The use of any building, structure or land which is lawful prior to the enactment or amendment of any zoning ordinance or regulation and subsequently fails to conform to the requirements of this title, shall be considered nonconforming use/structure and may be continued. Alteration of any such use may be permitted to reasonably continue the use. Alteration of any such use shall be permitted when necessary to comply with any lawful requirement for alteration in the use. (Prior code § 10.540)