Z2 is a striking office building in south-west Stuttgart. Measuring 94 x 12 metres, the six-storey structure features flowing curves and characteristic layering of glass and aluminium. The building belongs to the ZÜBLIN Campus, the central management and innovation district of this construction company. ZÜBLIN itself is part of the international company STRABAG, which has set itself the aim of becoming climate-neutral by 2040.

Designed and planned by Eike Becker Architekten in 2002, Z2 is now undergoing a general overhaul and comprehensive renovation. The roof, façade and underground car park have been optimised for energy efficiency and heat pumps and photovoltaic systems have been installed. The most cutting-edge technology, innovative planning tools and so-called generative design were used for this. These data-based design methods use parameters and algorithms to create a range of alternatives in a very short period of time, which probably would not have been taken into account with traditional ways of planning.

Ribbon windows in the upper storeys

When it came to the external appearance of Z2, which features window areas that run all the way around the building, refurbishing the existing units proved to not be viable. That is why they were replaced with the AWS 75.SI⁺ optimized system from Schüco in storeys one to five. This highly thermally insulating standard window system with a basic depth of 75 mm is available with a wide range of opening options and is ideal for use in energy-efficient buildings.

The characteristic ribbon windows are comprised predominantly of individual fixed glazing measuring 1350 mm wide, combined with AWS VV ventilation vents and opaque areas. The safety barrier triple insulating glass (LSG/float/float or LSG/float/LSG) boasts an outstanding U_g value of 0.6 W/m²K. The U_w value of the units averages 0.85 W/m²K.

Forster Fassadentechnik GmbH fabricated and installed more than 2500 square metres of window area across the five storeys. In order to meet the structural requirements of the 2400 mm high units, Forster commissioned Schüco to extrude window profiles with the external blind guide tracks directly on them. This helps to limit the deflection of the profiles caused by the prevailing loads.

Mullion/transom façade on the ground floor

In one half of the building on the ground floor, around 340 square metres of FWS 60.SI mullion/transom façade from Schüco was installed. The system with a 60 mm face width offers a high degree of design freedom with a large selection of pressure plates and façade cover caps, as well as the option of being combined with window, door and sliding systems. The entrances, for example, were constructed using the AD UP 75 door system which, in accordance with DIN 18040, is fitted with a barrier-free, level threshold and electric door drives. The other half of the building has a timber/aluminium façade construction, for which Forster supplied the tailor-made Schüco insert units.

As part of ZÜBLIN’s approach to sustainability, a total of 38 tonnes of Schüco Ultra Low Carbon aluminium (ULC) was ordered for the windows and façades. ULC consists of at least 75% post-consumer recycling material and has a GWP value of 1.99 kg CO₂e/kg of aluminium profile. In comparison with standard aluminium, it saves around 72% CO₂.

Spandrel cladding with curved PV units

A particular challenge was the renovation of the all-round spandrel cladding made from aluminium sheets at the height of the intermediate floor. In addition to the complete dismantling and processing of the units, damaged sheets were replaced with new ones, and the substructure was reinforced structurally and in terms of its physical characteristics. To generate energy in a regenerative way, some of them were fitted with building-integrated photovoltaics (BIPV). To avoid negatively impacting the external appearance, Schüco worked with Forster Fassadentechnik to develop a project-specific, discreet retaining profile. The noteworthy thing about it is that, alongside conventional flat PV modules, specially fabricated concave and convex PV modules from Schüco following the shape of the spandrel cladding on the building were also used.

Fire protection: for sure

The doors installed inside the building had to take into account the requirements of fire protection and sound reduction (class 3). The double-leaf Schüco ADS 90 FR30 fire doors to the stairwell ensure the safety of the users. They are tested in accordance with EN 1634/EN 1364 and DIN 4102 and guarantee 30 minutes of fire resistance. The units are fitted with automatic drives. In the corridors, double-leaf doors from the ADS 90 FR90 range with 90 minutes of fire resistance are installed in the fire wall at the centre of the building. They have an electric hold-open device. In total, 17 units from the Schüco FireStop system platform were used. They also feature an impressive design, creating maximum transparency with very narrow profile face widths, while integrated closers and concealed door hinges support the minimalist look.

Cradle to Cradle certified materials

For the interior, a mobile 3D printer produced the concrete units. To further divide up the space, a prototype of reusable drywall was used in one area of the ground floor. Wherever possible, ZÜBLIN used recyclable and Cradle to Cradle certified materials and components. By retaining the building shell, the aluminium spandrel cladding, the access cores including the lifts and underground car park as well as the majority of the sanitation facilities, Z2 is a prime example of resource-friendly adaptive reuse.

Support through the DGNB

The whole project, including the building process, was supported by the German Sustainable Building Council (DGNB). With solutions like Ultra Low Carbon aluminium and building-integrated photovoltaics, Schüco makes a significant contribution to the success of the project. The building will be awarded the DGNB Platinum certificate and the QNG “Premium” seal. For Ed. ZÜBLIN AG, as part of the STRABAG Group, this successful project is a further step on the path to climate neutrality.

Project details

Project: Z2
Location: Campus of Ed. ZÜBLIN AG, Stuttgart
Client: ZÜBLIN AG, part of STRABAG Group
Metal fabricator: Forster Fassadentechnik GmbH
Schüco systems used:
AWS 75.SI⁺ optimized window system (C2C Silver)
AWS 75 VV.SI⁺ ventilation vent (C2C Silver) with safety barrier triple insulating glass (LSG/float/float or LSG/float/LSG)
FWS 60.SI mullion/transom façade (C2C Silver)
AD UP 75 door system (C2C Silver) with barrier-free level threshold Building-integrated photovoltaics (BIPV)
FireStop ADS 90 FR 30 (C2C Silver) and ADS 90 FR 90 (C2C Bronze) fire doors
Completion date: December 2024