The Housing Board of Review is hereby authorized to hear and decide appeals from compliance orders. The Board shall have the power to reverse or affirm wholly or partly or to modify any order of the Director of Zoning and Code Enforcement, and in specific cases to authorize such variance in the application of the terms of this chapter, where, owing to unusual conditions, a literal enforcement of the provisions of this chapter would result in unnecessary hardship, and so that the spirit of this chapter shall be observed and substantial justice done.