Originally there were five kilns on the site of the “Obere Fabrik”, but only one has survived. With an external diameter of 10.3 metres and measuring four storeys – or 16 metres – in height, it is the largest porcelain kiln in Germany and one of the few to remain largely in its original state. A little over a hundred years ago, from 1839 to 1942, porcelain was fired here on three of the storeys. In 1942, production was stopped due to a coal shortage and was never resumed following the war. However, that was by no means the end of ceramic production for Zell am Harmersbach. The “Untere Fabrik” (Lower Factory) has existed for a long time, gradually being expanded over the years, and is currently renowned throughout Germany and beyond for its “cock and hen” motif. It is largely down to this poultry pair that Zeller Keramik continues to exist today.

The fact that the Rundofen circular kiln is also still standing today is thanks to some dedicated local people who were determined to stop this historic landmark of porcelain production from falling into disrepair. They made sure that the remains of the Obere Fabrik were declared an industrial heritage site back in 1989. But it took almost another 30 years before this industrial heritage site was put to new use. The architectural competition that went out to tender in 2016 was won by Biberach-based architectural practice wwg-architekten. The judging panel liked their design in particular because the angled façade of the new extension creates a clear break with the existing building while also providing a view of the historic Rundofen circular kiln from afar. Three intermediate floors were arranged around the circular kiln as an open gallery, enabling you to view it from all sides and to even go into each of

The construction works began in 2019. As part of the renovation, the existing outer brick walls were strengthened with reinforced concrete pillars that were mounted in front of the walls inside and colour-matched to the bricks. The outer walls of the extension have been constructed as a double-skin, coloured exposed concrete construction with core insulation. The load-bearing roof structure, an untreated timber construction, emphasises the industrial feel of the interior. To create the large glass façade, the architects opted for the VISS façade steel system because “a steel façade can accommodate more slimline dimensions and steel profiles better reflect the old industrial style,” explains Stephan Wussler from wwg-architekten. In his opinion, the benefits of a steel façade come to the fore when large module dimensions are involved, such as those of the circular kiln's ‘display window’. The façade modules measure 2.50 metres high by 2.50 metres wide, with the exception of the top row, which is connected to the floor below with trapezoidal fields (also angled inwards).

In the end, fabrication of this unusual mullion/transom façade proved to be the biggest challenge of the project for the Haslach-based façade engineers from Haser Metallbau GmbH, particularly when it came to concealing the attachment of the glass façade to the exposed concrete of the walls as much as possible. Haser Metallbau resolved this complex issue with the help of pre-assembled mounting brackets to connect the mullions to the primary structure at the top attachment point. The fields were then glazed with a double insulating glass that provides thermal insulation and sun shading. The glazing is designed to withstand soft body impact and the large panes weigh 55 kg per square metre, which amounts to around 350 kg per module field. Extra-high, automatic side-hung doors ensure barrier-free access. They were made from the Janisol steel system, which can be combined with the VISS façade with no visible transition.