Any building, structure, or use of land existing at the time of the enactment or subsequent amendment of this appendix but not in conformity with its use regulations and provisions, may be continued subject to the following limitations. A nonconforming use shall not be:

(1)

Changed to another nonconforming use;

(2)

Extended or enlarged;

(3)

Reestablished after discontinuance for 12 consecutive months; or

(4)

Rebuilt, altered, or repaired after damage exceeding 50 percent of the value of the building. The value shall be computed from the amount the building is assessed for tax purposes by the city.