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Are green roofs beneficial from an energy standpoint in all climates? Why or why not?
The energy benefits from installing a green roof can be difficult to assess, but there are good tools to quantify the energy benefits. The difficulty arises from the fact that air is a good insulator and when the growing media is dry the insulation value is quite good. However water is not a good insulator and when the soil is wet the insulation value is significantly reduced. Insulation values of green roofs are a relationship between soil moisture content, thickness of growing media, wind exposure and solar orientation. Generally it can be stated that the action of adding a growing media to a roof surface will improve the energy benefit of any building. In some cases the energy savings may be less than you would think, because the roof area of the building can be relatively small in comparison to the entire building envelope. The larger consideration for cost payback of a green roof is extending the life of the roofing membrane, possibly eliminating the need for two or three roofing replacement cycles.
Answers provided by Jeffrey L. Bruce, FASLA, LEED, ASIC, GRP. Bruce is owner of Jeffrey L. Bruce & Company (JBC) a national landscape architectural firm. Founded 1986, JBC provides highly specialized technical support to many of the nation’s leading Architectural and Landscape Architectural firms on a wide variety of project profiles including engineered soils, green roof technologies, urban agronomy, green infrastructure, performance sports turf, water harvesting, and irrigation engineering. Bruce is a Fellow of the American Society of Landscape Architects, Past President of the American Society of Irrigation Consultants (ASIC), and Chairman of Green Roofs for Healthy Cities (GRHC).
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