When the smelly and unhealthy mining industry disappeared from the Ruhrgebiet in the 1980s, the region was left to deal with heavily polluted land and high unemployment. The Internationale Bauaustelling (IBA) Emscher Park, which started in 1989, put the area and the problem on the agenda. The aim was to transform the defunct and polluted industrial areas into one landscape park and to give the former industrial complexes a new function. IBA proved a success, which was underlined in 2001 when UNESCO added Zollverein to the list of World Heritage Sites. The site, the buildings and the machines are now on the same list as the Tai Mahal, the pyramids in Giza, and the Alhambra in Granada.

The reason why Zollverein was earmarked as a World Heritage Site is largely down to the Shaft XII industrial complex. The developers of this complex, which was built from 1927 to 1932, wanted a factory that functioned in an extremely rational manner and its architecture had to reflect the productive might of the German mining industry. Architects Fritz Schupp and Martin Kremmer were responsible for aesthetics but were also involved in the technical and industrial side of the design. The result was an architectural and urban design ensemble that puts Zollverein in a class of its own among complexes in the Ruhrgebiet. The buildings are neatly arranged in a taut framework based on symmetry and sightlines. One and the same structural principle is applied to all buildings: a steel skeleton into which brickwork panels are inserted.

But architectural beauty and cultural-historical value alone are not enough to secure a place on the World Heritage List. A plan and vision of how the area should develop is equally important. OMA/Rem Koolhaas and Floris Alkemade were recruited in 2001 to draw up a master plan for the 100-hectare site.

The master plan is based on the situation 'as found'. In other words, what is already there is taken as point of departure to shape a new reality. Zollverein was the driving force of Essen. To let it fulfil this role once again one central theme – design – was chosen and plenty of programme was added, mostly in the form of office space, exhibition space and congress facilities, all of which has still to be realised.

A physical hallmark of Zollverein was the wall that enclosed the complex. The wall, which has largely vanished, has been ‘reconstructed’ by OMA in the form of new additions. All new buildings are arranged around the edges of the site and divide the heritage from the surrounding workers’ housing. The choice of location was also pragmatic, since the edges of the site are the least polluted. An important aspect of the master plan is the reprogramming of the complex’s infrastructure. The rail tracks and elevated walkways have been earmarked as the most important public spaces. 

A large number of the buildings on the site have been earmarked as exhibition spaces, among them the Coalwash Building (where coals were washed and filtered) built in 1932. In 2001 OMA was commissioned to make the building suitable to house the Ruhrland Museum. In the process, the office worked closely with Heinrich Böll (Böll und Krabel), which was previously involved in the transformation of the Coking Plant and the Boilerhouse, both on the Zollverein site.

Most of the available budget was spent on cleaning and restoring the building. When the Coalwash Building was built, its life expectancy was an estimated 30 years. The combination of this temporary character and the exposure of the steel structure to water and coal grit proved disastrous. Damage to the steel was so severe that almost the entire structure needed to be replaced and a mere 15% could be saved. To make the building suitable as a museum, the original walls had to be thickened. After much discussion, UNESCO eventually agreed with the proposal to place the façade 20 centimetres outside the original building line so that the structure remained entirely visible from inside. A little historical falsification yes, but the solution looks more original than the boilerhouse converted by Norman Foster. This building houses the Red Dot Design Museum. Foster opted to thicken the walls on the inside. As a result, the façade structure is only visible as stripes in a smooth white layer of plaster. Foster chose to contrast old and new elements. Additions such as stairways, lifts and inserted floors are made of glass and shiny stainless steel and are clearly legible as new elements in and on the existing building.

In contrast to Foster, OMA took a radical approach. The additions and interventions in the Coalwash Building are restrained and sometimes scarcely recognisable. Plenty of black steel was deployed, openings in the concrete connect spaces, walls are left untreated, and the new roof pavilion hardly attracts attention. Points of vertical circulation provide some spectacle. These are coloured orange to emphasise movement and transport. The central hall, lifted 24 metres off the ground, is reached by an escalator that rises up the building’s exterior. Although the 56-metre-long escalator is clearly legible as a new element, it forms a fitting addition to the system of tubes and transport belts leading to and from the building. Inside, the central stairwell is located in the Rohkohle bunker. The stairwell has an unfathomable dark depth and receives indirect light only.

Until recently, the mood of discovery and excitement in the Coalwash Building also typified Zollverein. But that is slowly disappearing. Signposts now show the way across the site, concrete paths cross the railway tracks, and low tunnels have been blocked. The wild growth of butterfly bushes and brambles is being curtailed. Total control is also a feature of the recently completed Zollverein School designed by Japanese firm SANAA (Karuyo Sejima and Ryue Nishizawa). The light-grey cube-shaped building located next to the site entrance looks like a monument to the new start for Zollverein: clean and transparent, a place of education for management and design.

A personal favourite remains the Coking Plant, designed by Frits Schupp, where coke was once produced. Built between 1957 and 1961, the factory was one of the first buildings in Zollverein opened to the public within the framework of the IBA Emscher Park. Heinrich Böll made a magical exhibition space when he connected the coal bunkers to one another by cutting openings in the concrete and adding a sculptural stairs. Now the Coking Plant is something of a local gathering spot. Children swim in the pool in the summer while adults enjoy a beer at the picnic tables. Last summer the achievements of the German football team could be followed on a large screen.

According to the master plan, Zollverein must be fully transformed by 2010. Under construction in the northern section is Designstadt, containing office and studio space. Offices are also planned on the west and south sides, and a hotel is proposed on the edge of the site parallel with the Coking Plant. OMA is no longer involved in the master plan, and outdoor space has now been entrusted to Planergruppe Oberhausen (Licht Kunst Licht from Bonn, F1rstdesign from Keulen and Observatorium from Rotterdam).

The transformation of Zollverein seems to be a success: the car park is full, buses arrive and depart, and people with name badges are everywhere. To judge by the many guided tours of the complex, industrial heritage is valued, and Essen can boast a fine new park. Perhaps Zollverein is being manicured a little too neatly, but let’s hope that the penetrating stench of tar that shrouds the Coking Plant, an invisible memory of what was once here, never disappears.