Abstract: An insulating double glass pane which is intended particularly for glazing roofs such as the roofs of hothouses comprises a first pane and a second pane spaced apart from each other with spacer pieces between them around their edges. The first pane has a portion along one edge projecting beyond the second pane and the distance between the first pane and the second pane decreases from the edge at which the first pane has the projecting portion towards the opposite edge. Preferably the decrease in the distance between the panes from one edge to the other is substantially equal to the thickness of the first pane so that when two of the double panes are laid edge to edge with the projecting portion of an upper pane overlapping the upper edge of a lower pane, the outside faces of the two second panes are substantially flush with each other.