Winterthur is the sixth largest city in Switzerland, and the second largest in the Canton of Zurich. Baltensperger AG was established in 1952 just 5 kilometres outside Winterthur in Seuzach. The company specialises in timber construction and has been very successful over the years. As the old factory site became too small to cater for the ever growing business, it was decided to relocate operations to the nearby Winterthur, the regional business hub. For its new premises, the family-owned company employing around 270 people wanted to bring together tradition and innovation, as Baltensperger believes that these are two core principles that will secure its future success. The first building erected on the new site was a 107 m long, 16 m high and 46 m wide production hall. The machine park including a CNC joinery machine with an interface to the CAD design department, a high-bay storage facility with a computer-controlled crane and a fully automated cutter reflects the processes that are involved in modern timber engineering. Modern timber construction has moved from the actual building site to a factory hall, where components and modules are prefabricated with millimetre precision – protected from the elements. While this requires obviously much more detailed planning, the on-site construction time is significantly reduced, so that the overall building costs are lower.
New offices with 45 spatial units
After the factory hall was fully operational, the company proceeded with building the 3D timber construction modules for its new administrative block. These were assembled in record time, as the work preparation team used CAD planning tools that communicated directly with the machine software for the cutting to size and machining of the individual elements in the joinery machine. The three-storey administrative block rests on a two-storey reinforced concrete construction that serves as a delivery and storage facility of the factory and also houses the canteen, changing rooms and toilets. The timber structure of the administrative building consists of 45 identical spatial units measuring 3.10 m (W) x 16.30 m (L) x 3.50 (H) and weighing around 15 t each. The floors consist of an 8 cm glulam layer covered by 15 mm plasterboard and a 45 mm hollow space. On top of this construction, there is an equally thick hollow box with a solid timber frame, insulated with 260 mm blown-in cellulose. The box is glued to three-layer panels that give it the necessary structural strength. The finished floor surface consists of a durable anhydrite screed installed on top of the impact sound insulation. The load-bearing hollow box element is designed as a three-span beam. The external walls of the timber construction are made from 240 mm structural solid timber frames insulated with cellulose. At the inside, we have a 15 mm layer of OSB panels that are glued together and acts as a vapour barrier while providing extra stiffness to the construction. Towards the outside, 40 mm wood fibre panels and 15 mm plasterboards form the substructure for the batten and counter-batten construction to which a back-ventilated façade made of 22 mm silver fir clapboards is attached.
Double-shell module joints
The roof is made with 200 mm glulam elements and a 15 mm OSB layer supporting 270-300 mm EPS sloped insulation elements. A double layer of welded bitumen sheets protects the construction against the elements. On top, we have a 20 mm diffusion-open and root-resistant roofing underlay for the stonecrop cover of the green roof. To meet the stringent impact noise insulation requirements for office spaces, the partition walls between the modules are two-shell constructions. The modules come with a frame made in BauBuche. The beams measure 100 x 2000 mm and 160 x 400 mm respectively, while the posts measure 100 x 360 mm or 100 x 400 mm. The vertical load transfer of the post and beam system with rigid corner connections is through the girders onto the posts. The BauBuche posts and beams are force-fit by means of timber screws inserted through predrilled holes.
BauBuche – a material of many outstanding qualities
The individual offices with around 40 workstations in total are located along the windows, while the space further inside the building houses the general meeting areas and conference rooms. As the room modules were prefabricated to a large extent, the construction time could be reduced to a minimum. Production in the new factory hall commenced in October 2016, and the offices in the administrative block were ready in May 2017. This successful symbiosis between good architectural design and efficient construction is not least due to the use of BauBuche as one of the main materials. The beech laminated veneer lumber provides structural strength and stiffness, and brings a natural atmosphere paired with timeless elegance to the offices of Baltensperger AG. BauBuche elements also provide a consistent structure to the open-plan office area measuring 46.50 x 16.30 x 15.40 m. In combination with the serial production of the 3D modules, the designers were able to give the room a distinctive look, while adhering to a predefined grid layout, which simplified and sped up construction.
Timber construction – inside and outside
About 80 m³ of BauBuche form the structural frame of the building. Another 570 m² of BauBuche in the form of boards were used for the furniture, staircases and solid parquet flooring. The result is a pleasing design and room concept where the support structure, the interior furnishing and floors form a harmonising unit. The timber structure of the building is further emphasised by the exterior cladding in pre-greyed fir. The chamber-dried and planed elements were treated at the factory with a special glaze that ensures consistent greying over time so that there is no need for future sanding or painting. The façade will thus grey naturally and without spots so that the building will eventually acquire the matte grey look and character of old wood. Over the years, it will gradually gain that distinct silver patina that makes old timber buildings so attractive.
– Text by Marc Wilhelm Lennartz –