The Langenhagen school complex is 190 m long and 180 m wide and caters for around 1700 pupils, 200 teachers and other staff members. To ensure the smooth running of the school day, the school grounds and buildings are structured as a campus, featuring a complex layout that mirrors the functions of the various areas and rooms. There are four cluster buildings housing the class rooms, and a central assembly hall suitable for all types of events. In addition, the school complex includes two sports halls with dividing walls for flexible use. One sports hall is a two-court hall, while the other comprises three courts as well as a stand for spectators. 

Ground Floor:

1st Upper Floor:

As the old school buildings had to be vacated due to concerns in connection with fire safety, the designers were under enormous pressure to complete the new campus. They therefore chose a construction and building materials that enabled them to meet the tight deadline. The cluster buildings are hybrid constructions, while the sports halls are made in mineral building materials with reinforced concrete supports and walls, topped by lattice girder roof structure made in BauBuche, a top-quality beech laminated veneer lumber. The roof of the assembly hall is supported by trusses made in larch glulam. 

BauBuche helps protect resources 

As the span in the rectangular structure of the three-court sports hall measures only around 38 m (L = 46.35 m) and corresponds to that in the square structure of the two-court sports hall, it was possible to use a single lattice girder type for both roofs. This resulted in substantial cost savings in both the planning and the production phase. 

Both sports halls now feature a roof structure consisting of 37.60 m long lattice girders with curved top chords carrying a barrel roof. The shape of the roof ensures proper drainage. For the lattice chords and posts, the proprietors chose BauBuche of strength class GL 75, as this exceptional hardwood material allows for high-strength constructions with minimum material. The sports halls feature a filigree roof supporting structure whose dead weight is significantly lower than that of a comparable spruce glulam construction. Therefore, the dimensions of the posts, walls and foundations could also be reduced. 

For architectural design reasons, the lattice girders are placed at a relatively small distance of 3.75 m to each other and rest on reinforced concrete posts and walls. Despite their large span of 37.60 m, their height at the bearing points is only 2.85 m, extending to 3.60 m at the centre of the roof. The top and bottom chords are 28 cm wide with a height of 24 cm (bottom) and 37.7 cm (top) respectively. The diagonal elements measure 24 cm in width (h = 20 cm), which means that they are 4 cm smaller than the chords so that there is an offset of 2 cm on both sides at the respective connecting points. As these offsets are not easily visible, the engineers designing the supporting structure decided to leave them that narrow rather than increasing the cross-section to 24 cm. Again, this decision helped save material and further reduce the deadweight of the girders. The lattice posts have the same width as the diagonal elements, i.e. 24 cm, so that all elements in the lattice plane are of the same depth. The posts measure 10 cm in width at the visible front side of the girders and therefore appear particularly slim. They support the top chord at spans of 7.50 m and transfer the vertical loads to the supporting structure. 

Prefabricated girder sections for easy transport 

The lattice girders including the steel connectors were prefabricated and assembled at Holzbau Amann. To facilitate their transport from the southern part of the Black Forest region to Hanover, they were manufactured in three parts with offset assembly joints in both the top and bottom chords respectively (individual element lengths: 2x 13.90 m and 12.60 m). The factory-installed slotted plates allowed for easy manual assembly and installation on site, whereby the three lattice girder sections were connected with steel dowels and then lifted into position. Subsequently, a layer of purlins was installed at right angles to the top chords, preventing the upper chords from tipping while serving as the substructure for the three-layer panels. Providing a continuous, strong roof pane, these panels act as the stiffening construction of the roof. The entire construction can withstand a fire for 30 minutes (class R-30). 

The three-layer panels are covered by roof insulation followed by a water-proof bitumen layer and a green roof structure. The roof also carries photovoltaic elements that feed the school’s power system. Inside the two sports halls, the stunning support roof structure is clearly visible from below. Acoustic panels for sound insulation are installed between the rafters, together suspended lighting elements. The halls are heated by rows of suspended radiant heat panels. 

Load-bearing beams of equal length reduce construction time of two halls 

With the chosen methods for element production and construction, it was possible to build the roofs of the sports halls in a most efficient and economical manner, saving resources. Thanks to the high degree of prefabrication of the girders, the workers on site only needed to produce two joints per girder and position the assemblies on the supporting elements. This helped reduce the construction time. As the lattice girders of the two sports halls are of the same length, the planning and production costs were also significantly lower. 

-Text by Susanne Jacob-Freitag-