The sealing of the landscape by human building activities has several negative effects on the ecosystem and the human habitat. This applies in particular for urban areas, where a large share of the total land area is sealed. Vegetated Roofs can compensate for lost green areas. As "step-stone habitats", they create lively and vigorous places and connect isolated refuges for flora and fauna within sterile city centres. Low maintenance extensive Green Roofs especially promote biodiversity, as wild bees, butterflies, and beetles find food and shelter there. Even rare and protected species can be found on Green Roofs. The natural cycle of plant growth, self-seeding and stress-selection lends to ecological systems with unique character.
Green Roofs are very important instruments in preventing local flooding. Depending on the Green Roof system and the depth of the growing medium, the immediate water run-off can be reduced by 50-90%. Most of this water returns directly into the natural water cycle by transpiration/evaporation of the Green Roof. The excess rainwater is filtered and drained off with a temporal delay. This leads to reduced stress on the sewer system during the year and at peak flow periods. As a result less or smaller dimensioned sewerage systems can be installed. In combination with other forms of modern rain water management (for example, storage tanks or retaining trench-soaking hole-systems) the rainwater can be entirely infiltrated on the landowners ground. The benefits of Green Roofs for stormwater management can lead to incentive programs for Green Roofs in various cities, such as, reduced stormwater taxes.
Global warming, increasing sealed surfaces and excess heat from residential buildings, industry and traffic are leading to continually rising temperatures within urban agglomerations. The temperature difference between a city and the surrounding countryside is referred to as the urban heat island effect. In summer this effect can reach nearly 10 °C. The urban heat island effect drastically reduces the quality of life and impairs health of the city's inhabitants. Natural "air conditioners" such as green areas and parks can absorb up to 80% of the energy input; however, in densely populated districts green areas are rare. Landscaped roof surfaces are an alternative, as they decrease the "urban heat island effect" through the process of transpiration and humidify dry air. This process lends to a better climate for the occupants of adjacent apartments and buildings.
Inner city air pollution can cause serious adverse health effects, which has been proven by numerous studies over the last years. In particular, nitrogen oxides, carbon monoxides, volatile organic compounds, and diesel exhaust gases are creating dangerous combinations of toxic substances for urban inhabitants. Plants are able to enhance the quality of the air. One square metre of Green Roof can filter approximately 0.2 kg aerosol dust and smog particles per year. In addition, nitrates and other harmful materials in the air and from rainfall are deposited in the growing medium.
Green Roofs are visually enhancing the quality of life in the cities. Already a few blooming "islands" are able to interrupt the monotony of the grey, dismal city centres and better people´s mental and physical health. Not only in cities, but also in rural areas, Green Roofs allow industry buildings to blend harmoniously with the scenery.