Completing the last part of the Eisbärhaus – the so-called polar bear house – took almost exactly one year. The ensemble of buildings that lends its name to the animal from the Arctic comprises two existing buildings (Segment A and B) and a now a new building (Segment C). The idea was to do things as differently as possible compared to conventional building projects. Looking back, the architect and the DGNB project auditor tell the story behind the building. It’s a tale of twelve months, torn between the desire to try anything remotely possible, ambitious goals, Swabian records and working with so-called moon phase timber.

BANKWITZ, an architectural firm that offers consulting, planning and construction services, is headquartered in the so-called Eisbärhaus in Kirchheim unter Teck, not far from Stuttgart. Its headquarters are not so much a building as an ensemble of three building sections. BANKWITZ laid the foundation stone for its ensemble with Sections A and B, which were completed in 2008. These were followed by construction of the third and final part, Segment C, which was started in 2019.

“Our aim was to take on the challenge of certification,” explains Matthias Bankwitz, Managing Partner of BANKWITZ. “Since Sections A and B were already certified under the Buildings in Use scheme when they were completed, this time we decided to apply for New Construction certification.”

The decision provided Bankwitz, who has been dealing with sustainable building issues for many years now, with the ideal chance to dig deeper into the fine detail of sustainable value creation over the course of a building project – and walk through every concept to the point of completion. As the building owner constitutes and thus belongs to a German ‘property community’, this was a golden opportunity to provide a counterexample to ‘investor architecture’ and be present at every stage of the process.

Volker Auch-Schwelk, the DGNB auditor for the project, was also interested in the potential it offered, especially compared to the existing sections of the ensemble: “Something I found particularly fascinating, right from the beginning of this project, was how much sustainable building had moved forward compared to Sections A and B of the Eisbärhaus,” he recalls.

A new chapter in the Eisbärhaus project

Although Bankwitz, his experts and Auch-Schwelk had already witnessed a whole host of sustainable building projects first-hand, the new Section C of the Eisbärhaus greeted the team with a number of new challenges. For example, the architects had already decided that all concrete should be made from recycled materials, including the foundations and impermeable areas of the building.

Going against convention, they also wanted the heating for the building to be based completely on internal sources. Heating is supplied exclusively through a local heating network. The existing parts of the building ensemble often generate a surplus of energy, so excess thermal energy can simply be diverted to the new building. To serve as a cooling system for Section C, four geothermal boreholes were drilled, each measuring 130 metres. Cabinets housing computer servers are cooled using naturally pre-cooled air. To do this, 80 metre-long ventilation pipes were laid underground.

“Things have also evolved in terms of ventilation,” reports Bankwitz, with a sense of satisfaction. “We already use a mechanical system for internal ventilation and heat recovery in the existing Eisbärhaus, and this ensures there’s an optimal supply of fresh air at all times. But unlike Sections A and B, the volumes of air pumped into Section C are controlled by a CO₂ sensor. Its job is to continuously measure indoor air quality and introduce the right amount of fresh air according to the number of people in the room.”

Local craftsmen and traditions

One challenge was to find skilled craftsmen in the area capable of meeting the required quality standards. Interior work on the building was completed in partnership with Swabian craftsmen and firms from the Bregenz Forest in Austria. “One priority from the beginning of the project was to ensure the building benefits from good air quality, so the plan was to finish the interior wall surfaces and floors with exposed and untreated wood,” recalls Auch-Schwelk.

Sourcing the required materials was a fascinating aspect of the building project. The aim was to only use timber that had been specifically felled for the building. The timber used for the silver fir floorboards came from the Bregenz Forest and was selected according to location and age, before being cut into shape and dried. The underfloors, the substructures of the walls and exposed coverings nailed onto the walls were made of spruce.

Some sections of the building were made from so-called moon phase timber. Moon phase harvested wood is only felled in waning moonlight. According to a number of forestry and carpentry traditions, wood harvested during the waning moon is of particularly high quality in terms of non-warping properties, durability, fire resistance and hardness. This tradition is still observed with particularly high-quality woodwork, and even the concert halls in in the Elbphilharmonie in Hamburg were built with moon phase wood.

Using this material for Section C of the Eisbärhaus also had a positive impact on the smooth running of the building process. “A major advantage when building with wood is that you can maximise the number of prefabricated components supplied ex-factory. You can work much more precisely in the workshop than on site, and this safeguards really high standards of workmanship. You can also complete work regardless of the weather. Apart from significantly improving quality, prefabricating materials in the factory offers another key advantage by shortening construction time on site,” says Bankwitz, summing up the process.

Is the Eisbärhaus a new model project?

Even though every building project is subject to different conditions, DGNB auditor Auch-Schwelk believes this quality-oriented (yet pragmatic) approach and the meticulous attention to detail are an important element of the philosophy applied to the Eisbärhaus – and thus something other projects can learn from. “Being willing and prepared to implement sustainable building principles down to the very last detail – even for criteria such as using local materials and untreated wood, or supporting biodiversity – could also be applied within other contexts, although it often takes more courage on the part of the building owner!”

The DGNB System was not just used to certify final quality standards, it also provided a thread of continuity for the overall building process: “The entire design, planning and building process had to be checked repeatedly according to the specified DGNB criteria – and then evaluated and, if necessary, adjustments had to be made. This provided us with a step-by-step checklist that ran through all stages of the project according to the HOAI,” reports Bankwitz.

Highest ‘overall degree of fulfilment’ rating for a new building assessed under the DGNB system

For everyone involved in the project, attaining such a high score for ‘overall degree of fulfilment’ was a nice reward for what had been an extremely intensive building process – one everyone was also able to learn a lot from. Hailing the project in September 2020, newspapers announced that “The world’s most sustainable building is in Kirchheim”. Matthias Bankwitz smiles to himself: “Section C of the Eisbärhaus was built to be above average in terms of environmental friendliness; running the entire ensemble is climate-neutral. As things currently stand, essentially we’re 29 years ahead of the German government’s Climate Action Plan 2050 for the entire building ensemble.”

Although requirements to build sustainably present the building sector with complex challenges, Auch-Schwelk still believes the task is achievable if individual stakeholders focus more clearly on the overall objective: “Sustainable building is an interdisciplinary undertaking, so accordingly, all project stakeholders must be determined to make sustainability the objective. It takes many small steps to reach a big goal!”