California Code, Education Code - EDC § 17074.54

(a) A portable building that is sited with the intent that it be at the site for less than three years and is sited upon a temporary foundation in a manner that is designed to permit easy removal, is exempt from Sections 17074.50 and 17074.52 for a period of three years from the date of siting.

(b) After the three-year exemption set forth in subdivision (a), a school district may request an extension of the exemption for an additional period not to exceed three additional years. The board shall grant the request if the school district presents convincing evidence demonstrating to the satisfaction of the board that the extension is necessary.

(c) For purposes of this section, “portable building” means a classroom building of modular design and construction that meets all of the following criteria: