Iowa Code § 414.14: Vote required.

The concurring vote of three members of the board in the case of a five-member board, four members in the case of a seven-member board, and five members in the case of a nine-member 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 on any matter upon which it is required to pass under any such ordinance or to effect any variation in such ordinance.