Bosco Verticale Case Study: Balconies, Trees and Structure (Boeri Studio)

Bosco Verticale ("Vertical Forest") is a pair of residential towers in Milan's Porta Nuova district, designed by Boeri Studio (Stefano Boeri, Gianandrea Barreca and Giovanni La Varra) and finished in 2014. Each balcony is a cantilevered concrete slab with a planter on its edge, and the towers carry about 800 trees, 4,500 shrubs and 20,000 plants by the architects' count. This case study covers the brief, the plan and section, how the trees were engineered against wind, how they are watered and maintained, what critics said, and what designers in India should take from it.

If you are writing this up for a studio or thesis, our guide on how to document a building sets out the method a jury expects.

The brief and the client

The towers are part of Porta Nuova, a large redevelopment in central Milan; its Isola section replaced a light industrial site, a 2014 Construction Management report says. Arup lists the client as Hines Italia SGR, now COIMA SGR.

The programme was luxury housing: Dezeen counts 111 flats, and the architects' project page gives sizes from 60 to 400 sq m (about 650 to 4,300 sq ft). The unusual part was the second client: Boeri calls the building, as Dezeen quotes him, a "home for trees that also houses humans and birds", and the architects' page gives at least 2 trees, 8 shrubs and 40 plants per resident.

Site and context

The towers stand in the Isola district near Porta Garibaldi station, on Via de Castillia and Via Confalonieri, Il Post reported in 2015. Around them Porta Nuova added the UniCredit Tower, Piazza Gae Aulenti and new parks. Next to the towers is BAM, the Biblioteca degli Alberi Milano, a public park owned by the City of Milan and run by the Riccardo Catella Foundation.

Below ground, Arup reports that the towers sit above Metro line M2 with two railway tunnels nearby, which were monitored during construction; the towers have a vibration base-isolation system that, Arup says, also gives seismic protection. Draw these tunnels in a site analysis.

Bosco Verticale design concept

The idea is simple to state: put a forest on a tower instead of spreading it across land. The architects claim the planting equals about five hectares of flat parkland on roughly 1,000 sq m of footprint, and that housing the same people in detached houses with gardens would cover almost 75,000 sq m. These are the architects' own comparisons; other sources give smaller forest equivalents (see below).

In 2014 the studio called it "biological architecture" in its text for Dezeen. Read that against what follows: the planting needed wind tunnels, steel cages and central irrigation to work.

Bosco Verticale floor plans and zoning

The towers are plain rectangular blocks, Dezeen notes, clad in dark ceramic panels. The plan has three ideas a student can draw:

• Core on the edge. The architects' page says the stairs and lifts are "not placed in the center" but on the perimeter of the floor plate, to keep light and shared space in the flats.
• Balconies on all four faces. Terraces run round the towers, each just over 3 m deep and up to 14 m long, with the planter on the outer edge, according to the AIPH Green City case study.
• A shifting pattern. The balconies change position from floor to floor, so a tree is not capped by the slab directly above. The architects say this lets canopies grow up to three storeys high; AIPH says the terrace profile repeats every six floors.

Planting follows orientation: evergreens on the south-west and deciduous species on the north-east (architects), or olives and fruit trees to the south and leaf-shedding trees to the north to save winter daylight (AIPH). It was also specified floor by floor, as wind and humidity change with height.

We have not reproduced the architects' plans. Dezeen's 2014 article publishes the studio's section and concept sections; use those for the real drawings.

Bosco Verticale structural system: section and wind

The structure is a post-tensioned concrete frame. Arup's tests, Construction Management reported, showed that a "fairly conventional" post-tensioned frame would carry the planting, although the design had no corner columns, which made the balcony cantilevers longer. Arup and Dezeen give the balcony projection as 3.35 m (about 11 ft); the architects' page says three metres.

The surprise for most students is that weight was not the main problem. AIPH states that the trees produce most of their load through the wind force they pass to the structure, not their mass. Arup's project manager Luca Buzzoni told Construction Management that "there is very little available literature on the subject of trees growing on facades", and that in strong winds the trees could create "a significant bending moment on the slabs".

Two rounds of wind tests

Arup ran two wind tunnel campaigns. According to AIPH:

1. Scale model. A 1:100 model in the Politecnico di Milano wind tunnel mapped local wind effects around the facades and found the most exposed spots.
2. Full-size trees. Real trees were tested in the "Wall of Wind" at Florida International University's hurricane research centre at 67 m/s (150 mph), a speed AIPH calls extreme for Milan. These tests gave the aerodynamic coefficients of real trees and checked the forces on their restraints.

