Fraud alert: 600+ CA homeowners lost deposits to ADU scammers. Verify before you pay.
Find verified ADU builders in California
Every ADU scam in California starts the same way — a quietly expired license.
California’s verified ADU builders
CSLB-verified daily. Browse the full directory for search, filters, and detailed profiles.
ADU builders by city
Browse verified builders in California’s most active ADU markets
ADU types & average costs
California allows multiple ADU types on most single-family lots
Detached ADU
Garage Conversion
Prefab / Modular
Junior ADU (JADU)
California caps contractor deposits by law
Under California Business & Professions Code §7159.5, a contractor cannot ask for more than $1,000 or 10% of the contract price — whichever is less — as a down payment.
If your ADU contractor asked for more, that’s a legal violation and a red flag.
ADU cost guide — California 2026
Average costs from California projects and permit data
| ADU Type | Typical Range |
|---|---|
| Detached ADU400-1,200 sq ft, new construction | $200K – $450K |
| Attached ADU400-800 sq ft, shares wall | $150K – $300K |
| Prefab / ModularFactory-built, installed on-site | $90K – $350K |
| Garage ConversionExisting structure, no new foundation | $70K – $150K |
| Junior ADU (JADU)Under 500 sq ft, within existing home | $40K – $100K |
750 sq ft detached ADU in California
Interactive calculator with California pricing