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.
LiveVerify™All licenses checked daily via CSLB
California’s verified ADU builders
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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
$200K – $450K
Standalone unit, up to 1,200 sq ft. Most popular type in CA.
Garage Conversion
$70K – $150K
Convert existing garage. Lowest cost option. No new foundation.
Prefab / Modular
$90K – $350K
Factory-built, installed on-site. Faster timeline, pre-approved designs.
Junior ADU (JADU)
$40K – $100K
Under 500 sq ft, within existing structure. Shared or separate entrance.
California caps contractor deposits by law
Under California Business & Professions Code §7159.5, a contractor cannot ask for more than $1,000 or 10% of the contract price — whichever is less — as a down payment. If your ADU contractor asked for more, that’s a legal violation and a red flag.$
$1,000
Max legal deposit
Misdemeanor
Criminal charge if violated
$5,000
Max fine per violation
ADU cost guide — California 2026
Average costs from California projects and permit data
Average cost by ADU type
California
| 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 |
Design & permitting$10K – $25K
Site work & utilities$15K – $40K
750 sq ft detached ADU in California
Construction$225,000
Design & permits$18,500
Site work & utilities$22,000
CalHFA grant (if eligible)-$40,000
Estimated total
$225,500
Calculate your ADU cost
Interactive calculator with California pricing