Polar Bear House: the most sustainable building in the world

After the certification by the DGNB (German Sustainable Building Council) last year, it is clear: the Polar Bear House in Kirchheim unter Teck near Stuttgart is currently the most sustainable building in the world.

The BANKWITZ beraten planen bauen office set new standards in sustainability back in 2008 with its own company headquarters, the so-called Polar Bear House. Around ten years later, this was once again confirmed by the DGNB with a platinum certificate. As if that were not enough of an honour, the company followed up with another groundbreaking achievement in 2020: Its extension to the existing Polar Bear House was once again awarded platinum and, on top of that, achieved the highest overall degree of fulfilment ever achieved by a new building in the DGNB certification process. This means that the Polar Bear House can now rightly call itself the most sustainable building in the world.

Like the existing building next door (Building A+B), the extension (Building C) is designed as a passive house, but unlike the two previous buildings, it does not need its own heating system. In terms of construction, the climate-positive residential and commercial building in Kirchheim unter Teck is a reinforced concrete-wood hybrid building. All concrete work was carried out in recycled concrete. A wooden post and beam construction made of prefabricated wooden elements with cellulose insulation forms the exterior walls. The façade of untreated, rough-sawn timber can be deconstructed and recycled without interfering with the supporting structure due to the combination of reinforced concrete skeleton and elemental exterior walls. All building materials were selected according to the criteria of the Vorarlberg Eco Guidelines and the specifications of the DGNB.

A pleasant indoor climate is ensured by decentralised comfort ventilation units, which ventilate and deaerate each of the utilisable units, as well as a heat exchanger with a heat recovery rate of 85 percent. The temperature is controlled via underfloor heating and concrete core activation. The heat required for this is obtained from surplus local heat from the existing Polar Bear House. Meanwhile, brine pipes and four geothermal boreholes provide cooling in summer. Thanks to a central shaft and clever arrangement of the heating/cooling supply, any future conversion measures can be carried out largely without adjustments to the building services.

The new building also draws its hot water from the existing building. Thanks to a battery storage system, the electricity generated by a photovoltaic system can also be used at a later time. WC flushing and garden irrigation use rainwater from a cistern. The screens for heat, sun and glare protection are controlled by software that reacts according to the current weather conditions. In any case, the entire building technology is software-controlled, and all consumption figures are also recorded and controlled via a central data acquisition system. This enables early detection of errors or optimisation possibilities and appropriate adjustments.

The building was designed as a 3D building model and using the BIM method in ALLPLAN, which had a positive effect on the result in three ways. "The 3D building model facilitated detailed design and enabled a comparison of variants in the room layout," explains Ralf Pimiskern, BIM manager as well as architect and business unit manager at BANKWITZ. "The two-way data exchange via IFC model with the carpentry company that carried out the timber construction, among others, enabled the alignment of the components in the design process and smooth execution. In addition, the DGNB Platinum certification of the building, which also includes sustainability assessments and a life cycle assessment of the building, could be achieved with the help of massing from the building model, among other things."

"Our ambition is to raise public awareness of sustainability in a credible, genuine and human way," says Matthias Bankwitz, managing partner of BANKWITZ consulting, planning and construction. "Authenticity is important to us - we do what we say. That's why we built our company headquarters, the Polar Bear House in Kirchheim unter Teck, the way we think is right." And it could hardly have been more right: In the certification by the DGNB, the new Building C achieved an overall degree of fulfilment of 94.2 per cent - a new building sustainability world record that had never been achieved before.