Both extensive and intensive green roofs offer many benefits for the environment, property owners and local communities. They improve air quality, producing more oxygen and absorbing carbon dioxide and other airborne pollutants, which translates into an overall positive effect on public health and wellbeing. They also help biodiversity by providing a natural habitat for plants, birds and beneficial insects such as pollinators (bumblebees, bees, butterflies, etc).
Green roofs also have an important insulating effect, which means less energy is required to heat or cool the building. In the summer, they regulate heat, keeping the interior of the building cooler. In cold weather, they ensure that the building loses less heat. In addition to this thermal insulation effect, green roof systems also absorb sound and contribute towards the overall reduction of noise pollution caused by the urban environment.
A green roof installation also helps mitigate the ‘urban heat island effect’, a condition in which cities absorb and trap heat at higher rates than rural areas. This is achieved by returning moisture to the environment through evapotranspiration. In addition, the surface of the vegetation reflects more sunlight than standard roof formations, which further contributes to the cooling effect.
Improved stormwater management is another key feature of green roofing systems in urban landscapes. In cases of excessive rainfall, the plants and the substrates on green roofs absorb a certain amount of rainwater and then release it back slowly to the drainage system and into the atmosphere through evaporation. This relieves the pressure on sewage systems, minimising the risk of flooding and erosion. The vegetation on green roofs also purifies rainwater. Plants act as a filter, contributing to a lower concentration of nitrates, phosphorus and toxins in the runoff rainwater.
Green roofs are actually also beneficial to the roofing system itself, significantly extending the lifespan of the waterproofing membrane underneath. The vegetation layer acts as a natural barrier, providing extra protection from weather conditions such as hail, wind, extreme temperature fluctuations, UV rays, and so on.
Last but not least, specifying a green roof system is a choice that improves the overall score of the building in sustainability rating systems such as BREEAM (Building Research Establishment Environmental Assessment Method) and LEED (Leadership in Energy and Environmental Design). These certifications confirm high environmental credentials of a building and, as a consequence, increase its market value.