4. März 2021
Hotel Motto – Cofrastra composite ceilings used for refurbishments and roof extensions.
Hotel Motto – Cofrastra composite ceilings
From an architectural perspective, Vienna is increasingly becoming known for its roof extensions. Alongside the refurbishment of historic building stock, that’s leading to a modernisation and revitalisation of many inner-city properties. Many of the designs are characterised by contemporary, often multi-storey, roof structures sitting on top of distinctive, traditional facades.A typical example is the former Hotel Kummer, a Gründerzeit era property steeped in history, situated on the corner of Mariahilfer Strasse (71a) and Amerlinstrasse. With a 50 million Euro investment from Wertinvest in partnership with Schadekgasse 20, it has been gutted, refurbished and extended, with a new two-storey, barrel-shaped roof structure added. This new structure links all the different parts of the building, coordinating with the magnificent, original façade and connecting with the new, modern cityscape.
The building is remaining as a hotel. Under the new name ‘Hotel Motto’, it will be operated with 91 rooms, a restaurant, bar and meeting areas. A branch of a well-known clothing brand has taken a lease on the ground floor and an organic bakery and outdoor café area will move in directly next door. The striking roof structure, designed by architect Arkan Zeytinoglu and set back slightly from the façade, will house a restaurant and roof terrace which will be open to the public.
In structural engineering terms, the project has been a considerable challenge. During the course of the work, a wide variety of ceiling constructions were uncovered within the fabric of the historic building, including in-situ concrete ceilings, wooden beam ceilings and brick ceilings. In planning for the additional roof levels however, the civil engineers Thomas Lorenz ZT GmbH decided to use steel, or more precisely a steel composite ceiling construction, because of the many advantages it offers.
Working in partnership with the manufacturer, the engineers chose Cofrastra composite slabs from ArcelorMittal Construction Austria. This composite slab profile, made from galvanised sheet steel with additional embossed cams, serves as both the formwork for the in-situ concrete and the lower reinforcement layer to absorb the bending moments. The stackable trapezoidal shaped panels are ideal for the inner-city site because they can be easily transported and stored efficiently without taking up unnecessary space. The ribs also reduce the dead weight by up to 15% for the same static height, crucial for the deflection of the slab and resulting in a slim construction with lower loads on the building stock below. Fire protection (REI 90) is achieved by simple bar reinforcement in the ribs (Ø12mm) without additional, time consuming measures, in line with EN1994-1-2.
Assembly of the 1100m2 composite slab could largely be carried out by hand, without the use of a crane, saving valuable crane capacity and construction time. The special dovetail geometry allows for a reversible installation of building services and suspended ceilings, so that the new composite ceiling, as well as the original ceiling constructions, remain hidden from view.
Complex construction taking place at height – Cofrastra 70 composite ceiling over 5.20m, with temporary support during concreting.
The widened lower flange on the Cofrastra 70 allows the steel girder to be integrated flush with the slab
Facts: Cofrastra 70 composite slab:
Loads:
Permanent extension loads: 2.7kN/m²
Live loads: 5kN/m²
Plate thicknesses : variable between tN=0.75mm and tN=0.88mm
Spans : 1,60m double span system - 5,20m single span system with 2 supports in construction condition
Slab thickness : 15cm and 22cm
Concrete requirement: 200l/m2 - 125l/m2
Slab weight: < 500kg/m2 - approx. 320kg/m2
Multiple advantages:
Ceiling weight and reduced depth
Fire protection REI90 - bar reinforcement in rib Ø12mm
Dovetail geometry reversible installation of building services and suspended ceilings
1100m² Cofrastra 70
Info collection
Roof extension Falkestraße, Vienna
"This roof extension is the world's first deconstructivist architectural project to be realised," says Wolf Dieter Prix, co-founder of the architectural firm Coop-Himmelb(l)au together with Helmut Swiczinsky. The roof extension in Vienna's Falkestraße was completed in 1988, at the same time that the exhibition "Deconstructivist Architecture" was running at the Museum of Modern Art in New York.
Completed: 1988
Architecture: Coop Himmelb(l)au
Address: 1010 Vienna, Falkestraße 6
"This project was presented as a model and the funny thing is that many colleagues stood around the model and said, you'll never build that," Prix recalls, "because it's impossible to build. I laughed, because at that very moment the very first curved windows were just being put in here.”
Coop-Himmelblau designed the roof extension for the law firm Schuppich, Sporn, Winischhofer on a Viennese Ringstrasse building in Falkestraße. With this build, the architectural firm achieved an international breakthrough, and the roof extension effectively became the most famous piece of Austrian post-war architecture - an architectural landmark and a pilgrimage site for architectural enthusiasts from all over the world.
So how would you describe the Falkestraße roof conversion? It’s either a dynamic-looking glass sculpture with steel struts that extend beyond the building or it’s a glass sculpture that virtually tears open the historic roof.
Plan
COOP HIMMELB(L)AU
But how would the star architect himself describe it? "In the same way as Roman Polanski, who said that if he could describe the film, he wouldn't make it. You can't do it verbally or in pictures. A steel backbone holds the whole construction, which you might call a dome, but it's not a dome, it's a reinterpretation of a dome. Obviously, it wasn’t easy to build this volume here on this building, neither from the position of the authorities or from the construction point of view. Today, I doubt whether this project would be achievable" says Wolf Dieter Prix, adding: "The roof extension is thirty years old, but I am always surprised by how young and fresh it looks."
https://oe1.orf.at/artikel/644852/Dachausbau-Falkestrasse-Wien
Hotel Motto
Roof extensions have given a historic city like Vienna the opportunity to modernise and revitalize inner-city properties like the former Hotel Kummer that will open again to the public as the “Hotel Motto”. This project from Wertinvest will have a new two-storey, barrel-shaped roof structure which is coordinated with the magnificent façade.
The civil engineering company Thomas Lorenz ZT turned to ArcelorMittal Construction Austria to use its Cofrastra 70 composite slabs to serve as the formwork for the in-situ concrete as well as the lower reinforcement layer to absorb the bending moments. As a result, the extension has a slim construction with lower loads for the building stock below.
Find out all the details of this project in the first 2021 special supplement from @Handwerk+Bau.
Hotel Motto Cofrastra composite slabs for refurbishment and roof extensions