Quick Answer: Converting a garage to an ADU in San Jose costs $60,000–$150,000 depending on the garage size, finishes, and whether mechanical/electrical upgrades are needed. No replacement parking is required (California law). Permits take 4–10 weeks. Construction takes 6–14 weeks. It’s the fastest and most affordable way to add an ADU.
Garage Conversion to ADU in San Jose 2025
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A garage conversion is the most popular and affordable way to add an ADU in San Jose. Converting an existing structure eliminates the cost of a foundation and much of the framing, reducing costs by 30–50% compared to a detached ADU. Here’s everything you need to know.
Garage Conversion Cost in San Jose
| Garage Type | Size | Conversion Cost |
|---|---|---|
| 1-car garage (attached) | 200–300 sq ft | $45,000–$90,000 |
| 1-car garage (detached) | 200–300 sq ft | $55,000–$100,000 |
| 2-car garage (attached) | 400–500 sq ft | $80,000–$150,000 |
| 2-car garage (detached) | 400–500 sq ft | $90,000–$165,000 |
| 3-car garage (detached) | 600–800 sq ft | $120,000–$220,000 |
What’s Included in a Garage Conversion
- Insulation — Walls, ceiling, and garage door opening infill
- Drywall — Full interior drywall, fire-rated between attached garage and home
- Electrical — New panel circuit (or subpanel), outlets, lights, kitchen range circuit
- Plumbing — Bathroom and kitchen rough-in, water supply and drain connections
- HVAC — Mini-split system ($3,000–$6,000) or extension of existing system
- Kitchen — Cabinets, countertop, sink, appliances
- Bathroom — Toilet, shower, vanity, tile
- Flooring — Concrete leveling + LVP or tile flooring
- Windows & Doors — Garage door removal, infill framing, new windows, entrance door
California Garage Conversion Rules in San Jose
- No replacement parking required: California law (AB 2097) prohibits cities from requiring replacement parking for garage conversions near transit (within 1/2 mile). San Jose adopted this broadly.
- 4-foot setbacks: Only required if expanding beyond the existing garage footprint
- Fire separation: Attached garages require 1-hour fire-rated wall between garage and home interior
- Ceiling height: Minimum 7 feet clear height required for habitable space
Garage Conversion ROI in San Jose
A garage conversion ADU in San Jose generating $2,200/month in rent produces $26,400/year gross income. At a $100,000 cost, that’s a 26% gross cash-on-cash return — among the highest available in real estate. The ADU also adds $120,000–$200,000 to home value. Total first-year return: $26,400 + $150,000 appreciation upside = exceptional investment.
Quartz Construction specializes in garage conversion ADUs throughout San Jose. Call (650) 749-7436 for a free garage conversion assessment. CSLB #1003436 | BBB A+ | 4.9⭐. Learn more about ADU construction.
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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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Phone: (650) 749-7436
Address: 1777 Hamilton Ave #1080, San Jose, CA 95125
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