For each species, in each of three size profiles, the team looked at maximum canopy size, centre of gravity and how much air passes through the leaves. The load on each slab was set by the weight of the deepest planter, AIPH notes.

Holding the trees down

Arup describes two kinds of restraint. Medium and large trees have a safety cable against trunk failure. The largest trees in the most exposed positions also sit in a steel cage that holds the root ball and stops the tree overturning in a major storm. AIPH puts these at about 6 to 7% of the trees and describes the cage as an underground steel frame that ties the roots to the inner face of the planter.

The soil itself was a balance: dense enough to anchor roots, light enough not to overload the pre-stressed balconies (AIPH). The trees were grown in a Milan nursery first, partly to limit their growth and weight (Construction Management).

Bosco Verticale building materials and construction

The frame is reinforced and post-tensioned concrete, with dark ceramic cladding and planters built into the balcony edges. Construction ran from 2009 to 2014 by Il Post's account, and the planting went in floor by floor. AIPH gives the sequence:

• 2012: trees on the first three floors
• 2013: trees on the central floors
• 2014: trees on the top three floors, then all shrubs and groundcover

Species were studied for over two years with agronomists (architects) or three years with botanists and ethologists (AIPH), then pre-grown in nursery containers so their roots suited the planters. AIPH lists the criteria: canopy and foliage, roots that live in a container, and resistance to cold, wind, pollution, pests and drought. Arup says about 1,200 ladybirds were released for pest control.

Construction Management also noted a planter waterproofing system that still lets air reach the soil. For the basics, see our guide to waterproofing by climate in India.

Light, climate and services: the irrigation system and the flying gardeners

The greenery is run as one system, not 111 private gardens. The architects say it is shared by all residents like the lobby, and that owners cannot modify, remove or replace it. AIPH adds that the balcony planting areas are not sold with the flats and that one contractor follows a plan written by the landscape consultant.

• Water. The architects name groundwater plus recycled greywater. AIPH says groundwater from the heating and cooling system meets all irrigation needs, about 5,700 cubic metres a year, so no drinking water is used. Construction Management's 2014 report said treated rainwater.
• Delivery. Drip lines switched by humidity sensors (AIPH), a remotely managed system that monitors each pot (architects), and pumps run on rooftop solar power.
• Pruning. Arborists on ropes, the "Flying Gardeners", prune from outside: twice a year (architects) or once a year (AIPH). Gardeners also work from the balconies by agreement with residents.

Climate claims come from the architects and should be read as claims, not measurements we have seen. The project page says shading and evapotranspiration lower surface temperatures "by up to 30 degrees" and indoor temperatures "by 2 to 3°C", cutting air-conditioning demand, and cites a 2022 European Space Agency map in which the towers and BAM appear on a par with Parco Sempione in lowering land surface temperature. AIPH reports about 19,000 kg of CO2 absorbed a year and says the planting helped the building gain LEED Gold.

Reception, criticism and problems

Praise

The towers won the International Highrise Award in 2014 and CTBUH Best Tall Building Worldwide in 2015 (Arup also lists CTBUH Best Tall Building Europe 2014). In January 2025 Dezeen's Tom Ravenscroft named it the most significant building of 2014, quoting Ellis Woodman of the Architects' Journal, who called it a "pioneering project". Dezeen counts eight vertical forests since complete, eight under construction and 24 in design, including social housing in Eindhoven.

Criticism

• Cost and resources. Dezeen sums up the case against: soil and trees add weight, which needs more concrete and steel, and irrigation and other systems add maintenance costs. It cites Tim De Chant, who estimated in 2013 that the trees added about 5% to construction cost and argued the same money could plant 860 times more forest on the ground.
• Who benefits. These are luxury flats; a lesson about green housing has to ask who pays for upkeep.
• Claims versus data. Most environmental figures (CO2, temperature, forest equivalents) come from the architects or developers, and they differ between sources. Treat them as stated claims unless you find an independent measurement.

The numbers do not agree

Item	Architects' page	Other sources
Heights	110 m and 76 m	112 m and 80 m (Dezeen 2014, AIPH); 111 m and 76 m (Il Post)
Trees	800	900 (Arup; Construction Management); 730 in Dezeen's 2014 project text
Shrubs	4,500	5,000 (Arup; Dezeen 2014 and 2025)
Other plants	20,000	11,000 (Arup); 15,000 (AIPH; Dezeen 2025)
Forest equivalent	about 5 hectares	over 2 hectares (AIPH); about 30,000 sq m (Boeri quoted by Dezeen 2025); 7,000 sq m (Il Post)
Balcony depth	3 m	3.35 m (Arup; Dezeen); just over 3 m (AIPH)

Counts were made at different dates and plants are replaced, so quote the architects' figure and note the range.

