The building cubes consist of a cast concrete skeleton with massive brick walls, and the long corridor comprises a steel framework filled with brickwork. The cubes and corridor have horizontal ribbon windows with single glazing. The Comb Building was derelict before basic maintenance of the roof and facades (Dach- und Fachsanierung) was started in 2011, following a two-year period of preparation and planning in order to find an appropriate concept for this specific technical building. The conservation-restorer’s recommended treatments for the architecture, machinery, and pipe alignment were initially limited to a test area.

In 2010 and 2013, detailed concepts were worked out for the conservation of the architecture and machinery: The first stage of construction (Dach- und Fachsanierung) focussed on preservation principles, while the second stage included enhancements due to the specific reuse concept, adhering to the principles of minimal intervention and aiming to achieve energy savings and upgrade basic thermal comfort. The following guidelines were applied to the historic technical facilities: To clear the cubes up to a height of 2.5 m; To conserve pipes that do not limit the reuse, and that have a reference function to cleared and maintained machinery; Pipes, lines, and cables without a reference function, and those smaller than 50 mm, were removed; Pipes that penetrated the facades were closed, and were cut before and after the former penetration point. Furthermore, the historic pipe surface could be conserved in some parts, including its historic signs and scratches. Rather than using common de-rusting and restoration treatments, steel pipes were given a specific, transparent protective coating. 

The successful basic interventions in 2011 triggered a vision to conserve the building and machinery through reuse as commercial spaces. The Zollverein Foundation launched the project together with its architect and conservation partners, achieving a tailored application of conservation through reuse. The building benefits from double accessibility: at the front through the connecting corridor, while the rear is accessible for deliveries. Most of the cubes now serve as spaces for ateliers and showrooms. The two-floor cube building that previously housed electrical transformers has been reused as flexible office space. Small- and medium-sized creative companies were approached and successfully acquired as tenants. It is interesting that three of them came from the Triple Z incubator (also located in the district), and required the larger spaces for further expansion. The building is open to Zollverein visitors and the companies’ customers.

The retail committee of the city of Essen (Konsultationskreis Einzelhandel) was consulted by the urban authorities as part of the planning consent process. Local retail associations and communities were informed about the project at one of the Katernberg conferences, a long-established forum at which various agents from the district meet to discuss local matters.

The project contributes generally to environmental issues through reusing existent structures and saving the embodied energy associated with the original construction. Furthermore, the approach of minimal intervention, focused on efficient enhancement of thermal comfort, is environment-friendly. The specific treatments were: efficient internal insulation, insulated concrete baseplates, and partly upgraded windows through insulation glazing. 

Addressing small- and medium-sized creative businesses already located in the district, and searching for spaces them to expand, supports local economies and thus contributes to inclusive social and economic development at a small scale.

Information about the project was disseminated through a diverse range of magazines and the Foundation’s marketing efforts. It would be interesting to extend the offered guided tours of Denkmalpfad Zollverein to buildings that have already been converted, such as the Comb Building. This would give visitors a more detailed understanding of the previous technological processes and workflows.

The reused Comb Building contributes to the revitalisation and attraction of the former Zollverein industrial area. With its established tenants from the creative industries, the building’s reuse concept supports the development of Zollverein as a location for culture, design, and economy. Their business activities range from painting workshops and hand-made furniture to international trade in interface design and consultancy. The six tenants provide job opportunities, although on a small scale and requiring specific skills; consequently there is a mismatch between their requirements and the qualifications of the local community. The legally binding land-use plan (Bebauungsplan) specifies the types of business permissible in the Comb Building, in order to avoid further destabilising the retail structure of the district centre, which already faces trading-down challenges. Some companies might serve the touristic demand at Zollverein by offering souvenirs and special artefacts, whereas others might contribute to the awareness of Zollverein as an international business location.

The machinery present prior to the conservation and reuse is documented and evaluated via visual documentation, description, and discussion with conservationists, architects, and former workers with specific knowledge of machinery and industrial construction. The 10-metre-long test field supported in-situ research on preservation techniques. At least two supervision reports on the conservation of the machinery were prepared during the construction phase. They can be understood as part of a monitoring process. The Comb Building is documented online as an example of good practice (https://www.indumap.de/content/kokerei-zollverein-ausgew%C3%A4hlte-anlagenteile-kammgeb%C3%A4ude-rohrleitungstrasse).

The Zollverein Foundation is proprietor, investor, and developer, and conducted the project together with a team of specialists in heritage conservation. Diverse planning instruments were used in the transformation process: listing of historic objects, formal planning process with a legally binding land-use plan (Bebauungsplan), and cooperation between owner and architects. Early consultation with conservation and real estate experts allowed a tailored reuse concept. While the basic conservation was financed by national funds, the Zollverein Foundation was also able to use funds from the private capital market through the refinancing secured by future rents. The project’s development allows for directly implementing the Foundation’s objectives of protection, conservation, and development of the UNESCO World Heritage. 

Core resources, such as visual integrity, were preserved. New resources are activated through reuse: the new accessibility of the building interior, some souvenirs and goods, and economic development. The hosted creative industries and their national and international business connections might serve the supra-regional attractiveness of Zollverein and the Ruhr region. Discussions are considering whether the project can create the types of jobs required locally, or can attract new district inhabitants. There is even more potential for the future in education about this part of the UNESCO World Heritage site: information about the monuments and the historic technical systems can be added.