Green roofs have measurable benefits on communities and buildings where they are installed.
Lower urban temperatures
One of the main objectives of green roofs is mitigating the urban heat island effect through evapotranspiration and transpiration. Green roofs can reduce urban ambient temperatures by up to 5 degrees, according to a 2011 report by the General Services Administration. Green roofs may be between 30 degrees and 40 degrees cooler than traditional roofs.
Reduced energy demand for green roofs
With the reduced temperatures brought about by green roofs, as well as additional insulation provided by the roof, building HVAC systems don’t have to work as hard. The GSA report found green roofs can reduce the transfer of heat between a building’s exterior and interior by up to 72%. That insulating effect can also help with winter energy needs, as less heat is lost.
Stormwater management on green roofs
Green roofs create more pervious surfaces to collect water, preventing it from running into streets and sidewalks. A 2005 study of green roofs in Michigan found that vegetation on a roof with a 2% slope and a media depth of four centimeters retained 87% of stormwater it was exposed to. Green roofs might also have a positive impact on water quality by preventing some pollutants from running into the water supply. However, GSA notes that green roofs might also contribute to water pollutants from fertilizers.
The impact a green roof has on air quality depends on what is planted there, but generally speaking, leafy plants can help remove carbon dioxide and carbon monoxide from the air.