The Zoning Board of Appeals may authorize upon appeal, in specific cases, such variance from the terms of the Zoning Code as will not be contrary to the public interest where, owing to special conditions, a literal enforcement of the provisions of the Zoning Code will result in unnecessary hardship and so that the spirit of the Zoning Code shall be observed and substantial justice done. No variance shall have the effect of allowing in any district uses prohibited in that district, permit a lower degree of flood protection than the flood protection elevation for the particular area, or permit standards lower than those required by state law.