No building or lot shall be devoted to any use other than one which is specified, or a conditional use, by the district regulations applicable to the district in which such building or land is located, as herein set forth in chapters 4, 6 and 7 of this title. However, where a building permit for a building or structure has been issued in accordance with law, prior to the effective date of this title, and where construction has been begun within six (6) months of such effective date and is being prosecuted to completion, said building or structure may be completed in accordance with approved plans on the basis of which the building permit was issued; and further, may, upon completion, be occupied under a certificate of occupancy by the use originally designated subject to the provisions herein set forth in chapter 10 of this title. (1977 Code)