Some weeks ago, a new mixed-use building designed by Stefano Boeri Architetti for the Antwerp based developer ‘Triple Living’ was officially inaugurated in Antwerp. ‘Palazzo Verde’ boasts abundant greenery on the rooftops , and also offers a pleasant garden on street level, at the entrance to the subterranean ‘Circularity Center’. In this way, Boeri remains faithful to his conviction that buildings should actively remediate the climate crisis by integrating more greenery into their design, but this has resulted in a building that is markedly different from the much-publicised ‘Bosco verticale’ towers In Milan, built in 2014, who made Boeri almost overnight world-famous.
Even before he built ‘Bosco Verticale’, Stefano Boeri was a kind of architecture star, at least in Italy. He was not just an architecture professor, but was also the editor in chief of the leading magazines Domus and Abitare and took a leading role in many a cultural event. He also instigated ‘Multipicity’, a research agency that investigates through art, photography and urbanistic analysis the complex relationships between geopolitics and urban planning.
It is in projects such as these that one can see the influence of Bernardo Secchi, whom he studied with at the IUAV in Venice. There is indeed an obvious link between Boeri’s work for ‘Multiplicity’ and the interest that Secchi, as a professor and a designer (in collaboration with Paola Viganó) showed in the complex relations between geological formations, territorial policies and design, from the very large scale to the most minute scale of a neighbourhood or even simply a public square.
It was only quite late in his career that Boeri started his own architectural office. ‘My first project was the design for the geothermal power plant Bagnore 3 of the Italian energy group ENI’, he explains. ‘It was later followed by the redevelopment of quite some former harbour environments. But I have always been almost obsessed by trees, and that has led ultimately to the work I am doing now: designing buildings in which trees and shrubs form an essential part of the building, not just some kind of decoration’.
The construction, in 2014, of two high-rise buildings in Milan is abundant proof thereof. In terms of floor plans, these two towers, 110 and 76 ms high are not that different from most of the recent high-end residential buildings in Milan. What is striking about them however is that the enormous protruding balconies are planted with 88 trees, 4500 shrubs and some 15000 ornamental plants. The result is a street front that is not as much determined by architectural details as it is by its abundant greenery. Considering the relatively small footprint of the buildings, this amount of greenery largely compensates for the carbon footprint of the building, and it has of course a lasting beneficial effect on the air quality and the ‘heat island effect’ in this heavily polluted city.
Boeri explains that this was by no means an evident feat: ‘It took a lot of research to find out how to plant trees on such a height, considering the effects of the static and dynamic impact of the trees on the construction. The maintenance of the greenery was another major issue: although most terraces are in private use, the greenery is a collective asset, because it calls for a complex system of water supply and plant care that cannot be left to individual decisions at will. The endeavour even called for highly specific ways of tree nursing. We learned a lot from this project. It was expensive, for sure, but we can apply this knowledge now in a social housing development in Eindhoven, Holland’.
‘Palazzo Verde’ in Antwerp has a quite different approach. The footprint of the building is relatively modest and L-shaped. It consists of a ground floor for commercial use (450 m2). In the corner between the two wings of the building there is a garden, and a sunken patio that gives access to an underground commercial space with ample daylight. Three to six floors of flats (a total of 6000 m2) rise up on top of this ground floor in a slightly irregular manner. The project is part of ‘Nieuw Zuid’, an 21st century extension of the popular 19th century neigbourhood ‘het Zuid’. It is built on grounds that had an industrial use before, after an urbanistic plan by Secchi and Viganó that gives a lot of attention to environmental qualities.
Despite the modest scale, ‘Palazzo Verde offers a striking aspect because of staggering skyline and the slender dimensions of the all-white concrete floors and wall slabs of the upper floors. It is only on top of that construction that lush greenery is applied on all rooftops. On closer inspection, one discovers that this specific look owes a lot to an building concept that is related to a strategy that the French architecture firm Lacatton & Vassal often applies. The building indeed has a double façade: terraces made of concrete are hung in front of the basic construction, providing veranda’s and terraces with an intermediate climate for the flats.
That is not only an interesting way to control the internal climate of these dwellings, it also offers them a large amount of extra private space. Most of the greenery on the rooftops on the other hand is collectively used. The numbers are again impressive. The project boasts 86 (small) trees, 1000 shrubs and some 1200 ornamental plants on a surface of 780 m2 of roof gardens. In this building, as well as in the other projects Boeri works on, the question remains however how sustainable such rooftop gardens can really be. That led to an interesting discussion.
PTJ: Quite some recent research pointed out that trees have the capacity to ‘communicate’ amongst each other, for instance by means of underground networks of fungi through a process called mycorrizha. The German author Peter Wohlleben also pointed out that trees have quite some more ways to help each other to survive, for instance by sharing their root systems or allowing each other enough space to reach for air and light. I wonder how this can work in buildings such as this one, or the ‘Bosco Verticale’, because the roots of these trees are mostly locked up in concrete containers and have no way to reach each other.
SB: That is a good question. We have been studying this for a long time, in collaboration with many specialists such as ornithologists and botanist. The input of Laura Gatti, a botanist, has been vital to all our experiments with green buildings. As you know, we didn’t stop at the experiment in Milan but continued working on forested buildings since then. The basic image that gave us confidence in the feasibility of vertical forest was the fact that you often see solitary trees grow in rocky landscapes, on a soil that at first sight is not welcoming to them. But this is hardly the case in our projects. In Milan for instance, the branches of the trees are but a few centimeters away from each other. I could not explain how it actually works, but it seems that this in itself allows them to make a kind of contact. Trees have this kind of ‘diffused intelligence’ that we are only learning about now. It is a field of knowledge that is still developing. We are still monitoring most of our projects closely to understand how the trees evolve over time.
PTJ: Buildings such as ‘Palazzo Verde’, who provide greenery in a mineral environment such as these former harbour grounds are evidently beneficial for the environmental quality, but I can’t help to think that, considering carbon emission and greenhouse effects, it would be better not to build at all, especially in a densely built city as Antwerp that has a lot of vacant or underused spaces.
SB; You have a point of course. We should reduce new constructions to the minimum. There is no need for the European city to grow, but there is a lot of work to do in readjusting what we have in view of actual needs. Still, if we are to build, and Palazzo Verde is an example of that because it is part of the masterplan by Secchi and Viganó to redevelop this part of the city, we had better do it this way. I am convinced that cities have to be greener in any way possible, and this is one of them. But we apply the same strategies to existing buildings too. We are for instance working now on ’Val d’ Or’ in Brussels for Triple Living. We want to redevelop former office buildings into residential premises with a green façade. In this case, we are adding greenery to an existing building instead of building new constructions. That is twice beneficial for the environment. But we should of course not stop there. We are considering now a plan for planting 3 million trees in Milan in the next years’.