How Much Does an ADU Cost in San Jose? (2026)
San Jose ADUs cost $120,000-$500,000+ in 2026 depending on type and scope. Garage conversions start at $120K. Attached ADUs run $150K-$300K. Detached ADUs cost $250K-$450K+. San Jose offers reduced ADU permit fees and impact fee waivers for units under 750 sqft, making it one of the most ADU-friendly cities in the Bay Area.
How much does an ADU cost in San Jose?
ADU costs in San Jose range from $120,000 for a garage conversion to $450,000+ for a large detached unit in 2026. The average detached ADU costs $250K-$400K. Attached ADUs average $150K-$300K. San Jose's reduced permit fees and impact fee waivers for units under 750 sqft help keep costs below Bay Area averages.
ADU Costs in San Jose: What to Expect in 2026
San Jose is the largest city in the Bay Area and one of the most ADU-friendly. With a population of over one million, strong rental demand, and city policies designed to encourage accessory dwelling units, San Jose homeowners are in a strong position to add value to their properties. But understanding costs before you start is critical.
This guide breaks down 2026 ADU costs specific to San Jose: what each type costs to build, what you will pay in permits and fees, what drives costs up or down, and how to plan your budget. Custom Home Design and Build is headquartered right here in San Jose, so we build ADUs in this market every day.
For Bay Area-wide ADU pricing, see our ADU cost guide.
Cost by ADU Type
The type of ADU you build is the single biggest factor in your total cost. Here is what San Jose homeowners are paying in 2026:
| ADU Type | Cost Range | Cost/Sqft | Timeline | Typical Size |
|---|---|---|---|---|
| Garage Conversion | $120,000-$150,000 | $150-$350 | 4-6 months | 400-500 sqft |
| Attached ADU | $150,000-$300,000 | $300-$450 | 6-10 months | 400-800 sqft |
| Detached ADU | $250,000-$450,000+ | $350-$500 | 8-14 months | 500-1,200 sqft |
| Junior ADU (JADU) | $80,000-$150,000 | $200-$350 | 3-5 months | 200-500 sqft |
These ranges cover construction costs. Permits, design fees, and utility connections are additional expenses covered in the sections below.
Garage Conversions: The Budget-Friendly Option
Garage conversions are the most affordable ADU type because the structure already exists. You skip foundation work, framing, and roofing. The core investment goes toward insulation, drywall, flooring, a kitchen, a bathroom, plumbing, electrical upgrades, and HVAC.
In San Jose, a one-car garage conversion (250-400 sqft) runs $80,000-$120,000. A two-car garage (400-600 sqft) costs $120,000-$150,000. Attached garages cost less to convert than detached garages because utility connections are shorter and easier to tie into the main house. Detached garage conversions run 20-30% higher due to the need to trench and extend utility lines.
Attached ADUs
Attached ADUs connect to the main house, sharing at least one wall. This makes utility connections simpler and reduces foundation and roofing costs compared to a fully detached unit. In San Jose, attached ADUs are popular on tighter lots where a detached structure would not meet setback requirements.
Expect to pay $150,000-$300,000 for an attached ADU in San Jose. The wide range reflects differences in size (400-800 sqft), the complexity of integrating with the existing structure, and finish level.
Detached ADUs
Detached ADUs are standalone structures, completely separate from your main home. They offer maximum privacy and rental potential, which is why they command the highest rents. In San Jose, a detached ADU costs $250,000-$450,000+.
The higher cost reflects new foundation, full framing, roofing, independent utility connections (water, sewer, electrical), and site work. For properties on larger lots (9,000+ sqft), San Jose allows detached ADUs up to 1,200 sqft, which pushes toward the top of that range.
San Jose ADU Permit Fees and Soft Costs
Construction is only part of the total budget. Here are the other costs San Jose homeowners should plan for:
| Cost Category | Typical Range | Notes |
|---|---|---|
| Building permit fees | $3,000-$15,000 | Based on project scope and valuation |
| Architectural/design fees | $8,000-$25,000 | Plans, engineering, Title 24 energy compliance |
| Utility connections | $5,000-$15,000 | Water, sewer, electrical; detached ADUs cost more |
| Impact fees (750+ sqft) | $5,000-$15,000 | School and parkland fees for units 750 sqft and above |
| Impact fees (under 750 sqft) | $0 | Waived under California law since 2020 |
| Survey and soils report | $2,000-$5,000 | Required for new detached structures |
| Landscaping and site restoration | $3,000-$10,000 | Driveway repair, fencing, yard restoration |
Total soft costs typically add $20,000-$60,000 on top of construction, depending on the project.
