A double wall panel member for use in a panel wall is provided which includes a tongue-configured end and a groove-configured end. The panel member includes a first outer wall spaced laterally from a second outer wall, and the groove-configured end has a first groove wall portion extending from the first outer wall and a second groove wall portion extending from the second outer wall, where the first groove wall portion extends further outward than the second groove wall portion. When connected, the wall panel members are assembled with the groove end pointing or oriented upward (not downward) and the tongue end pointing or oriented downward (not upward).
