A green roof or living roof is a roofing system that incorporates vegetation, such as plants, grasses or even small trees, to cover part or all of a building’s roof surface. This type of roofing system offers numerous environmental and aesthetic benefits. It helps improve energy efficiency, reduce the urban heat island effect, manage and reduce stormwater runoff, improve air quality, provide insulation and create green spaces in urban environments. The plants and soil on a green roof provide natural insulation and absorb rainwater, which can reduce the load on stormwater management systems and help mitigate the effects of heavy rainfall.

A green roof indicates that incorporating nature-based solutions can contribute to the improvement of the urban environment and to a more attractive city. In addition, it reduces the negative effects of urbanization and climate change. At a local level, green roofs help to protect biodiversity and create a point that favors its development, while at the same time helping to promote the idea of the green city according to European standards.

Green roofs are a perfect example of nature-based solutions that provide ecosystem services and functions at varying scales. When integrated and replicated in the city, along with other nature-based solutions, as decentralized systems, the impact of their services and functions is enhanced. The opportunity to spark a transformation in cities is to consider them as a living organism.

Therefore, in order to have an integrated approach and a holistic view, the interactions between green and gray infrastructures should be considered. Green solutions are spread in, on and around buildings, at different scales (building, neighborhood and city). Furthermore, the urban landscape will fit the future vision when it combines biology and technology for human well-being and safety and considers areas as a continuum of flows. Buildings with this approach are no longer static elements of the city, but instead are dynamic and interactive elements with their environment and inhabitants.
Although green roofs have a long history, only recently have they been considered artificial ecosystems, designed based on scientific knowledge and on technical guidelines and standards. They are by definition systems installed on an artificial structure and include vegetation planted on a substrate followed by different layers, depending on the type of green roof.

Integrating nature-based solutions into the built environment
(Source: Calheiros C.S.C., Stefanakis, A.I, 2021. Green Roofs Towards Circular and Resilient Cities. Circ.Econ.Sust. 1, 395–411)

Green roofs are nature-based solutions, also known as planted roofs, ecological roofs or living roofs, that include a system with different layers. These systems include flows of energy, water, nutrients and very specific organisms that are not usually quantified and properly valued. They can be classified, according to standard guidelines, as intensive, semi-intensive and extensive, depending on their structural composition and maintenance specifications.

Typical green roof cross-section layers and classification (not to scale)
(Source: Calheiros C.S.C., Stefanakis, A.I, 2021. Green Roofs Towards Circular and Resilient Cities. Circ.Econ.Sust. 1, 395–411)

Green roofs improve the energy efficiency of building by providing better insulation on the building structure, thus reducing the energy demand for cooling or heating. They also decrease the concentration of air pollutants, sequester carbon, reduce urban noise, enhance urban biodiversity and provide aesthetic and health benefits. Green roofs are a nature-based solution that contributes to climate change mitigation and helps achieve the goals of the European Green Deal. As such, this project aligns its vision and scope with the objectives of the European Climate Pact.