Iowa Stormwater Education Program

Green Roofs/Living Walls

A green roof incorporates vegetation, soil or another growing medium, and a drainage layer over a waterproof membrane as an alternative to an impervious roof surface. A green roof will eliminate 50% to 80% of roof runoff. The soil and vegetation absorb precipitation and release what is not used by plants over several hours rather than the rapid runoff associated with impervious roofs. Runoff volumes from frequent, small precipitation events are eliminated and runoff from larger events is reduced.

A green roof provides air quality and aesthetic benefits. They reduce the heat island effect in heavily populated urban areas. Green rooftops also improve the energy efficiency of buildings, especially for air conditioning when HVAC units are located on the roof as is often the case in large commercial or institutional buildings. The air temperatures just above green roof sites are significantly lower than those above impervious roof surface sites.


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