Cities are characterised by the extent of impervious surfaces and the existence of buildings that occupy a large proportion of urban areas. This results in biodiversity loss as well as a lack of green spaces. An effective way to mitigate these negative impacts is constructing green roofs in new and existing public or private buildings as they provide habitat for insects, birds and microorganisms.
A green roof is a common roof (or a deck) of a building where vegetation is intentionally grown for wildlife. Green roofs are classified into the following categories according to the vegetation used:
- Extensive green roofs are ideal for growing drought-tolerant plants (e.g. sedum). These plants need very little maintenance and no irrigation, which means reduced maintenance costs, making them one of the most popular choices for this type of roof.
- Semi-extensive green roofs include plants like shrubs, perennials, herbs and grasses – in general, plants that need little irrigation and which do not depend on local weather conditions.
- Intensive green roofs usually have a fairly deep growing medium that can support trees. Examples of this type of roof are a rooftop garden or a patio.
Green roofs can be combined with photovoltaic or solar panels, thus contributing significantly to the energy efficiency of the photovoltaic panels while promoting biodiversity. The efficiency of the photovoltaic panels is negatively influenced by the high temperature, and the evapotranspiration generated by the plants on a green roof decreases the ambient temperature of the air around the photovoltaic panels.
Public administration bodies can develop policy schemes that support the deployment of green roofs, such as incorporating economic incentives, reducing bureaucracy, specific technical support to include green roofs in the construction or renovation of buildings, and subsidising technical projects.
Green roofs provide a series of environmental benefits in terms of storm water attenuation, water and energy savings, reduced urban heat island effect, air pollution reduction, carbon absorption and habitat provision.