Lawful uses, buildings or structures, existing at the time of annexation or zone change, may be continued even though they do not conform with this title and will be considered legal, nonconforming. Such nonconforming uses, buildings or structures may be maintained and repaired as such in accord with all applicable codes and regulations. Any expansion of a nonconforming use, building or structure is limited to twenty-five percent of the original floor area, or cubical content of the building, or of the service capacity conducted all or partially in the open. A nonconforming use, building or structure may not be changed to another nonconforming use, building or structure. Except for a nonconforming residential use, building or structure, if a nonconforming use, building or structure is destroyed by any sudden cause to the extent of not more than sixty percent of either its bulk or value, it may be reconstructed. The provisions of this subsection are only available if the applicant applies for a building permit within twelve months after the sudden damage or destruction and construction is commenced and completed under that building permit. Provided the applicant shows good cause for the need for an extension, the city council may grant one six-month extension.