25 Verde in Turin: 63 apartments, 150 trees, and the structure beneath

25 Verde is in Turin, was completed in 2012, and is almost always photographed in summer from the street corner, so that the trees fill the frame and the building disappears behind them. That is a fair representation of the intent and a poor representation of the engineering.

Luciano Pia’s design contains 63 apartments, ranging from roughly 50 to 140 square metres. No two are the same. Each has wide terraces of irregular shape wrapping around it, and distributed across five storeys of those terraces, balconies and roof gardens are more than 150 trees.

Why the irregularity is functional

A conventional approach to a green building puts vegetation on one plane: a planted facade, or a roof garden, or both. That is easier to build and easier to maintain, and it produces a green surface rather than a green volume.

The irregular terraces at 25 Verde do something different. By varying the depth and orientation of the outdoor space at every level, the design creates a large number of separate planting positions at different heights and exposures. The result reads as a mass of vegetation with the building inside it rather than as a building with vegetation attached.

The steel columns visible rising through the planting are part of that logic. They give the terraces the structural depth they need without a continuous concrete plane at every floor, which is what would otherwise be required to carry that load and what would have closed the section up visually.

The loads nobody photographs

Planting at this scale changes the structural brief in three ways.

Permanent dead load. Soil is heavy, and saturated soil is heavier. A planted terrace carries that weight for the life of the building, unlike a balcony designed for occasional occupancy.

Variable wind load. A mature tree is a sail. Wind load on a planted terrace changes between summer and winter as the canopy fills and empties, and it acts on the structure at height, where leverage is greatest.

Waterproofing under root attack. Roots find and exploit any defect in a membrane. A planted terrace needs a root barrier that will outlast the trees, in a position where replacing it means removing them.

None of this is exotic; it is standard practice for intensive green roofs. What is unusual is doing it on five storeys of irregular terraces rather than on one flat plane, which multiplies the number of details that have to work and the number of places where they can fail.

The maintenance question

Buildings of this kind are judged, unfairly, on photographs taken shortly after completion. The meaningful test arrives later.

Trees on a terrace are in containers, however large. They need irrigation, feeding, pruning to a size the structure was designed for, and replacement when they fail. That is a permanent operating cost carried by the residents, and the difference between a building like this at ten years old and the same building neglected for three is total.

25 Verde has been discussed as a climate-adaptation case study, which is the right frame for assessing it: shading and evaporative cooling from dense vegetation are real effects with measurable magnitudes, and those magnitudes depend on whether the planting is actually maintained.

Why it keeps getting called a treehouse

The nickname is understandable and slightly misleading. A treehouse is a structure supported by a tree. Here the relationship runs the other way: a steel and concrete frame supports 150 trees, at considerable expense, in order to look as though the trees came first.

That inversion is the whole design, and it is what separates the project from a facade planted for the rendering.

Species selection is the hidden specification

The part of a project like this that never appears in the published photographs is the plant list, and it is where the design either survives or slowly fails.

A tree on a fifth-floor terrace faces conditions its species did not evolve for: a restricted root volume, exposure on several sides, higher wind speeds than at ground level, reflected heat from adjacent surfaces, and an irrigation supply that is somebody’s responsibility rather than the weather’s. Species that thrive in a Turin park may be unsuitable twenty metres up.

The selection therefore has to trade several things against each other. Mature size has to be small enough that the structure’s design load is never exceeded, which usually means accepting a smaller tree than the visualisation implies, or committing to pruning in perpetuity. Deciduous species reduce winter wind load and let light into the apartments in the season when it is wanted, at the cost of looking bare in the months when the building is photographed least flatteringly.

None of that is visible from the street, which is why buildings of this type are best judged a decade after completion rather than at the opening.