If the work described in any zoning permit has not begun within one year from the date of issuance thereof, said permit shall expire; it shall be revoked by the Zoning Administrator; and written notice thereof shall be given to the persons affected. If the work described in any zoning permit has not been substantially completed within two and one half (2 1/2) years of the date of issuance thereof, said permit shall expire and be revoked by the Zoning Administrator, and written notice thereof shall be given to the persons affected, together with notice that further work as described in the cancelled permit shall not proceed unless and until a new zoning permit has been obtained or an extension granted.