Vertical Forest “Bosco Verticale” in Milan

This book in English traces the history of the project, from the initial  impossible challenge to the creation of the Porta Nuova neighbourhood, analysing all those aspects that make it unique thanks to contributions by Beatriz Colomina, Emanuele Coccia, Paul Hawken, Vittorio Lingiardi, Manuel Orazi, Matilda van den Bosch and James Wines together with a hitherto unpublished collection of photographs by Iwan Baan which has been created specifically for the book, as well as shots by Paolo Rosselli, Giovanni Nardi, Dimitar Harizanov, Elisa Galluzzo, Laura Cionci and the extraordinary graphic images created by the cartoonist Enrico Pinto.

The book takes us on a unique narrative journey that calls to mind the growth of a tree, starting from its roots, up to the trunk and the branches. The ROOTS represent the starting point, the germ of an innovative idea resulting from a number of creative and artistic inspirations while the TRUNK instead represents the birth of the project, the challenges faced in both structural, technological and environmental terms along with those involving the construction site and finally the impact of the Bosco Verticale on the transformation of the surrounding area and the urban landscape. Finally, the BRANCHES tell the story of the life of the Bosco Verticale: on the one hand, they describe its position within the panorama of international architecture, which marks a change of direction towards the integration of living nature in the urban environment, while on the other, they represent an independent journey as a symbol and catalyst of biodiversity, not least in the eyes and imagination of the general public.

THE ROOTS

The American artist and architect James Wines, a pioneer with his studio SITE in terms of the issues of ecology and the integration of buildings with the surrounding context, offers a number of observations on the duty of architecture to go beyond its formal and functional responsibilities. This is followed by a section in which the “roots” of the book retrace the inspirations behind the Bosco Verticale project. These include the following:

Adriano Celentano with his song “Un albero di trenta piani” in 1972; the Guinigi Tower in Lucca, with its trees growing at a height of 44.25 meters above the ground; the German painter, sculptor and artist Joseph Beuys in whose vision the act of planting trees becomes a collective ritual; the Austrian painter, sculptor, architect and ecologist Friedensreich Hundertwasser, who preached the idea of ​​a new style of architecture based around the presence of trees in houses, courtyards and rooms and who on the night between 27^th and 28^th September 1973 in Milan, during the International Exhibition at the Triennale di Milano, had fifteen trees in Via Manzoni lifted using a crane that were then planted in various apartments along the street, protruding from the windows and clearly visible from the outside; ethologist and anthropologist Jane Goodall, whose pioneering studies on chimpanzees challenged humanity’s perceived dominance of the natural world, urging us to adopt a non-anthropocentric stance towards all living creatures; Davi Kopenawa Yanomami, shaman and representative of the Yanomami people in Brazil, a leading advocate for tribal rights and the conservation of the Amazon rainforest; British biologist Colin Tudge’s reflections on the role of plants in contributing to the life of all living species on the planet; English town planner Ebenezer Howard and his vision of the garden city; Italo Calvino with his interpretation of human/tree and tree/human interaction on a different level in Il Barone Rampante (The Baron in the Trees) and finally Madeleine de Scudéry, an extraordinary and eccentric figure from the early 1600s, who reconsidered architecture and urban planning from a psycho/geographical point of view.

THE TRUNK

The “trunk” of the book traces the entire evolution of the project from the birth of the Porta Nuova neighbourhood (2004/2010) to the development of the Bosco Verticale project; from the idea to the creation (2010/2014) and retracing the first 10 years of the building’s life from 2014, the year of its inauguration, to the present day.

“If you look closely, the Bosco Verticale is unlike any other project because it is repeatable, even if subject to a number of variations on the theme. As such it is therefore serial and this is a characteristic that very few other architects have managed to implement, perhaps only Santiago Calatrava, and even then only with regard to bridges. In actual fact, the types currently produced by modern thinking are mostly anonymous; for example, the infrastructures or the pure white, unadorned and repetitive volumes of early modernism, or the warehouses that invaded every continent after the war. Boeri’s interlocutor for about three decades, Rem Koolhaas is undoubtedly a great admirer of these types of buildings; what he particularly appreciates in those volumes is “an almost infinite capacity to absorb diversity while remaining monolithic, enigmatic and neutral”. The words of architecture professor Manuel Orazi in the text he wrote at the beginning of the section dedicated to the “trunk”.

