Nothing in this chapter shall require any change in the plans, construction or designated use of a building or structure for which a lawful building permit has been issued prior to the effective date of this chapter or any amendment thereto affecting such building or structure, or the use thereof, provided that:
(1) The construction of such building or structure shall have been begun and diligently prosecuted within six months from the date of such permit.
(2) The entire building or structure shall be completed according to such filed and approved plans upon which the issuance of such permit was based, within one year from the effective date of this chapter or any such amendment thereto.