(A) All buildings erected hereafter, all uses of land or buildings established hereafter, all structural alteration or relocation of existing buildings occurring hereafter, and all enlargements of or additions to existing uses occurring hereafter shall be subject to all regulations of this chapter which are applicable to the districts in which the building, uses, or land shall be located.
(B) Where, however, a building permit for a building or structure has been issued in accordance with the law prior to the effective date of this chapter, and provided that construction is begun within one year from the effective date and diligently prosecuted to completion, the building or structure may be completed in accordance with the approved plans on the basis of which the building permit has been issued, and, further, may upon completion be occupied under a certificate of occupancy by the use for which originally designated, subject thereafter to the provisions of § 153.27, nonconforming uses, buildings, and structures.
('69 Code, App. A, § 4.3)