my ADU in Santa Ana?

Yes, and it’s one of the most common reasons homeowners decide to build one. A rental unit on your property can bring in consistent monthly income while also increasing your overall property value. California state law gives homeowners broad rights to rent out ADUs, and we can help you design one that makes a great rental from the start.

What's the difference between a detached ADU and a junior ADU?

A detached ADU is a fully separate structure on your property, completely independent of your primary home, with its own entrance, kitchen, and utilities. A junior ADU (JADU) is typically built within the existing square footage of your main home, like converting a bedroom or portion of the house. Junior ADUs are often less expensive but more limited in size and configuration. We’ll help you figure out which one makes the most sense for your yard space and goals.

Ready to Add Real Value to Your Santa Ana Property?

Alexsander Cornejos

At Cornejos Builders, we’ve made ADU construction our specialty for a reason: it’s one of the best investments a Southern California homeowner can make, and we know how to get it done right.

Give us a call or visit our contact page here and tell us what you’re working with. We’ll take it from there.

Every month you wait is a month you’re not collecting rental income, not housing a family member comfortably, and not building toward the full potential of your property.

(takes 1-2 min)

Santa Ana is the county seat of Orange County and one of the most historically rich cities in Southern California. If you haven’t walked through the Bowers Museum, one of the premier cultural institutions on the West Coast, you’re missing something genuinely worth your afternoon. The Santa Ana Zoo at Prentice Park is another local favorite. As one of the oldest cities in Orange County, Santa Ana has a housing market that makes ADU development an especially smart move for homeowners looking to maximize their property’s potential.