When architecture meets trees . . .

As urban tree-houses go, Verde 25 is more than a little out of the ordinary. In fact, this residential building in the Italian city of Turin, which was designed by the architect Luciano Pia and completed in 2012, is not so much a tree house as a house of trees.

More than 60 apartments are housed within its five-storey walls, each one of them home to at least one, sometimes two, irregularly shaped wide terraces or balconies planted with an extraordinary collection of trees, shrubs, trailing plants and climbers. These grow in giant pots and vases, designed as an integral part of the architecture, so that their foliage seems to erupt or cascade out of the façade, giving the building the appearance of an urban jungle or some strange tropical temple.

It is an impression underscored by the fact that the walls are clad in wooden shingles while the top-floor apartments have private green roofs. Even the externally visible, load bearing steel girders that support this extraordinary structure are clad in sections of Corten steel designed to look like the twisting boughs of a large tree, so that the building seems to be growing out of the ground. The fact that the planting is a mix of evergreen and deciduous further adds to its charm, striking a strong note of seasonality often missing from other “green” buildings.

Importantly, Verde 25 isn’t just green in name and appearance, but also in terms of its health-enhancing and eco-build credentials. Not only does the lush and abundant planting help to regulate interior temperatures and cushion residents from the noise of a busy city, it also does a fine job of filtering pollutants, producing up to 150,000 litres of oxygen an hour while absorbing carbon dioxide at an impressive rate of up to 200,000 litres an hour through the processes of photosynthesis and respiration.

As for the plants themselves, they are watered via a rain-harvesting system that collects rainwater from the surface of the building. There is even a small allotment area contained within the building’s tree-filled inner courtyard where its residents are experimenting with growing their own food.

This cutting-edge green building has garnered many plaudits. The influential international architecture magazine, Architectural Review, recently described it as a design that evokes a child-like sense of wonder, yet which "despite its playfulness, shows a rigour that is still hard to come by when architecture and plants meet".