Nothing in this chapter shall be deemed to prevent normal maintenance and repairs or to prevent the strengthening or restoring to a safe condition any building, structure or part thereof declared to be unsafe by any official charged with protecting the public safety.

If a nonconforming structure or portion of a structure containing a nonconforming use becomes physically unsafe or unlawful due to lack of repairs and maintenance, and is declared by any duly authorized official to be unsafe or unlawful by reason of physical condition, it shall not thereafter be restored, repaired, or rebuilt except in conformity with the regulations of the district in which it is located.