Any building which houses a nonconforming use and
which is damaged or destroyed by less than 50% of its sound value
or floor area, exclusive of the foundation, from any cause, may be
restored, but not enlarged, and the nonconforming use reinstated within
six months of such damage. If the restoration of such building is
not completed within the said six-month period, the physical operation
of the nonconforming use of such building shall be deemed to have
ceased, unless such nonconforming use shall have been carried on without
interruption in the undamaged portion of such building.