As part of the refurbishment of the Botanical Gardens of the University of Bern, built in 1860, the filigree steel structure, which is protected as a historic monument, must be preserved. In order to ensure the load-bearing safety of this structure with as few reinforcement measures as possible, the weight of the roof glazing is reduced to an absolute minimum. A variant study of possible insulating glass units was carried out within the boundary conditions of building physics and monument preservation, as well as taking into account the radiation that is important for plant growth. The further development of glass refinement and the resulting improved glass properties play a decisive role in this. Lightweight, high-performance, chemically strengthened glass just 0.7 mm thick from the Xensation product family and 4 mm thick low-E coated toughened safety glass (ESG) are combined in an insulating glass structure. The toughened safety glass on the outside serves to transfer the load resulting from external influences, while the low-E coating completes the thermal insulation. The space between the panes of the insulating glass unit is completed on the inside by the chemically strengthened glass with an absolute minimum use of material.

A test concept was developed to investigate the load-bearing safety and personal safety of lightweight insulating glass unit and chemically strengthened glass. The strength, the influence of surface damage, the fracture pattern as a result of various impacts and the residual load-bearing capacity are analysed. The hail resistance is analysed by firing a hail cannon. The radiation transmission of the entire lightweight insulating glass unit is measured using a spectrophotometer.