Health and Safety Code Section 18009.3
18009.3. (a) "Park trailer" means a trailer designed for human habitation for recreational or seasonal use only, that meets all of the following requirements:
(1) It contains 400 square feet or less of gross floor area, excluding loft area space if that loft area space meets the requirements of subdivision (b) and Section 18033. It may not exceed 14 feet in width at the maximum horizontal projection.
(2) It is built upon a single chassis.
(3) It may only be transported upon the public highways with a permit issued pursuant to Section 35780 of the Vehicle Code.
(b) For purposes of this section and Section 18033, "loft area" means any area within a unit that is elevated 30 inches or more above the main floor area and designed to be occupied. In order for the floor of a loft area to be occupied and excluded from the calculation of gross floor area for purposes of subdivision (a), the loft area shall meet all of the requirements of Section 18033. Loft areas not meeting the requirements of this subdivision and Section 18033 shall not be occupied and shall be posted with a permanent label conspicuously located within 24 inches of the opening of each noncomplying loft. The label language and design shall provide the following:
This area is not designed to be occupied and shall be used only for storage.
Lettering on this label shall contrast with the label's background and shall be not less than one-quarter inch in height, except for the word "WARNING" which shall be not less than one-half inch in height.
(c) A park trailer hitch, when designed by the manufacturer to be removable, may be removed and stored beneath a park trailer.
(d) If any provision of this section or Section 18033 conflicts with ANSI Standard A119.5 Recreational Park Trailers as it is published at any time, the statutory provision shall prevail.