(a) Vacancy. Any lot or structure, or portion thereof, occupied by a nonconforming use, which becomes vacant or ceases the use by the present owner or occupant for a period of six months shall not thereafter be occupied, except by a use which conforms to this code.
(b) Damage. If any nonconforming structure or use is, by any cause, damaged to the extent of 50 percent of its value as determined by the building official, it shall not thereafter be reconstructed as such.