If, for a continuous period of two years, either the non-conforming use of land with minor improvements is discontinued, or the active operation of substantially all the non-conforming uses in any building or other structure is discontinued, such land or building or other structure shall thereafter be used only for a conforming use. Intent to resume active operations shall not affect the foregoing.

The provisions of this Section shall not apply where such discontinuance of active operations is directly caused by war, strikes or other labor difficulties, a governmental program of materials rationing, or the construction of a duly authorized improvement project by a governmental body or a public utility company.

Except in Historic Districts as designated by the Landmarks Preservation Commission, the provisions of this Section shall not apply to vacant ground floor or basement stores in buildings designed for residential use located in R5, R6 or R7 Districts where the changed or reactivated use is listed in Use Group 6A, 6B or 6C excluding post offices, veterinary medicine for small animals, automobile supply stores, electrolysis studios and drive-in banks. In addition, the changed or reactivated use shall be subject to the provisions of Section 52-34 (Commercial Uses in Residence Districts).