Frank Barkow And Regine Leibinger Discuss Their First High-Rise Project, Which Anchors A New 40-Hectare Development In Berlin.
In designing this new tower, specifically in the context of a new 40-hectare development inserted into the urban fabric of Berlin, did you have examples of successful new neighborhoods or things you sought to avoid?
Frank Barkow: In Berlin, you have these new building cycles where things happen very quickly. Before this master plan, we were working at Potsdamer Platz where you have huge cycles of construction. The hope that this new Europacity development [planned by ASTOC Architects and Planners] isn’t simply an autonomous master plan dropped into the city, but that through agent adjacencies to the Hauptbahnhof [Berlin’s main train station], it will automatically generate a certain amount of animation and allow it to integrate into the city very quickly. It’s difficult to say, because this is literally the first building within this master plan, but I think the plan is adaptable. It can transform and react depending on clients or housing—I’m optimistic about this one.
How is the new tower meant to respond, urbanistically, to the scale of the neighborhood?
Regine Leibinger: We were really meant to stick to the master plan, and there were three blocks with internal courtyards and towers of different heights right across from the train station, and then the urban fabric flattens out to the north. But for our project, the developer could only rent out the tower—they didn’t have another client who would rent the rest of the space. That was actually very good for us because we were able to create a freestanding tower that really responds to the public space. It meant that we had to really think about the urban scale on different levels. So the base, at street level, has these colonnades that connect to a public square, and we’re also hoping for a public café in there so people can use it. And then there’s a major bend in the middle of the tower—like a curtain that’s moving. It’s really important to have this bend to experience this tower completely differently from other parts of the city. So we’re thinking about ideas that you have to incorporate in a high-rise.
Barkow: I think part of this for us is to give us a chance to, at least locally, transform the master plan with this solitary tower to the west. We’re working on the second phase of construction now for a low-rise that will form a pedestrian passage with the double-story arcade at the base of the tower. So the building will be part of our local ensemble of two buildings.
At what point in the design process did the tower’s reticulated concrete façade strike you as the best design solution?
Barkow: In a way, we established the mapping of the building to begin with, and then began looking for a construction system to achieve it. This idea of a framed façade is a typical German typology. In this case we wanted to generate a load-bearing façade in order to generate more rentable space. And then there was the formal addition of this almost origamilike folding of the surface, in terms of the visual effect we could produce. I think the subversion of the Berlin typology is that, particularly in an oblique view, you have this highly dynamic, practically formed façade.
What are some of the innovations that you developed in connection with this rather beguiling effect on the façade?
Barkow: We’d done precast concrete buildings and structural systems before, but this is the first time we did it for a full-blown high-rise project. And what I think we’re exploring is quite interesting: The skin has a tooth-shaped element on the exterior and a comb-shaped element on the interior, and trapped between is the thermal installation and glazing. I think the next step for this technology is that we will take a single layer of precast on the exterior, connect it to the floor deck with an insulated connection, and eliminate the interior layer. It’s really interesting because of the speed of construction, precision of the elements, the capacity for sustainability, and this exo-structure that limits all the columns on the interior.
Are there technical explorations that proceeded the design that led you to attempt this solution?
Barkow: For me, if you look at the World Trade Center, the original towers used this logic in steel and, in a way, I think they were on the right path in terms of technology, sustainability, and the idea of the skin having a kind of depth for controlling light, energy use, and a column-free interior. But the huge advantage of this concrete is the speed at which it generates its own fireproofing—there’s highly protected steel inside this material. We have floor-to-ceiling triple glazing, exterior sun screening, and the windows open so you can get natural ventilation. You have to remember this was a developer core-and-shell building. There was not an unlimited budget for this project. It’s quite compelling to have the kind of agility to work through these construction systems to get the design you want in an economical way that still feels quite functional.
Toolbox: Façade System
Barkow Leibinger has long made sustainability and materials science the twin cornerstones of its practice: For this firm, design begins with the investigation of prospective materials and strategies for performance enhancement.
For the ribbed façade of Tour Total, the team determined that a 60:40 ratio of glass to concrete was ideal to reach the energy-efficiency target as determined by its goal of a DNGB Silver rating. (DNGB is Germany’s answer to LEED.) The balance of materials offers “a better insulated surface,” Frank Barkow says; it also reduces the need for interior columns, as the concrete exoskeleton bears most of the load.
Concrete has been a special focus of the firm’s recent material research: Of particular interest is infra-lightweight concrete, a variety that can achieve weights of as low as 800 kilograms per cubic meter. And though the firm has completed concrete projects in the past, Tour Total marks the first time that Barkow Leibinger is deploying the material in a tower—as, indeed, the building marks its first finished high-rise to date—and so the firm workshopped its approach extensively before proceeding.
Working with fabricators Dreßler Bau of Stockstadt, Germany, the team devised a bilayered section that sandwiches triple-glazing and insulation inside the concrete frame. Sunshades reduce heat gain and operable windows allow for natural ventilation. But the firm isn’t finished innovating yet: The next step for the system, it says, will entail going from two layers of concrete to one, further speeding construction and lowering costs.