The Best ADU Contractor Builder in San Marino, CA
If you’re looking to add value, functionality, and long-term flexibility to your property, building an Accessory Dwelling Unit (ADU) in San Marino, CA is one of the smartest investments you can make.
- 24 ADUs built in 4 years
- Fast completion timelines
- Constant project updates
- Seasoned and friendly pros
Scroll down to discover options, pricing, and process
Give Everyone You Love The Extra Living Space They Need
As families grow and lifestyles change, the need for more space becomes inevitable. Whether it’s creating a private suite for aging parents, a comfortable home for adult children, or a rental unit for passive income, an ADU offers flexibility without sacrificing your home’s character.
In a prestigious community like San Marino, quality matters. That’s why our approach focuses on thoughtful design, premium finishes, and long-lasting craftsmanship ensuring your new ADU feels like a natural extension of your property, not an afterthought.
Here are some ADUs you can get:
- Granny flat
- Home addition
- Garage conversion
- ADU construction
- Bump-outs
- Porches and decks
- Second-story additions
- Attached garages
- Other conversions
Understanding San Marino, CA Zoning Laws & Building Permit Requirements
San Marino has some of the most detailed zoning and design standards in Los Angeles County. ADU construction here requires careful planning, precise documentation, and a deep understanding of local regulations.
Key considerations often include:
- Maximum ADU size based on lot dimensions
- Height and setback requirements
- Architectural compatibility with the primary residence
- Utility connections and sewer capacity
- Historic property considerations (when applicable)
Our team manages the entire permitting and approval process, working closely with the City of San Marino to ensure your ADU meets all zoning, building, and safety requirements without unnecessary delays.
Top benefits of building an ADU:
- Small enough to fit on smaller inner city lots and large estate properties
- Turn-key solutions for both design & construction
- Can be converted, attached, or detached to your existing house
- Built off-site in 90 days and delivered to your residence
- Little or no debt and reduced expenses, ready to move in
ADU Contractor Project Cost Near San Marino, CA
While every ADU is unique, reviewing real-world project examples helps homeowners understand how design choices and finishes impact overall cost. Below are examples of recent ADU builds completed near San Marino.
New 735 sq. ft. Two-Story ADU in Alhambra, CA
This two-story detached ADU builder project included:
- New foundation
- New plumbing
- New electrical
- New HVAC
- New Spanish style finishes
- New custom kitchen cabinets
- New separate Utility connections
Total project cost: $250,000.
The most significant investment was the architectural and structural design package, totaling $15,000.
New 535 sq. ft. ADU in Whittier, CA
This compact yet efficient ADU featured:
- 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
Total project cost: $150,000.
Custom kitchen cabinets with marble countertops were the largest expense at $12,550.
New 798 sq. ft. ADU in Downey, CA
This high-end ADU builder 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
Total project cost: $200,000.
The premium bathroom tile package was the most expensive feature at $8,000.
Fully Enjoy The Excitement Of Your Home Upgrade
Building an ADU should be exciting not overwhelming. Our proven 3-step process keeps everything organized and transparent:
1
Collaborate
Contact us and let’s plan your ADU together with our designers.
2
Build
Remain comfortable and on top of everything at all times.
3
Enjoy
Have everyone over for dinner and enjoy your new ADU!
A Lifelong Partnership With A Reliable Expert
An ADU is a long-term investment, and choosing the right contractor makes all the difference. We don’t disappear once construction ends we stand behind our work and remain a trusted resource long after your project is complete.
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.
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.
Y
Had a truly great experience with Alex. Cornejo’s Builders just completed converting my crawlspace/basement into an ADU (studio with new bathroom and kitchen).
What made the experience even more valuable was that the owner himself (Alex) came over for a consultation. Other companies just send their sales reps and most of the time they don’t even know anything. Feeling important is always a positive I can’t wait to work with them again.
I highly recommend them. You can tell Alex is passionate about what he does, his clients, and his company.
The Perks Of A Seasoned ADU Contractor In South CA
Take advantage of the best perks of working with a local, trusted ADU contractor here in Downey, San Marino, and surrounding areas.
- Peace Of Mind
Everyone involved in your project is 100% committed to your satisfaction. You’ll be treated with utmost respect 24/7.
- Quality Craftsmanship
You’ll enjoy the best tradesmen here in South California, all ready to deliver the best product you could ever find around here.
- Dialed-in Processes
Remain comfortable while fully enjoying the excitement of getting an ADU. We have the know-how to make it happen!
ADU Contractor FAQs in San Marino, CA
How long does it take to build an ADU in San Marino?
Can I build an ADU on a smaller lot in San Marino?
Yes, but size, setbacks, and design must comply with city zoning rules. A site evaluation is critical.
Do ADUs increase property value in San Marino?
In most cases, yes. ADUs add livable square footage and long-term income potential, both highly valued in this market.
Can an ADU be used as a rental property?
Yes, ADUs can be rented, though short-term rentals may have restrictions.
Start Building Homes & Get a Free Quote
- Cornejos Builders ADU Construction & Home Building
- 8909 Elmont Ave. Downey, CA 90240
- (562) 319-3178
- alex@cornejosbuilders.com