What designers in India can take from it

These lessons are our reading. Towers sold with "a tree on every balcony" often copy the image; the lessons are in structure, soil, water and upkeep.

1. Design the slab for the tree, before the tree. In Milan the deepest planter set the slab load, and wind on the canopy, not weight, governed. Fix planter depth, soil and tree size at concept stage, and have the structural engineer treat each tree as a wind load with a restraint and anchor. On cyclone coasts and in pre-monsoon squalls this matters more, and soil is heaviest when saturated, through the monsoon.
2. Find the water before you draw the planters. Bosco Verticale uses about 5,700 cubic metres a year from groundwater and greywater, not the drinking supply. Where water runs short every summer, a planted facade needs its own source (treated water from the building's sewage treatment plant, or stored rainwater), a separate drip network and sensors. If you cannot name the source, do not draw the trees.
3. Make upkeep a building service, in writing. In Milan the greenery is common property, not sold with the flats, and owners cannot change it. In India, put this in the sale agreement and society bye-laws, budget the maintenance contract, design rope-access anchors on the roof, and agree in writing how gardeners reach balconies through private flats. Our guide to balcony design for flats covers the smaller-scale version.
4. Grow the plants before the building is ready. Start the nursery when the structure starts, choose species face by face for local heat and dry seasons rather than for the render, and size nursery containers to the planters.

If you are comparing ratings, our guide to IGBC, GRIHA and LEED in India explains what a green certificate does and does not measure.

Visiting Bosco Verticale

The towers are private homes, and the architects' page lists no public visits, so plan to see them from outside. The towers stand on Via de Castillia and Via Confalonieri near Porta Garibaldi station (Il Post), and the BAM park next to them is public. Look for the change of planting between faces and the balcony pattern shifting up the towers.

We use diagrams rather than photos in this post. Wikimedia Commons' freedom of panorama table lists Italy as having no freedom of panorama for buildings, and the architects are alive, so photos of the towers are not free to reuse.

Planning a terrace garden or planted facade? Find an architect on MOA.

FAQ

When was Bosco Verticale built?

Construction ran from 2009 to 2014, according to Il Post, and the architects list the project from 2007 to 2014. Trees went in from 2012 to 2014, floor by floor (AIPH).

Who designed Bosco Verticale?

Boeri Studio: Stefano Boeri, Gianandrea Barreca and Giovanni La Varra. Arup Italia was the structural engineer, and Studio Emanuela Borio and Laura Gatti were the botanical consultants. The client was Hines Italia, now COIMA SGR.

How many trees are on Bosco Verticale?

The architects give 800 trees, 4,500 shrubs and 20,000 plants of about 100 species. Arup and 2014 press reports give 900 trees; counts differ by source and date.

How tall is Bosco Verticale and how many floors does it have?

The architects give 110 m and 76 m; Dezeen and AIPH give 112 m and 80 m. Dezeen counts 27 and 19 storeys.

How are the trees watered and maintained?

A central, remotely managed drip system with humidity sensors, fed by groundwater and recycled greywater and pumped with solar power. One team maintains all the greenery, including the "Flying Gardeners" who prune the trees from ropes.

Sources

• Stefano Boeri Architetti: Vertical Forest, Milan (project page) (accessed 3 Nov 2026)
• Arup: Bosco Verticale (project page) (accessed 3 Nov 2026)
• AIPH Green City Case Study Collection: Bosco Verticale, Milan (accessed 3 Nov 2026)
• AIPH Green City Case Study Collection: Bosco Verticale, Milan, structural design (accessed 3 Nov 2026)
• AIPH Green City Case Study Collection: Bosco Verticale, Milan, selection of species and maintenance (accessed 3 Nov 2026)
• Dezeen: Boeri Studio's Bosco Verticale was the most significant building of 2014, Tom Ravenscroft, 20 Jan 2025 (accessed 3 Nov 2026)
• Dezeen: Stefano Boeri's "vertical forest" nears completion in Milan, Amy Frearson, 15 May 2014 (accessed 3 Nov 2026)
• Construction Management (CIOB): World's first "vertical forests" bloom in Milan, 6 Jun 2014 (accessed 3 Nov 2026)
• Il Post: Cos'è il "Bosco Verticale", per i non milanesi, 3 May 2015 (accessed 3 Nov 2026)
• BAM, Biblioteca degli Alberi Milano: home page (accessed 3 Nov 2026)
• Wikimedia Commons: Freedom of panorama (accessed 3 Nov 2026)