In a city choked with pollution and starved for green space, a five-year quest to build a forest in the sky is almost complete.
Considered to be the world’s first “vertical forest,” Milan’s Bosco Verticale twin-tower condominium project is an experiment in urban architecture that aims to filter some of the dirtiest air in Europe and provide its residents with a vision of the future.
Located in the city’s Porta Nuova district, the 260- and 367-foot-tall buildings feature 900 trees planted in balcony planters designed for the plants’ heft. Additionally, the buildings will hold more than 19,000 shrubs, perennial flowers, and ground cover plants positioned around the buildings’ perimeters.
According to building designer and Italian architect Stefano Boeri, the hectare of greenery will absorb some of Milan’s small-particle pollution, produce oxygen, and create a microclimate around the plants, which will be irrigated with the building’s gray water.
“The first reaction was that I was completely crazy,” Boeri told the Discovery Channel. “The idea to have 20,000 plants in two towers was considered a madness.”
Selecting the kind of trees hardy enough to withstand the building’s cramped quarters was essential, Bosco Verticale botanical consultant Laura Gatti told the Discovery Channel. She considered the trees’ wood type, size, rooting, and form of branching. The trees were transplanted to the building’s planters via a crane, and workers wrapped cables around the base of their trunks to prevent them from toppling over before they took root.
Even developing the planters was a process. Boeri needed a design that would allow for the trees’ growth and flexibility. To make sure they would survive strong winds, his team tested the planters in wind tunnels.
While the project has been noted for its novelty, it has also been criticized as a false facade of urban sustainability—and for inadequate design.
“In reality, trees on skyscrapers will likely be anything but sustainable,” wrote Boston-based science journalist Tim De Chant on his blog. “A skyscraper that’s built to support trees will require more concrete, more steel, more of anything structural.”
Lloyd Alter, managing editor of Treehugger and a sustainable building architect, is also a skeptic. Last year, he told ArchDaly that while he believes the trees will have a “perceptible” improvement on air quality, the concrete planters will inhibit the trees’ growth because of their limited access to oxygen. Safety concerns such as tree limbs breaking and falling to the ground also need to be taken into consideration.
Still, Boeri is optimistic that his project will help remake his native city in a fresh light. “I really hope that these two buildings can become the landmark of the new Milan,” he said.