Green roofs

Abstract

Green roofs are roofs that have been covered with a growing medium, creating a habitat on what would otherwise be a bland, lifeless surface. It is for this reason that green roofs are sometimes call 'vegetated' or 'living' roofs (Cantor 2008). A growing medium can be applied to a flat roof or a pitched roof: generally the steeper the pitch the more complicated the coverage becomes especially with regard to soil and moisture retention. The type of growing medium is determined by the requirements of each application. There are three primary green roof types, namely intensive, extensive, and simple intensive. Intensive green roofs make use of a deep growing medium (greater that 15 cm) which, in turn, facilitates the growing of a wide range of plant types including shrubs and trees that in appearance it looks similar to vegetation found at natural ground level. An extensive green roof makes use of a shallow growing medium (less than 15 cm) which limits the range of plants to those with a shallow rooting system, typically herbaceous perennials or annuals. Extensive roofs place less loading on a roof structure and generally require less maintenance and are therefore more popular than intensive roofs. Simple intensive is constructed using various substrate depths and is thus a combination of intensive and extensive.