The concept of the green roof is not a new phenomenon; with its basic functionality being utilised for several centuries. A green roof (also known as an eco-roof, nature roof, living roof or roof greening system) is a living, vegetative system that contains a substrate (growing media) and a vegetation layer at its outermost surface. Green roof systems can be used as a way of compensating for the increase of impervious surfaces, providing a visual and recreational escape from the ‘concrete jungles’ of urban landscapes.
One of the most attractive qualities of green roofs is that they wholly encompass the idea of sustainability. Sustainability can be broadly defined as an attempt to provide the best outcomes for the human and natural world both now and into the indefinite future. It relates to the continuity of economic, social and environmental aspects of human society, as well as the non-human environment.
Green roofs offer advantages socially, economically and environmentally which are all necessary to fully achieve any step towards sustainable development.
•Storm-water management Retrofitting a green roof system on a pre-existing rooftop can become an onsite water retention facility. Depending on the rain intensity and the soil depths runoff can be reduced by 15 to 90 %.
•Reduction of the urban heat Island effect:
Concrete and asphalt structures absorb the ultraviolet radiation from the sun during the day. At night however, this radiation is released as thermal infrared radiation which creates a dome of higher temperatures over cities. Because green roofs store water in the growing media and plants, latent heat loss is accomplished via transpiration from plants and evaporation of moisture from the growing medium collectively referred to as evapo-transpiration.
•Reduction of air pollution:
Plants can reduce the concentration of airborne pollutants in a number of ways. The leaves of the plant fix particulates, and then when it rains the particulates are washed down into the soil substrate where they become trapped in the soil substrate or growing medium. Through plant photosynthesis and respiration air containing carbon dioxide and toxins is absorbed through the stomata and transformed into glucose and water. Airborne particulates become trapped on the plant foliage until it rains. The particulates are then washed into the soil substrate and become entrained in the substrate mix preventing the dusts being dispersed downwind.
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