Designing for Maximum Energy and Climate Benefits of Green Roofs and Walls

  • Increased energy consumption due to elevated temperatures and increased demand for air conditioning. In addition, increased peak loads in the summer require expensive and often dirty peak power plants.

  • Increased Air Pollution – Elevated temperatures caused by the UHI effect promote chemical reactions in which volatile organic compounds, nitrogen oxides and other industrial pollutants mix to form ground-level ozone.

  • Health Effects – Air pollution has a host of negative health effects, including heart and respiratory problems, while extreme heat also leads to increased levels of heat stress.

  • Effects on the ecosystem – Increased heat and air pollution can damage vegetation by affecting natural processes, while also stressing plants and animals and reducing their survivability.

  • Economic Impact – In addition to higher costs for energy, health care, water and transportation, more extreme heat negatively impacts tourism and related activities.

  • Increased water use – More water is needed to support stressed vegetation. More power generation also requires more water.

  • Many of the areas of cities that suffer from the UHI are also lower-middle-income areas.

Green roofs, along with green walls, trees and other greenery, are important tools in an overall strategy to reduce UHI. The UHI effect is caused by a change of land from natural to artificial surfaces; green roofs help reverse that phenomenon by returning vegetated surfaces to the urban environment, especially in tight areas with limited ground floor space for trees or other vegetated surfaces.

Carbon sequestration and avoided emissions

Carbon capture is the process of capture and long-term storage of atmospheric carbon dioxide. The process of photosynthesis removes carbon dioxide from the atmosphere and stores it in plant biomass. Some of this carbon is transferred to the growing media via plant litter and exudates. Green roofs and walls can take advantage of photosynthesis to capture and capture carbon from the atmosphere, both in plants and growing media.

In addition, by using energy both directly (by reducing the heating and cooling energy required by moderating the heat flow through a building envelope) and indirectly (by reducing the UHI), green roofs can reduce the emissions associated with any electricity production.

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