Deep guide
The approval stack is not one license.
A modular ADU buyer often asks one question: "Is it approved?" The safer and more useful answer is: approved for what, by whom, and for which address? A California Factory-Built Housing packet can support the model and factory-built structure. A city or county permit can approve the project at a specific property. A contractor license governs who can contract for and perform the installation or construction work. These are connected, but they are not interchangeable.
The ADU Cost product has a stronger starting point than a generic prefab pitch because the supplied R-22345 and R-22348 packets show California Factory-Built Housing approval references dated July 15, 2026, with expiration shown as July 14, 2029. Those documents should be surfaced clearly. They help the buyer see the model identity, engineering packet, product scope, and factory-built lane. They also carry a warning: local site work still needs review.
The first job is to protect the buyer from a thin quote. A thin quote says one number and makes everything else invisible. A real ADU budget separates product, freight, crane or setting, foundation, utilities, permits, design coordination, finish allowances, site restoration, contingency, and closeout. The approval and license checklist below explains what proof should be collected before those lines are tightened.
1. State factory-built product approval
HCD's Factory-Built Housing program is the state lane for factory-built homes and building components manufactured for sale in California. The product must have a model-specific design basis, plan set, calculations, quality assurance path, and inspection path. HCD's public materials explain that plan approval is required for each FBH model or design designated for sale in California, and that review can be performed by a certified Design Approval Agency.
For the ADU Cost product, the R-22345 and R-22348 packets are the starting evidence. They let the site explain a real product path: 3L three-bedroom and 1L one-bedroom. The buyer should be able to download the PDFs, see drawing snapshots, and understand that the factory-built structure is not a loose visual concept.
2. HCD insignia and manufacturing quality
HCD's factory-built insignia page says FBH components and systems offered for sale in California to first users must bear an insignia of approval issued by HCD, and that the insignia is placed on the unit or component prior to shipment. It also says insignia are issued through an HCD-approved Quality Assurance Agency for units with prior plan approval. This is why the sales page should not treat the approval as a decorative badge. It is tied to prior plan approval and manufacturing quality control.
The practical buyer question is not only "do you have a PDF?" It is "will the delivered unit have the proper state evidence, installation instructions, and model documentation that the local official and installer can review?" That is a much stronger question than asking for a discount on a square-foot price.
3. City or county ADU permit approval
Local approval begins when the project becomes site-specific. The local authority reviews placement, zoning or objective ADU standards, setbacks, utility routing, foundation, grading, drainage, access, and inspections. HCD's FBH handbook says local planning and building departments have jurisdiction over installation and assembly once onsite, and it lists local site development, property line, foundation, utility, and inspection items in the local enforcing agency lane.
HCD also maintains statewide ADU resources and reviews local ADU ordinances for compliance with state law. That statewide framework matters, but it does not remove the need for a complete permit package. A buyer should send the product packet, city, address context, preferred placement, utility notes, site photos, and any known constraints before expecting a serious permit or price conversation.
4. Contractor licensing and who can perform the work
California's Contractors State License Board says contractors must be licensed when California construction work requires a permit, uses additional workers, or reaches the current statutory cost threshold listed on CSLB's applicant guidance. CSLB also explains general qualifications, including age and experience requirements, and publishes current application and licensing fees. For full ADU construction, CSLB's ADU guidance says a B General Building Contractor can build or install ADUs because that classification manages work involving multiple unrelated trades.
CSLB materials also discuss C-47 General Manufactured Housing Contractors, but the older CSLB classification guide distinguishes manufactured homes from factory-built housing as defined elsewhere in California law. The safest site copy is therefore not "any C-47 can install this." The safe copy is: the correct license depends on the exact scope and product classification; a B General Building Contractor is the broad ADU construction lane; specialty trades may be subcontracted; and license verification should happen before contracting.
5. Contracts, payments, and consumer protection
CSLB's 2025 contractor newsletter tells contractors to confirm permits before starting construction, use required written contracts for residential ADUs, include scope, schedule, materials, and change-order handling, and keep progress payments tied to actual work or delivered materials. That matters for ADU Cost because a buyer-focused calculator should not stop at "unit price." It should remind the buyer that the quote process must become a written scope with permit, contract, and payment discipline.
A strong landing page can make this a selling point. Serious buyers know that cheaper can become expensive when a contractor buries exclusions. ADU Cost can position itself around clean documentation: product packet, local approval path, contractor license check, written scope, and transparent allowances.
6. What "not everyone has this" should mean
The phrase should not be used as empty hype. The credible version is: not every ADU product page can show state factory-built product packets, engineering snapshots, a local permit boundary, official HCD/CSLB source links, and a calculator that separates the unknowns. That is the advantage. The site can say the product has serious documentation for buyers and professionals to review. It cannot say that every site is approved, every contractor is licensed, or every cost is known.
7. The proof checklist before a buyer moves forward
- Download and review the R-22345 or R-22348 product packet for the selected model.
- Confirm whether the delivered unit will carry the required state evidence and installation documentation.
- Identify the city or county and review its ADU intake process, forms, plan review process, fees, and inspections.
- Prepare site photos, measurements, utility distances, access route notes, grading/drainage concerns, and preferred placement.
- Ask the project team to separate factory unit, freight, setting, foundation, utilities, permit fees, finish allowances, and contingency.
- Verify contractor license classification and status through CSLB before contract signing.
- Require a written scope, payment schedule, change order path, and permit responsibility before work starts.