CARL Timber Hybrid High-Rise

In June 2021, the Karlsruhe office was awarded the contract by Arlinger Baugenossenschaft eG for the turnkey construction of the "CARL" timber high-rise building project in Pforzheim, including outdoor facilities and execution planning. The aim was to create a striking landmark at the western entrance to the city, with the implementation of the timber façade in particular posing major challenges under strict fire protection requirements.

Ensemble CARL: Building structure and use

The ensemble comprises the CARL timber-hybrid high-rise building (Building 1) and two conventionally constructed longitudinal buildings (Buildings 2 and 3).

• Building 1: 14 storeys, on the first floor an entrance area and a bakery with café, above 37 apartments.
  
• Building 2: 6 floors, daycare center on the ground and 1st floor, 24 apartments above.
• House 3: 4 storeys, technical and cellar storage rooms on the first floor, 12 apartments above.

All buildings meet the KfW 55-EE standard and share a basement with underground parking (73 parking spaces, all with electric charging stations). Buildings 2 and 3 have photovoltaic systems whose electricity benefits the tenants via a tenant electricity model. The upper floors of buildings 2 and 3 are accessed via arcades and are barrier-free thanks to external elevators.

Close cooperation for future-oriented solutions

As part of planning phase 5, the implementation planning, special solutions had to be developed and coordinated with all project participants and authorities due to ambiguous regulations for a timber high-rise building. Thanks to the comprehensive and solution-oriented cooperation, all planning challenges were overcome.

Gliding upwards like a tower

The core of the timber high-rise building was constructed from in-situ concrete using the slipform method from the basement to the roof ceiling up to a total height of approx. 48 meters. As fire protection plays a special role in a timber hybrid high-rise, the core had to be made of concrete. It also serves to provide access to the floors and contains a safety stairwell and two elevators, one of which is designed as a fire department elevator.
It took a total of two weeks to construct the core with all the interior walls. The ceilings and stairs were then installed in the stairwell core, meaning that the concrete work was almost complete when work began on the residential floors.

Special elements for "CARL"

In the "CARL", the ceilings of the residential floors are timber hybrid ceilings. This means that they consist of 10 centimeter cross-laminated timber panels and 12 centimeters of concrete.
The exterior walls were designed as prefabricated timber frame elements and delivered just-in-time, so that the space required for intermediate storage could be reduced to a minimum.
Due to the high loads on the lower floors, beech columns were integrated into the exterior wall elements, as they have a very high load-bearing capacity. This posed the challenge that the wall elements had to be positioned so precisely during assembly that all of the supports integrated into the wall elements had to be exactly on top of each other.
The exterior timber façade of the "CARL" is very distinctive. Once the wall elements and windows had been installed, it was constructed as a curtain-type elemental timber façade. For logistical reasons, the façade elements were already temporarily stored on the floors during the shell construction work, so that subsequent transportation to the 14 upper floors was no longer necessary.

Fire protection as a safety guarantor

Fire protection played a central role in the timber hybrid high-rise building, as a safe concept had to be developed that met all requirements and preserved the special features of the building project. For example, a "brim" of visible precast concrete solutions was built between the storeys.
As a result, the façade meets the fire protection requirements for fire flashover from storey to storey and a sustainable, weather-resistant solution was found.
The entire timber high-rise was equipped with a fire alarm system. The access core contains a pressurized smoke system and a wet extinguishing water pipe with two extraction points per storey.

The strength of the Group

The timber construction work, including the façade, was carried out internally by ZÜBLIN Timber. The close cooperation enabled the development of project-specific solutions as well as the use of new technologies and access to the Group's own expertise.
The complexity and innovative nature of the project to construct a high-rise building in timber generated a great deal of interest from the public and experts. Numerous information events organized by the client and visits to universities were also supervised by the project team.

The project is aiming for DGNB "Sustainable Building Site" certification from the German Sustainable Building Council.

Certified by the German Sustainable Building Council (DGNB)

Ed. Züblin AG is pursuing several goals with this project: A sustainable construction site organisation, the conservation of resources as well as the minimisation of emissions, responsibility for the health and well-being of the builders, the cultivation of good neighbourliness and, of course, high-quality construction. For this, Ed. Züblin AG was the first company to be recognised by the German Sustainable Building Council (DGNB).

Here you can find more information about the DGNB system for sustainable construction sites: https://www.dgnb.de/en/certification/buildings/construction-site

Selected measures in the project