An apparatus and method for joining panel members into walls or dividers is provided which allow thermal expansion of the panel members to be absorbed by the joints. The panel construction includes turned down edges having grooves on the inside faces of the edges. Each edge is sized to fit side-by-side in a channel with the edge of an adjoining panel and with their grooves over ridges on the inner walls of the sides of the channel. An insert member having protrusions on its sides is wedged between the side-by-side edges for maintaining the grooves over the ridges while allowing pivotal movement of the edges around the ridges.