No nonconforming building may be enlarged or expanded to cover a larger area than it occupied at the date of adoption of this chapter, except that where an existing lot is improved with a building or structure which is nonconforming due to location, such lot may be further improved by an addition to such building or structure, provided that the existing nonconforming setbacks may be extended but not further encroached upon. No nonconforming use may be extended or expanded over a larger area than it occupied at the time of enactment of this chapter, any nonconforming single-family residence located in any nonresidential district where residences are prohibited may be expanded, provided that yard areas as required in the SF Zone shall be applicable to such property and shall not be encroached upon, and further provided that the expanded structure shall continue to be used as a single-family residence.