Quick Answer: Converting a garage to living space (either an ADU or a family/bonus room) in San Jose in 2025 costs $60,000-$150,000 for a standard 2-car garage (400-500 sq ft). The cost is higher than a typical room addition because garages weren’t built for habitation — they need: (1) Insulation in all walls, ceiling, and floor (often requires applying rigid foam over concrete slab); (2) Electrical service upgrade (garages often have 15-20A circuits; a living space needs 20A circuits, GFCI outlets, and dedicated circuits for kitchen appliances); (3) HVAC — mini-split installation ($3,000-$6,000); (4) Plumbing — if making it an ADU, full kitchen and bathroom rough-in through the concrete slab ($10,000-$25,000); (5) Drywall, flooring, windows, and door reconfiguration. If it’s an ADU, a permit is required; if it’s a bonus room (not a separate dwelling), a building permit is still required to change its use from garage to living space.
Garage Conversion Cost Breakdown — San Jose 2025
| Cost Category | Bonus Room | ADU (with kitchen + bath) |
|---|---|---|
| Structural (floor leveling, slab) | $0 – $5,000 | $0 – $8,000 |
| Framing (interior walls) | $3,000 – $8,000 | $5,000 – $12,000 |
| Insulation (walls, ceiling, floor) | $3,000 – $8,000 | $4,000 – $10,000 |
| Drywall | $3,000 – $7,000 | $4,000 – $9,000 |
| Electrical (panel upgrade + wiring) | $5,000 – $12,000 | $8,000 – $18,000 |
| Plumbing (ADU kitchen + bath) | $0 | $12,000 – $28,000 |
| HVAC (mini-split) | $3,000 – $6,000 | $3,500 – $7,000 |
| Windows and door (replace garage door) | $5,000 – $12,000 | $6,000 – $14,000 |
| Flooring | $3,000 – $8,000 | $4,000 – $10,000 |
| Kitchen (ADU only) | $0 | $8,000 – $20,000 |
| Bathroom (ADU only) | $0 | $15,000 – $35,000 |
| Paint, trim, finish | $3,000 – $6,000 | $4,000 – $8,000 |
| Permit fees | $1,500 – $4,000 | $3,000 – $8,000 |
| Total | $30,000 – $72,000 | $76,500 – $177,000 |
Quartz Construction handles complete garage conversion projects in San Jose — from permit application through final inspection. Learn about ADU and garage conversion services. CSLB #1003436 | Call (650) 749-7436.
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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."
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"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."
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Phone: (650) 749-7436
Address: 1777 Hamilton Ave #1080, San Jose, CA 95125
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