“We are arboreal primates: trees gave birth to our species. Our way of life derives from a very special environment: the forest. Life in trees has shaped our form. Even the opposable thumb, which distinguishes us from other biologically close species, is the result of our body to body relationship with trees: it is the solution that has allowed us to move more easily among their branches. Our very anatomical identity derives from our relationship with trees: relating to our body means relating to the trees that have shaped it. And yet the house, the device that allows individuals to isolate themselves from the rest of humanity and find a way to relate to themselves, no longer possesses that arboreal quality, it no longer has anything of the anatomy of trees about it, and retains traces of them only in the form of their corpses” writes the philosopher Emanuele Coccia, professor at the École des Hautes études en sciences sociales in Paris.

The Bosco Verticale project

Two residential towers, one 110 and the other 76 meters high that are home to 800 trees, 4,500 shrubs and 20,000 plants from one hundred different plant species, distributed depending upon the façade’s exposure to the sun. This is equivalent to about five hectares of parkland on the ground, but concentrated on an area of ​​about 1,000 square meters. Each apartment hosts at least 2 trees, 8 shrubs and 40 plants for each tenant, allowing proximity to the natural green element and the related physical and psychological benefits.

The shade effect and the evapotranspiration action of the trees regulate the microclimatic conditions, reducing humidity levels and lowering surface temperatures by up to 30 degrees. This significantly reduces the energy requirement for air conditioning the interiors, lowering internal temperatures by 2-3 °C.

On the urban level, the trees planted in the Bosco Verticale play a fundamental role in mitigating the urban heat island effect. This is demonstrated by the European Space Agency map which measured the temperature of the earth’s surface in different cities in 2022: in Milan, as shown by thermal satellite images, the Bosco Verticale and Biblioteca degli Alberi Milano (BAM) ecosystem stand out as fundamental tools for lowering temperatures, on a par with much larger green systems such as the Parco Sempione.

The ceramic finish of the facades reflects the dark color of the tree bark, providing a backdrop to the plants and evoking the idea of ​​a tree house, rich in literary and symbolic references.

“We had to face challenges that had never been encountered before in an architectural project: how to manage the roots of the plants, how to manage the maintenance of the greenery. The Bosco Verticale was not simply a visionary project, it was an industrial project. During the construction phase, a further accident made the risk of failure even more evident, namely the bankruptcy of the construction company. After overcoming this complication, when we finally managed to complete the project the satisfaction was immense. When we finished and looked up, what we had created without realizing it had become a cultural manifesto” Manfredi Catella, co-founder and CEO of COIMA SGR.

“Right from the moment when the first images began to circulate, public opinion was positive; developing and promoting it during the following months was a daily commitment, safeguarding it from technical problems and constantly strengthening the link between architecture and nature. There was absolutely no reason to think that there should be any dichotomy or contrasting difference of ideas between building and nature” Gianandrea Barreca and Giovanni La Varra, founders of the Boeri Studio with Stefano Boeri.

“The Porta Nuova neighbourhood with Piazza Gae Aulenti, the Bosco Verticale and the Biblioteca degli Alberi Milano (BAM), the largest unfenced park in the centre of Milan […] is the first project in Italy to be implemented through a public-private partnership (PPP) agreement for the management of a public space” writes Kelly Russell Catella, Head of Sustainability & Communication at COIMA, Managing Director of the Fondazione Riccardo Catella.

The greenery

In the section dedicated to the “trunk”, the book presents an authentic herbarium which describes the main plant species (geraniums, bellflowers, periwinkles, ornamental apple trees, etc.) that grow throughout the Bosco Verticale, also showing their location on the different facades of the building through the use of specific graphics.

The choice of vegetation to be planted was made by a group of landscape agronomists with technical consultancy by Emanuela Borio and the Studio Laura Gatti, managed by the agronomist Laura Gatti and took place over two years. The selection was based on the combination of two primary parameters: the aesthetic and physical properties of each plant, in particular the height of the trunk and the width of the crown foliage development, as well as adaptability and intrinsic safety. In addition, ornamental characteristics, ease of maintenance and allergenicity, and their expected positioning on the façade were also taken into consideration.

In the summer of 2010, the trees for the towers were transferred to the Peverelli Botanical Nursery which together with the team of botanists took care of planting and maintenance. During the growth period, the experts monitored and adjusted the structure of the trees in order to ensure a crown foliage compatible with the eventual final location.

Arup’s wind engineering team conducted a thorough analysis of the climate and wind conditions, including rigorous wind tunnel testing of the trees’ structural stability. The first set of tests, conducted at the Politecnico di Milano wind tunnel facility assessed the strength of the tree using a 1:100 scale model, ensuring an optimal balance between the size of the model and the size of the boundary layer test section. The second set of tests, performed at the twelve-fan Wall of Wind hurricane simulator at FIU’s College of Engineering and Computing Campus in Miami, aimed to validate the forces on real trees, using purpose-built dynamometers to measure the forces.

