Exceptions. Any use, building or structure which is in existence, or for which a building permit has been issued, as of the effective date of the ordinance codified in this section, and which, as of such date, conformed to all zoning regulations of the city then in effect, shall not be rendered nonconforming within the meaning of Chapter 17.100 of this code, solely by reason of the application of the development standards, as set forth in this section, thereto; provided that any such existing use, building or structure, in case of expansion or reconstruction, shall, as to that portion thereof, comply with the provisions of this section.