“Designing a house for trees”, as he puts it, Stefano Boeri is working across the planet, exporting his approach with trees from Mexico to Shenzhen. Building a whole ecosystem, rather than just a green facade, the architect understands the need to redefine our relationship with nature, especially in cities.
ArchDaily’s Christele Harrouk had the chance to interview the architect in Eindhoven, during the inauguration of the Trudo Tower, Stefano Boeri’s first social housing project, in collaboration with Francesca Cesa Bianchi, his partner at Stefano Boeri Architetti, Laura Gatti, botanist and plantation consultant, and Paolo Russo, Project leader. Discussing mainly his approach with nature, the environmental quality, and his exported perspective around the world, the conversation also tackled the 4 ongoing vertical forests in West Europe: A first that has just started in Utrecht, a second in Brussels, a ready to go building in Eindhoven and a last one in Antwerp.
ArchDaily (Christele Harrouk): First, can you tell us about your approach to forests? How did this become your signature move?
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Stefano Boeri: It's not easy to go back to a specific moment when I started to cultivate this kind of obsession with green, and how to put together plants, forests, and cities. Basically, I have always been extremely distracted by trees. I think trees are a population of individuals that we don’t know much about, how they communicate, for example, their intelligence or their capacity to involve insects and other animals in their life. That was kind of implicit in my personal background and my architecture, but I started to concretize this perception 20 years ago, in Milano, with a project that sought to create a suburban orbital forest all around the city.
The idea came together around 2003-2004 but started in 2006. In collaboration with the province of Milano, we planted 350,000 trees in three years. At that very moment, no one was talking about forestation. And in those years, while I was teaching at GSD, with my students we were talking a lot about Dubai because it was exploding. Actually, I was in Dubai when I started to imagine this idea of a tall building with trees and probably -but this is my, let's say post-explanation, it was also this paradoxical eruption of glass facades everywhere in the desert that provoked the vision of something totally different.
After that trip, when I came back to Milano, I was first approached to design a middle-sized system in Isola, one of the three parts of the Porta Nuova project, now completely developed. After thinking it through, I came back to the developers saying that I would love to do a highrise with trees. Of course, they told me that I was crazy and that it was impossible to grow trees at that height, that it would be very costly and that putting together the layouts of apartments would be pretty complicated. They gave me a list of very strong and technical questions to see if I am in a position to answer.
Well, this was a dream, but why not?
I started working promptly with a botanist, structural engineers, etc. and we filled the list with very convincing answers that permitted us to start. That was the beginning of the vertical forest. The whole idea is based on considering the plants as a component of our buildings rather than a decoration.
Right at the beginning, there were too many technical troubles. First, it was the wind, then irrigation, the selection of plants, maintenance, etc. but step by step, we tried to solve each and every challenge. Then, there was also the financial crisis that hit, in 2008. The construction company in charge of the project collapsed at that time. We restarted the works in 2012, at that time, the first plants started to be moved from the Botanic garden to the construction, although the building was ready by October 2015. This actually means that we have almost 10 years of experience on how trees live in different conditions.
AD: A lot of skepticism roams around your approach. What can you tell us about this?
SB: After the first Bosco Verticale was ready, we started to study and monitor the structure. IIT Chicago was the first center to research the production and emission of CO2, after that, a lot of other centers participated, from all over the world. It’s true that there was extreme skepticism around us. People claimed that in 2 years, 80% of the plants will be dead, the roots will completely destroy the concrete, that we will have humidity problems and that these trees will attract too many insects. Also, people talked about vertigo, and that it was impossible to have balconies at a height of 50, 55, and 60 meters. In reality, trees gave off a sense of calm and serenity. With Laura Gatti, we had selected specific types of plants, so we didn’t have any insect-related issues.
I pretty much think that in 50 years, it will become a jungle. Nature will progressively take over the building. It’s not so bad, no?
AD: How did environmental quality become an integral part of your work and where did you find inspiration?
SB: Honestly, the awareness of the necessity to make our city greener, came a bit later. People ask me about where the initial inspiration came from. For me, inspiration is everywhere. I can recall Italo Calvino’s 1957 “Baron in the trees”, Joseph Beuys who planted 7000 oak trees over the city and changed the space, and Friedensreich Hundertwasser who came to Milano in 1972, walked the streets saying “trees are our partners”.
AD: From Mexico to Shenzhen, people are seeking your proposals. How do you explain the success of this approach and also its universality?
SB: I don't think it's specifically about Bosco Verticale. In my opinion, people have a very strong demand to have new proximity with nature. It’s also related to what has happened in the past 18 months with Covid, and also psychological, with the sense of serenity that the plants can give you. The other thing that is prevailing is the demand for having outdoor spaces. That's the reason we are working so much with roofs in cities.
