California’s ADU laws changed everything. Here’s what it actually costs to build an ADU in San Jose in 2025.
ADU Cost Summary — San Jose 2025
Helpful Resources:
| ADU Type | Cost Range | Timeline | Rental Income |
|---|---|---|---|
| Detached ADU (500 sq ft) | $150,000–$250,000 | 8–12 months | $2,500–$3,500/mo |
| Detached ADU (1,000 sq ft) | $250,000–$400,000 | 10–14 months | $3,500–$4,500/mo |
| Garage Conversion (500 sq ft) | $60,000–$120,000 | 4–7 months | $2,000–$3,000/mo |
| Junior ADU (JADU) | $40,000–$80,000 | 3–5 months | $1,500–$2,500/mo |
| Attached ADU | $120,000–$280,000 | 7–11 months | $2,200–$3,800/mo |
What’s Included in ADU Construction Cost?
- Design & Engineering: $5,000–$20,000. Architectural drawings, structural engineering, energy calculations
- Permits: $8,000–$25,000. City building, planning, utility connection fees
- Foundation: $15,000–$40,000. Concrete slab or raised foundation
- Framing & Structure: $25,000–$60,000. Wood or steel framing, roof structure
- Mechanical (Plumbing/HVAC/Electrical): $25,000–$60,000. Full utility systems for self-contained unit
- Exterior: $15,000–$35,000. Siding, windows, roofing, exterior doors
- Interior Finish: $25,000–$60,000. Kitchen, bathroom, flooring, paint, trim
- Utility Connections: $5,000–$25,000. New meters, service connections
ADU ROI Calculator for San Jose
Example: 600 sq ft detached ADU
- Construction cost: $200,000
- Monthly rent: $3,000
- Annual income: $36,000
- Annual ROI: 18% on construction cost
- Payback period: 5.6 years
- Property value increase: $300,000–$450,000
San Jose ADU Permit Process
San Jose has streamlined ADU permitting under California state law. Key points: (1) All residential zones allow ADUs, (2) Permit processing: 30–60 days for some projects (California mandate), (3) Owner-occupancy requirement was removed statewide, (4) Pre-approved ADU plans can speed up the process significantly. Quartz Construction manages the entire permit process.
Ready to build an ADU in San Jose? Quartz Construction has built 50+ ADUs throughout the Bay Area. Call (650) 749-7436 for a free site assessment. CSLB #1003436 | BBB A+ | 4.9⭐
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What Our Bay Area Clients Say
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"Quartz Construction did an amazing job on our kitchen remodel. The team was professional, on time, and the results exceeded our expectations. Highly recommend to any Bay Area homeowner!"
— Michael T. |
"We hired them for a bathroom remodel in our San Jose home. From permitting to final walkthrough, everything was handled perfectly. The tile work is stunning. 5 stars without hesitation."
— Sarah L. |
"Just finished our ADU garage conversion. The project came in on budget and on schedule — rare in the Bay Area! The rental income already started. Could not be happier with Quartz Construction."
— David R. |
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