
In September 2007, the museum invited eight architecture firms to research about to extension’s Museum. Among these, three German architects: Kuehn Malvezzi Architekten ; schneider+schumacher Planungsgesellschaft ; Wandel Hoefer Lorch + Hirsch Müller and five foreign architects : Diller Scofidio + Renfro (New York) ; Gigon/Guyer Architekten (Zurich) ; Jabornegg & Pálffy Architekten (Vienne) ; Sanaa / Kazuyo Sejima, Ryue Nishizawa & Associates (Tokyo) ; UNStudio (Amsterdam). The mission of these architects was to conserve the memory of this place. The jury presided by Louisa Hutton (Sauerbruch & Hutton) announced the winner in February 2008: schneider+schumacher.

To better respect the historic museum built in 1815, an extension of 4 151 m2 was built in underground. His facade is composed of 195 portholes which spring from the soil. The portholes have a diameter between 1,50m and 2,50m. The architects from schneider+schumacher play with the topography to animate this fifth facade and to create a signage for the museum. As a result, a big gallery of 76m long and 53m large with 8,20m height at the central point.

There is no need to look for a door to this building, once again, the entrance is underground, more specifically by following a stair in the axis of the main museum. This gallery is partitioned by a tall wall flushed the ceiling. German architects choose white to fade in front of the painting.

The porthole symbolizes the “eyes of the art”. They were specifically built for this museum by Licht Kunst Licht. The renforced glass permit to pedestrians to walk on them with care. This portholes permit to control the interior luminosity during the day, with elements to attenuate the light source. Next during the night, LED Lighting act in opposite to display a neccessary lighting for the gallery. Each porthole has its own lighting system which authorizes a specific type of scenography.

The floor of the Städel Museum wasn't easy to build. In fact, groundwater is located under this museum. Therefore, the building is weighted down by 160 stakes to prevent it from floating. The main structure is hidden from the visitors because of 12 renforced concrete columns. In addition to the stakes, 32 drilling site of 82m in depth to the geothermal. The produced energy is then distributed among flooring heating.

Once after the roofing is completed and the support deployed, a frame of wooden model will cover the roofing of the gallery. A early slab was created to form the roof of the gallery. A second slab has permitted a link between all panels and constituted the support of the roof. Next, a watertight support was installed at each of the portholes covered by a landscaped roofing.

The building cost was 52 millions €. The museum had a chance to benefit from some aid such as a local private family banker (3 million euros for the construction and 3 million for the museum foundation).

- Architect: schneider+schumacher
- Client: Städelsches Kunstinstitut
- Location: Frankfurt-am-Main, Germany
- Project Manager: Michael Schumacher, Kai Otto, Till Schneider
- Construction chief: Hans Eschmann
- Team: Miriam Baak,e Christoph Bonke, Karlo Filipovic, Manuel Mauder, Vita Redliha, Iva Resetar, Miodrag Stojsic, Felicitas Adler, Gerhard Breuss, David Bujanowski, Mark Delle, Diana Djekic, Florian Haus, Kerstin Högel, Miriam Huesgen, Patricia Kaufmann, Johannes Klorer, Florian Mieden, Carsten Nawrath, Wolfgang Schneider, Joachim Schulze, Sebastian Stange, Christopher Unger, Tim Unnebrink, Ragunath Vasudevan, Alexander Volz, Volker Westmeier
- Structure: B+G Ingenieure / Bollinger und Grohmann, Manfred Grohmann, Jörg Schneider
- Engineering: IPB ; Ingenieurbüro Freudl & Ruth ; IBO Ingenieurbüro Dieter Bohlmann ; TOHR Bauphysik
- Bureaux d’études géotechniques : BFM Baugrundinstitut Franke-Meißner und Partner
- Landscape design: Keller + Keller, Landschaftsarchitekten Gartenarchitekten BDLA
- Économiste : Grandjean & Kollegen ÖbVI
- OPC : Drees & Sommer
- Façade : OSD Office for Structural Design
- Sécurité Incendie : Hilla - Sachverständigenbüro für vorbeugenden Brandschutz
- SPS : GefAS - Gesellschaft für Arbeitssicherheit
- Fabricant des éclairages : Licht Kunst Licht
- Installation des oeuvres : Kuehn Malvezzi, Winfried Kuehn, Nina Beitzen
- Compétition start: September 2007
- Competition date: March 2008
- Building start: September 2009
- Completion date: February 2012
- Surface area: 4 151 m² (extension)
- Cost: 52 000 000 € (extension 34 000 000 € ; rénovation 18 000 000 €)
- Photographers: Kirsten Bucher, Helen Schiffer