All exceptions to and variances from the provisions of this Planning and Zoning Code and the Building Code of the City, granted by the Zoning and Building Standards Board of Appeals, shall be void after twelve months from the date of approval thereof, unless, in the case of new construction, work has been done above the foundation walls, and unless, in the case of occupancy of land or reconstruction or occupancy of buildings, the operation called for by the permit is well underway, in the judgment of the Zoning Administrator, by the end of such twelve-month period.