Prefab ADU Companies in California — CSLB Checked | VerifiedADU

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Prefab ADU Companies in California — CSLB Checked.

Every company below is checked against CSLB public records — license, bond, workers’ comp, complaints. Companies with issues are flagged, not hidden.

CSLB verification confirms license status, bond, workers’ comp, and complaint history. It does not cover product quality, pricing accuracy, or financial stability. Full verification methodology →

How Much Does a Prefab ADU Cost in California?

Prefab ADU pricing has two numbers — the unit cost (what the manufacturer charges) and the total installed cost (unit + foundation + utilities + permits + site work). Most companies advertise the unit cost. The installed cost is 40–70% higher.

Cost componentTypical range
Unit (manufacturer price)$80,000 – $200,000
Foundation$15,000 – $40,000
Utility connections$10,000 – $30,000
Crane + delivery$5,000 – $20,000
Permits + soft costs$8,000 – $25,000
Site prep + landscaping$3,000 – $15,000
Total installed$150,000 – $300,000+

Ranges are for a 400–800 sq ft prefab ADU in California. Bay Area costs run higher. Sacramento and Inland Empire run lower. For a detailed comparison, see Is It Cheaper to Build an ADU or Buy a Prefab?

Before You Sign

License type matters.
Is the company a licensed contractor (turnkey) or manufacturer only? If manufacturer only, the installation requires a separate CSLB-licensed general contractor — and that contractor needs to be verified independently. A turnkey company with an active CSLB license gives a single point of accountability.
Get the total installed price in writing.
The unit price on a company’s website is the starting point, not the final number. Foundation, utility connections, delivery, crane, permits, engineering — these add 40–70% on top. Any company that quotes without a site visit is guessing.
California law caps contractor deposits.
$1,000 or 10% of the contract price, whichever is less (BPC §7159.5). This applies to the installation contract. Any licensed contractor asking for more upfront is violating state law. Full deposit law guide →

Frequently asked questions

Do prefab ADU companies need a CSLB license?
If the company manufactures AND installs the unit, a CSLB contractor license (Class B) is required. Manufacturer-only companies may not need one, but the installing contractor does. The cards above note which companies are licensed contractors and which are manufacturers only.
What’s the difference between prefab and modular ADUs?
In California, “prefab” and “modular” are used interchangeably for factory-built ADUs. Both must meet California Building Code and pass the same inspections as site-built ADUs.
Can I buy a prefab ADU and hire my own contractor to install it?
Yes. Some manufacturers sell the unit only. Installation requires a CSLB-licensed general contractor (Class B) for foundation, delivery, utility connections, and inspections. Verify the installer’s license independently using the license lookup tool.
Are prefab ADUs eligible for CalHFA ADU grants?
The CalHFA ADU Grant Program provided up to $40,000 regardless of construction method. The program is currently paused — funding was fully allocated by late 2023. Full CalHFA grant guide →
How long does a prefab ADU last?
Same as site-built — 50+ years with normal maintenance. Prefab ADUs are built to the same California Building Code standards and use the same materials.
What size prefab ADUs are available in California?
Most manufacturers offer 400 to 1,200 sq ft — the maximum allowed under California ADU law for detached ADUs on single-family lots. Common sizes: 400 sf (studio), 500–600 sf (1-bedroom), 750–1,000 sf (2-bedroom).

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