The greenery in the building is owned by everyone and may not be modified, removed or replaced by individual apartment residents. To ensure the health of the plants, regardless of the expertise and attention of individual residents who may not have the time or experience to manage the greenery, maintenance and pruning activities are centralized.

The Flying Gardeners, a team of professional gardeners, climb the two towers with ropes, helmets and safety harnesses to take care of the trees twice a year. On two other occasions each year, maintenance is managed from inside the apartments, in agreement with the tenants.

Irrigation is centralized and managed remotely at the condominium level, through a digital system that constantly monitors the plants to ensure that each pot and tub has the right amount of water. The water management system uses groundwater and recycles the building’s grey water while solar panels on the roof provide the energy needed to pump water to all floors via the irrigation system. Just like a tree, the building draws energy from the soil and the sun to support and nourish its foliage.

“The first two years following construction were a period of adaptation: we began to understand how the ecosystem worked. The process was constantly evolving; for example, a plant that thrived on the third floor on the western facade might not be as successful on the sixth floor on the eastern facade. Some tree varieties had to be replaced due to unsuitable positioning. Apart from that, no significant problems or noteworthy pathologies emerged. Even during the violent downpour that hit Milan in July 2023, with wind speeds over 100 km/h, no damage occurred [..] You have to trust the trees’ capabilities, understand how they work.

Over time, the inhabitants themselves have become scientific consultants: living every day in the midst of greenery, they are the first to monitor the plants. This direct relationship, which we had initially underestimated, is essential at this point, because it helps in understanding the changing dynamics over the years” Laura Gatti, landscape agronomist who designed and managed the Bosco Verticale greenery.

“About ten years ago, I was sitting in my studio when the phone rang and it was Stefano (Boeri) who said “For some time now I’ve been thinking about a building with lots of trees, a kind of forest… but a forest that doesn’t grow horizontally, but vertically, on a skyscraper. What do you think?” Emanuela Borio, a landscape agronomist who designed and managed the Il Bosco Verticale greenery during the initial stages.

The contribution of Matilda van den Bosch, doctor and researcher at the European Forestry Institute and the Institute for Global Health in Barcelona, ​​analyses the impact of the Bosco Verticale on health:

“It is difficult to think of a more distinct example of a NbS (Nature-based Solution) than the Bosco Verticale. Designed with a focus on biodiversity, it creates the ideal conditions for human-nature connections and answers the demand for more greenery per capita in densifying cities. Could the Bosco Verticale also be part of the solution to the current health crisis? Worldwide we are replacing natural terrain with concrete surfaces and built infrastructures, and as a result of this, humans are becoming increasingly disconnected from nature […] The Bosco Verticale is a great example of science put into practice by embracing nature. Acting as a home for human beings, birds, butterflies and various other species, it contributes to an unprecedented level of urban biodiversity with immediate benefits for human health. In the Bosco Verticale, human life and natural ecosystems coexist, a symbiotic relationship that promotes ecological awareness and provides health benefits throughout life. Future cities should continue on this path to ensure a healthy and peaceful relationship with the natural world to which we belong.”

“The forest is inside the building, rather than the building being inside the forest and once again, the story is not just about humans living with plants, but about life with insects, even inside the insects. The building encourages swarms of insects. In 2014, about 1,200 ladybirds were introduced to the Bosco Verticale terraces to combat aphids that were happily feasting on the leaves. But the ladybirds reproduced much faster than expected, and for a few weeks the building was overrun with these particular guests. In a sense, the building was remade by insects. The insects defined the space. Human beings became the guests, temporary visitors to the complex ecosystem of plants, birds, insects and pets. The insects, and their uncontrollability completed the building. Human-centered design sounds good, but it has been terrible for human beings, other species and the planet in general. Humans are not just a single entity, but an infinitely complex and ever-evolving trans-species collaboration. The human being is little more than a bag of bacteria, bacteria that have existed for billions of years, while the human being itself is a very recent arrival on this Earth and may already be leaving. We are nothing without all these foreigners. We live in them more than they live in us” is how Beatriz Colomina, professor of History of Architecture at Princeton University puts it in her contribution to the book.

