The revitalisation and conversion of the laboratory faculty building into a Biomedical Engineering Centre is a very interesting challenge. Issues of energy efficiency, protection of historic buildings, functionality, economy in construction and operation have to be combined into an overall concept. The focus thereby is the exposition and the optimal utilization of the building's existing structural potential designed by the architect Karl Raimund Lorenz in the mid 1950s.

The facade of the existing building remains mainly untouched - as required by the authority for protection and conservation of historical monuments. But within the building, everything except the main supporting structure and the staircases has been torn down. Every new non-structural component is selected based on its potential for an optimal atmospheric environment. The material selection combined with the preserved building structure turn into an integral design concept.

Overlooking the city

The reason for the extension and conversion of the former Chemistry Institute buildings on the 'Neue Technik' campus in Graz back in 2009 was a mere lack of space. Gangoly & Kristiner architectural practice, who won the competition, saw themselves confronted with specific questions concerning monumental preservation. Built in 1961, the clearly defined wing providing access via a central corridor and equipped with highly specialised laboratory technology was to be transformed into a new building for the Institutes of Biomedical Engineering at Graz University of Technology. Following the competition, one could barely imagine that building a canteen would turn the building into a main point of attraction on and around the campus. Since 2015, meals are cooked and eaten on the roof where building service equipment once stood. It is a unique rooftop experience for everyone at Graz University of Technology, which offers excellent conditions for study and research as well as social life. The architects' concept has proved to be an amazing success. Up here, the roof architecture frames a breathtaking - almost unobstructed - view to the World Heritage Site, Schlossberg and Plabutsch Hill. It is a view to the city that you'll never forget.

It is lunchtime. A packed elevator takes us straight up to the new canteen above the city's roofscape. The rooms are darkish. Black hardboards on the walls and a suspended ceiling made of oak wood beams step back elegantly, forming a backdrop for the key attraction. Looking out from the crouched 'penthouse', the viewer senses the quality of the design: these rooms set the stage for panorama views to the city's skyline. On the terrace up here, you can let your thoughts wander freely, or maybe just stop thinking at all, since the hustle and bustle of the offices and seminar rooms on the lower floors seems so far away. The concept of openness and accessibility is repeated on the ground floor. Here, large spaces are available to students for meeting and working. Next to the main entrance, a thin bright concrete roof extending across the front of the building contrasts sharply with rough travertine surfaces. This additional forecourt merges with the building's interior to form the foyer of an auditorium. A choice had to be made between the elegance and immateriality of an atrium in the building and higher quality utilisation with less linearity, less clarity due to additional columns, extensive roofing and oversized lights. On the outside, however, nothing much has changed. The facade was able to be maintained without any additional insulation. It is worth taking a closer look to appreciate the quality of low-tech ideas in connection with the adaptation of the lab building in the late 1950s. Climatic conditions in the building's interior are extremely well adjusted without requiring expensive air-conditioning technology. The windows, which were optimised by applying interior insulating glazing, can still be tilted to enable mechanical ventilation. A waist-high loam parapet wall regulates air humidity and the ribbed concrete floor was uncovered to act as a thermal mass. Moreover, the open ribbed floor was sound insulated and soundproof partition walls were added to divide the spaces into smaller areas, thus creating quiet workplaces. Where experiments and tests were once carried out in open chemistry labs, today's offices provide appropriate space for the institute's employees and doctoral students. The key objective of the adaptation was to devise a careful and modern project that would update the building within the restrictive bounds of monumental preservation, energy efficiency and ire protection regulations, fall protection and lightning protection, etc.

Karl Raimund Lorenz, Head Engineer of the Reichsautobahn in 1940 and later Rector of Graz University of Technology, was appointed in 1954 to build one of Europe's most modern laboratory buildings. He built quite in the style of the time, adhering architecturally to simple and clear-cut lines. 60 years on, the building's conversion had become an urgent matter, too. General structural references to thefashion of the 1960s dilutes its strict clarity of form. Even more powerfully evocative of the late 1950s, though (or what we consider the prevailing style of that time), are the sky blue in the stairwell, gold-coloured bars of the railings and anodized aluminium edges. The people using the building on a daily basis love it. Five hundred midday meals are cooked and served every day in the rooftop canteen, but students have suggested that they could do with much more. Considering the quality of the place overlooking the city's roofscape, it is always worthwhile to make a mad dash for a table by the window or on the terrace. No doubt about that.

• Claudia Gerhausser