INNOVATIONS: Historic Zurich school modernised with energy-efficient window retrofit

A landmark school complex in Zurich has undergone a sensitive refurbishment, preserving its historic architecture while upgrading it to meet modern energy-efficiency standards. The Lavater school, originally built in 1896/97 by city architect Gustav Gull, is considered a key example of late 19th-century school design in the city. Its neo-historicist style, modelled after the Swiss National Museum, has been retained through an extensive restoration that combines heritage conservation with forward-thinking technology.

A focal point of the project was the refurbishment of the building’s original windows. Carried out by Holzmanufaktur SWISS AG, in partnership with Holzmanufaktur Rottweil, the work involved careful restoration in line with conservation guidelines. The historic timber frames were preserved while being fitted with new insulating glazing that includes Swisspacer Ultimate, a warm edge spacer designed to enhance thermal performance.

This approach allowed the school to maintain its original window aesthetics while improving energy efficiency. The new insulating glass units deliver a Ug value of 1.4 W/m²K, with Swisspacer Ultimate contributing low Psi-values and a discreet design suited to the historic context.

Energy performance was a key consideration throughout the renovation. The complex is now fully powered by renewable energy, including a photovoltaic system on the flat roof and a geothermal heat pump. The original ventilation ducts in the classrooms were also reactivated, enabling mechanical ventilation that improves indoor air quality while respecting the building’s historic fabric.

Further upgrades include the addition of automatically controlled fabric awnings to prevent overheating during the summer months. The project team employed complex logistics to carry out the installation, including cranes and special transport containers for upper-level windows, reflecting the care taken in preserving the building’s character.

Dirk Obser, project manager at Holzmanufaktur Rottweil, said the choice of materials was critical. “For a project like Lavater, which is subject to both heritage conservation and energy efficiency requirements, it was important for us to choose a spacer bar that could deliver both technological performance and design restraint,” he explained.

The Lavater school refurbishment demonstrates how traditional architecture can be adapted to meet modern standards without compromising on heritage values. It serves as a model for integrating sustainability into protected buildings, preserving their historic significance while ensuring their functionality for future generations.