San Jose’s ADU-Friendly Fee Structure
San Jose has taken deliberate steps to reduce barriers for ADU construction. Key advantages include:
- Impact fee waivers for units under 750 sqft. Since January 2020, ADUs smaller than 750 sqft are exempt from parkland and school impact fees. This can save $5,000-$15,000.
- ADU Ally service. The San Jose Permit Center offers a dedicated ADU Ally to help homeowners navigate the permitting process, reducing confusion and delays.
- Pre-approved ADU plans. The city maintains a library of pre-approved architectural plans that automatically meet local building requirements. Choosing a pre-approved plan can cut approval time significantly.
- Online Building Fee Estimator. San Jose provides an online tool that gives you a project-specific estimate of permit fees before you apply.
These programs make San Jose one of the most cost-effective cities in the Bay Area for ADU construction.
What Drives ADU Costs in San Jose
Size and Layout Complexity
Cost per square foot drops as the ADU gets larger, but total cost increases. A 500 sqft ADU costs less overall than a 1,000 sqft unit, but the per-square-foot rate is higher because fixed costs (kitchen, bathroom, utility hookups) are spread over less area. In San Jose, expect $350-$500 per sqft for smaller units (under 600 sqft) and $300-$400 per sqft for larger units (800-1,200 sqft).
Foundation and Site Conditions
Detached ADUs need new foundations. In San Jose, soil conditions vary by neighborhood. Areas near downtown and in Willow Glen tend to have stable soil, while parts of Evergreen and East San Jose may require deeper footings or additional grading. A soils report ($2,000-$4,000) will tell you what to expect before construction starts.
Finish Level
The gap between basic and premium finishes can be $50,000-$100,000 or more on the same-size ADU.
| Finish Level | Description | Added Cost vs. Standard |
|---|---|---|
| Standard | Laminate countertops, vinyl flooring, builder-grade fixtures | Baseline |
| Mid-range | Quartz countertops, LVP flooring, upgraded fixtures, tile backsplash | +$15,000-$30,000 |
| High-end | Stone countertops, hardwood flooring, custom cabinetry, premium appliances | +$40,000-$80,000+ |
Most San Jose homeowners building for rental income choose mid-range finishes. Homeowners building for family members or aging parents tend to invest in higher-end finishes for long-term comfort.
Utility Connections
Attached ADUs and garage conversions share utility infrastructure with the main house, keeping connection costs low ($5,000-$8,000). Detached ADUs require independent lines for water, sewer, and electrical, running $10,000-$15,000 or more. California law also requires a separate electrical panel for metering in all ADUs.
San Jose ADU Regulations to Know
Understanding the rules before you plan saves time and money. Here are the key San Jose ADU regulations for 2026:
- Lot zoning. Your property must be zoned R-1, R-2, R-M, or PD.
- Maximum size. Lots under 9,000 sqft: detached ADU up to 1,000 sqft. Lots 9,000 sqft and above: up to 1,200 sqft.
- Setbacks. 4 feet from side and rear property lines for detached ADUs.
- Rear yard coverage. Structures cannot cover more than 40% of the rear yard or 800 sqft, whichever is greater.
- Parking. No additional parking is required for ADUs in San Jose (per state law).
- One ADU plus one JADU per lot. You can build both on a single-family property.
San Jose’s diverse lot sizes, from compact neighborhoods in Central San Jose to larger parcels in Almaden Valley and the Evergreen foothills, mean that the right ADU type varies by location. A builder with local experience can assess your lot and recommend the best approach.
How San Jose Compares to Other Bay Area Cities
San Jose is one of the most affordable Bay Area cities for ADU construction. Here is how a typical 600 sqft detached ADU compares:
| City | Estimated Cost | Permit Timeline | Key Difference |
|---|---|---|---|
| San Jose | $250,000-$350,000 | 6-10 weeks | Reduced fees, ADU Ally support |
| Sunnyvale | $270,000-$380,000 | 8-12 weeks | Standard processing |
| Cupertino | $290,000-$400,000 | 8-14 weeks | Higher finish expectations |
| Palo Alto | $320,000-$450,000 | 10-16 weeks | Design review adds time and cost |
| Saratoga | $320,000-$460,000 | 10-16 weeks | Hillside lots increase site work |
San Jose’s lower labor costs, streamlined permitting, and fee waivers contribute to savings of 10-25% compared to premium South Bay and Peninsula cities.
