Abstract: The self-supporting element (1) is of great length and of the type formed by a framework of metal section members (7-9-10-11-14-15) and an insulating cladding supported by the framework. The element is characterized in that its cladding is in a single unit and formed by a composite comprising an outer skin (17), an inner skin (18) and an insulating blanket (19) formed by mineral wool fibres which extend in a direction perpendicular to the parallel planes of the skins. The cladding (16) is supported exclusively by the two lateral beams (9,10) of the framework.