Implement green walls or roofs to lower indoor temperature and provide insulation

The project focused on implementing multilayer blue-green roofs in four Italian cities—Cagliari, Palermo, Perugia, and Viterbo—as part of a broader European initiative to address climate change impacts in urban environments (1,3). Spearheaded by a collaboration between multiple Italian universities and the Dutch company Metropolder, the project began in 2019 (1,3). The primary goal is to enhance urban resilience by integrating green infrastructure capable of mitigating climate-related urban hazards such as flooding and heat waves, which are increasingly severe due to climate change and urbanisation (2,3).
The multilayer blue-green roofs combine the ecological benefits of traditional green roofs with an added water storage layer, allowing them to retain rainfall and manage runoff effectively (2,3). This dual function helps reduce pluvial flooding and the urban heat island effect, while also improving thermal insulation in buildings (2,3). Each installation was planted with low-maintenance, climate-adapted vegetation, and equipped with sensors to monitor ecohydrological and thermal performance over several years (1,3). These roofs are capable of retaining up to 100% of rainfall from significant events, thereby easing the burden on urban drainage systems and contributing to climate adaptation in Mediterranean cities (2,4).

The Torre Sevilla is a commercial building complex with extensive green roofs. The green roofs cover 11000 or 12000 m2 (different sources report different numbers) and aim to contribute to thermal isolation and energy efficiency of the building, improve air quality and provide an urban green space for relaxation and recreation [Ref. 1-3]. The green roofs include a mosaic of different vegetation types and about 60 mostly native plant species. There is a rainwater recovery system that allows the gardens to be irrigated in a sustainable way [Ref. 1-3, 6]. The building finished construction in 2017 and the gardens were initially not available to the public. In 2023, the owner applied for a permit to host events in the gardens, which will allow the public to visit on occasion [Ref. 1, 3-5].

The Institute of Physics at Humboldt University of Berlin is an outstanding example of ecological urban development and a global pilot project integrating rainwater management with building cooling through greening. A key feature is the cooling system, which relies on air circulation processes supported by green roofs, facades, and an artificial wetland/pond incorporated into the building's exterior and courtyard.
Rainwater is collected in cisterns and used to irrigate the green façade, enabling evaporative cooling in air conditioning systems. Excess water is either evaporated in the inner courtyard through a pond or allowed to seep away. (Ref. 1; Ref. 4) The greening of the façade is directly linked to energy optimization. During summer, the green façade provides solar shading against extreme heat, while in winter, sunlight passes unobstructed through the glass façade. Additionally, evaporative cooling improves the microclimate inside the building and its surroundings. (Ref. 3)
Berlin, as a densely built city, faces challenges like urban heat and high energy demands for cooling. This project offers a research-driven solution. Monitoring measures water usage for various plants, evaluates evaporative cooling effects, and assesses impacts on the building's energy balance and overall economic and ecological performance. The findings aim to create a foundation for the long-term implementation of innovative, cost-effective technologies. This process is conducted by multiple regional universities. (Ref. 1)
The project was initiated and financed by the state of Berlin and implemented after the building's construction. (Ref. 4; Ref. 5) It serves as a benchmark for sustainable urban development and a research model for similar initiatives worldwide.

The Alexandria Governorate is especially susceptible to the impacts of climate change, a vulnerability exacerbated by its dense coastal communities and rapidly growing population (2). Both demographic shifts and urban development intensify how climate phenomena affect the people and infrastructure of Alexandria (1). Buildings, roads, and other concrete structures absorb and release solar heat, significantly contributing to the urban heat island effect, which is causing temperatures in the city to rise faster than in less developed areas (1). Despite Alexandria’s growing need for cooling green spaces, they currently make up only 0.25 percent of the total area within the Governorate, highlighting an urgent need for environmental interventions (3-6).
In response, Ahmed Gaber, chairman of the Alexandria Water Company, initiated a public awareness campaign in 2023 focused on the numerous benefits of planting green roofs (3-6). Green roofs serve multiple purposes: they extend the longevity of buildings, lower energy consumption, improve air quality, increase biodiversity, manage rainwater runoff, and mitigate the urban heat island effect (3). Furthermore, Gaber has emphasized the visual appeal of eco-friendly roofs, noting that green roofs offer an aesthetically pleasing option that enhances the urban landscape while serving critical environmental functions (4).
This initiative by the Alexandria Water Company marks a pioneering step among governmental organizations in the region, as they lead efforts to address climate and environmental challenges actively. The company has begun planting green roofs across its facilities, including the new Al-Mashishya water station, where green spaces atop buildings are set to bring lasting environmental benefits to Alexandria. Through these efforts, the Alexandria Water Company is working to set an example for public and private sectors alike (3-6).

