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.
Trusted by 100+ Families in CA & LA
Transparent pricing, no hidden costs
Constant updates & easy communication
Licensed, insured, and built to code, with warranties
100+
projects completed
30+
5-star reviews
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 long does it take to build an ADU?
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?
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.
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.
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.
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.
Natasha Martin
I had a great experience with Cornejo Builders.
Their work exceeded my expectations! And at a reasonable price too! Alex is easy to talk to and worked with my requests. Thank you Alex!! I recomend them for any construction needs.
Esther Rosas
Alex and his team were very easy to work with. They helped us build a JADU and ADU. He handled the planning and permitting of both units.
As well as the inspections. He was very helpful when we had questions and made sure to maintain excellent communication with us. I would recommend Alex and his team to anyone looking for a good contractor. He’s also a pretty cool guy and will make you feel comfortable as these projects can make people uneasy.
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!