Green roofs, or living roofs, increase ecological equity by creating a habitat for wildlife, which in turn decreases stress of members of a community by providing a more aesthetically pleasing and interactive landscape. They serve several energy mitigation purposes for a building and effectively use the natural functions of plants to filter water and treat air in urban and suburban landscapes. Green roofs are beneficial to more than just the humans who reside below, they are an expression of respect and understanding for the land on which a dwelling is constructed.
Green roofs create natural habitat as part of an urban wilderness. Even in high-rise urban settings as tall as 19 stories, it has been found that green roofs can attract beneficial insects, birds, bees and butterflies. Rooftop greenery complements wild areas by providing stepping stones for songbirds, migratory birds and other wildlife facing shortages of natural habitat. Green roofs also serve as a green wall, filtering pollutants and carbon dioxide out of the air, helping to lower rates of diseases such as asthma. They can also filter pollutants and heavy metals out of rainwater.
Green roofs improve and reduce energy consumption. They can reduce heating by adding mass and thermal resistance value, and also reduce the heat island affect by increasing evapotranspiration. Traditional building materials soak up the sun's radiation and re-emit it as heat, making cities at least 4 °C (7.2 °F) hotter than surrounding areas. A 2005 study by Brad Bass of the University of Toronto found that adding green roofs to 50 percent of the available surfaces in downtown Toronto would cool the entire city by 0.1 to 0.8 °C (0.2 to 1.4 °F), Studies show that if all the roofs in a major city were greened, urban temperatures could be reduced by as much as 7 °C (13 °F), and show that green roofs can also reduce heat loss and energy consumption in winter conditions.
Green roofs decrease the total amount of runoff and slow the rate of runoff from the roof. It has been found that they can retain up to 75% of rainwater, gradually releasing it back into the atmosphere via condensation and transpiration, while retaining pollutants in their soil. Many green roofs are installed to comply with local regulations and government fees, often regarding stormwater runoff management. In areas with combined sewer-stormwater systems, heavy storms can overload the wastewater system and cause it to flood, dumping raw sewage into the local waterways. Often, phosphorus and nitrogen are in this category of environmentally harmful substances even though they are stimulating to the growth of plant life and agriculture. When these substances are added to a system, it can create mass biological activity since they are considered limiting factors of plant growth and by adding more of them to a system, it allows for more plant growth.