Located in the Lima district of San Isidro - the heart of commercial activity in Peru - the Real Dos Tower is a prime office building in the Centro Empresarial Real de San Isidro. It was inaugurated in 2018, and it is distributed over 23 levels (14 floors and 9 basements) and enjoys a landscaped green roof (1162 m2) at the crown of the building and numerous outdoor vertical gardens at full height (2365 m2) on the three main fronts (1, 4). This project was a finalist in the 2018 Mipim Awards, considered the ‘Oscars’ of world architecture, and stood out for its architecture and design, due to its attributes of innovation and sustainability (2).
This building has managed to create harmony between design and efficient use of resources. It is characterised by a glass façade with colourful movable shutters and symbolic Peruvian designs (2, 3, 6). It has green walls on the three main fronts, four daylight fronts and a roof garden (2). The architect, Jean Nouvel, worked together with ARVE Peru on the overall landscape plans for the Real Dos tower (1, 3).
This is part of the façade remodelling project of the Camino Real Towers in the Real Business Centre, led by the real estate company Grupo Centenario (1, 2, 3, 4, 5, 6). This overarching Project has sought to develop 4,475 m2 of vertical gardens and roof gardens, which have a technified irrigation system to generate efficiencies in water use, meeting the plants' water requirements in the different seasons of the year. Their implementation helps to filter CO2 and renew the O2 in the office complex.
The ARVE group describes these actions as conducive to creating thermal barriers and sound insulation, a better environment for rest, work and entertainment and increasing property value (7)

Biotope City Wienerberg is located in the southern part of Vienna on a 5.4-hectare site that once housed a Coca-Cola factory. It lies at the edge of the Wienerberg recreational area, surrounded by business parks and tower blocks to the west and predominantly detached houses to the east (Ref. 1).
The project embodies the concept of an "urban biotope" (Ref. 2), grounded in the principle that nature's mechanisms of self-regeneration are essential for mitigating the challenges of urban living and climate change. By integrating urban and natural spaces, Biotope City fosters both human-nature connections and social interactions through activities like community gardening. The project’s centerpiece is its extensive green infrastructure, including trees and green roofs, which serve to cool the microclimate, purify the air, enhance water retention, and create carbon sinks while providing habitats for local wildlife. These green spaces aim to improve physical health through cooling effects on hot days and support mental well-being with their calming influence (Ref. 1; Ref. 2).
Biotope City encompasses:
Around 980 flats, including 400 subsidized flats and 200 SMART flats
A school, a kindergarten, and 2,000 square meters of children's and youth playgrounds
600 square meters of community gardens and 3,850 square meters of ground-floor gardens
250 trees, 8,900 square meters of meadows, and 13,600 square meters of green roofs
2,200 square meters of façade greening
The inner courtyards and roof areas are designed for gardening, while façades are greened, and balconies are equipped with integrated plant troughs. Even the spaces between buildings are climate-effective, featuring unsealed catchment and seepage areas to manage water sustainably (Ref. 1).
The project’s implementation took 18 years and involved collaboration among various stakeholders. The concept was initiated by the Biotope City Foundation and funded by eight different investors (Ref. 2).

