Expiration, lapse, extension and reinstatement of special permits. Any special permit granted pursuant to this chapter shall automatically expire and be of no further force and effect six months after the granting thereof unless, within such six-month period, substantial construction shall have been commenced. Such construction must be completed within one year of the date of commencement of substantial construction. The Zoning Board of Appeals shall be authorized, upon application and without hearing, to grant extensions of the special permit for periods not to exceed six months in duration or to reinstate a lapsed special permit for good cause shown. Any special permit issued prior to the effective date of this section shall be deemed to have been issued on such effective date.