Continued conformity with bulk regulations. The maintenance of yards, courts, usable open spaces and other open spaces and minimum lot area legally required for a building shall be a continuing obligation of the owner of such building or of the property on which it is located as long as the building is in existence. Furthermore, no legally required yards, courts, usable open spaces, other open spaces or minimum lot area allocated to any building shall, by virtue of change of ownership, or for any other reason, be used to satisfy yard, court, usable open space, other open space or minimum lot area requirements for any other building.