After I first wrote about Bosco Verticale about five years ago, I received an email from a reader decrying the notion that you could build a tall apartment building with a forest up and down its façades.
"Common sense," he wrote, "tells you that you can't put a 30-foot tree on an apartment balcony."
Balconies aren't designed to hold such a load, he added, predicting that the trees would either blow off, landing on some innocent passerby, or the whole balcony would come tumbling down, tree and all.
But common sense, I've found, is the phrase often used to mean a simplistic solution to a poorly defined problem. And Bosco Verticale architect Stefano Boeri and his team of design professionals defined the problem very well. That team included Arup, the British-based multinational design and engineering firm, plus botanists and horticulturalists. Together the team figured out how to grow trees on balconies.
So the building was built, finishing late last year, and just last week Bosco Verticale was named the "2015 Best Tall Building Worldwide" by the Council on Tall Buildings and Urban Habitat, an international group of professionals dedicated to improving the design of tall buildings.
The annual competition was pretty stiff. The council received entries representing 33 countries. It narrowed things down this past summer by naming four regional winners representing the Americas, Asia and Australasia, Europe and the Middle East and Africa.
From that group of four, Bosco Verticale, which translates as "Vertical Forest," emerged as the winner.
The jury lauded Bosco Verticale for its "extraordinary implementation of vegetation at such scale and height." The building supplants traditional cladding materials with screens of greenery so that the plants act as an extension of the tower's exterior envelope, creating a distinct microclimate.
This "living façade," incorporates many trees of varying heights and more than 90 species of other plants, shrubs and smaller greenery.
The result is a façade with an active interface to the surrounding environment, cooling and shading while scrubbing some of the pollutants from the surrounding air.
This is no small-scale experiment. Bosco Verticale stands 116 metres tall. It has 27 storeys above grade, with another three levels of underground parking.
It's part of the rehabilitation of the historic centre of Milan, a city in northwestern Italy. The city was founded by the Celts in pre-Roman times. From those ancient roots, it has grown into a thriving industrial city of 5.3 million.
That many people in an industrial setting means that air quality is often poor, which is part of the rationale for the green façade. In all, the tower is sheltered and cooled by 480 large and medium-sized trees, 350 smaller trees, 5,000 shrubs, and 11,000 ground-cover plants. Taken together, they form the equivalent of an entire hectare of forest cover.
The building's performance is being carefully monitored. Researchers are assessing the façade's ability to improve air quality by filtering out dust and sequestering carbon, while it mitigates the urban heat-island effect and reduces noise pollution.
Already, a companion tower, just 76 metres tall, has been built on an adjacent property. With 18 floors, it only has about 350 trees, still an impressive number.
The idea of growing vertically rather than horizontally means we're starting to see more things like vertical farms, in which entire buildings are devoted to growing vegetables. More and more rooftop farms are being built atop buildings that can sustain the additional weight involved.
The concept of growing vertically is by now pretty well proven. What remains is to build them on a bigger scale and Bosco Verticale is an example of that.
The realities of a warming world mean that such experimental buildings are sorely needed, as we try to find a way out of the global mess we've created for ourselves.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.