Structures existing at the effective date of any application of the FP zone which are inconsistent with the provisions thereof, will be allowed to remain under the conditions set forth in chapter 18.184 of this title, except that:
A. If the useful life of a structure has not expired by a date fifteen (15) years after the effective date of the application of the FP zone, the life of the structure shall be considered to have expired automatically, and the structure shall be removed;
B. Any existing structure damaged in excess of seventy five percent (75%) of its reasonable value, by fire, explosion, floods, acts of God or the enemy, shall be removed;
C. The enlargement, expansion, extension or change in use of any structure is not permitted. (Ord. 1000 § 31.65, 1955)