Green Roofs : A Soil Layer Of Absorbent Materials On The Roof

912 WordsNov 24, 20154 Pages
Green roofs are example of green infrastructure that provides storm management through layers of absorbent materials on the roof’s surface capable of holding water. These layers consist of some form of vegetation like grass, a growing medium that enables the vegetation to cultivate, a filtering layer that allows only water to pass through, a draining layer, a waterproof barrier that prevents water from going through the roof and the roof structure that is made from a material like concrete, wood or steel (City of Alexandria). Green rooftops absorb 15%-90% of runoff rainwater that comes in contact with the roof, and that large variation in absorbency is based on the vegetation and growing medium used (Lake Superior Streams). The type of vegetation selected ultimately depends on several factors, such as the climate, access to sunlight and the depth of the growing medium as shallow growing mediums (5cm) can only sustain plant species with short roots such as sedum while grasses, herbs and wildflowers can be sustained in medium-depth growing mediums (10cm) and columbines and asters can live in growing medium with deeper depths (15cm+ (Green Garage). The depth of the growing medium correlates with the vegetation that can be grown, as the roots of more absorbent plants tend to need more space. It is important to note that the soil used on green roofs is not the same type as ordinary soil found in the ground, but that it is instead engineered to have certain characteristics

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