Discontinuance Of Use Of Non-Conforming Building Or Structure. A building, structure, or portion thereof, all or substantially all of which is designed or intended for a use which is not permitted in the district in which it is located, and which is vacant on the effective date of this Chapter or thereafter becomes vacant and remains unoccupied, or is not used for a continuous period of one hundred and eighty (180) days, shall not thereafter be occupied or used, except by a use permitted in the district in which the building or structure is located. A building or structure which is non-conforming only as to height, yard, parking or loading requirements shall not be subject to this provision.