When a lot which is a lot legally of record at the time of adoption of this chapter does not comply with the length, width or area requirements of this chapter, and it was a legal lot under the provisions of the City’s zoning chapter at the time it was created, it shall be considered a conforming lot under this chapter, provided that any structure erected upon it shall comply with the setback requirements of this chapter. If the setback requirements are so prohibitive as to make the property unusable, an application for a variance to the provisions of this chapter should be sought; however approval may be granted only as provided in Section 165.54 of this chapter.