Biparting panel assembly

A panel assembly comprising first and second panel groups, each panel group having at least a first and a second panel, each panel in said assembly being movable between a retracted and an extended position for opening and closing said panel assembly, said first panel group being located above said second panel group, the panels in said first panel group travelling downwardly and upwardly when moving respectively to their extended and retracted positions, the panels in said second panel group travelling upwardly and downwardly when moving respectively to their extended and retracted positions, all of said panels being of at least substantially identical weight such that said assembly is counterbalanced between said first and second panel groups, the panels being laterally offset in a manner such that when the panels reach their extended positions there is a consistent downward inward stepping of the panels over an opening to be closed by the panels, the second panel travelling further than and vertically across the first panel in each group when the panels move between their retracted and extended positions, the second panel in the first group meeting with the second panel in the second group when all the panels are in their extended positions and the second panel lying side by side aligned with the first panel in each group when all of the panels are in their retracted positions, the first panel in the first panel group being attached by a first chain around a first sprocket gear to the first panel in the second panel group and the second panel in the first panel group being attached by a second chain around a second sprocket gear to the second panel in the second panel group, both the first and second sprocket gears being journalled on a common drive shaft to produce simultaneous movement of all of said panels, said second sprocket gear being larger than and of a ratio relative to said first sprocket gear such that all of said panels reach their respective retracted and extended positions coincidentally with one another.