Cal. RTC § 6012.7

(a) For the purposes of this part, “gross receipts” from the sale of factory-built housing, and the “sales price” of factory-built housing, sold or stored, used, or otherwise consumed in this state shall be 40 percent of the sales price of the factory-built housing to the consumer.

(b) For purposes of this section, “factory-built housing” includes:

(1) 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, which is either wholly manufactured or is in substantial part manufactured at an offsite location to be wholly or partially assembled onsite in accordance with regulations adopted by the Commission of Housing and Community Development of the State of California pursuant to Section 19990 of the Health and Safety Code or in accordance with applicable local building requirements if such factory-built housing is inspected and approved by the local enforcement agency at the place of, and during the time of, manufacture.

(2) “Modular housing,” which is a three-dimensional box or cube-shaped structure or structures making up one or more rooms of a residential building.

(3) “Sectionalized housing,” which generally consists of two modules which form a total living unit.

(4) “Modular,” “utility,” or “wet cores,” which are three-dimensional habitable rooms or modules and which are generally comprised of a kitchen or a bathroom or bathrooms.

(c) For purposes of this section, “factory-built housing” does not include:

(1) A “mobilehome,” as defined in Section 18008 of the Health and Safety Code.

(2) “Precut housing packages” where more than 50 percent of the package consists of precut lumber only.

(3) “Panelized construction,” such as walls or components that may become one or more rooms of a building, unless a complete housing package is provided by the builder or manufacturer, such as by providing wall panels, floors, and a roof which will form a complete housing structure.

(4) “Porches” or “awnings” which are not purchased as a part of the original housing package.

(d) If a purchaser certifies in writing to a retailer that the factory-built housing purchased will be consumed in a manner or for a purpose entitling the retailer to exclude 60 percent of the gross receipts or sales price from the measure of tax, and uses the property in some other manner or for some other purpose, the purchaser shall be liable for payment of tax measured by 60 percent of the sales price.