The strength of  the Bosco Verticale lies in its different levels of meaning

by Simone Marchetti, Sofia Paoli, Luis Pimentel and Livia Shamir

First, there is its philosophical dimension, which considers the interaction between humanity and other species, promoting interspecies sympathy and understanding; secondly, there is its technical dimension, which deals with the complexity of a building in which plants and trees inhabit its surfaces, and the consequent need to adapt building engineering to their specific needs; and third, there is the conception of the Bosco Verticale as a device capable of offering multiple benefits through the specific properties of its different composite parts, trees and shrubs, and their natural processes: the removal of particulate matter, carbon storage, improvement of the microclimate through evapotranspiration and the reduction of energy consumption for cooling during the summer, thanks to the natural shading of their foliage.

Since its initial conception, the Bosco Verticale has embodied the power of trans-scalability, the potential to be reproduced as part of a multi-scale system similar to a tree in a forest or a forest in an ecosystem

During the ten years from 2014 to 2024 the Bosco Verticale has become the catalyst for the development of a new paradigm of thinking, based on the global understanding of the ecological interaction of urban forests and other nature-based solutions with the urban environment, together with broader issues related to decarbonization, recycling and regeneration of processes in the building and construction sector.

“The Bosco Verticale can therefore be thought of, psychoanalytically, as a transitional object, that is, an object that creates “transitions” between places that have almost always been conceived as separate and usually opposed: inside-outside, internal-external, above-below (and also individual-collective, if we consider that greenery is a private and expensive property that can also be enjoyed by the community). […] The Bosco Verticale project seems to contain a number of the essential elements of an ethical-aesthetic approach to psychological well-being” writes psychiatrist and psychoanalyst Vittorio Lingiardi in the book.

THE BRANCHES

The final part of the book, the “branches”, is dedicated to the research and design work carried out around the world by the Stefano Boeri Architetti studio starting from the Bosco Verticale experience. This has branched out into various formal and functional typologies, giving rise to projects that although different are  united by the overwhelming priority of integrating living nature in architecture. These include the first Bosco Verticale for social/council housing in Eindhoven, the proposal for a new Stadio Bosco (Bosco Stadium) in Milan, experiments with retrofitting techniques in Belgium and Italy and finally the low-density experiences in Milan, Antwerp, Treviso and Bari. Particular attention to integration with living nature is given to healthcare projects, including the Shenzhen Rehabilitation Centre in China, characterised by alternating green terraces, and the new Milan Policlinico Hospital (Boeri Studio), whose roof will host a hanging garden of around 6,000 m² dedicated to patient rehabilitation. On an urban scale, the Città Foresta proposes a new vision for the metropolises of the future.

In his contribution at the beginning of the section dedicated to the “branches”, the American entrepreneur, ecologist and writer Paul Hawken writes “After ten years, the Bosco Verticale remains a celebration of design and architecture that imagines a different form of urban life, an invitation to merge the natural world into our urban spaces. I believe we will look back on the Bosco Verticale as a kind of urban pioneer species, an ecological term that describes how resilient new organisms can populate degraded and disturbed areas. The Bosco Verticale is like a tree emerging from dehydrated earth, an unexpected visitor in a landscape of scrub and sedge where such a tree has never been seen before. […] Boeri puts life at the center of his work. Nature and humanity are made up of exquisitely complex networks of relationships, without which forests, lands, oceans, societies, countries and cultures perish. For millennia, cities have distanced themselves from nature. Walls are crumbling. Now there are variations of vertical forests everywhere in the world. Regeneration is a non-extractive design ethic, a civilisational imperative to create more life. When we bring the city back to life, we bring people back to life.”

In the final part of the book, the Stefano Boeri Architetti studio partners Francesca Cesa Bianchi, Pietro Chiodi and Marco Giorgio write the following: 

“For us, the Bosco Verticale was a great “school”. It was the first prototype of a new architectural typology that combines nature and architecture, working with living materials. It provided the initial opportunity to experiment and test different technological and design solutions in a single project that are still the fundamental principles underlying the design of vertical forests. Over the last ten years, starting from the application of these principles, we have had the opportunity to reflect on how to combine the environmental benefits of the Bosco Verticale with a wide range of local conditions, specific social contexts and different economic constraints. From this point of view, one of our most notable projects is the Trudo Vertical Forest, the first vertical forest built taking rent-controlled social housing for low-income residents into consideration. Located in Eindhoven on land previously owned by the Philips company, this project is a significant part of one of the most intriguing urban redevelopment experiences in Europe” Francesca Cesa Bianchi.

