With 8% pre-1940 in Larkspur, many properties have room for an ADU alongside the original structure. moisture damage from heavy winter rain on aging postwar roofs often make ADU construction the ideal time to address deferred maintenance on the primary residence.
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ADU Builder in Larkspur
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For local cost factors and planning, read our ADU construction cost guide for Larkspur.
For detailed ADU pricing factors, use our 2026 Bay Area ADU cost guide.
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Start Your ADU Consultation Online
Share your property and project goals. Our team will discuss feasibility, design, permits, and the next planning step.
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Responsive from consultation through project closeout
Architect and general contractor
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ADU Services 
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.
Larkspur's housing stock spans 8% pre-1940, 20% 1940-1959, 35% 1960-1979. Architectural styles range from 1950s-60s California ranch homes in Greenbrae to postwar subdivisions in Bon Air and Murray Park. Each era and style presents different adu requirements — from material compatibility to structural considerations. Our crews know what to expect before they arrive on site.
Neighborhoods We Serve
ADU Across Larkspur Neighborhoods
Local planning starts with the site, neighborhood context, access, and applicable city review.
Downtown Larkspur
Downtown Larkspur homeowners frequently choose Hamilton Exteriors for adu. With 8% pre-1940 in Larkspur, many properties have room for an ADU alongside the original structure. With Larkspur's Moderate fog, shielded from direct Pacific exposure, material selection in Downtown Larkspur requires local expertise.
Greenbrae
In Greenbrae, homes are predominantly postwar subdivisions in Bon Air and Murray Park. moisture damage from heavy winter rain on aging postwar roofs often make ADU construction the ideal time to address deferred maintenance on the primary residence. Our crews are familiar with Greenbrae's architectural character and building requirements.
Baltimore Park
Baltimore Park lots accommodate garage conversions and detached ADUs. Our architect-led process handles all design, engineering, and permitting so homeowners can add living space without managing multiple contractors.
Murray Park
Murray Park's flat lots and 1960s-era garages are ideal candidates for ADU conversions. We handle structural upgrades, utility connections, and interior finishes to transform underused garage space into comfortable rental units.
Hillview
Hillview's hillside properties present unique ADU opportunities including terraced units with separate entries. We engineer foundations and drainage systems suited to sloped terrain while maximizing usable square footage.
Project Management How Hamilton Exteriors
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.
Google rating 4.6 ★ from 47 public reviews
ADU Project Reviews
Verified public reviews from homeowners who hired Hamilton Exteriors.
Y
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.
R
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
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!
J
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.
Google rating: 4.6/5 from 47 public reviews
Read reviews on Google Premium Market
ADU Costs in Larkspur
$300,000–$600,000
Median home value in Larkspur: $1,800,000
Prices reflect Larkspur's premium market and Marin County labor rates. Actual costs depend on home size, materials, and project complexity. We provide free, itemized estimates with no hidden fees.
Get Your EstimateCompare 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 |
ADU Financing
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 areas do you serve?
We serve Northern California across three regions: the San Francisco Bay Area, Greater Sacramento, and the Central Valley. Our published guides cover 14 counties and 88 cities. Our Castro Valley and Sacramento offices support local estimating, permit coordination, and project planning across these regions.
How does billing and financing work?
Financing may be available for eligible projects with approved credit. Available terms depend on lender approval, project scope, and current programs. Your project manager can review the options that apply before work begins. We also accept checks, ACH, and major credit cards.
Are you licensed and insured?
Yes. Hamilton Exteriors holds CSLB License #1078806, active general liability coverage, and the required contractor bond. We also hold GAF Master Elite and James Hardie Elite Preferred credentials. We can provide current proof of coverage before work begins.
Do I need a permit for my exterior project?
Permit requirements depend on the project scope and local jurisdiction. Hamilton Exteriors coordinates required applications, plan documents, corrections, and inspections. Permit fees and allowances appear in the proposal before construction begins.
Why Choose an Architect-Led ADU Builder in Larkspur?
Most ADU contractors in Marin County are general contractors who subcontract design work to independent architects. This creates a gap between what is designed and what gets built. Change orders, miscommunications, and budget overruns are common. Hamilton Exteriors is different. Alexander Hamilton Li is both a licensed architect and a licensed general contractor (CSLB #1078806). He oversees every project from initial inspection through final walkthrough. This integration means: - Design decision
How much does an ADU cost in Larkspur?
A detached ADU in Larkspur typically costs $200,000 to $375,000 for 400 to 1,200 square feet (Hamilton Exteriors 2024-2026 project data). Garage conversions run $150,000 to $200,000. Junior ADUs start around $150,000. These ranges include design, engineering, permits, and construction but exclude site preparation, utility connections, and optional upgrades. Contact us for an itemized estimate specific to your property.
Do I need a permit to build an ADU in Larkspur?
Yes. All ADUs in Larkspur require a building permit from the Larkspur Building Division. California law requires the city to approve or deny your application within 60 days of receiving a complete submission. Hamilton Exteriors handles the entire permit process.
Can I build an ADU on my property in Larkspur?
If you own a single-family home in Larkspur, you almost certainly can. State law overrides most local zoning restrictions that previously blocked ADUs. Your lot must meet setback requirements (typically 4 feet from side and rear property lines), and the ADU cannot exceed certain size limits. A site feasibility review during your consultation confirms what is possible.
How long does it take to build an ADU in Larkspur?
Plan on 8 to 12 months total from design start to move-in. Design and permitting take 2 to 4 months, and construction runs 4 to 6 months for detached ADUs or 10 to 14 weeks for garage conversions. The permitting phase is the most variable, though state law requires a 60-day decision.
Your Next Step
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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