Wall panels and methods of constructing a wall system for a building are described. In some embodiments, a pre-assembled wall panel may include a panel frame including a perimeter member defining a perimeter side of the panel frame, first and second wall boards attached to opposite sides of the panel frame to define first and second major sides of the wall panel, each of the first and second wall boards comprising non-combustible material, and a waterproofing assembly enclosing the perimeter side of the panel frame and extending along a full length of the perimeter side, wherein the waterproofing assembly includes a non-metallic elongate member comprising first and second opposing flanges disposed against respective exterior surfaces of the first and second wall boards, and wherein the first and second opposing flanges are attached to the perimeter member.