No building or tract of land shall be devoted to any use other than one which is specified as a permitted or special use under chapters 4, 5, 6 and 7 and section 9-11-9 of this title in the zoning district in which such land or building is located. However, where a building or structure permit has been legally issued in accordance with law prior to the effective date of this title, and provided that construction is begun within ninety (90) days of such effective date and diligently prosecuted to completion, said building or structure may be completed in accordance with 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 for the use for which originally designated. (Ord. 190, 3-19-1973)