If the work described in any building permit has not begun within 180 days after the date of issuance thereof, said permit shall expire; it shall be canceled by the administrative official, and written notice thereof shall be given to the persons affected. If the work described in any building permit has not been substantially completed within two years after the date of issuance thereof, said permit shall expire and be canceled by the administrative official, and written notice thereof shall be given to the persons affected, together with notice that further work as described in the canceled permit shall not proceed unless and until a new building permit has been obtained.