No building or land devoted to a use not permitted by this chapter in the district in which such building or land is located, except when required by law, shall be enlarged, extended, constructed, reconstructed, substituted or structurally altered, unless the use thereof is changed to a use permitted in the district in which such building, structure or premises is located, except as follows:

   1.   Substitution. If no structural alterations are made, a nonconforming use of a building or structure may be changed to another nonconforming use of the same or of a more conforming use, but not less conforming. Whenever a nonconforming use has been changed to a more conforming use or to a conforming use, such use shall not thereafter be changed to a less conforming use.

   2.   Discontinuance. In the event that a nonconforming use of any building, structure and/or land is discontinued for a period of one year, the use of the same shall conform thereafter to the uses permitted in the district in which it is located. The use of land upon which no building or structure is erected or constructed which either does not conform to the provisions of this chapter and the use of land upon which no building is erected or constructed or which becomes nonconforming by reason of a subsequent change in this chapter, shall be discontinued if vacant for a period of 30 days.

   3.   Replacing Damaged Nonconforming Buildings. Any nonconforming building or structure damaged more than 60 percent of its replacement cost, as determined by the City Engineer, exclusive of the foundations at the time of damage by fire, flood, explosion, war, riots, or act of God, shall not be restored or reconstructed and used as before such happening; but if damage is less than 60 percent of replacement cost above the foundation, it may be restored, reconstructed or used as before provided that it be done within 12 months of such happening.

   4.   Additions and Expansions. A structure which does not conform with district regulations shall not be added to, expanded or enlarged unless such addition, expansion or enlargement conforms to all the regulations of the district in which it is located, provided, however, that such addition, expansion or enlargement maintains a side yard width not less than the side yard width of the nonconforming structure existing prior to such expansion or enlargement. A nonconforming use of land shall not be expanded or extended beyond the area it occupies at the date of adoption of these regulations.