A roof surface covered by a waterproofing membrane, a drainage plane, a water-retention medium, and plantings of drought-resistant species. The benefits of a green roof include control of stormwater runoff, which can reduce urban water pollution; absorption of airborne toxins and an increase in oxygen in the air; and a reduction of surface temperature of the roof, called the heat island effect. A living roof can also increase the lifespan of the roof system and provide building and noise insulation. Green roofs are most common in multifamily or other large urban buildings.
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