California Code, Health and Safety Code - HSC § 19971

“Factory-built housing” means a residential building, dwelling unit, or an individual dwelling room or combination of rooms thereof, or building component, assembly, or system manufactured in such a manner that all concealed parts or processes of manufacture cannot be inspected before installation at the building site without disassembly, damage, or destruction of the part, including units designed for use as part of an institution for resident or patient care, that is either wholly manufactured or is in substantial part manufactured at an offsite location to be wholly or partially assembled onsite in accordance with building standards published in the California Building Standards Code and other regulations adopted by the commission pursuant to Section 19990. Factory-built housing does not include a mobilehome, as defined in Section 18008, a recreational vehicle, as defined in Section 18010.5, or a commercial modular, as defined in Section 18012.5.