Custom ADU Contractor in Fullerton, CA
Why Cornejo's Builders Is the ADU Contractor Fullerton Homeowners Trust
Cornejo’s Builders has been working across Southern California long enough to know that every ADU project starts with a person, not a property.
Some families need space for aging parents, close by but not underfoot. Others are thinking about what a rental income stream would do for their monthly budget. Whatever your reason, we listen before anything else.
We’ve completed 24 ADU projects in four years, working across LA County and into Orange County, from communities like Woodland Hills and Pacific Palisades down to cities throughout the greater region.
Fullerton has its own permit timeline and local regulations, and navigating those takes genuine familiarity. When a step in the process stalls a less experienced team, we’ve usually been through that exact situation on a prior project, and we plan around it.
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.
- 24 ADUs built in 4 years
- Fast completion timelines
- Constant project updates
- Seasoned and friendly pros
- 1-year warranty included
- All ADU types covered
What Fullerton Homeowners Are Saying About Building Their ADU With Us
m
Marisabel Gomez
There are always things you do not expect when building a home/ADU, but Alex and his team worked fast and assisted with city permit issues. He worked with me on unforeseen costs too . I’m very happy with the work !
w
Walter Salcedo
Working with Cornejo’s Builders was an excellent experience! They specialize in ADU projects and truly know their craft—from planning to final inspection.
Professional, responsive, and detail-oriented throughout the entire process. Highly recommend them for anyone looking to build an ADU the right way!
What Does an ADU Actually Cost in Fullerton, CA?
ADUs range from around $80,000 on the lower end to $250,000 or more for a larger, fully custom two-story build. That gap exists because ADU construction is unique from property to property.
To give you a real sense of what these projects look like in practice, here are three actual builds from our portfolio:
- New 735 Sq. Ft. Two-Story ADU in Alhambra, CA. This ADU project included a new foundation, new plumbing, new electrical, new HVAC, Spanish-style finishes, custom kitchen cabinets, and separate utility connections. Total quote: $250,000. The largest single line item was the architectural plans, which came to $15,000.
- New 535 Sq. Ft. ADU in Whittier, CA. Central AC, an open-concept kitchen and living room, a rental-ready layout, custom bathroom tile, vinyl engineered flooring, and level 5 drywall finish. Total quote: $150,000. Custom kitchen cabinets with marble countertops came in at $12,550.
- New 798 Sq. Ft. ADU in Downey, CA. Vaulted ceilings, a level 5 smooth interior finish, smooth exterior stucco, a smart home electrical setup, a curbless walk-in shower, and central AC. Total quote: $200,000. Bathroom tile on this one ran $8,000.
Five Things That Shape the Final Price
- Size and Square Footage
- ADU Type
- Finishes and Custom Features
- Site and Foundation Conditions
- Permits and Architectural Plans
Keeping Your ADU on Budget and on Schedule
How a Cornejo's Builders ADU Comes Together
From the first walk of your property to the final inspection, we’re present throughout the entire construction process, and you’ll always know where things stand.
1
Collaborate
2
Build
3
Enjoy
Questions Fullerton Homeowners Ask Before Starting an ADU Project
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.
Ready to See What Your Fullerton Property Can Do?
Alexsander Cornejos
When you’re ready to talk specifics, call us at (562) 319-3178 or reach out through our contact page.
We’ll come out to your Fullerton property, walk the lot with you, and give you a straight answer on what a successful ADU project could look like there.
If you want to get a clearer sense of everything we build before that conversation, take a look at our ADU contractor services page.
Fullerton is home to California State University Fullerton, a genuine downtown arts and music scene, and a housing market that rewards smart property decisions. The Fullerton Arboretum draws visitors year-round with more than 4,000 plant species across a beautifully landscaped setting. The Muckenthaler Cultural Center has become a beloved city landmark and gathering place for art, music, and community events. For homeowners looking to add an ADU contractor in Fullerton, CA, to their plans, it’s a city where investing in your property tends to pay off.