The governing body may provide for the appointment of a board of adjustment consisting of five members, each member to be appointed for a term of three years. The board of adjustment shall hear and decide appeals from and shall review any order, requirement, decision, or determination made by an administrative official charged with the enforcement of any ordinance adopted pursuant to this chapter. It shall hear and decide all matters referred to it or upon which it is required to pass under any such ordinance. The concurring vote of four members of the board shall be necessary to reverse any order, requirement, decision, or determination of any such administrative official or to decide in favor of the applicant any matter upon which it is     required to pass under any such ordinance, or to effect any variation in such ordinance. Upon request of the board, the governing body shall have the right to appoint an alternate member of said board of adjustment, who shall sit as an active member when and if a member of said board is unable to serve at any hearing.