“In our field, its impact was revolutionary almost immediately: we opened a studio in Shanghai, China, where we undertook several urban forestry projects, including the creation of vertical forests in Huanggang, Shenzhen and Nanjing, the last being the tallest of its kind in the world. Through our work we’ve managed to create something that didn’t exist before, something distinctly “ours”. Over the past ten years, we’ve built up considerable experience through collaboration with numerous experts in various contexts and this has allowed us to improve the system as a whole and to learn from each other through mutual reciprocal exchanges. With each new opportunity, we have refined the details, discovered new management methods and explored different construction techniques. Working in different social, environmental and political contexts has added an exciting dimension to the challenge of building vertical forests around the world” Pietro Chiodi.

“The common denominator in every vertical forest project is the vegetation, which creates a “multisensory diaphragm” that filters the relationship between the intimate dimension of the houses and the public nature inherent in every example of built architecture. The trees that give life to the facades create a unique experience both for those who look at the architecture from the outside but above all for those living inside. As a result, a new, unusual and completely original relationship with the vegetal elements is created. The branches, the foliage, the leaves and all the organisms that find their ideal habitat among the foliage of the trees become the leading characters in the daily life of the inhabitants. The Bosco Verticale in Milan’s Porta Nuova was the forerunner of a long and complex path of design research that led Stefano Boeri Architetti to develop technical and compositional solutions all over the world. These solutions have allowed the studio to combine technological challenges with reflections on environmental contextualization and emerging lifestyles” Marco Giorgio.

 The Bosco Verticale as a multi-award-winning pop icon

The last pages of the book by Alberto Berruto, Maria Lucrezia De Marco and Guoying Jiang are entirely dedicated to the Bosco Verticale as an icon in the popular imagination.

Just one year after its construction, in 2015 the Bosco Verticale was chosen from among 800 international skyscrapers, winning both the International Highrise Award, promoted by the Deutsches Architekturmuseum (DAM) and the City of Frankfurt, and the title of Best Tall Building Worldwide by the Council on Tall Buildings and Urban Habitat (CTBUH), awarded at the Illinois Institute of Technology in Chicago. From that moment on, the image of the Bosco Verticale has taken a dual path, both in the collective imagination and in terms of institutional recognition. It has appeared in the renowned BBC series Planet Earth II narrated by Sir David Attenborough as an example of innovative housing solutions that address urban climate challenges, it has appeared in advertisements for the Fiat 500 electric car against the backdrop of a city of the future with Leonardo Di Caprio and it had the starring role in the episode of the Netflix series The Future of which was dedicated to sustainable skyscrapers and future ways of living.

The Bosco Verticale has thus become an important interpreter of architectural and urban progress moving towards integration with the natural sphere. Yet the image, which has been revisited in various ways and techniques by brands such as Gallo or LEGO has transformed it into a popular cultural icon, earning a place in television programs such as Chi vuol essere milionario? (Who Wants to Be a Millionaire?) or L’Eredità, in records and songs like the Bosco Verticale by the rapper Nasty K and in entertainment media such as La Settimana Enigmistica or games such as Taboo. At the same time, the image of the Bosco Verticale has experienced a virtuous parallel path within national and international institutions as a model of green architecture and a new way of conceiving architecture in relation to living nature.

The 2022 World Cities Report by UN Habitat includes it in the chapter “Nature-based Solutions and environmental features” while the Nature-based Solutions Handbook, developed as part of the ThinkNature project funded by the European Union’s Horizon 2020 research and innovation program featured it on its cover; the UN, in its 17 Sustainable Development Goals, created with the aim of promoting peace and prosperity for people and the planet, combating climate change and working to preserve oceans and forests, chose the Bosco Verticale as the leading image for the eleventh goal: “Make cities and human settlements inclusive, safe, resilient and sustainable”.

After the significant first two awards, the Bosco Verticale was then selected from among the twenty winners of the prestigious Royal Institute of British Architects (RIBA) 2018 International Award for Excellence, in addition to receiving the Award of Excellence from the Council on Tall Buildings and Urban Habitat (CTBUH) in 2024 as a finalist in the 10 Year Award category, restating its importance in the architectural panorama after a decade.

The last lines of the book read as follows “The Bosco Verticale specifically does not have its own copyright, so that an increasing number of green buildings can become part of the urban landscape, and so that cities can transform surfaces from mineral to green, both horizontally and vertically. The Bosco Verticale is just a way of reforesting our cities. Replacing parking spaces with rows of trees, creating lawns on flat roofs, surrounding cities with orbital forests and crossing them with green corridors are challenges that must be faced collectively and no longer postponed. Urban forestry is not an option: rather it is the most effective, convenient and inclusive choice with which to counteract the effects and root causes of climate change.”