When Sergei Tchoban talks about his recently built EDGE South Cross Berlin complex, he emphasises, quite passionately, that the key reason he chose hybrid timber construction is to achieve lightness. In our video conversation out of his Berlin office, Tchoban Voss Architekten, with two other branch offices in Hamburg and Dresden, he told me that the reliance on this material reduced the overall weight of the building, consequently, leading to a 40 per cent lower carbon footprint during construction. Located in Berlin’s Schöneberg, the complex comprises two freestanding seven-story structures - a larger Carré Building and a smaller Solitaire Building. Occupying a full block, the pair is currently the largest hybrid-timber complex in Germany and one of the largest in Europe.

The EDGE is distinguished by its airy atrium. Topped by a transparent ETFE foil roof, it is carried by a system of wooden trusses at a height of 26 meters. This membrane is more economical and lighter than traditional glass; it has better acoustic performance and sun protection and offers a more effective structure to withstand wind pressure. The atrium provides unique meeting, work, recreation and eateries at various heights on top of four tree-like sculptural structures interconnected by stairs, platforms and adjacent office floors. The tallest of these objects reaches almost 15 meters and has a platform with a diameter of more than 6 meters. The shortest “tree” is almost 4.5 meters high with a diameter that exceeds 7 meters. Tchoban discussed some of this project’s unconventional features, the connection between his drawings and architecture and the issues architects must pay attention to.  

Vladimir Belogolovsky: What are some of the main components of your EDGE South Cross (Suedkreuz) Berlin office complex?

Sergei Tchoban: I started working on this project about seven years ago before it was completed in 2022. The project is the largest free-standing hybrid timber building in Germany and one of the largest in Europe, at least outside Scandinavian countries where hybrid timber construction is more common. In Germany, where regulations are stricter, timber architecture is still somewhat of a novelty, especially on this scale. The EDGE complex comprises two buildings—the smaller one is 12,000 square meters, and the larger one is 18,000 square meters. The planning department gave us the parameters of the buildings quite precisely, so we did not have much flexibility on our buildings’ forms. Therefore, we couldn’t introduce unusual angles or cantilevers.

Initially, the intention was to create a sustainable building for the German development market. EDGE, our client, is well known for its sustainable projects. They previously worked with architects such as Rem Koolhaas and MVRDV. From the beginning, the decision was made to use hybrid timber in this project. There are two main components in this construction type—beams and columns. They are all exposed and quite sizable.

That was my primary objection—if we make our building out of timber, let’s make it visible. So, our facades are load-bearing. This project is prefabricated, which made it possible to reduce the construction to less than one year, while a similar building relying on traditional construction would take 2.5 years. Most importantly, we wanted to build our building out of hybrid timber to achieve lightness. That was our overarching goal. This method reduced the overall weight by at least 40 per cent. So, we used 40 per cent less energy and made a smaller carbon footprint during construction. In other words, our building is 40 per cent more sustainable than typical buildings. What is also important is that we don’t simply replace all materials with timber but use different materials to reduce the overall weight. Thus, our stairs are made of steel because to make the same stairs out of timber would weigh twice as much. So, we need to be smart about using different materials for different purposes.

The idea was to improve communication within the building and to make it in ways that are imaginative and fun. Architecture is about improving communication. – Sergei Tchoban

VB: Of course, the heart of this project is the atrium within the bigger of the two buildings. What was the main concept for designing this space?

ST: The main idea was to create the centre of communication and express it as a manifesto in which light materials, especially wood, play an enormous role. The space is navigated by climbing the stairs and manoeuvring between and around the wooden “trees.” There is a steel core inside each of the trees. Wood here makes good acoustics due to its ribbed surfaces. However, the big idea is to make all floors connect, work, and mix together. There is a new requirement in Germany to allocate 10 per cent of office space to public amenities. This followed the COVID-19 pandemic to incentivise workers to come to work instead of working from home. For our project, we tried to offer various environments with a mix of open and informal meeting areas to complement more conventional office spaces and to enrich the working environment experientially. Such spaces bring value to working in the office. The atrium comprises a canteen with many informal meeting points and conference spaces at various levels. It also serves as a communication link between all floors through stairs and bridges. 

VB: The four central structures evoke trees in a forest. Was that the main metaphor for this project?

ST: You must realise that the outer skin must be straightforward to create a sustainable project. This is because if your skin is very complex and elaborate, you will inevitably lose a lot of cold or warm air, depending on the season. In other words, increasing the overall surface will cause a lot of lost energy. So, the exterior surface should be tight. Buildings’ skins should be modest; elaborated facades waste much energy through the increased surface. However, we don’t have this problem inside the building because we are already inside the warm space enclosed by a transparent ETFE foil roof, so it is appropriate to do something special formally, spatially and sculpturally.

In any case, the idea was not to dream up a forest-like space but to create different levels where everyone would meet each other. In a way, I dream through sketches. The idea was to create platforms on each level; the higher you go, the bigger they become. These stairs also encourage people to walk up and down instead of taking elevators. It is healthier and more social. In a way, this space functions like a large living room in a big house. The idea was to improve communication within the building and to make it in ways that are imaginative and fun. Architecture is about improving communication. 

VB: When discussing your work, you often use words and phrases such as materiality, urban mise-en-scène settings and the importance of juxtaposing historical and contemporary buildings. You also talk about the city and the role buildings play in relation to each other. What is your approach to architecture and what kind of architecture do you aim to achieve?

ST: This is all true. My main concerns in architecture align with today’s three most relevant issues. First, we need to deal with older buildings, both listed and ordinary ones. Demolition is not the answer. Not even a gorgeous new building can justify a significant demolition. We must be aware of the damage to our environment by new construction. We have to rethink our design and build attitudes completely. Then, we need to construct new buildings in ways that could be reused and recycled in the future with changing circumstances. We must learn from our experience in the last 50 years of endlessly constructing buildings that cannot be reused. Finally, we need to bring social integration into our projects. It is essential to account for the different ways of life of people from different regions and cultures. So, we need to learn how to coexist and discuss different issues. Many opinions are contradictory and controversial, but we need to be able to confront these issues.

These three principles should be the foundation for any modern project. They must be discussed before considering one style versus another. However, once these three points are prioritised, we can focus on creating urban mise-en-scène settings, selecting interesting materiality, juxtaposing new layers with the old ones innovatively, etc. Thus, we can no longer simply replace old buildings with new ones. We should work with existing materials; each place should point to the right solutions. Our imagination should be adjusted to the reality we are working in.

Drawing is a form of a diary for me. I express in my drawings what I feel about what is in front of me and what is in my mind. – Sergei Tchoban

VB: You said, "I came into architecture through drawing and this is how I think. My architecture arises from my drawings. Drawings are the key to understanding architecture." How do your drawings influence your architecture?

ST: First, I start with an analytical approach. Architecture has to be rational. However, once I know the basic requirements for my building, I draw intuitively, dreaming with my drawings. Once I reach a certain level of development and like what I see on my page, I will focus on transferring my idea into reality. That’s how a drawing makes architecture. In a way, I try to continue with my hand, what I have started with my mind. I like the idea that one’s body is an intrinsic part of one’s soul. I think not only with my brain but with my entire body. So, when I draw, I let my hand be free to see where it will take me. Drawing is a form of a diary for me. I express in my drawings what I feel about what is in front of me and what is in my mind. But reflecting on history is always a part of our contemporary moment. My drawings are about the past, our time and the future.