499A.18A  Upkeep of the cooperative.
  It is the duty of the cooperative to maintain generally all portions of the cooperative’s real property other than the apartment units. The maintenance, repair, and replacement costs of the cooperative’s real property shall be contributed to by each of the members in accordance with the proration formula set forth in the bylaws. Each member is responsible for maintenance and repair of the person’s apartment unit in the manner provided for in the bylaws and as prescribed by each member’s proprietary lease.
91 Acts, ch 30, §11