Lightweight support grid in BauBuche – roof structure of auditorium H9 at Bochum University of Applied Sciences

Product: BauBuche

With 350 seats, H9 is currently the largest auditorium of Bochum University of Applied Sciences and is located right beside a protected forest. For that reason, the proprietor wanted to make sure that the new building fitted well into the natural environment and came with a sustainable concept. The university thus put the project up for public tender. Banz + Riecks Architekten eventually won the contract, for a variety of reasons. The firm already has extensive experience in the construction of timber and zero-energy homes, and came up with a design that forms a seamless bridge between the existing teaching block and adjacent forest. The new building has a relatively small footprint, as it cantilevers above the ground and rests on a compact concrete base. Two other outstanding features that won over the jury are the filigree roof structure and the large glass façade opening the room to the forest. The new auditorium is thus not only filled with light and air, but its design and materials also reflect the surrounding nature.



Hochschule Bochum, Bochum, DE




May 2019

Timber construction

Haveloh GmbH, Ahaus-Alstätte, DE

Support structure design

Unconventional room concept

The main access to the new auditorium is from the large, introverted foyer on the first floor of the teaching block. The foyer connects the new auditorium to eight other lecture halls. When opening the door to H9, students enter however a space that is completely different from the other lecture halls in the building that have no daylight, where the lecturer is at the front of the class and one normally only see the back of fellow students. At H9, they enter a light-filled atrium at gallery level. Daylight floods through the huge triple-glazed windows. Their eyes might wander over the treetops of the forest outside. As they walk down the steps to find a free place, they enter a space where they can actually see the faces of other students, connecting with them. Other features that catch the eye in auditorium H9 are the elegant BauBuche posts and the box grid structure of the ceiling with an element width of 22 m, also made in BauBuche.


Three-dimensional supporting structure in BauBuche

From the outset, Banz + Riecks Architekten wanted to build a roof supporting structure in timber that was not to be hidden behind a suspended ceiling but to be exposed as a design feature. Initial plans were based on a combination of main and auxiliary beams. Given the large span, such a construction would have required rather high girders. Also, the auditorium would have looked a bit like an factory or sports hall, which was not deemed appropriate for a place of learning. In order to avoid this, the designers opted for a construction without a defined main axis. In close cooperation with the structural engineer Burkhard Walter they developed a 3.6 x 3.6 m square grid construction with a uniform element cross-section. One of its innovative structural features are the jointed connectors, transforming the construction from structure designed to withstand bending forces to one transferring shear forces. As loads are only transferred in vertical direction to the grid level, the cross-section of the individual elements could be kept small. For the construction of the grid structure, BauBuche offered two distinct advantages over other materials. On the one hand, it allowed for much smaller dimensions than would have been possible with hardwood. This is of course due to BauBuche’s superior load capacity and high bending and shear strength. On the other, the technical look of BauBuche was exactly what the architects wanted for their exposed roof construction. “We wished to create a space in which architecture and engineering are accessible to the public. At the same time, we had to meet high acoustic standards and energy efficiency requirements. BauBuche proved to be the ideal material for this project, ticking all the boxes,” explains Dietmar Riecks of Banz + Riecks Architekten.


Concealed connectors

The grid structure consists of BauBuche beams with a cross-section of 20 x 128 cm that were shipped to the site as prefabricated elements in three different lengths for butted installation. They are connected by means of shear force connectors made in steel, with suspension fittings along the long sides and milled recesses at the front sides the beams. Thanks to the milled recesses at the intersections, these connectors are effectively concealed so that the roof structure appears made entirely in wood. The concealed installation of the steel elements also enhances the fire safety of the construction, as the connectors are shielded from the impact of fire.

Equally concealed are the steel fasteners that link the timber gird to the 20 x 40 cm BauBuche posts along the glass façade to which it is butted. These fasteners consist of steel rods and screws that hold the various elements in place. The posts along the walls are exceptionally slim and elegant. This was made possible as the grid construction acts as a structural plane transferring horizontal forces to the concrete wall that separates the auditorium from the foyer rather than to the timber posts. Without this plane, the designers would have been forced to install interconnections at the post level, or opt for a frame construction.


Installation of timber support grid completed in twelve days

The installation of the support grid started in one of the corners of the building. Using a scaffold, the BauBuche elements were connected to each other as the workers progressed towards the opposite corner, securing the elements with full-thread screws and working without a roof over their heads. It took only twelve days in November for the construction to be completed. Only at this point did it become a load-bearing structure. In order to protect the beech lumber against the elements, it was wrapped in tear-proof foil after having been equipped with a diffusive, water-repellent coat. Permanent protection is provided by the 10 cm board stack ceiling and the roof superstructure. Below the board stack ceiling, there are acoustic panels made in spruce. Together with the suspended LED luminaires, they accentuate the individual timber grid squares when seen from below.


A room dominated by sustainable timber

Timber is the dominant material in the auditorium, from the supporting structure and the industrial oak parquet flooring to the folding seats and the anthracite-painted wall panelling. This gives the room an atmosphere of great calm, anf enhances its acoustics. As timber is a renewable building material, the auditorium meets the requirements of energy efficiency and sustainability as specified by the university in the call for tender. The building is actually 50% more energy-efficient than required by the German Energy Saving Ordinance (EnEV), and is heated and cooled from a geothermal source. Auditorium H9 is without doubt a showpiece for contemporary building design and will hopefully soon be the venue of lectures by the university’s Department of Architecture

-Text by Roland Pawlitschko-

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