Trusted by 100+ Families in CA & LA
Turn Your Garage or Backyard Into a New Home In as Little as 90 Days
The South California ADU experts who keep your project on time, on budget, and stress-free.
Transparent pricing, no hidden costs
Constant updates & easy communication
Licensed, insured, and built to code, with warranties
60+
projects completed
3D
design visualization
1-year
workmanship warranty
Give Your Family the Extra Space They Deserve
- A private suite where aging parents can stay close without losing independence
- A rental unit that pays for itself and puts extra income in your pocket
- A quiet, separate space for work, hobbies, or simply breathing room
The truth is, most homeowners want more space, but dread the headaches of permits, timelines, and contractors who overpromise. That’s where we come in.
At Cornejos Builders, we build ADUs for any life stage. From the very first design sketch to the final inspection, we take care of everything for you.
✖️ No chasing down subcontractors, no permit nightmares, no hidden costs. You get the keys to a move-in-ready ADU and the confidence that it was done right the first time.
More Space, More Freedom, More Possibilities
ADU Contractor
Give loved ones their own private space while keeping family close.
Garage Conversions
Turn wasted square footage into a cozy home or income-producing rental.
Detached ADUs
Enjoy a fully independent living space right in your backyard.
Home Additions & Bump-Outs
Give loved ones their own private space while keeping family close.
Second-Story Additions
Turn wasted square footage into a cozy home or income-producing rental.
Porches & Decks
Enjoy a fully independent living space right in your backyard.
From Empty Spaces to Beautiful Living Places
Frequently Asked Questions
How fast can you build my Accessory Dwelling Unit?
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.
Who is going to be working on my project?
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.
Can I buy the materials on my own?
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.
Will you provide a 3D design for my new ADU?
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.
Is there any warranty?
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.
What does an ADU project include?
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!
How much does an Accessory Dwelling Unit (ADU) cost?
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.
Do I need a permit for an ADU?
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.
Accessory Dwelling Unit (ADU) Pricing Insights Here In South CA
While ballparking an estimate never works out, we still want to show you what some of our ADU projects include and what they look like. Check below!
New 735 sq. ft. Two-Story ADU in Alhambra, CA
This ADU builder project included:
- New foundation
- New plumbing
- New electrical
- New HVAC
- New Spanish style finishes
- New custom kitchen cabinets
- New separate Utility connections
New 535 sq. ft. ADU in Whittier, CA
This ADU contractor in Whittier CA project included:
- New central AC
- New open concept kitchen/living room
- New rental income property
- New custom finish bathroom tile
- New vinyl engineer flooring
- New level 5 drywall finish
New 798 sq. ft. ADU in Downey, CA
This ADU contractor in Downey CA project included:
- New vaulted ceilings
- New level 5 smooth finish
- Smooth finish on exterior stucco
- Customized electrical smart home finish
- Curbless walk-in shower
- Central AC
This project was quoted at $200,000, where the most expensive item was the bathroom tile which came out to be $8,000.
Proof You’re in Good Hands
Every ADU we build comes with stories like these: clear communication, quality work, and results that make homeowners proud.
L
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.
A
After browsing some time to find a contractor that met our standards, we finally had the pleasure to work with Cornejos Builders.
From the beginning of the project to the end Alex and his team committed to being consistent with communication in every aspect and was extremely informative when we had any questions regarding the project.
They turned our existing garage into a comfortable and livable space which is exactly what we wanted! The garage was converted into an ADU and was completely renovated from inside and out.
Not only did it add value to our home but also brought much satisfaction to our friends and families when visiting. It really helped that he was flexible with our budget and was able to compromise on a price with us.
The price was very reasonable considering how efficient and outstanding everything turned out to be. We really appreciate someone that is thorough from the beginning and Alex proved himself that he is dynamic, professional and coordinates well to our needs. We are extremely content with the final product and will definitely be considering any future projects with Cornejos Builders.
S
I want to begin by highlighting the prompt response I received when I inquired about their services. One of the most important details for me is quick response. Alexsander was quick to respond and made an availability that was not only quick but worked for me.
I’m a registered nurse who has two jobs and flexibility and time management is big for me. I appreciated the understanding and willingness to work with my schedule.
The home inspection was very thorough. I am looking to tear up the laminate floor (disgusting) and thanks to Alexsander I found out that my old home (built in 1930s) lacks more foundational support. How did he know?
He got down and fit himself as best as he could to check the foundation on the floor (also very well dressed and professional attire).
Without asking him Alexsander checked every detail of my home from the inside,outside,corner, etc. […] You can’t go wrong with this team.