Within districts herein established, uses, structures and lots which were lawful prior to the passage of this Code, (or lawful prior to the passage of an amendment or addition to those), but which would be prohibited by this Code, are considered to be nonconforming uses. It is the intent of this Code to permit such uses to continue until they are removed or abandoned, although they are considered to be incompatible with the permitted uses in the districts established by the Code. It is further the intent that nonconforming uses shall not be enlarged upon, expanded or extended; that nonconforming uses be changed only to a more restrictive use; and that the rebuilding of nonconforming structures damaged in excess of fifty percent of their reproduction value shall conform with this Code.