Now Booking Fall 2026 ADU Projects: Schedule Your Consultation
Bay Area ADU Builder From Feasibility to Final Inspection
Our architect-led team coordinates lot feasibility, plans, engineering, permits, utilities, construction, and final inspection.
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Since 2018
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An accessory dwelling unit is an independent living unit on a property with an existing or proposed primary home. An ADU project can include feasibility, architecture, engineering, permits, utility planning, construction, inspections, and closeout. The right path depends on the lot, existing structures, access, utilities, and local review requirements.
For detailed ADU pricing factors, use our 2026 Bay Area ADU cost guide.
Reviewed by Alexander Hamilton Li, Architect & General Contractor · CSLB #1078806 · Updated August 2026
Your next step
Start Your ADU Consultation Online
Share your property and project goals. Our team will discuss feasibility, design, permits, and the next planning step.
Start With the ADU Service Your Property Needs
Detached ADUs
A new backyard structure planned around the lot, setbacks, access, utilities, fire requirements, privacy, permits, and construction logistics.
ADU Design
Architect-led feasibility and plans shaped by the property, existing home, program, code constraints, utilities, and budget.
ADU Permits
Plan-check coordination for architecture, engineering, energy documents, utility requirements, agency comments, revisions, and inspections.
Garage Conversion ADUs
Conversion planning for the existing slab, framing, ceiling height, fire separation, insulation, utilities, windows, access, and permits.
ADU Project Reviews
Verified public reviews from homeowners who hired Hamilton Exteriors.
Yaku Escobar
via Google
We worked with Hamilton Exteriors to build a small ADU in our backyard. from the beginning the process felt organized and clear. Alex Lee was very responsive and always kept us in the loop, especially during planning and inspections. The crew was consistent and respectful of the space which we appreciated since we were living there during the build. overall everything moved pretty smoothly and the final result looks exactly like what we had in mind. really happy with how it turned out.
Rafa Simons
via Google
My family hired Hamilton after seeing the neigbours new ADU, the whole team were super organized and tecnological and also very patient to undestand my needs before starting the construction. But what i like the best is that they are really preocupated with the final result and they kept us well inform with details and everything. Definitely recomend them.
H.T.
via Google
I had a great experience working with Hamilton exteriors. From start to finish, their team was professional, responsive, and detail-oriented. They made the entire process smooth and stress-free, keeping me updated every step of the way. The quality of their work really stands out. Everything was done efficiently and exceeded my expectations. If you’re looking for a reliable company that takes pride in what they do, I highly recommend them!
Jessica W.
via BBB
The team was professional, communicative, and completed the job in a timely manner. They kept me informed throughout the entire process and arrived as scheduled. The work was well supervised, and the crew paid close attention to every detail. They left the property clean and organized when the job was finished. Overall, the entire experience was smooth, stress-free, and exceeded my expectations. I would definitely recommend their services to others.
How Hamilton Exteriors
Manages Your ADU Project
Property Feasibility
We review the lot, setbacks, existing structures, access, utilities, drainage, fire requirements, and likely permit path.
Design and Permit Coordination
Our team coordinates architecture, engineering, energy documents, utility requirements, submittals, comments, revisions, and approved construction documents.
ADU Construction
We manage site work, foundation, framing, building envelope, mechanical, electrical, plumbing, finishes, inspections, and documented changes.
Final Inspection and Closeout
We coordinate corrections and final inspections, complete the punch list, and organize closeout and applicable warranty information.
Compare Broad ADU Project Paths
Swipe to compare all options.
| Feature | Detached ADU | Garage Conversion | Junior ADU |
|---|---|---|---|
| Location | Separate backyard structure | Within an existing garage | Within the primary home |
| Existing shell | New foundation and structure | Existing shell requires verification | Existing conditioned structure |
| Main feasibility focus | Lot, access, setbacks, and utilities | Structure, slab, height, and utilities | Interior layout and required shared systems |
| Privacy planning | Separate building and entrance | Entrance and yard relationship | Connection to the primary home |
| Dedicated guide | Detached ADUs | Garage conversions | Start with an ADU consultation |
Plan Your ADU Project With Approved Credit
Financing may be available for eligible ADU construction projects with approved credit. During feasibility and scope planning, we explain current lender programs, terms, amounts, and payment timing that may apply to the design and construction path.
Ask which current options fit your ADU project scope.
Call Now (650) 977-3351 Frequently Asked Questions
Didn't find the answer to your question? Call Now (650) 977-3351
What does a Northern California ADU builder handle?
An ADU builder can coordinate feasibility, architecture, engineering, energy documents, permits, utility planning, site work, construction, inspections, and closeout. Hamilton Exteriors keeps these parts under one architect-led project team.
How do I know whether my property can support an ADU?
We review the lot, existing structures, setbacks, easements, fire access, utility routes, grading, drainage, and local overlays. That early study identifies the practical project paths before detailed design begins.
Which ADU type should I start with?
The right path depends on available space, the existing garage or home, privacy goals, utility access, construction access, and budget. We compare detached, garage-conversion, and junior-ADU options during feasibility, then define the next design step.
Do you handle ADU design and permits?
Yes. Our architect-led team coordinates plans, engineering, energy documents, permit submittals, agency comments, revisions, and required inspections. Review time and required documents vary by jurisdiction and site conditions.
Can an ADU be used for family or rental housing?
ADUs can support family housing, long-term rental use, or flexible living space. Occupancy and rental rules vary by jurisdiction and property. We design the approved use and life-safety features into the plans, but owners should confirm local operating rules before renting.
Plan Your Project With a Clear Scope
Financing may be available with approved credit for eligible projects.
Tell us about your project. We usually call within 3–5 minutes to schedule the next step.
21634 Redwood Rd Unit F, Castro Valley, CA 94546
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