As is unfortunately common in rural communities, Bingen has been suffering from rural flight, resulting in an increased number of vacant properties and commercial sites. To stop this trend, the community decided to renew its town centre. One the one hand, the people of Bingen wanted to turn the site of a former brewery into an attractive residential area with affordable housing units. On the other, they wished to build a new town hall serving as a focal point for the community and demonstrating its commitment to sustainable development.

In 2016, the town council engaged a number architectural firms and town planning offices to come up with a simple, yet sustainable concept for urban renewal. The proposed two-storey, eaves- and gable-fronted houses with pitched roofs and rectangular ground plans reflect the traditional layout of the historic town centre. The focal point of the urban renewal project is the new town hall designed as a modern timber construction, which is to set the standard for further development projects in the community.

Large windows and light-coloured timber signal transparency and openness

That the town hall is a timber construction is clearly visible from the outside: the building is clad in silver fir panels that are painted to give them the appearance of pre-greyed fir. Overall, the building signals transparency, openness and friendliness. This was achieved with large windows, some extending from floor to ceiling, especially at ground floor level, and bright rooms clad in silver fir throughout the building. The architects wanted to provide a warm and friendly atmosphere inside the administrative block. The main supporting structure made in BauBuche is visible throughout the building and recalls the village character of Bingen with its historic half-timbered houses.

BauBuche promoting innovative hardwood use

When opting for BauBuche as the key building material, the designers took the challenges of the future into account, considering that hardwood trees, and in particular beech, are more climate-resistant that spruce. The innovative use of hardwood in construction is also one of the cornerstones of the German Federal Ministry of Food and Agriculture initiative for the promotion of renewable resources, and the available grant aid was of course very welcome in Bingen.

By opting for BauBuche, the architects were able to come up with a design with slim, elegant posts and beams. Thanks to the exceptional strength and stiffness properties of the high-performance hardwood product, the dimensions of load-bearing elements are much smaller that would have been possible with a softwood construction. This resulted of course in considerable material savings. In addition, BauBuche is a visually attractive material, and the architects therefore decided to leave the support structure exposed.

Striking timber supporting structure from ground to roof pitch

The gable end of the 13 m high building, which is reminiscent of the traditional longhouses typical for Upper Swabia, faces the street. The town hall’s rectangular footprint measures 28.40 by 10.60 metres. The timber supporting structure made in BauBuche combined with timber frame wall elements rests on a reinforced concrete basement in the shape of a white tub. The timber skeleton features BauBuche posts measuring 8.20 m (w x d = 28 cm x 14 cm) reaching from the ground to the attic. They are positioned at a axial distances of 2.40 m to each other, while BauBuche beams (w x d = 28 cm x 30 cm) act as flush girders at the respective floor levels.

The beams are secured to the external posts by means of concealed timber construction connectors (Sherpa-L50 fittings). The glulam elements designed as 4.70 m single-span beams extend from one flush girder to the next, forming girder-free floors. For the large multi-purpose area at floor level with a width of 10 m, the structural planners chose a steel girder. Otherwise, they used BauBuche throughout, including for the ridge purlin and the two wall plates that support the rafters made of solid structural timber carrying the 45°-pitch roof. The ridge purlin (w x d = 20 cm x 20 cm and 20 cm x 36 cm respectively) rests on the heads of the BauBuche posts, while the wall plates (w x d = 28 cm x 20 cm) are screwed to the posts.

The handrails of the stairs, conventionally made from glulam, are made in durable hardwood, while the steps are covered with BauBuche Panel elements. Even the elevator runs in a “timber shaft constructed from prefabricated glulam wall panels.

The vertical load is transferred primarily through the timber skeleton consisting of BauBuche girders and posts. The floor slabs and some of the timber frame walls serve as stiffening elements. In the attic, the architects wanted to create an open-plan space with minimum partition, and there are therefore only a few timber frame wall elements at that level. To transfer the horizontal load from the attic floor, the structural engineers chose BauBuche posts extending along the external wall from the ground level to the roof. These posts measure 8.20 m and are connected at each level to the floor construction. Horizontal load transfer is thus through the floor slabs and then to the timber frame wall elements.

Prefabricated timber elements facilitate easy installation on site

The high degree of prefabrication of the components and elements made sure that the timber construction could be assembled in minimum time. First, the pre-fabricated timber frame wall elements were placed on the basement structure. They were then screwed to each other and to the concrete floor above the basement. While this work was in progress, the timber construction firm began already with erecting the BauBuche skeleton structure along the centre axis, followed by the installation of the BauBuche posts at the outer walls. After installation of the walls and posts, the BauBuche girders were put in place. In a next step, the glulam floor elements were placed on the girders and connected to each other to form rigid, shear-resistant slabs. The glulam wall elements of the elevator shaft of 12 cm in thickness and around 3.50 m in height, and the glulam wall panels of the stairwell were installed storey by storey. Finally, the fitters erected the centre walls and the two cross walls in the attic space. After the rafters and the roof substructure were in place, the roof was covered with square, anthracite BRAAS Tegalit tiles. In a last step, the building was fitted with the cladding.

Exceptional interior design and finish

Silver fir cladding was not only used at the outside of the building but also inside the new town hall. For the interior elements, the timber was given a bright, natural colour. While the fir slats along the ceilings are quite narrow, the wall features wider cladding elements. The recessed lamps are installed in narrow slots that run parallel to the cladding of the ceiling, which even extends to the wet rooms of the building. In the stairwell, the timber frame walls had to be covered with gypsum fibre boards for fire safety reasons.

The care and dedication that has gone into the planning and execution of this project is visible throughout. For example, two BauBuche posts of the outer walls were tapered by 3 cm at the room side to ensure seamless silver fir cladding at the interior.

Machining of BauBuche – a challenge?

Many timber construction companies still hesitate to machine BauBuche at their own workshop, as the high strength of the material is bound to lead to greater tool wear. During the planning phase, Holzbau Riester, the timber construction contractor in this project, asked for BauBuche samples in order to estimate additional costs they might face. It became clear that the machining of BauBuche would require more sawblades and mills (4 each extra) as well as additional drill bits (50 extra). The company considered this manageable and decided to machine the material in-house with conventional carpentry machinery. Given the attractive end product and the optimised workflows on site, the CEO of Holzbau Riester would be more than happy to be again involved in a project that requires the machining of BauBuche.

Text by: Susanne Jacob-Freitag

Photos: Michael Setz, Schaudt Architekten, Riester Holzbau

Dessins: Baustatik Relling