Above: Bosco Verticale, Credit: Chris Barbalis
The iconic Bosco Verticale – or Vertical Forest – completed in 2014 by Stefano Boeri Architects in Milan, Italy, is arguably one of the most recognisable buildings of the last decade. It is often used as inspirational imagery for the green building movement due to its pioneering incorporation of a vertical forest into 44 storeys across two towers.
With the release of WorldGBC’s report ‘Bringing Embodied Carbon Upfront’ which calls for urgent action to address embodied and upfront carbon, we are taking a closer look at this ground breaking project: exploring the benefits of its sustainability features and how it dealt with the challenge of considering whole lifecycle emissions, both operational and embodied; the trade-offs and co-benefits, and lessons for future projects.
Bosco Verticale is a fantastic example of a building that encapsulates the themes of 2019’s World Green Building Week ‘Building Life’ campaign, with its innovative ways of thinking to create its stunning green façade. The two residential towers are home to 2,280 m2 of trees and shrubs, presenting a soft green shell rather than typical urban concrete, brick or glass. With a ratio of two trees, eight shrubs and 40 bushes for each occupant, the building is championed as a “tower for trees, occupied by humans”.
This amount of green vegetation brings with it a number of benefits:
Pollution The greenery acts as a buffer between the city and the apartments by absorbing polluting particles, noise and sequestering carbon whilst also producing oxygen and improving air quality.
Energy efficiency The green façade results in reduced energy consumption due to increased insulation against outside temperatures and shading. This keeps the building cooler during summer – a reduction of nearly 3 degrees – and warmer during winter, reducing the need for active cooling and heating of internal spaces. One study placed the approximate yearly energy consumption reduction from this feature alone at 7.5%. Overall, the building was designed to achieve significantly lower energy consumption than a typical building in Milan.
Biodiversity Hosting around 100 different plant species, the façade promotes biodiversity by providing a vertical urban oasis for nesting birds and wildlife.
Urban heat island The cooling benefit of the façade contributes to reduced temperatures in the vicinity of the building. This further reduces the need for cooling capacity and the urban heat island effect often found in cities caused by the thermal mass of concrete and asphalt that absorbs the sun’s radiation, meaning city centres are typically several degrees hotter than the surrounding countryside.
Internal comfort Shading from the green façade results in natural temperature control, light management and improved air quality. During summer months, some residents rely purely on natural ventilation to achieve comfortable internal temperatures. In extreme external temperatures, an underfloor passive-cooling system, fed by groundwater, further helps prevent overheating.
Occupant satisfaction Residents of the building have expressed a high degree of satisfaction with comfort levels and thriving green areas.
All of this sets Bosco Verticale apart from traditional buildings, creating a striking focal point in a redevelopment of the Porta Nuova area, benefitting its residents as well as the wider urban area and city throughout its entire lifetime.
Above: Bosco Verticale under construction, Credit: Stefano Boeri Architects
So, does the enhanced operational performance of the building come at a cost for embodied emissions?
To support the extensive planters that house the ‘green façade’, the architects designed cantilevered concrete terraces to sustain the added weight of the vegetation. This meant that additional building materials were used in its construction and therefore added to the embodied emissions and natural resources required to achieve the benefits outlined above. The amount of concrete needed was reduced through measures such as composition of soil for the planters – a mixture of agricultural soil, organic matter and volcanic material – allowing reduction of weight in the balconies.
As reflected in its LEED Gold certification, a comprehensive analysis of the carbon emissions saving was carried out to estimate the benefit of implementing the plants. A holistic approach ensured the vegetation was a key element of the building, not simply for aesthetics, but as a technical feature to achieve environmental and human wellbeing benefits. Water usage for the irrigation system was a significant design consideration. The increased energy use required to pump the water is offset by a solar powered pump system and the extra water supply needed is taken from a groundwater source, therefore not negatively impacting any potable source.
The huge success of the project has led to export of the concept to different scales and countries all around the world, including the Netherlands, Switzerland, China and France. As awareness around lifecycle emissions has evolved, so has the exploration of alternative construction materials and other technical solutions to reduce the cantilevered structure and loads to maintain the operational benefits of the vertical forest, whilst reducing embodied carbon emissions.
For example: La Forêt Blanche in Paris is conceived entirely with a wooden structure to support 400 trees. This design option will reduce the whole life emissions impact of the building by using lower upfront carbon materials in the form of sustainably sourced timber.
Above: Bosco Verticale under construction, Credit: Stefano Boeri Architects
Refining the model
Bosco Verticale encompasses an innovative approach to addressing some of the most critical challenges facing urban development; utilising new practices and ways of thinking in working towards reducing carbon emissions. Its innovative design actively contributed to a greener, healthier and more climate resilient built environment for both its residents and Milan.
Introducing the green façade design helped realise multiple benefits that could arguably outweigh the added embodied emissions from the extra building materials required to achieve it. However, given this approach does rely on extra building materials, ultimately increasing the embodied emissions, future projects must further revolutionise the concept by balancing the benefits of enhanced greenery with innovative solutions to the resulting additional materials required. This will be crucial as the building and construction industry turns its efforts to significantly reducing the upfront emissions incurred from new buildings, and seeks to bring alternative low carbon solutions to the market.
Stefano Boeri Architects are continuing to research the scientific, technical, economic and social aspects of their designs, adapting to specific applications and refining the approach to design completely sustainable and smart “forest cities”.
Buildings such as Bosco Verticale can therefore act as a catalyst for the changes needed in order to meet our carbon emission reduction targets, in a way that inspires and challenges the industry to re-evaluate how buildings can serve society.
WorldGBC sets out its vision to achieving full decarbonisation of the buildings and construction sector across the entire lifecycle in order to achieve 2030 and 2050 goals in ‘Bringing Embodied Carbon Upfront’.
Victoria Kate Burrows is the Director of Advancing Net Zero at the World Green Building Council. With thanks to the Green Building Council of Italia, Stefano Boeri Architects and COIMA for their contribution to this piece.
To find out more about Bosco Verticale and urban forestry, visit https://www.stefanoboeriarchitetti.net/en/
 Giacomello & Valagussa, 2015, p.58