A panel assembly including a panel that can be positioned in an opening, the panel including a plurality of locking members spaced apart along at least part of a length of and proximate to opposing longitudinal edges of the panel and a guide extending along either side of the opening, each guide including at least one locking flange extending along at least part of a length of the guide, wherein in use the panel is received in the guides so that the locking members selectively engage the flanges to limit lateral movement of the panel edges.