Green Roof

A green roof, also known as a living roof or vegetated roof, is a roof system that is partially or completely covered with vegetation planted over a specialised growing medium, installed above a waterproofing membrane. In addition to plants and substrate, a complete green roof system typically incorporates several engineered layers, including a root barrier, drainage layer, filter fabric, and, where necessary, irrigation systems. Green roofs are a recognised form of green infrastructure and are increasingly adopted in urban environments to address environmental, social, and economic challenges associated with dense development.
Green roofs should be distinguished from simple rooftop container gardens, where plants are grown in pots, as these generally lack integrated structural and drainage layers and are not usually classified as true green roofs. Rooftop ponds used for greywater treatment are sometimes considered a related or specialised form of green roof technology.

Structure and components

A green roof consists of multiple functional layers designed to protect the building while supporting plant growth. These layers generally include:

• Roof deck and waterproofing membrane, which protect the building structure from moisture intrusion
• Root barrier, preventing plant roots from penetrating the waterproofing
• Drainage layer, allowing excess water to flow away from the roof
• Filter fabric, preventing fine particles from clogging the drainage system
• Growing medium (substrate), providing physical support, nutrients, and water retention
• Vegetation layer, comprising selected plant species suited to roof conditions

The precise configuration depends on the roof type, climate, structural load capacity, and intended use of the building.

Types of green roofs

Green roofs are commonly classified into two main categories based on substrate depth, weight, and maintenance requirements.
Extensive green roofs are shallow systems, typically with substrate depths ranging from approximately 5 to 15 centimetres. They are relatively lightweight, require minimal maintenance, and usually support hardy, drought-tolerant vegetation such as sedums, mosses, and grasses. Extensive roofs are the most widely used type, particularly for large commercial and industrial buildings.
Intensive green roofs have deeper substrates, often exceeding 20 centimetres, and can support a wider variety of plants, including shrubs, lawns, and even small trees. These roofs are heavier, more complex, and require regular irrigation and maintenance, making them closer in function to rooftop gardens or parks.
Hybrid or semi-intensive systems also exist, combining characteristics of both categories to balance biodiversity, weight, and maintenance needs.

Applications in the built environment

Green roofs can be installed on new buildings or incorporated into retrofit and redevelopment projects, provided structural conditions allow. They are suitable for a wide range of buildings, from small residential garages to large industrial, commercial, and municipal structures. Many cities encourage or mandate their use through planning regulations, incentives, or stormwater management requirements.
Beyond conventional flat roofs, green roof systems have been adapted for sloped roofs and complex architectural forms, broadening their applicability across diverse building types.

Thermal regulation and energy efficiency

One of the most significant benefits of green roofs is their contribution to thermal reduction and energy conservation. Vegetation and substrate add thermal mass and insulation, reducing heat transfer through the roof. During warm periods, plants cool the surrounding air through evapotranspiration, lowering roof surface temperatures and reducing cooling demands.
Research has shown that green roofs can reduce building cooling loads by up to 50–90 percent under certain conditions, particularly when combined with passive solar design strategies. They also help reduce heat loss during winter by providing additional insulation.
At the urban scale, clusters of green roofs contribute to mitigating the urban heat island effect, a phenomenon in which cities experience higher temperatures than surrounding rural areas due to heat-absorbing building materials. Studies have demonstrated that green roofs can lower rooftop surface temperatures by an average of around 30 °C during summer months, offering substantial climate regulation benefits.

Stormwater management

Green roofs play a vital role in stormwater runoff reduction, making them an important component of low-impact development strategies in both Europe and North America. Rainwater is retained within the substrate and vegetation, where it is either stored temporarily or returned to the atmosphere through evaporation and plant transpiration.
Empirical studies have found that green roofs can retain up to 75 percent of rainfall, significantly reducing both the volume and speed of runoff entering urban drainage systems. This delayed release helps prevent flooding, reduces pressure on combined sewer systems, and lowers the risk of untreated sewage discharges into natural waterways during heavy rainfall events.
In addition, green roof substrates can retain and filter pollutants such as nitrogen, phosphorus, and heavy metals, improving the quality of runoff water.

Ecological and biodiversity benefits

Green roofs create new habitats within urban environments, contributing to urban biodiversity and ecological connectivity. Even on high-rise buildings, green roofs have been shown to support insects, birds, bees, butterflies, and other wildlife. They function as “stepping stones” between fragmented green spaces, aiding species movement across developed landscapes.
Research has identified diverse pollinator communities on green roofs, with particular representation of small, ground-nesting bee species. Studies conducted in North American cities have also demonstrated increased bat activity above green roofs, linked to higher insect abundance.
By integrating vegetation into densely built areas, green roofs help counter habitat loss and support ecosystem services such as pollination and pest control.

Air quality and human well-being

Vegetated roofs contribute to air quality improvement by filtering airborne particulates and absorbing carbon dioxide. Vegetation can also trap dust and reduce the concentration of pollutants that exacerbate respiratory conditions such as asthma.
From a social perspective, green roofs provide visual and psychological benefits. Exposure to greenery has been linked to reduced stress, improved mental well-being, and enhanced aesthetic value in urban settings. When accessible, intensive green roofs can also offer recreational and social spaces.

Carbon sequestration and climate mitigation

Green roofs contribute to carbon sequestration by storing carbon in plant biomass and soil substrates. Carbon absorbed during photosynthesis is retained in vegetation, root systems, and organic matter within the growing medium. Studies have reported measurable amounts of carbon stored both above and below ground, with sequestration rates varying according to plant species, substrate depth, and management practices.
Deeper substrates and diverse vegetation communities generally enhance carbon storage potential. In addition to direct sequestration, green roofs indirectly reduce carbon dioxide emissions by lowering building energy demand, thereby decreasing reliance on fossil fuel–based heating and cooling systems.
Given that buildings account for a substantial proportion of global carbon emissions, green roofs represent a complementary strategy within broader climate mitigation efforts.

Terminology and related concepts

Green roofs are also referred to by various alternative terms, including ecoroofs, living roofs, vegetated roofs, and oikosteges. In some contexts, the term “green roof” is used more broadly to describe roofs incorporating environmentally beneficial technologies such as reflective cool roofs or solar energy systems, although these do not involve vegetation.
Despite differences in terminology, vegetated green roofs are consistently recognised as multifunctional systems combining architectural, ecological, and infrastructural functions.