Ecological housing and business centre: The Prisma Building, Eble Architects in Nürnberg.

The latest building from Joachim Eble further explores his concerns with an ecological approach to urban architeture. Eble Architects, based in Tübingen in S.W. Germany, have a well established reputation for environmentally friendly building practice and are one of the few firms to have successfully transferred this approach from rural settings to the inner city.

They are perhaps best known for the Ökohaus - Kühl A.G.´s mixed use building in Frankfurt, finished in 1992. The project, with its glass house and north facing fortress wall, integrated landscape with building and brought together offices, a doctor´s surgery, a printers and recreational use; importantly it set precedents for an urban-eco-aesthetic. Another project, in the late 80´s, for a garden-courtyard housing scheme with shops and offices in Tübingen was financed by the Karlsruher Life Insurance A.G. The success of this project both architectonically and financially led the same investor back to Eble for the design of the Prisma building.

The Prisma building stands on the edge of the medieval core of Nürnberg, an infill site close to a major traffic node. Planning began in 1992, the first tenants moved in November 1996 and the planting of the interior and exterior gardens was finished in March this year. The format is similar to the Ökohaus in Frankfurt: mixed usage with 61 flats, 32 offices, 9 shops, a Kindergarten and a cafe. But with 18000m² net floor area it is some 7000m² larger than the Frankfurt scheme. The programme has been clearly defined into 3 blocks enclosing a courtyard space. The two northern blocks containing ground floor shops, 4 floors of offices and flats above are joined by a glasshouse with the anchor elements of the kindergarten at one end and the cafe at the other. The third block on the southern side sits independently from the rest and contains solely flats.

The glasshouse is seen as a public sunroom for the city, a covered market space in principle. It is without doubt the major identity of the project - a room to be discovered, hidden as it is from the street, orientated for passive solar reasons to the south. However the main public facade and entrance is to the street side on the north. Unlike the Ökohaus in Frankfurt, the northern facade does not play upon the enclosing fortress wall theme but is instead well-mannered and somewhat uninspiring - saying little about the real architectural intentions of the scheme. The main entrance is an extrusion of the glasshouse out between the end walls of the north and eastern blocks - an important signal but a little crude. One wonders whether this backwall street facade could have expressed more - perhaps the ground floor could have been more permeable through to the glass house or the rain water collection from the curving roof more accentuated?

The glasshouse is nevertheless the crux of the project both architectonically and in energy terms. As a space it is heavily planted, with a stream collecting in a pool fed with rain water off the roof. It is strongly structured by the inclined laminated timber struts supporting the roof and the column-ventilation ducts supporting the internal balconies. The glass skin is a sophisticated envelope, computer controlled with an antenna on the roof measuring wind, sun, temperature and rainfall. The computer then regulates the aperture of the openings and sunshading. Importantly, with over 50% of the roof surface area of the glasshouse openable, fire-regulations look upon the space as external. The importance of this is not only that no sprinkler system is necessary but that the two adjoining buildings can open out into the glasshouse to achieve the benefits of its controlled solar climate.

A further sophistication of the envelope is the use of water walls, using collected rain water, set in the glass facade. On a summers day, hot dry air is drawn in by natural air dynamics from outside over these walls and down across the falling water whereupon it is cooled, ionized and humidified, circulates through the glasshouse and either through the windows into the offices and shops or through the column ducts with fan assistance to the street facing offices. Computer controlled sunshading reflects unwanted sun´s energy from the glasshouse. It is in effect the traditional courtyard fountain technique placed more strategically in the outside wall. In winter the water walls can be by-passed and the glasshouse allows the sun´s energy to heat the internal air and the building.

The heavy planting in the glasshouse, not only on the ground but on every balcony, ensures not only an enriched oxygen content of the air but also a pleasant perfumed environment. The reduced energy costs through the solar benefits of the glasshouse are calculated at 69.8 MwH/heating period for a building of 85,000m³, a saving that already proved its worth at the Ökohaus in Frankfurt. This, so the architects inform, is equivalent to a saving of 8000 litres of oil over the same period, subsequently saving over a 10 year period circa 25,000 tonnes of CO² output. In winter, any additional energy is provided by the city´s block heating system. The city, too, provides drinking water for the building but all rain water that falls on the building is used. The run-off from the glass roof is collected in the external and internal pools for use in the garden and the water walls. The run-off from the aluminium roofs is used for the plantings on the balconies or to tank up the garage sprinkler system. Any excess rain water is then filtered through gravel lying under the basement garage and direct back into the ground water.

The rigour of material choice in evidence in other projects from Eble is also seen here in the Prisma building. Concrete ( an important contributor to global warming through CO² release in manufature ) is kept to a structural minimum. The floorslabs are built from hollow brick pots set in a concrete frame with subsequent increased insulation properties. The external walls are 40 cm thick brickwork requiring no additional insulation, simply lime plastered and coloured with mineral based paints and form as such a breathable skin. The flats above the offices are clad in a cement-wood chip board with mineral wool insulation in the walls and under the roof - there is no expanded polystyrene insulation in the building.

The internal balconies use a technique called `Brettstaple´- timber planks 16cm deep laid on their sides nailed continuously together in the workshop and brought to site as broad structural elements. They form an ecological alternative to concrete, need little additional insulation are cheap and look good.

All material usage is considered in terms of lifecycle costing: the energy needed to produce it, its environmental effects in production, usage, decay or reusage possibilities. Surprisingly, however, the curved roofs are of plastic-coated aluminium which has a very high energy requirement in production. The roofs are used for rain water collection which means copper and zink, both of which dissolve in rain water and would contaminate the soil, are out of the question. Clay tiling is suitable for rain water collection but does not suit such a curved form. Is, then, this curved form and its aluminium cladding the right solution, does it not actually unnecessarily increase environmental costs?

The importance of this building is that, in comparison to the Ökohaus in Frankfurt, which was fundamentally an experimental scheme, this project is an investors building with their ensuing stringent financial requirements. That this is so has perhaps weakened the strong, more radical aesthetic as seen in the Frankfurt project. However, that such a mixed-use, ecological based architecture can be successfully built in an urban context is a major step towards a wider acceptance, and recognition of this method of building.

Architect: Joachim Eble Architects.
Project Architect: Gorden Richter.
Landscape Architects: Adler and Olesch.
Structural Engineers. Schneck and Schaal.
Solar energy planning: Dr. W. Stahl, SUNNA.

M.P.G. Haslam 2:4:97; published in Architecture Today 1997