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.

Custom ADU Contractor in Rowland Heights, CA

If you’ve been sitting on that extra yard space, unused garage, or vague idea of a guest house, Rowland Heights is one of the best places in LA County to finally do something about it.

The ADU Contractor Rowland Heights Homeowners Keep Calling Back

We’ve built 24 ADUs in four years, and every single one of them started the same way: a homeowner with a great property and a rough idea of what they wanted.

What made the difference wasn’t just good construction. It was having a team that actually listened, answered questions without making you feel silly for asking, and showed up every day like it was their own house being built.

At Cornejos Builders, we handle the full picture. Architectural plans, permits, foundation, finishes, final inspection, all of it.

You won’t be chasing subcontractors or wondering what’s happening on site this week. We keep you in the loop from the first conversation to the day you get your keys.

Rowland Heights properties tend to have real potential, solid lots, room to grow, and a housing market where adding an accessory dwelling unit genuinely moves the needle on value.

We know this area, we know LA County’s requirements, and we know how to get a project done without the chaos that gives construction a bad reputation.

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 Builds We're Proud Of in Rowland Heights, CA

There’s a big difference between saying you do great work and showing it. Below you’ll find photos of completed ADU projects across Southern California, including garage conversions, detached units, and full custom builds.

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 Rowland Heights Homeowners Are Saying About Our ADU Work

Hearing from someone who’s already been through the process is worth more than anything we could tell you ourselves. Read through the reviews below to see what working with Cornejos Builders is like from the homeowner’s perspective.

shozib ikhtekhar

Rated 5 out of 5

Cornejos Builders was a great help for me and right choice for my ADU project in Anaheim.

Alex, helped me to get the final inspection done with reasonable price. We recommend Cornejos Builders for any construction and ADU project.

Walter Salcedo

Rated 5 out of 5

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 Cost in Rowland Heights, CA?

The honest answer is that ADU construction in Southern California ranges from around $80,000 to $250,000 or more, depending on the size, scope, and finishes you’re working with.

We know that’s a wide range, but let us show you why, with some real examples from past projects:

735 sq. ft. Two-Story ADU in Alhambra, CA. This project included a new foundation, new plumbing, electrical, HVAC, Spanish-style finishes, custom kitchen cabinets, and separate utility connections. It was quoted at $250,000, with architectural plans alone accounting for $15,000 of that total.
535 sq. ft. ADU in Whittier, CA. Central AC, an open-concept kitchen and living room, custom bathroom tile, vinyl engineered flooring, and a level 5 drywall finish. This turnkey rental unit was quoted at $150,000, with the custom kitchen cabinets and marble countertops totaling $12,550.
798 sq. ft. ADU in Downey, CA. Vaulted ceilings, level 5 smooth finish inside and out, smart home electrical, a curbless walk-in shower, and central AC. Quoted at $200,000, with the bathroom tile coming in at $8,000.

These are past project estimates, and your project will have its own set of numbers based on what you’re working with.

Here are five factors that tend to move the needle most:

A 500 sq. ft. junior ADU and a 1,200 sq. ft. two-story detached ADU are completely different animals. More floor area means more materials, more labor hours, and more of everything else.

A garage conversion in Rowland Heights usually costs less than a ground-up detached build, because the shell is already there. New construction, especially with a new foundation, adds significant cost.

Slope, soil type, and existing utility locations, all of these affect how much prep work is needed before a single wall goes up. Some lots in the hills require more grading and structural work than a flat yard would.

Custom kitchen cabinets, high-end tile, and smart home systems are choices that add up fast. They also add lasting value and rental appeal, so the conversation is always about what makes sense for your goals.

LA County and the City of Rowland Heights have their own requirements for ADU development. Architectural plans, engineering, and permits are a real cost, and skipping corners here causes problems later.

Reach out with your project specifics, and we’ll put together a real quote, not a guess.

Budget and Timeline, Handled

We know that handing over a large part of your property to a construction crew for several months is not a small thing.

An ADU in the $150,000 to $250,000 range sounds like a lot until you break it down. If your new unit generates $2,000 a month in rental income, that’s your full build cost recovered in six to ten years. You’re converting it into something that pays you back in more ways than one.

Construction feels daunting because the horror stories are loud. What you don’t hear about are the projects that finish on schedule, because those homeowners are busy enjoying their new space. We run on tight timelines, keep the site clean, and don’t disappear mid-project.

How We Handle the Whole ADU Build

When you work with Cornejos Builders on your ADU contractor project in Rowland Heights, you get a team that manages the entire construction process.

Collaborate

We work through your vision, your lot, and your budget together.

Build

Our crew handles permits, construction, and every detail in between.

Enjoy

Move in a family member, list it as a rental, or just revel in the added space.

FAQs About ADU Contractors in Rowland Heights, CA

Do I need permits for an ADU in Rowland Heights?

Yes, LA County requires permits for all ADU construction, and we handle the entire permitting process as part of our service. We know the local regulations, what reviewers look for, and how to keep your project moving without unnecessary delays.

How long does it take to build an ADU in Rowland Heights?

It depends on the type of unit and the complexity of the build, but most of our projects land in the four-to-eight-month range from permit approval through final inspection. Garage conversions are on the shorter end, and ground-up detached builds are on the longer end. We’ll give you a realistic timeline before any work starts, and we stick to it.

Can I rent out my ADU right away after it's built?

Once the final inspection is passed and the certificate of occupancy is issued, yes. Your new unit is a legal rental property. Many of our clients in Southern California start generating rental income within a few weeks of completion.

What's the difference between a detached ADU and a garage conversion?

A detached ADU is a completely separate structure built on the same property as your primary home, with its own foundation, walls, and systems. A garage conversion takes an existing structure and transforms it into a livable unit at a lower cost. Both are great options depending on your yard space, budget, and goals.

Ready to Add Living Space That Works For You?

Alexsander Cornejos

Cornejos Builders has spent four years building accessory dwelling units that add real value to real families’ lives, and we’d like to do the same for yours.

Give us a call at (562) 319-3178 or visit our contact page here to get the conversation started. And if you want to read more about our full range of ADU contractor services before reaching out, we’ve laid it all out for you.

The space is already there. The value is waiting. Let’s build something worth having.

(takes 1-2 min)

Rowland Heights is a community in LA County’s San Gabriel Valley, known for its cultural diversity and a tight-knit neighborhood feel. If you want to take a walk, Peter F. Schabarum Regional Park covers 575 acres of trails. Just a few minutes away, Hsi Lai Temple in neighboring Hacienda Heights is one of the largest Buddhist temples in the western hemisphere. For ADU contractor work in Rowland Heights, CA, Cornejos Builders knows this community and is proud to serve it.