The Tirana Vertical Forest is part of the city's 2030 Master Plan and aims to enhance urban biodiversity and create green spaces through innovative urban design (Ref. 1,2). The project was developed by Stefano Boeri Architetti, the same studio that has designed similar, well-known structures in cities like Milan, Utrecht and Nanjing (Ref. 6). The completion of the 21-floor building is expected in late 2024 and will feature 105 apartments and a commercial ground floor as well as 145 trees and over 3,200 shrubs and bushes which are integrated into the balconies and façade of the project (Ref. 1,2,3). Various Mediterranean plants have been incorporated, including colourful, scented and aromatic types, which harmonize with the local ecosystem. To maximise the space available for green features, a dynamic structure with alternating balconies and full-height windows has been built (Ref. 1,2). Ultimately, the project anticipates improving air quality, reducing noise, and providing insulation. The greenery is expected to capture fine particulate matter and up to 8 tones of Co2 per year while also creating a healthier microclimate for those inside the building (Ref. 1,6).

The city of Thessaloniki is tackling the energy crisis and climate change risks by prioritizing the installation of green roofs and green walls on school and municipal buildings as part of its resilience strategy, Thessaloniki 2030 (Ref 1, 2). One key project under this strategy has been implemented at EPAL Stavroupoli, one of the largest school complexes in the metropolitan area. The school, with a total built area of 11,918 sq.m and roof surfaces covering 6,042 sq.m, now includes a green roof covering 3,087 sq.m with 25,000 ground-cover plants, along with a vertical garden on three walls at the entrance, covering 100 sq.m and featuring 3,098 plants (ibid.).
The project is expected to yield multiple environmental benefits, such as reduced energy losses, improved thermal performance, enhanced sound insulation, better rainwater management, decreased runoff, and retention of harmful particles, all of which contribute to upgrading the area's green infrastructure (Ref 1). This initiative also strengthens the green fabric of western Thessaloniki and improves the local microclimate while addressing rainwater management issues (Ref 3, 4).

The Museum of Art, Architecture and Technology (MAAT) features a 2,920-square-meter green roof (Ref 8). Located on the riverfront of the historic Belém area in Lisbon, MAAT, inaugurated in 2017, comprises the repurposing of a thermoelectric power station built in 1908 (MAAT Central), a contemporary museum building (MAAT Gallery), connected by a garden that stretches along the Tagus River (MAAT Garden) (Ref. 3).
Blending structure into landscape, MAAT was designed to allow visitors to walk over and under its building, in which "the roof becomes an outdoor room, a physical and conceptual reconnection of the river to the city’s heart – where visitors can turn away from the river and enjoy the vista of the cityscape, and at night, watch a film with Lisbon as a backdrop sitting on the bank of steps" (Ref. 1). This roof, part of AL_A’s (design company) architectural vision, offers panoramic views of Lisbon and the Tagus River (Ref 1), and complementing the green roof is a 225-meter-long garden designed by Vladimir Djurovic, which connects MAAT to the Central Tejo power station. This garden features diverse vegetation (Ref 2, Ref 3, Ref 4).

The Köprüköy Mosque in Adana, commonly named "green mosque", is one of a kind in Türkiye (Ref. 2,5). Its building and minaret are almost entirely covered by poison ivy and appear in vivid green colour from afar. Founded in 1929, it had to be remodelled in the early 60s as it couldn't sufficiently accommodate worshippers in the growing district. The mosque was then entirely built and rebuilt by the community, with its maintenance overseen by the mosque's protection association (Ref. 4). In the 70s, the ivy was planted and has since helped to protect the building from environmental stressors and keep visitors inside the garden and mosque cool during the summer heat (Ref. 4,5,6) Furthermore, the mosque’s well-maintained garden, home to around 280 species, is adored by local, national, and international visitors and tourists, as well as the media (Ref. 1,3,7). Frequent maintenance and rotation of the garden's flowers keep its appearance and function intact, one of which is the profound impact on visitors’ well-being, with many praising the unique atmosphere of the mosque that evokes peace, comfort, and spirituality (Ref. 1,3,4).
During COVID-19, the mosque could only host worshippers during praying hours, after which it quickly continued to bring people back together to garden, rest and socialize throughout the day (Ref. 1).