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  • Writer's pictureChristiaan Gey van Pittius

The 'Vertical Forest': sustainable science or an aesthetic fantasy

Updated: Aug 11, 2023

"Want to make a skyscraper look trendy and sustainable? Put a tree on it!" Tim De Chant

Biophilia merges the world of human-designed habitats with the natural world. The concept of biophilia suggests the human need for connection with nature on physical, mental, and social levels, affecting our wellbeing, productivity, and societal relationships. The term biophilia stems from Greek roots meaning love of nature. A popular writer on the subject, Bill Browning, says the term came into use in the 1980s when Edward O. Wilson (an American biologist) realised that humans were increasingly detaching themselves from nature. He consequently pioneered a new paradigm focused on reconnection humans with nature as he believed biophilia is the pursuit of emotional affiliation of human beings to other living organisms.

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Biophilia can be used to transform "normative" designs into fantastically stimulating ones. Integrating elements such as plants and trees can effectively address several modern urban problems. It can and should help mitigate the negative impact of urban infrastructure's carbon footprint; one favoured contemporary design method is "Vertical Forests".

Today biophilic architecture is widespread due to a global mission to reduce carbon and greenhouse gasses (GHG's) in the atmosphere. The real estate industry is developing exciting new concepts and technologies to appeal to the ecologically conscious and is attempting new ideas to reduce the construction industry's carbon footprint following international directives and policies. Magazine literature has started promoting 'sexy' designs of buildings with luscious green facades, suggesting it as a promising solution to make cities more sustainable. The biophilic concept of vertical greening is not new, by the way: It can be dated back to Babylonian civilisation's Hanging Gardens constructed approximately 2500 years ago.

The roof area of buildings has been a prominent biophilic design favourite in recent decades with the adoption of roof gardens in general architecture due to its proven beneficial ecological and energy-saving characteristics. A building's facades are usually much more extensive in square meterage than the roof area. Naturally, roof greenery's success was bound to lead to vertical greening systems being developed and adopted by architects in the last decade, specifically for tall building typologies such as vertical forests.

Vertical forest architecture is a biophilic concept popularised by Stefano Boeri and his award-winning project, Bosco Verticale, completed in 2014. It has been called "The most exciting new tower in the world" and won countless architectural prizes and awards, including the International High Rise Award. Bosco Verticale is pair of two residential towers located in Porta Nuova, Milan, consisting of two towers covered in large amounts of vegetation.

Since Milan is a city facing increasing air pollution problems, Stephano Boeri proposed an attempt to mitigate these problems. Boeri revealed his concept in 2011, resulting in the proposal's renderings and illustrations going viral and receiving a great deal of support from mainstream media. Tucked away in some corners was some criticism as well: The key to this typology's future success lies hidden in the criticism (and the comment section). Some ecological aspects were overlooked in the media coverage, like the energy used to construct the buildings not justifying the claim of the building's realisation aiding in the reduction of Milan's air pollution.

His initial proposal's exposure brought his firm a sizable amount of attention, leading to many more similar proposals to be developed by his team worldwide. This project initiated a landslide of proposed buildings based on this project's success and has since been adopted by well-known architects like Diller+Scafido, MVDRV, Kengo Kuma, Jean Novel, Thomas Heatherwick, Koichi Takada, Foster and Partners, Morphosis and many more.

Vertical forest architecture is considered a more complex system than other greenery systems due to the need for a bulkier superstructure. A much larger volume of growing media is required for growing trees up to three meters high with a one-meter deep layer of soil base in balcony planters. The hundreds of garden balconies need sophisticated irrigation and drainage systems, not to mention the extreme exercise of waterproofing the planter from the rest of the building. Waterproofing is well known to be an architects nightmare. All these additional building components are made from high energy materials that release enormous amounts of greenhouse gasses into the atmosphere during their production.

