From stone to stable, sustainable wood: Accoya timber clads Herzog & De Meuron Stadtcasino Basel extension in historic style
After four years of construction, the expanded, renovated and updated Stadtcasino Basel (Switzerland) reopened on 22 August 2020 with 1,100m2 of Accoya wood cladding on the CHF 77.5m extension inspired by the look of the original building’s neo-Baroque stone architecture.
The unparalleled dimensional stability of Accoya wood made it the ideal material to profile, join and coat in a way that could match the original styling from a distance, then offer an interesting surprise up close: discovering it is, in fact, finely crafted and detailed wooden siding, combining the old and the new but with a consistent style.
Herzog & De Meuron architects re-envisioned the Stadtcasino’s Stehlin concert hall as a new, fully independent building. When originally built in 1876, budget constraints severely curtailed construction, and tacked-on extensions in the 1930s did little to help. This meant redesigning the entire west half of the site, developing what was a smaller annex into what now looks like a natural completion of the original design to include an entrance, foyer, backstage area and facilities that the concert hall deserves. While the east side’s historic stone masonry remains intact, the extension uses cleverly profiled and joined Accoya wood for its CHF 1.15m façade.
The architects approached engineers Pirmin Jung AG with a challenge: how to match the style of the original main building but with an interesting, surprising twist. From a distance the similarity is remarkable, but when approaching closer the new extension’s natural, sustainable provenance becomes clearer – the surprise is that it isn’t stone at all, but innovative wooden siding.
Mario Hess, Structural Engineering Project Manager with Pirmin Jung, said: “Accoya wood was chosen to fulfill the constructional challenge, the architectural expectation and the façade’s fine details. Its dimensional stability and durability were vital, and many other materials would be too heavy as well. The way Accoya works with coatings, while still retaining the un-mistakeable look and feel of real wood grain, was a real added bonus for this unique project.”
17 different profiles of Accoya timber were provided by distributor Holzpur AG and carpenter PM Mangold for the siding, and a ‘test wall’ was built to monitor performance of the wood and coating over a period of two years ahead of final construction. This made certain that the look and performance were suitable, and the result is a building with two very different finishes on its old and new halves looking like a single, complete and beautiful design with subtle distinguishing characteristics.
The image on the left clearly depicts the two different surfaces: Accoya wood (left half) and stone (right half) match in a common style.
The acetylation process that drastically improves Accoya’s dimensional stability and durability penetrates throughout the timber without adding toxic elements or chemicals that could leach out. This also means that even the cut faces of the boards could be safely visible, exposed and coated, allowing the precise work and clean, detailed finish that this project required without compromising on either aesthetics or durability.
The Stadtcasino Basel Stehlin concert hall dates back to 1876 and is one of Europe’s most important concert halls. Herzog & De Meuron began the project with an urban study in 2012, and the restoration, preservation and new construction work has been ongoing for the last four years to create a new public space befitting the Barfüsserplatz in the center of Basel.
Architecture: Herzog & De Meuron
Engineering: PIRMIN JUNG Switzerland AG
Accoya distributor: Holzpur AG
Carpenter: PM Mangold AG
Coating system: Keim
Main photo: © Stadtcasino Basel | © Roman Weyeneth
Other photos: © PIRMIN JUNG Switzerland AG
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