The energy-efficient renovation of the Lavater school complex is an example of how historical architecture and modern construction technology can be precisely interlinked. A central element was the technical optimisation of the window glass using modern insulating glass as part of the renovation of the windows from 1896/97 in line with conservation guidelines. Historic buildings in particular demonstrate how crucial an efficient edge seal and a coordinated overall design are for energy efficiency and comfort.
Modern edge seal and high-performance glass
Swisspacer
The new insulating glass features a Planiclear and Eclaz One coating, optimised for daylight, thermal insulation and energy efficiency. With a Ug value of 1.4 W/m²K, the selected glazing offers a good balance between thermal performance, building physics requirements and design restraint, according to those responsible. However, it is not only the glass itself that is decisive for the final energy input, but above all the edge seal.
Here, the project relies on the Swisspacer Ultimate, one of the most efficient warm edge spacers in its class. Its excellent Psi values effectively reduce heat loss and minimise the risk of condensation in the glass rebate – a key aspect in historic windows, which often have less tolerance for errors in their construction. At the same time, the spacer blends inconspicuously into the historic design with its matt, understated appearance.
The outer insulating glass panes were newly manufactured and installed, while the historic glass panes could remain visible on the inside. This double-shell construction combines monument protection with modern performance: efficient insulating glazing on the outside, original character on the inside. Automatically controlled fabric awnings provide summer heat protection without detracting from the simple aesthetics of the facade.
The installation took place under complex logistical conditions. Glass boxes and cranes had to be used for the upper floors in order to insert the sensitive glass panes safely and without damage into the historic sandstone facades.
Insulating glass as the key to energy efficiency
The new glazing makes a significant contribution to the overall energy concept of the school complex. Together with the geothermally operated heat pump, the PV system on the roof and the reactivated historic ventilation system, a harmonious system is created that combines renewable energies and structural efficiency.
In such a combined system, insulating glass is not just a passive component. It influences heating and cooling loads, room comfort, daylight utilisation and the overall cost-effectiveness of the envelope renovation. Especially in historic preservation, a well-coordinated glass structure with high-quality warm edge spacer bars is therefore a key factor – technically, energetically and in terms of design.
Swisspacer
