New soul behind historic walls: Cofrastra® composite floors for the Heidi Horten Collection museum

Tucked into the inner courtyard of a Gründerzeit building in Vienna’s city centre, the former chancery building of Archduke Friedrich has been converted into a private museum. In order to meet the requirements of a modern art museum, significant adaption to the existing structure was necessary: three above-ground levels and an underground level were newly constructed behind the preserved building facade with the help of a steel structure and Cofrastra® 56S composite flooring supplied by ArcelorMittal Construction.

Detailed information

Following the successful exhibition of art collector Heidi Goëss-Horten's collection at the Leopold Museum in Vienna in 2018 under the title ‘Wow!’, her assortment of masterpieces are now permanently displayed and accessible to the public in this private museum. The centrally-located site, in a completely architecturally redesigned building with fitting surroundings, is now open.

From archducal chancery to modern art museum: an architectural redesign with a ‘Wow-effect’

With the acquisition of the Stöckl building, built circa 1914 in the inner courtyard of a Gründerzeit building on the corner of Goethegasse and Hanuschgasse streets, Heidi Goëss-Horten secured a historic building in the heart of Vienna. This former archducal chancery is located opposite the Palais Erzherzog Albrecht (known as the Albertina) and has already housed other art and cultural institutions in the past - most recently, the State Opera Museum. The new use of the Stöckl building as a museum for one of the most important private art collections integrates itself seamlessly into the adjacent ensemble of the Burggarten park, the State Opera, and the Federal Museum in the Albertina.

However, the over one-hundred-year-old building did not meet the requirements of a modern art museum. This unique art collection, which includes significant works from famous artists of different epochs, calls for engaging architecture that corresponds to function. The design by the architects of the next ENTERprise (tnE) envisaged a necessary restructuring of the building's interior. To this end, the building was gutted and extended downwards with a basement level.

Only the facade of the Stöckl building was retained to enclose the newly constructed, almost free-floating exhibition levels. The three floors are offset from and rotated against each other. This new internal division forms a contrast to the classical facade and allows for new spatial relationships within the museum as well as to its external surroundings. The result? Spectacular architecture with a ‘Wow-effect’ that skilfully showcases this renowned collection of art.

Floating between old and new: construction challenges

When it comes to engineering, this exhibition venue planned by Bollinger + Grohmann is also a remarkable project from a technical point of view due to its location and the historical building fabric. In addition to the almost complete gutting of the building, the existing structure was also given a full basement and the ground floor facade was opened up at one corner of the building and underpinned to create a spacious entrance area to the museum. The new supporting structure is essentially based on steel girders with a maximum height of 600 mm and a span of up to 20 m. Thus, the individual exhibition areas are spanned in a self-supporting manner and are only connected vertically by the free-standing staircase made of stainless steel. The concentrated bearing loads of the girders are transferred to the building ground via steel supports, supplementary reinforced concrete structures, and deep foundations.

The steel construction as well as the assembly of the composite flooring profiles was carried out by Zeman & Co GmbH. In close coordination with ArcelorMittal Construction as the manufacturer of the Cofrastra® flooring, static and logistical issues were clarified promptly and delivery was timed to the construction schedule.

Cofrastra® 56S: for light, slim flooring construction with numerous advantages

Cofrastra® 56S, made of galvanised and organic coated steel (tN=1.0 mm) with a smooth bottom flange, serves as formwork for the in-situ concrete with spans from 1.65 m to over 2 m without the need for further support. In addition, the steel profile forms the lower reinforcement layer to absorb the bending moments of the slab construction, which is kept very slim with a thickness of 10 cm. This results in a lower floor weight of less than 250 kg/m2 with relatively high dead and live loads totalling just under 9kN/m2.

The profiled elements can be stacked compactly and so could be efficiently transported to the inner-city construction site.

Fire protection is ensured simply by reinforcement bars positioned in the ribs of the profiles according to EN1994-1-2, without additional, time-consuming measures.

Assembly of the approximately 680 m2 floor decking for this project was largely manual and crane-independent, saving valuable crane capacity and construction time.

The special dovetail geometry offers reversible installation of building services and suspended ceilings, so that the composite flooring remains hidden from viewers, allowing them to concentrate entirely on the art and sense of space in the new museum.


Cofrastra® 56S composite flooring in tN=1.0 mm
- Loads: permanent extension loads - 2.7 kN/m2, live loads - 6.25 kN/m2
- Spans: 1.65 m to 2.05 m, double-span system
- Slab thickness: 10 cm
- Concrete requirement: 90 l/m2
- Slab weight: 240 kg/m2

Project information

  • Vienna
  • Austria
  • 2022
  • Architect:
    the next ENTERprise – architects
  • Engineering office:
    Bollinger + Grohmann
  • Contractor:
    Zeman & Co GmbH
  • Investor:
    Palais Goëss-Horten GmbH
  • Text:
    Christoph Radermacher, ArcelorMittal Construction
  • Images:
    Rupert Steiner, © Heidi Horten Collection
    Stephan Oláh, © Heidi Horten Collection
    © Zeman & Co GmbH