With 10% pre-1940 in San Jose, many properties have room for an ADU alongside the original structure. UV degradation of asphalt shingles from heat cycling often make ADU construction the ideal time to address deferred maintenance on the primary residence.
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For local cost factors and planning, read our ADU construction cost guide for San Jose.
For detailed ADU pricing factors, use our 2026 Bay Area ADU cost guide.
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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.
San Jose's housing stock spans 10% pre-1940, 20% 1940-1960, 35% 1960-1980. Architectural styles range from Queen Anne Victorians and Craftsman bungalows in Naglee Park and Willow Glen to 1960s-80s tract ranches in Cambrian and Blossom Valley. 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.
San Jose's Planning Division has created a dedicated ADU resource center with pre-approved plans and an online permit portal. The city targets 60-day plan review for complete ADU applications and has waived many development impact fees for units under 750 square feet. For larger or custom ADUs, the city assigns a project planner who serves as a single point of contact through the approval process. Hamilton Exteriors works with San Jose's planning staff regularly and understands how to prepare applications that move efficiently through review.
San Jose's residential lots are among the most ADU-friendly in the Bay Area. Neighborhoods like Willow Glen, Cambrian, and Blossom Valley feature single-story ranch homes on 6,000 to 8,000 square foot lots with flat topography and rear alley access in some areas. These conditions allow detached ADUs of 600 to 1,000 square feet without impacting the primary home's yard space significantly. In Almaden Valley and Silver Creek, larger lots of 8,000 to 15,000 square feet accommodate full-sized 1,200 square foot units with two bedrooms and separate parking.
San Jose's rental market strongly supports ADU investment. With average one-bedroom rents at $2,400 and limited housing supply near major employers like Apple, Google, and Adobe, well-located ADUs attract quality tenants quickly. A detached one-bedroom ADU in Willow Glen or Rose Garden can generate $2,200 to $2,800 per month, providing annual gross rental income of $26,000 to $34,000 before expenses.
San Jose offers several ADU incentives beyond state programs. The city has waived school impact fees for ADUs, reduced utility connection fees, and offers an ADU forgivable loan program for homeowners who agree to rent at below-market rates for 15 years. Additionally, Santa Clara County's ADU Ally program provides free technical assistance for homeowners in the early planning stages. Hamilton Exteriors helps clients evaluate whether incentive programs align with their investment goals.
Neighborhoods We Serve
ADU Across San Jose Neighborhoods
Local planning starts with the site, neighborhood context, access, and applicable city review.
SoFA District
SoFA District homeowners frequently choose Hamilton Exteriors for adu. With 10% pre-1940 in San Jose, many properties have room for an ADU alongside the original structure. With San Jose's Downtown/north warmer than south (Almaden gets foothill breeze), material selection in SoFA District requires local expertise.
Naglee Park
In Naglee Park, homes are predominantly 1960s-80s tract ranches in Cambrian and Blossom Valley. UV degradation of asphalt shingles from heat cycling often make ADU construction the ideal time to address deferred maintenance on the primary residence. Our crews are familiar with Naglee Park's architectural character and building requirements.
Willow Glen
Willow Glen's tree-lined streets feature Craftsman, Spanish Revival, and midcentury homes on 6,000 to 8,000 square foot lots. The neighborhood's walkable downtown along Lincoln Avenue makes ADUs attractive to young professionals. Detached backyard ADUs are the most common type here, with rear setbacks that accommodate units of 500 to 800 square feet while preserving established landscaping.
Rose Garden
The Rose Garden neighborhood features 1930s to 1950s homes on generous corner and interior lots ranging from 6,500 to 9,000 square feet. The historic character of the neighborhood calls for ADU designs that complement existing Craftsman and Colonial Revival architecture. Hamilton Exteriors designs ADUs with period-appropriate exterior details while providing modern interiors.
Almaden Valley
Almaden Valley's large lots of 8,000 to 15,000 square feet and newer construction from the 1970s to 1990s make it ideal for full-sized 1,200 square foot ADUs. Many properties have flat rear yards with existing utility access points that simplify construction. The neighborhood's licensed schools and quiet suburban character attract family tenants for long-term leases.
Cambrian
Cambrian features primarily single-story ranch homes from the 1950s and 1960s on 6,000 to 7,500 square foot lots. The uniform lot depths and flat terrain make Cambrian one of the most cost-effective neighborhoods for ADU construction in San Jose. Garage conversions are popular here, transforming attached two-car garages into studio or one-bedroom units at lower cost than new construction.
Evergreen
Evergreen's newer housing stock from the 1980s to 2000s sits on lots of 5,000 to 8,000 square feet in planned subdivisions. The contemporary construction makes utility connections and foundation work straightforward. Two-story ADUs work well in Evergreen, where taller structures blend with the neighborhood's existing two-story homes and provide bay views from upper-level units.
Berryessa
Berryessa's mix of midcentury ranches and 1980s tract homes on 5,500 to 7,000 square foot lots provides consistent ADU opportunities. The neighborhood's BART extension station, opening nearby, has increased property values and rental demand. Detached ADUs in Berryessa benefit from the flat terrain and wide rear yards typical of the area's subdivision layouts.
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 San Jose
$210,000–$450,000
Median home value in San Jose: $1,350,000
Prices reflect San Jose's premium market and Santa Clara 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 San Jose?
Most ADU builders in San Jose are tradesmen-only — they build what you tell them to build. An architect-led approach means design and construction decisions are made by the same person, eliminating the gaps that cause change orders and budget overruns. Alex Hamilton Li brings an architect's eye to every project. He evaluates your lot for utility access, setbacks, fire department access, and local overlay zones during your initial consultation — at no cost. This upfront assessment prevents costly
How much does a detached ADU cost in San Jose?
A detached ADU in San Jose typically costs $200,000 to $375,000 for a 600 to 800 square foot unit with mid-range finishes (Hamilton Exteriors 2024-2026 project data). This includes design, engineering, permits, and construction. Permit and impact fees add $8,000 to $18,000. Site preparation, utility connections, and finish level are the main cost variables.
How much does a garage conversion cost in San Jose?
Garage conversions in San Jose cost $150,000 to $200,000 (Hamilton Exteriors 2024-2026 project data). You save 30 to 40 percent compared to new construction by reusing the existing foundation, walls, and roof structure. The finished space is typically 400 to 500 square feet for a two-car garage.
How long does it take to build an ADU in San Jose?
Plan on 6 to 12 months total from design start to move-in. Design and permitting take 2 to 4 months. Construction runs 8 to 12 weeks for detached ADUs and 10 to 14 weeks for garage conversions. San Jose's pre-approved plan program can shorten the design and permitting phase by 4 to 6 weeks.
Do I need a permit for an ADU in San Jose?
Yes. All ADUs in San Jose require a building permit from the Development Services Permit Center. California law has streamlined the process, but you still need approved plans and inspections. Building without permits creates code violations, insurance gaps, and complications when you sell.
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.
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