Revitalisation of a high-rise block in Halle

Baden-Baden, in Juli 23 - Visible from afar, a group of five linear high-rise blocks lends Halle-Neustadt a distinctive skyline. On behalf of the principal, SLS Vermögensverwaltungsgesellschaft Halle mbH, the middle building is being extensively renovated after lying unoccupied for at least 20 years. “Block C” – built at the beginning of the 1970s in the GDR era – was originally built as a student residence and now this use will be reinstated, and the building is to be powered entirely with renewable energy. A particular challenge here is the building fabric which is partially inadequate. Schöck Isokorb was used to create a reliable, load-bearing energy-efficient connection for the new balconies of each room. The Schöck Stacon dowel is used as the transverse structural connection between balcony slabs.

59 metres long, 16 metres wide and 18 floors high: the key data of “Block C” is impressive. Students will occupy the building once again from the end of 2024. It will contain 280 modern one-room flats with integrated bathrooms and 28 two-room flats. The design by Nuckel | Architekten, Hamburg, also includes communal areas for cooking, studying and leisure activities, etc. A roof area with catering facilities is also planned.

Research project for future-orientated refurbishment

The "Variowohnungen" model project is being funded as part of the Zukunft Bau innovation programme of the Federal Ministry of Housing, Urban Development and Building (BMWSB). The programme focuses on the sustainable and energy-efficient development of the building sector and responding to demographic change. “Block C” is to be refurbished as an ideal KfW Efficiency House 40 and supplied entirely with renewable energy.
Instead of demolition, the old self-supporting balconies were cut off and the building was gutted to conserve resources. The existing reinforced concrete walls and floor slabs were retained and now form the grid for the room modules which are prefabricated in series and inserted. In addition, the residential units have already been structurally prepared in such a way that they can be easily adapted and, if necessary, combined and used as living accommodation for the elderly.

Expansion of the building volume

In order to create contemporary living space, “Block C” was extended by two metres on both long sides. However, the planners discovered that the upper reinforcement layer in the floor slabs had been installed five centimetres too low. The load-bearing capacity of the slabs was therefore not guaranteed. Slots were therefore cut 20 centimetres apart into which reinforcing bars for strengthening were inserted and filled with a specially developed mortar. "Due to the old building fabric, we often came up against our limits. Time and time again, we had to develop individual solutions to stabilise the structure and the first thing we had to do was familiarise ourselves with the old GDR standards in order to get to grips with the building," recalls Jens-Marno Heimann of Brakemeier construction engineers. “On the other hand, however, that gave us an enormous increase in knowledge in general,” he remarked, and acknowledges that they were in the fortunate position that the structural engineer had already worked in GDR times and, thanks to his expertise, was able to provide invaluable support in the search for solutions.

Schöck Isokorb – the solution for even the most demanding applications

In-situ cantilevered balcony slabs measuring 1.83 x 3.50 metres are attached to the extended slab. A precamber is required in order to compensate for deformation. The forces of the relatively heavy slabs are transferred to a 60-centimetre-thick load beam. Heimann was in no doubt that the best solution in this case was Schöck Isokorb XT type K-O: “I know that Schöck products work and was familiar with the Isokorb. With the cranked tension and shear force bars with head bolts, Isokorb XT type K-O can be optimally anchored in the slab with a short installation depth and allows the downstand beam to be manufactured afterwards.”

Reliable load transfer

Schöck Isokorb XT type K-O reliably transfers the loads of the balcony to the neighbouring floor slab. Various load-bearing levels of Isokorb XT type K-O were used in this project. For structural reasons, the building extension could only be constructed in lightweight concrete, the composition of which was closely coordinated with Schöck in advance. As Schöck Isokorb is approved by the building authorities, it was necessary to ensure that the concrete used had the required properties.

Reliable compliance with the EnEV values

"With Schöck Isokorb, we fulfil the requirements of the Energy Saving Ordinance (EnEV) for a KfW 40 building," explains architect Leander Kadoke from the firm of architects, town planners and project coordinators in Lübeck commissioned to carry out the construction planning. As a load-bearing thermal insulation element, Schöck Isokorb minimises thermal bridges and thus ensures that cold exterior is thermally isolated from the heated, warm interior of the building. The architect relies on Schöck Isokorb for many of his projects: "Not only was it the first product on the market, since then it has been continuously developed and improved. What's more, the advice we receive from the manufacturer is also invaluable."

Schöck Stacon – the strong solution for expansion joints

In addition to Schöck Isokorb, project manager Michael Schmidt used another Schöck product for the challenging refurbishment: the Stacon type LD shear force dowel. Stacon ensures the constraint-free transfer of shear forces in the expansion joints without the need for conventional measures such as brackets or additional columns. Schmidt developed his own solution for the installation here: namely to cast the balcony slabs in one operation, instead of the usual two steps, which saves time.

Project information

Project: Block C, Halle, refurbishment as a student residence
Construction period: 11/ 2021 until end of 2024
Principal: SLS Vermögensverwaltungsgesellschaft Halle mbH, Berlin, Germany
Architectural design: Nuckel | Architekten PartG mbB, Hamburg, Germany
Construction planning: Haake Kadoke Architekten Stadtplaner Projektsteuerer, Lübeck, Germany
Structural engineering: Brakemeier GmbH, Ingenieurbüro für Bauwesen, Hamburg, Germany
Products: Schöck Isokorb XT Type K-O, Schöck Stacon Type LD