Quick Answer: Converting a garage to an ADU in the Bay Area costs $60,000–$150,000 for a single-car garage (240–360 SF) and $80,000–$200,000 for a two-car garage (440–500 SF). Key cost items: insulation and weatherproofing ($5,000–$12,000), bathroom addition ($15,000–$35,000), kitchen/kitchenette ($8,000–$25,000), electrical upgrade ($5,000–$15,000), and HVAC mini-split ($4,000–$8,000). Garage conversions are the most cost-effective ADU option in the Bay Area because the foundation and shell already exist. Under California law, existing garages can convert to ADU with zero property line setback.
Garage to ADU Conversion Cost Breakdown
Helpful Resources:
| Item | Cost Range | Notes |
|---|---|---|
| Foundation/slab assessment | $500–$2,000 | May need vapor barrier |
| Framing modifications | $3,000–$8,000 | Doors, windows, wall modifications |
| Insulation + weatherproofing | $5,000–$12,000 | Title 24 compliant (R-21 walls) |
| Electrical (new panel or sub-panel) | $5,000–$15,000 | Often requires main panel upgrade |
| Plumbing (bathroom + kitchenette) | $10,000–$25,000 | Tie-in to main or new sewer line |
| Bathroom complete | $15,000–$35,000 | Required for habitable ADU |
| Kitchenette or full kitchen | $8,000–$25,000 | Define as JADU vs ADU |
| HVAC (mini-split) | $4,000–$8,000 | Most efficient for garage ADUs |
| Drywall, flooring, finishes | $8,000–$20,000 | Based on finish level |
| Permits | $8,000–$20,000 | Varies by city |
Question: What is a JADU vs. ADU for a garage conversion in California? A Junior ADU (JADU) is a converted living space within the existing walls of a primary residence or attached garage — maximum 500 SF. A standard ADU can be up to 1,000 SF (or 50% of primary dwelling, whichever is larger). JADUs require an efficiency kitchen (mini-fridge, microwave, sink — full-size range not required) and must share entrance with main home initially (though separate entrance allowed). ADUs require a full kitchen and full bathroom. JADUs have fewer permit requirements and lower fees, but the 500 SF limit restricts their rental income potential vs. a full ADU.
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