No building or group of contiguous buildings shall exceed a footprint of 60,000 square feet. Notwithstanding this limitation, any building or group of contiguous buildings in lawful existence that exceeded this limitation on January 1, 2003, may expand its footprint, by not more than 10 percent of the footprint on January 1, 2003; provided, that the use of the building or combined contiguous buildings has not ceased for a period of six months or more ending at any time on or after January 1, 2003.