Roofs will probably play the same role that courtyards played 50, 60 years ago, a collective semi-private, semi-public place where tenants can come together.
It's amazing that in the last centuries we have treated nature as something that was just outside of us, outside of our bodies, outside of our houses, and suddenly we understood that there was a microorganism inside of us. That has probably created a strong collective shock. Our relation with nature needed to be completely redefined. This demand for proximity with nature is also a reaction to that.
AD: About your process of work, how do you tackle each and every project? You mentioned that you start from the tree/ context rather than the architecture. Can you tell us more about that?
SB: Yes we start from the tree, but for the very simple reason that, since we have this green facade where every species has its habitat, everything needs to be related to the needs of these specific species of plants. That means that the selection of plants and trees is a basic, or let's say, the main reference for our design. Of course, the selection of plants is conditioned by the climate, so I would say conditions and context, as the first step. The second step involves the selection of greenery and trees, with the help of botanists. At that very moment, we start thinking about colors, compositions, etc.
A lot of critics say that we are hiding the building because we are covering it with greenery. But for me, plants are part of it, not some sort of decoration that you can use to camouflage.
AD: After 6 years of Milano’s Bosco, what did you learn from this experience and what are you changing in new projects?
SB: Every single building is different. It’s true that we have to also answer the specific requests of the client, but every time we try to take a step forward, learn from the mistakes and think of new solutions.
Now if you go into an apartment, you notice that the level of the soil is different. Sometimes you have the trunks starting from lower levels, sometimes you have the pods in direct connection with the window, etc. There are around three or four different ways to be in proximity with plants. In Milano, when we first started, we only had two configurations. The variety of approaches creates a much richer relationship with plants. On another hand, we have recently developed a system of prefabrication for our project in Eindhoven that could be considered a very useful reference, for other developers and architects when creating green social housing buildings, everywhere in the world.
AD: It’s more than just a green facade. You are building a whole ecosystem. What would you say is the most important outcome of having trees on the facade? What are the consequences and advantages observed?
SB: Many. One, during summer, the building managed to reduce the temperature and lower the heat on the facade. In fact, the shadow of leaves is changing in a drastic way, how the building is hit by the sun. In August, for instance, you don't even need to use the air conditioners. There are far more advantages that are more general, like micro-dust particles, pollution, etc. Moreover, for example, there are more than 20 different species of birds nesting in the vertical forest. You feel like you are part of something more, a whole ecosystem. People who live there, in proximity with plants, also get to see their city in a different way, through this green filter of leaves. It's so unusual, and it changes your perspective.
I think we have done a lot in those 20 years to understand how to design and produce technical devices that help us emit less CO2. Nevertheless, if we want to absorb the CO2 that we are already producing, we need plants and photosynthesis, and that’s a great reason to multiply the number of forests in our cities.
AD: Going back to the projects, you have just inaugurated your first social housing project in Eindhoven- the Trudo vertical forest. How did this venture start? How is this project contributing to the city of Eindhoven?
SB: It started with a meeting with Jack Hopkins, a visionary person, who was already present in Eindhoven at the beginning of the regeneration of this powerful industrial center, once home to the Philips industry. Phillips is part of the history of Europe, in the last century, and what we have around Eindhoven is at the same time the concentration of the soul of the ancient settlement and the total reclamation of space and lifestyle. It is an amazing example of regeneration, and I was extremely attracted by the idea to do a social housing vertical forest here. The cultural and physical context is very dynamic.
AD: How different was it to create affordable housing from creating a luxury vertical residential building in Milano? How did you manage to basically lower the cost?
SB: That became my obsession. How to make your ideas really efficient, in a moment where everybody was asking for this. Basically, it was the selection and use of materials, a very articulate and profound study on prefabrication, and the cutting of maintenance cost with approaches such as the flying gardeners.
AD: For Antwerp, what are the particularities of the vertical forest? What makes it special and different? Also In Utrecht, you have started building your first mixed-use vertical forest Wonderwoods. The program is changing and adapting, how is the design transforming accordingly?
SB: We have four projects in this part of Europe, in this very close environment, where it’s so easy to commute from one city to another. In Eindhoven, we have created our first social housing. In Antwerp, we have a very simple L-shape building, where we had the opportunity to work on the roofs and to have green plants. In fact, we managed to have quite a large number of trees, like 80 trees on the roof, to create a commonplace for the tenants. In the beginning, this project was meant to be social housing, but then the owner decided to change that, but nevertheless, the prices are pretty fair. The other interesting feature in Antwerp is this variable geometry, made possible due to the sliding glass windows, that change easily the dimensions of the space. On another hand, in Utrecht, we are building the first mixed-use program, while in Brussels, we are experimenting, adding a green facade to an existing office building.
In terms of design, we take care of a certain language, but we are not obsessed with that. In fact, the moment that you start considering nature as a component of your work everything changes.