Hotel Motto – Cofrastra composite ceilings used for refurbishments and roof extensions.
04.03.2021 - Project

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 70 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.