In the case of a narrow corner lot or of any shallow, irregular or steeply sloping lot, existing as such at the effective date of this chapter, where conformity with the provisions of this article would, in the judgment of the Board of Appeals, make it difficult to erect a practicable building, the Board of Appeals, as provided in Article XI, § 216-108A(10), may allow such building or structure to project nearer to any street or lot line than is herein prescribed, provided that it can be done in a way to safeguard the neighborhood and provided that in no case, in a residence district, shall any part of the structure be within less than five feet of any street, lot or line.