Air pollution is the single biggest environmental health risk the world faces today, with outdoor pollution linked to 3 million deaths every year. It’s no wonder designers and engineers are racing to come up with all kinds of air-purifying solutions, from smog-sucking towers and bikes to moss-covered walls. But one of the most impressive ideas so far can be found in Milan, Italy — the design capital of the world and one of the most polluted cities in Europe.
The brainchild of Italian architect Stefano Boeri, Bosco Verticale (meaning “Vertical Forest”) is the concept of residential high-rises packed with greenery, which can help cities build for density while improving air quality. The first “vertical forests” were realized in 2014 in the Porta Nuova Isola area of Milan, where two towers — with over 100 apartments between them — together host nearly 500 medium and large trees, 300 small trees, 5,000 shrubs, and 11,000 plants.
TREES ARE THE CHEAPEST AND MOST EFFICIENT WAY TO ABSORB CARBON DIOXIDE
The science is simple: trees are the cheapest and most efficient way to absorb carbon dioxide. The 20,000 trees and plants across this pair of towers can transform approximately 44,000 pounds of carbon dioxide into oxygen each year. Trees, a perennial gift from nature, can also keep temperatures cool indoors and filter out fine dust particles and noise pollution from traffic below.
The logistics of making it all happen, however, were a lot more complex. The process began with bringing together experts in structural engineering and botany to answer all the essential questions. For example: how can a tree resist extremely windy conditions at 400 feet in the air? Engineers then had to devise a way to secure the roots of the plants in their containers while making sure they could be properly watered and fertilized.
Laura Gatti, an architectural botanist on the project, also conducted a three-year study about local plants to determine which species would survive the conditions of the towers. And, of course, even after they’ve been planted, the trees need regular maintenance. That’s done by a team of aerial arborists, who, like the familiar skyscraper window washers, make their way up and down the buildings, inspecting and grooming the vegetation.
AERIAL ARBORISTS MAKE THEIR WAY UP AND DOWN THE BUILDINGS
As cities continue to grapple with air pollution, housing shortages, and climate change, these vertical forests could very well be the residential typology we need for the future. And you can certainly expect to see more of them.
“I really hope many other architects, many other urban planners, many politicians will be in condition to replicate and improve what we have done,” Boeri tells us.
His firm itself is currently working on new vertical forests across Europe and in China, including an ambitious “Forest City” in the city of Nanjing. Meanwhile, similar projects are being proposed and developed all the time, from a spiraling high-rise in Taiwan that is expected to contain 23,000 trees when complete to new tree-tower variations in Toronto and Bogota, to name a few.