Accessory Dwelling Units In Downey, CA

Add a beautiful and solid new living space on your property with our expert accessory dwelling unit building services here in Downey, CA.

accessory dwelling unit built by Cornejos California

Homeowners in Downey, CA seeking to add new living quarters on their property have been choosing us here at Cornejos Builders as their contracting team. Our expertise ensures your project avoids costly errors and meets all legal requirements, turning your vision into a flawless reality.

Choosing us means sidestepping the hassle of redoing work, and instead, enjoying the peace of mind that comes with guaranteed compliance and maximized property value. No matter the design, style and size of your accessory dwelling unit, we are the right team for you.

adu contractor Downey California Cornejos
Alexsander Cornejo owner of Cornejo Builders California

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.

Services Packed With Benefits

Our standout service levels and benefits have rapidly redefined industry standards, raising the benchmark for quality and customer satisfaction. Check out the benefits we offer:

With us, you’re getting:

Your Accessory Dwelling Units Project Could Turn Out As Great As These

Your new accessory dwelling unit can mirror the excellence of our past projects showcased below. These serve as a great inspiration for your upcoming endeavor. Take a look at the gallery below to get a sense of the level of quality of our services:

60+ projects done

100+ of families helped

1:1 approach to your project

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Alexsander Cornejo owner of Cornejo Builders California

If you’re unsure about choosing us as your best option, why not request a pricing quote? Let’s have a discussion about your project so you can get to know exactly who you’ll be working with. Alternatively, feel free to give us a call at (562) 319-3178 to get in touch with us right away!

What The Community In Downey Thinks About Us

Our customers’ satisfaction speaks volumes, affirming the excellence of our work. We deeply appreciate their trust and heartfelt reviews. Check out the beautiful things people have to say about us:

Lanny Lam


Cornejo’s Builders did an amazing job remodeling our kitchen. Alexsander made this experience one of a kind, he was accessible and flexible throughout the process. 

This guy’s knowledge truly guided us to perfect our dream kitchen. He has endless recommendations. The workers were efficient. We appreciate how he handled minor changes we had with professionalism. 

After getting work done by different General Contractors, Cornejo’s Builders definitely sets the bar for the rest. Thank you, Alexsander.


Lety Ortega


Called Cornejo’s Builders after seeing their beautiful work on Tik Tok. Spoke to the owner regarding an ADU project. Alex always returned my calls, explained throughly how the project would be completed. 

Love how his company is an all in one stop. They definitely handle everything from getting permits, architect, plumbing, electrical etc. Turn key ready, his prices are very reasonable and is willing to work around your budget

Alex was very understanding when I explained why I had to put a hold on the the project. He definitely treats his customers like family.

Accessory Dwelling Units Costs In Downey

ADUs range from $80,000 to $250,000, depending on the scope of work and size. Avoid estimating the final cost – opt for a free quote, consultation, and discover a realistic price for your upgrade instead.

ADU Size Features Included Cost Estimate
New 735 sq. ft. Two-Story ADU (Alhambra, CA) New foundation, plumbing, electrical, HVAC, Spanish style finishes, custom kitchen cabinets, separate utility connections. Quoted at $250,000, with architectural plans at $15,000. $250,000
New 535 sq. ft. ADU (Whittier, CA) Central AC, open concept kitchen/living room, rental income property, custom finish bathroom tile, vinyl engineered flooring. Quoted at $150,000, with custom kitchen cabinets at $12,550. $150,000
New 798 sq. ft. ADU (Downey, CA) Vaulted ceilings, level 5 smooth finish, smooth exterior stucco finish, customized electrical smart home features, curbless walk-in shower, central AC. Quoted at $200,000, with bathroom tile at $8,000. $200,000

Factors Which Can Influence The Costs Of Accessory Dwelling Units In Downey

The cost of constructing an ADU in Downey is influenced by multiple factors, each significant in its own right. Understanding these variables can give you a clearer cost picture.

Simpler designs often mean lower costs. Intricate layouts may require more labor and materials.

The choice of materials affects not just appearance but also cost. Premium materials command higher prices.

Larger ADUs naturally consume more resources, which can escalate the project’s overall cost.

Personalized elements such as custom cabinetry or specialized fixtures can increase the final price.

