Quick Answer: Converting a two-car garage (typically 400–576 sq ft) to an ADU in San Jose costs $80,000–$180,000 all-in including design, permits, and construction. A basic studio conversion runs $80,000–$120,000; a one-bedroom with full kitchen and bath runs $110,000–$160,000; a high-end conversion with premium finishes reaches $140,000–$200,000. The larger footprint of a two-car garage (vs. a one-car) makes it one of the most valuable ADU conversion opportunities in the Bay Area.
Two-Car Garage ADU Conversion Cost Breakdown — San Jose 2025
Helpful Resources:
| Cost Item | Range | Notes |
|---|---|---|
| Architectural design + engineering | $8,000–$20,000 | Floor plans, structural, Title 24 compliance |
| San Jose building permits | $5,000–$12,000 | Building, plumbing, electrical, mechanical |
| Foundation modifications (if needed) | $5,000–$20,000 | Drainage, waterproofing under slab |
| Framing and structural (garage door wall) | $8,000–$20,000 | Replace garage door with wall + windows |
| Plumbing rough-in (kitchen + bath) | $12,000–$25,000 | New drain stack connection, supply lines |
| Electrical (panel upgrade + circuits) | $6,000–$15,000 | Sub-panel, new circuits, EV charger if needed |
| Insulation + drywall | $6,000–$14,000 | R-15 walls, R-38 ceiling per Title 24 |
| Kitchen + bathroom finishes | $15,000–$40,000 | Cabinets, countertops, fixtures, tile |
| Mini-split HVAC | $3,500–$7,000 | Required for habitable space |
| Solar (if required for new ADU) | $8,000–$18,000 | California mandate for new ADUs in most cases |
Two-Car Garage ADU vs. One-Car Garage ADU in San Jose
- Square footage: Two-car garages typically measure 400–576 sq ft (20×20 or 22×24 ft); one-car garages are 200–300 sq ft. Larger ADUs command significantly higher rent.
- Rental income potential: A 500 sq ft ADU in San Jose rents for $2,500–$3,500/month; a 250 sq ft studio rents for $1,400–$2,000/month
- Bedroom count: A two-car garage can accommodate a true one-bedroom ADU with separate kitchen, bathroom, and living room — significantly more rentable than a studio
- Construction cost per sq ft: Both one- and two-car garage conversions run $200–$350 per sq ft — the larger footprint doesn’t significantly increase the per-sq-ft cost
Frequently Asked Questions
Can I convert a two-car garage to an ADU in San Jose without losing parking? Yes — California law (AB 2221) prohibits cities from requiring replacement parking when a garage is converted to an ADU, as long as the property is within a half-mile of a transit stop. San Jose has adopted this state law, so most two-car garage conversions do not require adding new off-street parking.
How long does it take to convert a two-car garage to an ADU in San Jose? A two-car garage ADU conversion in San Jose typically takes 10–18 months total: 6–10 weeks for design, 8–16 weeks for permit approval, and 12–20 weeks for construction. Using pre-approved ADU plan sets can reduce permit time to 2–4 weeks.
What is the ROI on converting a two-car garage to an ADU in San Jose? A two-car garage ADU that costs $130,000 to convert and rents for $3,000/month generates $36,000/year in gross rental income — a 27% cash-on-cash return before expenses. It also adds $200,000–$400,000 to the property’s appraised value (typically valued at a 6–8% gross rent multiplier in San Jose).
Quartz Construction & Remodeling (CSLB #1003436) specializes in garage-to-ADU conversions throughout San Jose and the Bay Area. Call (650) 749-7436 for a free two-car garage ADU feasibility assessment and detailed cost estimate.
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