The historical centre of Oberhausen raises the question of how centrality, urban density and public spaces beyond commercial uses can be realised in light of economic structural change. As an answer to this question, the city's property management company OGM (Oberhausener Gebäudemanagement GmbH) has proposed a development that integrates two very different uses in a new way: For the first time in Germany, a building is being constructed that combines functions as diverse as a Jobcenter and a rooftop greenhouse, in which the Oberhausen based Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT) realizes its concepts in the area of building-integrated agriculture. Ultimately funding from the Federal Programme “Nationale Projekte des Städtebaus” (National Urban Development Project) created the conditions for the architecture competition in 2016, of which Kuehn Malvezzi was the winner.
The design, developed in collaboration with landscape architects atelier le balto, adds a third element to the two uses, going beyond the original brief. A vertical garden is an effective urban planning element that purposefully combines old and new landscape typologies into a public space. The varied course leads visitors from the lime tree lined market square up steps and platforms, past climbing plants and seating areas, up to the roof. Once at the rooftop, the view opens up over the centre of the historical centre of Oberhausen and offers a new view of the city.
The building, designed by Kuehn Malvezzi, blends confidently but calmly into the historical city. The specificity of this important urban location results from the tension between the physicality of the brick building and the filigree lightness of the greenhouse on the rooftop. From the regularity of its structure, the greenhouse on each of the three sides of the street forms its own conclusion, which responds sensitively to each context. On the Marktstraße, it appears clearly legible as an independent structure. At the Altmarkt however, it develops a clear visibility with its high ridge front, while the vertical garden communicates as an open, green link to the smaller, neighbouring building. On Friedrich-Karl-Straße, the building connects, via several steps, to the adjoining buildings. The greenhouse commences on the eaves and ends flush with the recess of the building. The three elements of the office building, the greenhouse and the vertical garden are modularly related to one another. A galvanized steel structure takes the basic dimensions as a starting point and varies them in different components: vertically as a division in the office windows, in the glass of greenhouse wall and the metal trellis; horizontally the platforms of the trellis continue storey by storey on the surrounding window sills.
The rooms inside the building receive a generous feeling through the floor-to-ceiling, opening, windows, exterior views and structural clarity. Contrasting the clinker cladding, the foyer on the ground floor is designed to have a raw, visible finish. The concrete construction is exposed, suspended ceilings were dispensed with in favour of the experience of the full room height, and the building services are installed visibly. In cooperation with the Berlin agency Double Standards, a signage and information system was designed that offers easy orientation within the Jobcenter. The warehouse typology of the building is sustainable in terms of adaptability to possible future developments of the city. With comparatively simple means, the office building can be flexibly transformed into living space and a combination of inner-city living and working can be realised.
The vertical garden is the spatially visible link between the traditional Altmarkt, where a market is held six days a week, and the rooftop greenhouse as a place of agricultural production. The basic structure of the green space consists of an open steel frame supporting platforms, staircases and a freight elevator, which also serves as a trellis for the various climbing plants. Sealed surfaces were completely omitted from the exterior of the project, which is also a new step. Hardy plants such as the crimson glory vine, common hop, Chinese wisteria and climbing hortensia have their roots at ground level. A bed of small shrubs and ground coverers marks the entrance to both the vertical garden and the inner courtyard. A seemingly floating surface of galvanized steel grids makes it easy to walk over the bed to the first staircase. New plants are added to the garden on each floor. A balcony at the end of the walk offers a view over the town and market square.
The rooftop greenhouse is the highlight of the parcours, with its U-form following the form of the inner courtyard. It is operated by the municipality and will be regularly accessible to members of the public. A seminar and conference room located on the 4th floor offers additional space for events, cooperation and training. In the rooftop greenhouse the three sides of the building, which respond to three different urban situations, can be experienced from the inside. The area intended for research and development is arranged along Friedrich- Karl Straße.
The courtyard can be experienced from different levels, each from a different perspective. A self-binding gravel surface frames the topography, which forms drier and more humid zones with height differences of up to 60 cm and represents a suitable habitat for various plants. The wave-like soil modelling accentuates the play with the colours and leaf structures of perennials, shrubs, ferns and grasses. From the open foyer of the Jobcenter with its floor-to-ceiling windows, the view over the courtyard drifts towards the vertical garden.
The integration of building services, which had previously been investigated in feasibility studies and has been implemented here for the first time, makes the office building usable as a resource for agricultural production. Here, various functions can benefit each other. Air removed from the office building, for example, is fed into the greenhouse, where waste heat and CO2 can promote plant growth. Rainwater harvested from the roofs is collected in a cistern and used to water the plants. The grey water from the sinks and washbasins is treated and reused as service water partly for flushing toilets in the office building and partly in the vertical garden. In the research area, the use in horticultural production is being investigated. The separate collection of all types of wastewater ensures that even more far-reaching synergies can be established in the future.
