School centre dining hall in Schwäbisch Gmünd

The unique roof construction in the new dining hall, nestled into the surrounding scenery, is the centrepiece of the regional college in Schwäbisch Gmünd. The new building is a multifunctional hall that is used for dining during the day and for events in the evening. The design team from Liebel/Architecten was able to create a versatile space with a compact and functional solution.

The building is placed in a sort of "hollow," one level below adjacent access to floor areas. Visitors see a floating roof, which is perfectly integrated into the landscape. The roof not only fulfils design aspects, but also several other functions. The exceptional roof construction was made possible by using Metsä Wood’s Kerto® LVL (laminated veneer lumber) Q-panels and S-beams.

Grillage frame structure 

The basic idea of the building was to use as many natural resources as possible, and also to create a low-energy building.

"As a result, we decided to construct a roof using wood," says Steffen Kainzbauer, architect and project manager at Liebel/Architekten. The roof is designed in such a way that ventilation occurs by means of a free ventilation concept, with transverse ventilation. "The roof construction was developed by an interdisciplinary team of seven specialists," Kainzbauer continues.

The result was a grillage frame structure supported on steel columns. For both aesthetic and structural reasons, the roof was constructed from Kerto LVL Q-panels and S-beams. The load-bearing and dimensionally stable LVL was used for the beams, as well as for the roof and floor panels.

"We achieved a consistent design with identical veneers on both the beams and the ceiling. Due to the load-bearing strength of the S-beams, we were able to design slender beams and use Q-panels for the roof and floor panels for lateral stability," explains Mark Lukas from the Dr.-Ing. H. Hottmann engineering bureau.

Using glulam would have required beams 16–24 cm wide. With S-beams as the main and secondary beams, widths of only 10–12 cm were needed. The slender-looking wooden beams thus made the girder framework possible. In addition, the S-beams show only a very small deflection.

Stability without steel bracing

The roof construction was divided into main and secondary beams. The roof and floor panels were used to brace the entire roof structure. This was ensured with Kerto LVL Q-panels, which are only 69 mm thick, so steel bracing was not needed.

The dimensionally stable Kerto LVL Q-panels wa also used for an overhanging roof design to provide shade during summer, and allow light from the low-lying sun to enter in winter. This means that the building would have little heat gain, despite the large window surfaces.

Connections hidden from the sight

The connections of the load-bearing structure were innovatively designed. Metsä Wood has approvals for Q-panel for glued-in rods and for the use of timber screws in Q-panel and S-beam. The designers and structural engineers used both these methods in the connections. This made it possible to hide screwed connections from underneath the roof.

Additionally, an installation space was created on top of the roof panel. The glued-in threaded bolts are screwed onto the horizontal steel supports. "This made it possible to hang high loads at the top," explained Kainzbauer. The high load-bearing capacity of Kerto LVL was again a great advantage for this type of connection.

Clever roof structure with Kerto LVL

Fire safety for the roof construction was also solved with the Kerto LVL roof panels. The 69 mm version not only ensures bracing, but also provides 30 minutes of fire resistance (F30). A further advantage of the innovative connections in the top installation zone was that the screw connections were installed behind the F30 roof plate, thus meeting the requirements for fire safety.

Fast, light and green

The entire project was a major challenge for all the participants, but their great commitment got the task completed in a construction period of 15 months. The roof design team created and implemented an elegant solution – a unique roof construction using Q-panels and S-beams fulfilling the requirements of sustainability, design and functionality. Remarkable also is the performance of the carpenters, Holzbau Moßhammer GmbH.

The interlocking roof construction with a girder grid framework required great precision. With a diagonal measure of 33 metres, only one centimetre of difference was permitted. Under the direction of the two master carpenters, Gerhard Moßhammer and Roland Brändle, the large, new dining hall construction project was carried out rigorously and fully on schedule.