An insulation system for glass buildings, in particular suitable for greenhouses. Pairs of parallel rails are provided over the roofs of the buildings, between which rigid insulating panels can be slid which in the operative position link up with each other to form a closed insulating cover. The panels are preferably hinged together so that they can be folded accordion-fashion. Similar insulating panels can be provided at the outside of the buildings between rails arranged along the side walls and end walls of the buildings.