In an INHABITAT article by Diam Phem in 2011, the following illustrated claims were shown by Boeri as the main reasoning behind the architectural choices and design:

The vertical forest (balcony gardens):

1. Protects the interior from direct radiation during the summer

2. Let's light into the interior during winter

3. Protects the interior from the wind

4. Releases humidity into the interior

5. Captures small dust particles

6. Produces oxygen for the interior occupants

7. Reduces acoustic pollution to the occupant

This now famous illustration just explains what trees do, which is incredible that the illustration was copied to hundreds of other publications, including academic journals, even though in reality it illustrates very little. The claim regarding reducing urban noise is a bit more troubling than the others: Proven data shows that trees and shrubs might have noise reduction results in experiments, but the reductions are so slight that the occupants will not notice the difference from within the building. However, it does create noise, as the mass of vegetation would create an ambient sound during breezes and windy days. This would drown out some city noise – but ultimately trees and plants do not reduce direct noise. It is worthy to note that the large soil-filled planters themselves will definitely reduce urban noise – due to their volume and density.

The founding editor NOVA Next and a lecturer at MIT, Mr Tim de Chant, said in a Treehugger article:

"There are plenty of scientific reasons why skyscrapers do not have trees, at least not to the heights which many architects propose. Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It's hot, cold, windy, the rain lashes at you, and the snow and sleet pelt you at high velocity. Life for city trees is hard enough on the ground. I can't imagine what it's like at 500 feet, where nearly every climate variable is more extreme than at street level".

The verdict regarding the effects of the wind forces on the vegetation is unclear; it is understood through experiments that damage will occur over time. The trees will also find it hard to thrive under the conditions, and falling debris from broken branches could be fatal. Wind studies vary as different trees and shrubs have various characteristics that influence their response to high winds. Many scientists (including Boeri) started testing trees' placement in such an environment, and the results vary due to context and vegetation selection. The dust filtration and pollutant absorption claims are also increasingly challenging to prove. The wind's effect on the trees minimises some normal functions that would occur if it was placed on the ground. As many of the trees will also shed their leaves in the winter resulting in the balconies being covered in foliage, as far as the claim of 'dust reduction', I am unsure it is relevant at all.

It is true and proven that vegetation's presence affects the occupants' wellbeing, but this is strangely not used to claim the success of the vertical forest concept in mainstream media as I guess the trend is with fancy greenery systems and not sociology. Boeri has placed most of his concept's legitimacy on the idea that the increased vegetation will reduce pollutants and carbon emissions from the atmosphere. This fact is true; all trees do this. Trees on the ground are just better at doing it as less energy was spent in their transport, positioning by cranes, complicated maintenance and eventual removal and replacement.

Evidently, the building needs a more substantial structure, which requires much more concrete. Architects can not just ignore the fact that concrete is an environmentally damaging product anymore. Only a few popular online sources discuss the structure's embodied energy in more detail, some written by Mr Alter Lloyd. Lloyd came under fire for his insistent critique of the current unsustainable vertical forests concept. The fundamental problem is climate change due to greenhouse gasses, which the project added to. I repeat: The project's "forest" has not and will not decrease the emissions its construction caused, ever!

"Concrete is responsible for as much as eight per cent of the carbon dioxide that is produced each year. The amount of concrete required to make the giant cantilevers and built those planters to hold up all those trees is so great that it might take those trees a thousand years to pay back the carbon debt of the planters they sit in." Lloyd Alter, 2020.

These fantastical claims by Boeri have been propagated by many architects following the trend. They are repeated in many mainstream articles and subsequent projects inspired by Bosco Verticale.

"This is a kind of biological architecture that refuses to adopt a strictly environmental, strictly technological and mechanical approach to environmental sustainability,"

said Boeri himself in a statement to Dezeen (Frearson, 2014).

Boeri has yet to publish his purported book, "A Vertical Forest: Instructions booklet for the prototype of a forest city", and has not published any peer-reviewed literature on his claims in support of vertical forests thus far either. I find myself wondering about the ethics of architecture in the push for new ecological ideas. Which leads to the introduction of the phenomenon known as "Greenwrapping".

