Modular, Manufactured, and Factory-Built: Decoding the Labels

"Prefab," "modular," "manufactured," "panelized" — sellers use these interchangeably; codes and lenders emphatically don't. Five minutes of vocabulary saves genuine confusion. Here's the decoder ring.

Panelized. Flat components — wall panels, floor cassettes, roof trusses — factory-cut, site-assembled in days, then finished on-site. Code-wise it's simply site-built construction with efficient parts: your city inspects everything per Module 12, appraisal and financing are ordinary. Lowest-drama factory option; the factory advantage applies mostly to the frame.

Modular (state-approved factory-built housing). Three-dimensional modules built to the same residential code as site-built houses — but inspected in the factory under California's factory-built housing program, arriving with state insignia. Your city then permits and inspects the site elements: foundation, utility connections, assembly. Appraises and finances like a house, because legally it is a house — built indoors. This is what most quality "prefab ADU" companies (13.8) actually sell.

Manufactured (HUD-code). Built on a permanent chassis to the federal HUD code — a different standard than the residential code. California allows manufactured homes as ADUs (on permanent foundations), and they're typically the cheapest factory option — but know the trade-offs: some lenders and appraisers treat HUD-code structures differently (financing menus narrow; appraisal comps get complicated), resale perception varies by market, and design selection is catalog-based. For pure budget-driven projects on suitable lots, honestly worth pricing; for value-maximizing projects, the modular or site-built appraisal treatment usually wins.

Why the label changes your project:

• Who inspects what: panelized = city inspects all; modular = state inspects the box, city the site; manufactured = HUD label on the box, city handles foundation/installation.
• Financing and appraisal: site-built and modular ride normal residential rails; HUD-code rides its own, narrower ones. If your exit math (Module 14) leans on appraised value, this line matters most.
• What your city reviews: in all cases the site — foundation, utilities, setbacks, everything from Modules 2, 7, and 10 — remains fully yours to permit. No label deletes the site work. (That was 13.8's brochure lesson; it's every label's lesson.)

The practical question that cuts through all marketing: "Which code is the unit built to, who inspects it, and how will my lender's appraiser classify it?" A seller who answers crisply is selling something real.