Green Roofs - Living Architecture Monitor - Winter 2009 - (Page 5) used to irrigate green roofs, also displaces the water used to generate the energy that is conserved by reducing cooling demand load. The water-energy, energy-water dynamic is important to understand in different contexts in order to establish effective public policies as Paul Mankiewicz’s article (page 20) points out. Strategies to reduce or eliminate the use of potable water for green roofs may inadvertantly help reduce the energy conservation. Alfredo Fernández-González’s article on page 26 gives us a framework for more integrated design which incorporates a variety of energy and water saving strategies while supporting living systems. Living systems, with their changing properties also complicate the issue of what is “green.” The huge variability of systems and their changing physical properties (e.g. moisture content) makes it very difficult to have a onesize-fits-all approach to creating policies or testing standards. We’ve been working with the Single Plying Roofing Industry (spri) to develop American National Standards Institute (ansi) design guidelines for wind uplift and fire, rather than expensive and unworkable testing protocol. Root repellency can be effectively tested and we are currently developing an ansi standard on this with spri . The third complicating factor is context, both the building/site, and the larger regional environment. The values of inputs and outputs are driven by design and the larger context. For example, a green roof that provides recreational opportunities in South Bronx and an opportunity for fresh produce in an economically disadvantaged neighborhood has a different set of values compared to a green roof on a high-end condominium in downtown Manhattan. Do we calculate the carbon offsets from the locally produced vegetables? Can we factor in social benefits to the analysis, the positive health impacts? More lifecycle impact assessments on green roofs need to be conducted to explore these issues fully. In terms of weighing the value of inputs, an irrigated green roof in Toronto, where there is no water scarcity, will differ when compared to similar green roof in Atlanta, where water scarcity is an important issue. (To learn more, please read Wayne King’s article on page 30.) The regional context sets the value of the water resource, particularly given that water can’t readily be transported between each region. In contrast, for example, it doesn’t matter where greenhouse gases are produced, since their effect is the same. The movement of the u.s. Green Building Council (usgbc) to a more regional approach to the new leed® rating system is a welcome change that strives to better recognize these important regional differences. Our local market development work in more than 30 cities across North America underscores significant regional differences in the benefits provided by green roofs. The Sustainable Sites Initiative, lead by the American Society of Landscape Architects, profiled in an interview with Nancy Somerville (page 10), is developing ‘green’ landscaping guidelines that will reflect regional differences. The importance of regional context, and the work of the usgbc is highlighted by ashraes 189.1, a draft effort to codify green building practices. They maintain that potable water should not be used for irrigation on green roofs. On the surface, this may seem reasonable. But if you dig deeper, the story is much more complicated. Non-potable water sources are not always available to building owners, and there are regulatory barriers to their use, particularly graywater. Potable water use is offset because irrigated green roofs offset energy used to produce electricity for cooling demand load. Moreover, water is not necessarily the input of the greatest value, relative to all of the other benefits of green roofs. We’ll explore these issues in more detail in Atlanta. Perhaps the greatest overall “green” values are the fresh local vegetables and improved social cohesion in an inner city neighborhood which result from a green roof that uses potable water. Those wishing to protect our environment, health and safety need to dig a little deeper, about lifecycle values and respond to regional context. Only by understanding and recognizing the complexities of being green, can we all move together towards the new paradigm of living architecture. D Sincerely, Steven W. Peck Founder & President, GRHC LIVING ARCHITECTURE MONITOR WINTER 2009 5
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