According to the US Energy Information Administration, “In 2014, 41% of total U.S. energy consumption was consumed in residential and commercial buildings, or about 40 quadrillion British thermal units.” Most of the energy consumed in buildings goes to heat or cool the spaces where we live and work.
Green roofs and green walls provide insulation, reducing the amount of energy required to cool or heat a building. Studies show that green roofs can reduce summertime heat gain by 87% and reduce winter heat loss by 37%. This means significant reductions in the amount of energy required to heat and cool the building. By using less energy to heat and cool a building, green roofs and walls are reducing greenhouse gases and utility bills.
Green roofs, walls and infrastructure can also help cool a city, which is especially important in places prone to the “urban heat island” effect. This term is used to describe the fact that cities are significantly warmer than surrounding rural areas due to human activities. The causes are roof tops, building walls and concrete land surfaces which reflect, store and later release heat from short-wave solar radiation and waste heat generated by energy use. The urban heat island effect is most noticeable during summer. Green roofs and walls absorb hot sun rays beaming down from above, or reflecting up from the ground level. This vegetation not only provides excellent insulation, but because it’s living it’s transpiring and creating natural air conditioning. This diagram from Sustainable Cities shows how green infrastructure can counteract the urban heat island effect during summer.