Sample ADU Budgets for San Jose
Budget Example: 450 sqft Garage Conversion
| Line Item | Cost |
|---|---|
| Construction | $110,000 |
| Building permits | $4,000 |
| Design and engineering | $8,000 |
| Utility upgrades | $5,000 |
| Landscaping/site restoration | $3,000 |
| Total | $130,000 |
Budget Example: 800 sqft Detached ADU
| Line Item | Cost |
|---|---|
| Construction | $300,000 |
| Building permits | $10,000 |
| Design and engineering | $18,000 |
| Utility connections | $12,000 |
| Impact fees (over 750 sqft) | $8,000 |
| Survey and soils report | $3,500 |
| Landscaping/site restoration | $6,000 |
| Total | $357,500 |
These are mid-range estimates. Your final number will depend on your lot conditions, finish selections, and any site-specific challenges.
How to Control Your ADU Budget
Lock in Pricing During Design
The biggest source of budget overruns is starting construction before the scope is fully defined. At Custom Home, our two-phase process separates design from construction. During Phase 1, we create full 3D renderings and lock in every material selection and line item. You approve the final number before a single shovel hits the ground.
Right-Size Your ADU
Bigger is not always better. A well-designed 600 sqft ADU can feel spacious and rent for nearly as much as an 800 sqft unit. Staying under 750 sqft also eliminates impact fees, saving you $5,000-$15,000 in San Jose.
Choose Durable Over Expensive
For rental ADUs, mid-range finishes with high durability (LVP flooring, quartz countertops, porcelain tile) deliver the best return. Premium finishes look great but do not proportionally increase rental income.
Work With a Local Builder
A builder headquartered in San Jose knows the permit process, the inspectors, the soil conditions, and the neighborhoods. That local knowledge eliminates surprises and keeps timelines on track.
Why San Jose Homeowners Choose Custom Home
Custom Home Design and Build is based in San Jose at 2092 Concourse Drive. We have been building ADUs, custom homes, and remodels across the Bay Area since 2005. Our design-build approach means one team handles architecture, permitting, and construction, so nothing falls through the cracks.
For ADU projects, our process works like this:
- Free consultation. We assess your lot, discuss your goals, and provide a realistic budget range.
- Phase 1: Design. Full architectural plans, 3D renderings, material selections, and a locked-in construction price.
- Phase 2: Build. Permitted construction with weekly progress updates and a dedicated project manager.
Every detail is decided before we build. No surprises, no change orders, no budget creep.
Start Your San Jose ADU Project
San Jose’s combination of ADU-friendly policies, diverse lot sizes, and strong rental demand makes it one of the best cities in the Bay Area for an ADU investment. Whether you are converting a garage, building a detached unit, or adding an attached suite, the key is starting with a clear plan and accurate numbers.
Ready to explore what an ADU would cost on your specific property? Contact Custom Home for a free consultation. We will visit your site, discuss your goals, and give you a realistic budget based on your lot, your neighborhood, and your vision.
Frequently Asked Questions
What are the permit fees for an ADU in San Jose?
San Jose ADU building permit fees range from $3,000 to $15,000 depending on the size and scope of the project. Units under 750 sqft are exempt from parkland and school impact fees, which can save thousands. Use the City of San Jose's online Building Fee Estimator tool for a project-specific estimate before you begin.
How long does it take to get an ADU permit in San Jose?
San Jose typically processes ADU permits in 6 to 10 weeks. The city offers an ADU Ally service at the Permit Center to help homeowners navigate the application process. Pre-approved ADU plans can cut approval time significantly. Plan for 8-14 months total from initial design through completed construction.
What is the maximum ADU size allowed in San Jose?
San Jose allows detached ADUs up to 1,000 sqft on lots under 9,000 sqft and up to 1,200 sqft on lots of 9,000 sqft or larger. Attached ADUs can be up to 50% of the primary residence area, with a maximum of 1,000 sqft (under 9,000 sqft lot) or 1,200 sqft (9,000+ sqft lot). JADUs are capped at 500 sqft.
Can I build an ADU and a JADU on my San Jose property?
Yes. San Jose allows one ADU and one JADU per single-family lot. A JADU is created within the existing footprint of your home (up to 500 sqft), while the ADU can be a detached structure, an attached addition, or a garage conversion. This combination lets you add two income-generating units to a single property.