Emergy Synthesis 5 :

We assessed the total energy required to manufacture, install and maintain an extensive, sedumplanted green roof over its assumed life of 20 years in the Mid-Atlantic region of the U.S. using the method of emergy analysis. We estimated its environmental benefits as the sum of summer electricity savings due to cooler building temperatures, primary production of biomass and reduction in intensity of stormwater runoff. Data on energy input requirements were based on a green roof installed at a primary school located in College Park, Maryland. Data on benefits was modeled based on published literature. The low-density, engineered growing media constituted 59% of the total energy requirements, while the petroleum-based root barrier and filter fabric contributed less than 4% combined. Electricity savings provided the largest benefit, but the sum of the three benefits equaled only 12% of total energy inputs, indicating that this type of green roof design used more energy than it saved or produced. Despite this, the green roof did reduce the local environmental loading ratio of the building by increasing the amount of locally renewable emergy captured by the vegetation. Our study showed that this extensive green roof design increased the overall ecological footprint of the building, and indicated that the energy footprint of the roof could be reduced by removing some of the engineered growing media.