Expedited constructions can incur additional costs due to the increased pace of work.

Easy access to the construction site can reduce costs, while challenging terrains may add to them.

Varying permit fees, depending on local regulations, can affect the total cost.

Costs can vary significantly based on the need for new connections or updates to existing systems.

Remember, our team at Cornejos Builders can help navigate these factors to optimize your budget without compromising on quality.

We Respect Your Time & Budget

At Cornejos Builders, our professionalism guarantees precise budget and timeline estimates for your ADU project, ensuring you stay informed and confident.

We honor your financial plan from start to finish. Once we set a budget, our commitment is to work meticulously within its bounds. There will be no surprises or hidden costs; transparency is the cornerstone of our service policy.

Adhering to deadlines is not just a promise, but a practice. We systematically approach each phase of construction to ensure your project is completed on or before our agreed deadline because we value your time as much as you do.

Easy 3-Step Process For Succesful Accessory Dwelling Units Projects

Embarking on your ADU project is a breeze with Cornejos Builders. Our refined three-step process is designed to ensure a seamless experience from start to finish.



We listen to your vision and plan collaboratively.



Our skilled team efficiently brings your ADU to life.



Delight in the comfort and style of your new dwelling space.

FAQs About Accessory Dwelling Units In Downey

Generally, we can build most ADUs in as quickly as 90 days. However, it’s important to understand that depending on the scope of work, complexity of the project, or your choice of materials and features, the timeline will increase. To avoid any guesswork, we’ll give you an exact time frame after our on-site visit.

Everyone who will step on your property are trusted, local tradesmen. We only work with the best in the industry, all experts who have your best interests at heart.

Yes. However, it’s important to know that if you buy the materials yourself, this automatically voids the warranty. If we’ll get the materials and install them for you, you’ll still enjoy their warranty, which can last anywhere from 1 year to a lifetime.

Of course! You’ll be able to see a 3D design of your new ADU so you don’t have to commit to any materials or design until you’re 100% satisfied with your upgrade. The 3D renderings are included in our design-build process to ease your experience.

Yes! You’ll get a 1-year warranty on all new ADUs built by us, and the materials warranty on all materials that we’ll buy and use. On top of that, you’ll always have our support, so whenever you need us again, you’ll have priority over anyone else.

A new ADU here in South California includes a kitchen, a bathroom, a living room, washer and dryer hook up, 1 bedroom or studio (depending on size of ADU), central heating, water, gas, and electrical installations. We’ll take care of everything, and you’ll get a turnkey ADU that you can use the very same day we’re done working!

ADUs vary from $80,000 up to $250,000.00 depending on scope of work and size. Ballparking the final cost is never a good idea, so it’s best to just request a free quote, have a consultation, and find out a realistic price for your upgrade.

Yes, all ADUs will require a permit here in South California. No need to worry though. Cornejo’s Builders Inc. handles all planning, permitting, and construction, so you don’t have to worry about anything. Just sit back, relax, and watch your dream home come to life.

Invest In A Smart Addition To Your Home

Alexsander Cornejo owner of Cornejo Builders California

Alexsander Cornejos

Don’t miss the chance to make a wise investment in your Downey home with Cornejos Builders. Contact us now at (562) 319-3178 for a smart addition that enriches your living space and financial portfolio. It’s the home improvement you’ll wish you’d made sooner!

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Andrei Hienadz​

I had a fantastic experience with Cornejos Builders! They exceeded my expectations in every way.  From the initial consultation to the final walkthrough, their professionalism and craftsmanship shone through.

Julie Bean​


Amazing experience with Cornejos builders. From beginning to end- communication was clear as well as expectations. Work was 5 star and every member of the crew was exceptional

I would highly recommend Cornejos builders for ANY project or build. I will continue to use them and refer them for as along as they are available. 

Thank you for your beautiful work at such a competitive price!!!!

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Downey, a vibrant city situated in the heart of Southeast Los Angeles County, boasts notable landmarks such as the world’s oldest McDonald’s and the renowned Columbia Memorial Space Center. This thriving community, steeped in culture and history, provides a dynamic backdrop for homeowners seeking to enhance their living spaces with accessory dwelling units.