It is a term used to describe the aesthetic addition of greenery around architectural structures to aid the architectural visual appeal. This term is becoming synonymous with the term 'greenwashing'. This is modern terminology, referring to business practices misusing 'eco-friendly' or 'green' initiatives to appear less destructive and more trendy during our shift towards global sustainability.

Tim Chants mentioned the critical problem with the impressive advances in architectural rendering:

"Architects use all kinds of tricks to make their buildings look better in renderings; mirrored glass used to be a favourite, with renderings of buildings showing reflections of sky and clouds as the building just blended into the landscape.".

The professional renderings for project proposals have become a large part of the architectural business, especially in the last decade as architects ramped up competition after the global economic crash in 2008. Initially, it was difficult to render greenery and trees into images due to the complexity of vegetation's shapes and shadows. Photoshop manipulation was primarily used in the post-production of proposal images to add greenery to avoid adding the complicated forms into the raw 3D model due to these computational problems.

Today the software sector for architectural renderings has exploded, and the advances are incredible. It is much easier to incorporate greenery and tree renderings into the original 3D model for a more appealing final picture. This advancement in rendering software could be considered a significant factor in why biophilic architecture is prevalent in mainstream media today. It is very visually appealing. Sexy, some might say. Architects happily use these advanced artistic computational tools as a powerful marketing instrument to sell their products in a highly competitive market.

On the 3rd of February, 2021, the mainstream media revealed the newest vertical forest building typology proposal by NBBJ Architects. They unveiled a "nature-infused" headquarters building for Amazon in Virginia, USA. The building's twisting shape and prominent vertical forest spiralling up the structure has received a flood of criticism and represents the peak of 'greenwrapping' absurdity. Even though the proposal's spiralling forest is suggested to be a walking trail, this concept of a connected greenery belt is an improvement to the isolated cellular structure of Boeri's balconies. The proposed design is wholly constructed from curved custom-shaped high-energy materials like glass, steel and concrete. This building has become a symbol of architectural failure to meet sustainability directives.

The main objective of biophilic architecture is to increase biodiversity, use greenery to improve a building's performance. Increase human wellbeing and, most importantly, absorb carbon emissions in cities. However, the vertical forest trend seems to have blurred into elitist fantasy.

Many developers have embraced the trend leading to architects having similar type of projects currently in progress worldwide. Still, scientists and commentators question these high-rise greenery systems' actual functionality. The concept is relatively novel, and long-term ecological success still needs to be proved. This architectural typology claim as sustainable is highly debated as these structures' total carbon lifecycle is not being taken into account.

Mainstream media has enjoyed presenting the popularity of the vertical forest trend. It seems to lead to an era where architecture and nature merge to support global efforts to reduce carbon emissions and meet global goals and agreements. In other words, a form of productive biophilia. Still, the problem lies with the reality of the buildings’ carbon footprint – this will determine its future success.

My hypothesis is that this vertical forest trend will eventually lead to a more substantial architectural movement as reliable data is presented over time. I argue that the current execution is propagated by 'sexy' visuals, starchitect egoism and financial gain. Architects will need to start addressing the elephant in the room, which is the carbon emitted by architectural projects. The quantification of these ignored aspects of sustainability should become compulsory, in my opinion. This also goes for the carbon cost of the occupants' happiness and wellbeing from using aesthetic choices like greenery systems.

Is vertical forest architecture an ecologically relevant typology? No, not yet; there is a long way to go before it is a sustainable ecological option. In the meantime, cities should probably invest in reducing their air pollution sources rather than add to them in a blind attempt of mitigation through trend-driven architecture.

Interesting further exploration could include the possible revival of brutalist architecture with vertical forests interventions, MVDRV's Pot Greening concept vs Boeri Vertical Forest concept as a better alternative to propose designs, the inclusion of urban farming in the vertical forest typology and looking into alternative structure materials like timber frames to attempt to reduce the building's carbon footprint.


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