Sebastopol ADU Sale Announcement | Sonoma County
February 24, 2026
Cost
Get a full breakdown of ADU construction costs in San Jose
Are you thinking about building an Accessory Dwelling Unit (ADU) on your property in San Jose? Whether you’re looking to create a rental income stream, build space for family, or increase your home’s resale value, understanding the true cost of building an ADU in San Jose is essential.
Here’s your complete 2025 guide to ADU pricing, including cost breakdowns, influencing factors, local permitting fees, and how to reduce expenses without compromising on quality.
| ADU SQFT | Cost |
|---|---|
| 300-500 SQFT ADU | $205k – $240k |
| 550-750 SQFT ADU | $260k – $325k |
| 800-1000 SQFT ADU | $330k – $390K |
| 1050- 1200 SQFT ADU | $400K – $415K |
What These Cost Include
- Architectural & structural design
- Permit processing
- Full interior build (kitchen, bath, plumbing, electrical)
- Final inspections & sign-off
Factors That Affect Your ADU Construction Cost in San Jose
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ADU Type
Detached ADUs typically cost more than garage conversions because they require their own foundation and utilities. Attached ADUs can also be pricey since they often involve demolition, removing parts of the existing roof and walls, and matching the look of your home.
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Size and Layout Complexity
Larger ADUs and open floor plans usually require more materials and labor. To save you time and money, we offer pre-designed ADU plans. Custom floor plans often involve more time working with architects and can significantly increase costs.
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Site Conditions
Lot slope, access, and soil conditions can add thousands in grading, excavation, or retaining wall costs.
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Utility Access & Upgrades
If your current main house utilities aren’t sufficient, you may need panel upgrades or sewer work.
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Finishes & Fixtures
Custom cabinets, premium tile, or high-end appliances will quickly raise the budget.
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Local Fees and Permits
San Jose’s permit and development fees vary by ADU size and location (covered below).
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Permitting & City Fees for ADUs in San Jose (2025)
Before breaking ground, you’ll need to budget for:
- Building Permit Fees: $8,000 – $15,000+
- Plan Review & Impact Fees: Varies by square footage
- School Impact Fees: Approx. $4–$5 per sq ft (for ADUs over 750 sq ft)
- Utility Fees: $2,000 – $7,000 for water/sewer/electric upgrades
- Title 24 Energy Compliance: Mandatory energy code compliance in California
Many ADUs under 750 sq ft are exempt from school fees and receive reduced development charges under California’s ADU laws (SB 9, AB 68, etc).
How to Save Money on Your ADU in San Jose
- Stick to proven ADU floor plans instead of fully custom designs to reduce design time and cost
- Use mid-range materials that balance quality and affordability without sacrificing appearance
- Choose a design-build firm like IMKAT to streamline communication and reduce project delays
- Conduct a feasibility study upfront to avoid costly surprises during construction
- Design your ADU under key square footage limits to potentially avoid local impact fees
- Prioritize quality and experience over the cheapest bid to prevent long-term issues
- Be cautious of lowball contractor quotes that may lead to excessive change orders later
What’s Included in IMKAT Construction’s ADU Package?
We offer full-service, start-to-finish ADU builds in San Jose, including:
- Free site evaluation
- Custom floor plans
- Permit handling with the City of San Jose
- Licensed, insured, local crew
- Transparent pricing & timelines
