If the work described in any zoning permit has not begun within one year from the date of issuance thereof, the permit shall expire and written notice shall be given to the persons affected. If the work described in any zoning permit is not more than 50% completed within two and one-half years of the date of issuance, the permit shall expire and written notice 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 extension granted.