Nothing contained in the Zoning Ordinance shall require any change in the plans, construction or designated use of a building completed at the time of the passage of this Zoning Ordinance, or for which a permit has been issued before the passage of this chapter, and construction of which is begun within thirty days of the issuance of the permit, diligently prosecuted to its completion, and completed according to the plans and descriptions on which the permit was issued, within one year of the issuance of the permit.
(1973 Code §151.25)