Renzo Piano Builds The “Weltstadthaus” In Cologne

Flowing, transparent, anatomical – this is how the “Weltstadthaus” designed by Renzo Piano fits into the corner of Antonsgasse and Schildergasse in Cologne city centre.

With his modern design, the star architect pushes the “blob” style of architecture forwards. The organically formed building has a harmonizing effect on the pulsating shopping district. The idiosyncratic jacket of the building, made of glass and wood, is both architectural vision and technical challenge.

In order to combine this extraordinary shape with a high degree of functionality, the planners developed an elaborate façade construction. Jacketed with ipasol natura 67/34 (Interpane) and supported on a skeleton of glue-laminated timber girders, the vitreous “blob” has been attracting shoppers since September 7th.

“Architecture at the highest international level” was the demand of the client Peek & Cloppenburg on their “Weltstadthaus” buildings. Prior to this project the German clothing company already worked together with professor Joseph P. Kleihues and Richard Meier.

Renzo Piano has now realized his ideas of a shopping palace in Cologne under difficult urban development conditions. Wedged between a busy shopping district and an arterial road with heavy traffic, surrounded by concrete façades from the seventies and in the neighbourhood of a late Gothic church, his idiosyncratic design of glass and wood flows into place. It is not a free-standing piece of art – Piano´s concept fits into the local structural conditions and deliberately confronts less desirable constructions nearby.

Designed in two parts, the building takes up the structures of its surroundings while at the same time creating flowing transitions and new spaces. On the Antonsgasse side, the natural stone façade with its classical cubic shape picks up the straight lines of the street. The counterpart to this angular form is the Schildergasse side with its rounded and delicate design. While the front has five stories, this sinks to only four stories on the side facing the Antoniterkirche.

The façade also decreases in width at this point to create more space.

The late Gothic church, which almost looked displaced in this urban and cold street of buildings, has now become a formative element and keeps its identity.

The building, optically split in two, appears like a glass whale winding around a cliff.

Renzo Piano´ s flowing glass construction frees itself from traditional architecture and at the same time makes reference to it. The architect describes his design as "A modern building with, however, a clear reference to tradition, through the use of wooden arches and glass”.

The glass house, which is 130 metres long and up to 34 metres high is reminiscent of a 19th century orangery. The foundation of the department store with a footprint of 22,000 square metres is a reinforced concrete construction. On top of this foundation rests a wooden construction which supports and shapes the glass jacket composed of round and elliptical profiles.

At the level of the fourth story the supporting framework for the roof and façade construction rests vertically on the reinforced concrete skeleton. 66 timber girders are connected like ribs to the steel ridge girder, the three-dimensional, slightly curved, “backbone” of the body. The glue-laminated girders are made of 60 millimetre thick and 160 to 220 millimetre wide lamellae of Siberian larch.

Only every fourth to sixth of these wooden ribs rests directly on the skeleton. In between, the façade is a self-supporting construction. This makes it possible to follow the organic forms while safely absorbing the forces. On the skeleton, an inner support structure on fine-lined double flat steel, supports the façade made up of the frames for the glass and silicone sealing profiles. Nestled into the curves The glass lightly and delicately encases the designer shops.

A “scaled” façade of modular stepped glazing units was created. Nearly every one of the almost 7,000 inserted glass panes is unique – the individual façade segments vary in angles and dimensions. The CNC controlled glass cutting makes it possible to follow the soft lines of the body.

In order to fully realize the architectural curves of the design the insulating glazing elements were slightly cold-forged after insertion. This generated an optically and functionally sophisticated building jacket which combines high transparency with a comfortable indoor climate.

Shopping under ideal conditions – the solar control glazing ipasol natura 67/34 (Interpane) fulfils the special demands of a trend setting department store: Rooms flooded with daylight (tL = 67%) and true colour presentation of apparel and accessories. Particularly important for a relaxing shopping expedition: A balanced relation of solar protection in the summer and thermal insulation in the winter. With a low solar factor of 37 percent (EN 410) and excellent thermal insulation (1,1 W/m²K as per EN 673), the "glass skin" made of ipasol natura 67/34 controls the temperature.

In addition, the ground floor of the building comprises approximately 1,000 square metres of thermal insulating glazing (iplus by Interpane).

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