Cities Skylines How To Clean Up Pollution

Walking down a certain city block in Turin, Italy, you won't see any trees lining the sidewalk. Instead, they're suspended in the air: A new five-story apartment building called 25 Verde is covered with 150 trees, each surrounded by custom-shaped terraces. It's the apartment building version of a treehouse.

"If the trees are integrated in the building, they are closer to the people who live there, and so there is more integration between man and nature," says architect Luciano Pia. The trees help filter pollution from traffic on busy nearby streets, absorbing around 200,000 liters of CO2 emissions every hour in one of Europe's most polluted cities. As the seasons change, the leaves help shade the apartments or bring in warmth, creating a microclimate for the building.

While tree-covered buildings keep showing up in architectural renderings (you could argue that "put a tree on it" is the new "put a bird on it"), the new building in Turin might be proof of how an urban treehouse can actually work.

Unlike many conceptual designs, this isn't a skyscraper, and that means the trees have a better chance at survival. "In tall buildings, the outdoor climate is considerably different from that on the lower floors to the ground level," says Pia. "At the top there is always wind. I don't think planting trees on skyscrapers is a way to go."

In Pia's design, each of the trees has room to grow. "You have to plant them in pots sufficiently large to ensure the nutrition and root growth," he says. The building also surrounds a courtyard with another 50 trees, and has a green roof. Basically, when residents look outside, they'll see a mini-forest instead of concrete.

"The building has been conceived as a living forest," Pia says.