Section 13. A zoning ordinance or by-law may authorize the appointment of a zoning administrator, who, unless otherwise provided by charter, shall be appointed by the board of appeals, subject to confirmation by the city council or board of selectmen, to serve at the pleasure of the board of appeals pursuant to such qualifications as may be established by the city council or board of selectmen. The board of appeals may delegate to said zoning administrator some of its powers and duties by a concurring vote of all members of the board of appeals consisting of three members, and a concurring vote of all except one member of a board consisting of five members. Any person aggrieved by a decision or order of the zoning administrator, whether or not previously a party to the proceeding, or any municipal office or board, may appeal to the board of appeals, as provided in section fourteen, within thirty days after the decision of the zoning administrator has been filed in the office of the city or town clerk. Any appeal, application or petition filed with said zoning administrator as to which no decision has issued within thirty-five days from the date of filing shall be deemed denied and shall be subject to appeal to the board of appeals as provided in section eight.