Another Look at Stefano Boeri's Vertical Forest

Vertical forest skyscraper standing tall in a city landscape

Boeri Studio

Stefano Boeri's Bosco Verticale has been called "The most exciting new tower in the world." It has won all the big prizes, including the International High Rise Award. I have been a skeptic about it, and have been called many nasty things in comments, including statements like "I can't help but realize that every post Lloyd writes has a downer ending. Can there just be one Treehugger post that doesn't have a negative tone?" But now that it is built and landscaped, and now that the architect has sent a review copy of his book "A Vertical Forest: Instructions booklet for the prototype of a forest city," it is perhaps time to have another look at it.

The Sustainability of Concrete

credit: Boeri Studio

Here's the rendering that launched a thousand blog posts, showing the two towers almost completely covered in greenery. Interestingly, those thousand blog posts actually helped get the project built; Boeri writes in the book:

To convince my clients, I asked a journalist friend to publish a picture in an Italian newspaper showing the two towers covered with trees and a compelling title: The first ecological and sustainable tower to be created in Milan." ...I added in that article, which was so successful as to push my clients to take this little "quirk" seriously- that in addition to carbon dioxide, the leaves of the trees would also absorb the pollutant micro-particles created as a result of urban traffic and so would help clean the air in Milan, as well as producing oxygen in turn.
credit: Boeri Studio

I was, to put it bluntly, outraged by these statements. Concrete is responsible for as much as seven percent of the carbon dioxide that is produced each year. The amount of concrete required to make those 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. I did not (and still do not) believe that you can't call a building sustainable unless you take the full carbon lifecycle into account.

Can Trees Really Survive at Such Heights?

credit: Boeri Studio

Tim de Chant wrote:

There are plenty of scientific reasons why skyscrapers don’t—and probably won’t—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..
I also checked with landscape architects regarding the size of the planters, and was told that while the tree might live, it will never thrive and grow much. And I worried about maintenance.
Nor do you know who maintains them, whether each owner is responsible, whether gardeners have rights of entry, or whether they rappel down the exterior of the building.
credit: Boeri Studio

But Boeri tells another story and apparently anticipates all these concerns.

It took months of research and experiments conducted with a group of outstanding experts in botany, ethology and sustainability to solve problems that architecture hand never before hand to deal with: How to prevent a tree being broken by the wind and falling from a height of 100 meters; how to ensure continuous and precise watering of trees panted at heights where conditions of humidity and exposure to sun are very different; how to prevent the life of the trees being jeopardized by the personal choices of the owners of the apartments.

Rendering vs. Reality

credit: Boeri Studio

So now we have the rendering vs the reality and does it live up to the billing? Was it just an architectural fantasy? I think the jury is still out, that it's too soon to tell. However I have to admit that it's pretty impressive. And the logic behind it is impressive too:

Like Friedensreich Hundertwasser, like the Florentine architects of the radical movement, Joseph Beuys shows us the great challenge of the coming decades: Transforming rocks into trees means in fact transforming houses and streets into places inhabited by thousands of living species. It means imagining an architecture that does not host or fence off portions of nature but which is created together with nature itself. It means living with trees, with their presence and their speed of growth, and with their extraordinary capacity, even in the most polluted and congested areas of the urban world, of accommodating and giving life to w a wealth of species.

Feasibility of the Balconies

credit: Boeri Studio

The balconies are obviously the defining feature of the building, and I remain concerned that they are big and heavy. Boeri:

From an architectural standpoint, the balconies are the most important element of the vertical forest.... in their final configuration, they all extend out for a distance of three meters and 25 centimeters. [10'-7"] This solution has allowed an expansion of the inhabited spaces in the open air and at the same time the creation of plant pots with a greater depth (up to 110 centimeters [3'-6"]) The overall surface of the balconies is approximately 8,900 square meters. [95,798 square feet]

Dare I repeat myself, but that is a lot of concrete, with a big carbon footprint.

credit: Boeri Studio

On the other hand, these are not your usual six foot deep balconies where you can barely place a chair; this is useable space, a real outdoor room, and those trees make it feel like a backyard in the city.

Tree Maintenance

credit: Boeri Studio

They also have an elaborate maintenance program, where they rappel over the side of the building and do maintenance while hanging in a bosun's chair. There is a crane on top for replacing trees as required. Watch the video for spectacular shots inside and outside.

Every four months they fly around the Vertical Forest. They hang by rope from the edge of the roof and descend by jumping between balconies. Botanists and climbers, only they have the consciousness of the richness of the lives that the Forest hosts in the Milan sky.

Refining the Vertical Forest Concept

credit: Boeri Studio

In the latest iteration of the Vertical Forest, the Tower of Cedars in Lausanne, Boeri appears to be refining the concept and perhaps addressing some of the concerns; the balconies have now morphed into projecting boxes, which have side walls that can act as deep structural supports; deep beams take less material. Also, the planters are now a full floor deep, which should let the trees grow even larger.

credit: Boeri Studio

Boeri calls the Vertical Forest an "anti-sprawl device."

VF01 constitutes an alternative urban environment that allows to live close to trees, shrubs and plants within the city; such a condition can be generally found only in the suburban houses with gardens, which are a development model that consume agricultural soil and which is being now recognized as energy-consuming, expensive and far from communal services found in the compact city. Through densifying the urban fabric, VF01 creates new and innovative relationships of proximity between nature and the built environment, creating new landscapes and new skylines.

Looking at the project through that lens, and thinking of all the concrete that goes into building that suburban house and the roads that lead to it, which this is replacing, I am rethinking my previous objections. Because these aren't just balconies, but a different way of looking at nature in the city. I was wrong about this.