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Abstract This poster presents a decision-making framework for vegetated roofing system selection incorporating the philosophy of the Choosing By Advantages.

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Presentation on theme: "Abstract This poster presents a decision-making framework for vegetated roofing system selection incorporating the philosophy of the Choosing By Advantages."— Presentation transcript:

1 Abstract This poster presents a decision-making framework for vegetated roofing system selection incorporating the philosophy of the Choosing By Advantages (CBA) decision-making system. The CBA system was originally developed by Jim Suhr to help the U.S. Department of Agriculture’s Forest Service make complex resource allocation decisions. One of the core tenets of CBA is to ground decisions in information pertinent to the case at hand rather than in abstractions. The framework for green roof system selection embraces this idea by assigning value to various attributes of green roof systems using a set of value functions drawn from the available literature. The decision-maker is asked to consider project-specific variables when determining the characteristics of different roofing systems. The Choosing By Advantages system guides the decision-maker to make choices based on the importance of advantages, i.e. the relevant and perceivable differences between alternatives. When applied to green roofing system selection, once the advantages of different green roof types and a base case conventional roof are determined, the green roof designer ranks these advantages according to their relative importance. Rather than anticipating which abstract concept, such as storm water mitigation or energy benefits, might be most valuable, the green roof designer decides which actual advantages are most important when systems are compared in the context of a particular project. The roof system with the greatest total importance of advantages is suggested for selection. While it is no substitute for the creative process, the framework assists the green roof designer by describing, formalizing, simplifying and justifying the process of decision- making. It also assures that the decision to implement a green roof is tied to current green roof research findings to the greatest extent possible. Choosing By Advantages in Green Roof Decision-Making Elizabeth Grant Doctoral Candidate Environmental Design & Planning elgrant2@vt.edu A. Storm Water The Life Expression Chiropractic Center was envisioned as a first step in the movement toward a more sustainable office facility. The green roof intercepts and delays the flow of incident rainfall, allowing it to flow through a gapped fascia at the edges. Although the green roof replaces some pervious surface displaced by the building footprint, building officials still required a full sized storm water retention basin behind the project. The green roof requires no additional irrigation thanks to its engineered lightweight growing media that simultaneously retains and drains water. Location Hazleton, Pennsylvania Architect Van der Ryn Architects Year Completed 2001 System Type Extensive Project Area 6,000 SF total LIFE EXPRESSION CHIROPRACTIC CENTER A+B The green roof compensates for the displaced landscape. A.Storm Water B. Energy C.Acoustics D. Structure E.Compliance F.Cost Limitations The decision-making framework is intended to assist, not replace, the process of green roof design. Potential green roof benefits such as gray water reuse and recycling, food production, cooling of water from mechanical systems, habitat creation, fire protection, processing of carbon dioxide, and visual amenity are excluded. Eight generic green roof system types as identified by the FLL Guideline (FLL, 2002) are used to simplify the analysis. The geographic boundaries of the study are the continental U.S. and Canadian provinces south of 60° north latitude. Continuance Following the creation, demonstration, and testing of the framework that forms the body of this dissertation, it will be possible to generate a more comprehensive decision-making methodology for the design of vegetated roof systems based on specific and relevant input data. The usefulness of any such methodology will depend heavily on the availability and reliability of data related to the key parameters involved. The ultimate goal of continuing research into the decision-making methodology for green roof system selection will be the creation of an interactive, computerized tool to assist roof designers in the selection of highly specific vegetated roofing systems. In the broader view, this tool will ultimately operate in conjunction with other tools being developed within the College of Architecture and Urban Studies at Virginia Tech to form an integrated framework to assist in the process of holistic building design. Project NameProject Location USDA Zone Urban, Suburban or Rural Project Area (sq. ft.) Green Roof Classification Media Depth (inches) Public or Private Year Complete Montgomery Park Business Center Baltimore, MD 7aUrban30,000Extensive 2 to 3Private, rented by public agency 2001 Life Expression Chiropractic Center Hazleton, PA 5bRural6,000Intensive5Private2001 Chicago City Hall Chicago, IL5bUrban20,300Extensive, Semi- intensive, and Intensive 3 to 18 Public2001 Ford Dearborn Truck Assembly Plant Dearborn, MI 6aSuburban475,000Extensive 2.5 to 3Private2002 Toronto Mountain Equipment Cooperative (MEC) Toronto, ON5bUrban10,000Extensive5Private1998 Woodward Academy Atlanta, GA7bUrban4,000Semi-intensive6.5Private2004 Methodology The Battelle Method The Environmental Evaluation System, or Battelle method (Dee, Baker, Drobny, Duke, Whitman, & Fahringer, 1973) is an approach to evaluating the environmental impact of alternative project solutions that is relevant to vegetated roofing system selection. The Battelle method allows incorporation of intangible criteria as well as quantifiable indices of performance by rating a proposed project according to various parameters. A hierarchical checklist is developed, divided into categories, components, and parameters. For each parameter, the project is rated on a cardinal scale of environmental impact units, from 0 to 1, worst to best. Projects are rated in a three-step process. First, the project is assigned environmental impact units for each parameter based on value functions that relate a measurable attribute on the x-axis to an environmental quality level ranging from 0 to 1 on the y-axis. Second, each parameter is weighted based on its relative importance. Third, weighted parameters are summed to determine the Environmental Index (EI) of the project outcome, as compared to a “do-nothing” approach. The higher the net EI, the more desirable the project. Case Studies Six case study projects listed in the table below were evaluated to determine key design factors for inclusion in the framework for vegetated roofing system design. Projects were selected to represent a range of building types, locations, and design features. Choosing By Advantages One of the basic tenets of Choosing By Advantages is the Principle of Anchoring, which states that “decisions must be anchored to the relevant facts” (Suhr, 1999, p. 4). Another is to base decisions only on the importance of advantages, i.e. the relevant and perceivable differences between alternatives. Within the framework for vegetated roofing system selection, the value functions described by the Battelle method may be used to assign a value to the attributes of various green roof systems. However, the parameter-weighting methodology called for in the Battelle method is replaced with a project-specific, designer-specific method based on weighing the total importance of the advantages of each system and accounting separately for the effect money will have on the decision. In the final phase of this research, detailed interviews of individual green roof designers will be conducted to demonstrate the framework’s functioning. The framework that results from the creation of value functions for green roof attributes, coupled with subjective valuations of the importance of the differences among these attributes in the context of a specific green roof design project, will not be conceived as an answer to the question, “Which green roof system should I select?” but rather as an answer to the question, “How might I go about making the selection?” References Dee, N., Baker, J., Drobny, N., Duke, K., Whitman, I., & Fahringer, D. (1973). An environmental evaluation system for water resources planning. Water Resources Research, 9(3), 523-535. Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e. V. (FLL). (2002). Guideline for the planning, execution and upkeep of green-roof sites. Bonn: FLL. Suhr, J. (1999). The choosing by advantages decisionmaking system. Westport, Connecticut: Quorum Books. A. STORM WATERB. ENERGYC. ACOUSTICSD. STRUCTUREE. COMPLIANCEF. COST Storm water flow reduction Potential energy savings Approximate Sound Transmission Class Surplus dead load of roof system Potential contribution to LEED certification Life cycle cost Storm water pollutant control Embodied energy and environmental impact Approximate Noise Reduction Coefficient Meets policy initiatives Runoff warming A. STORM WATER Mapping the Framework The decision-making framework for vegetated roofing system selection is mapped using a common graphic language shared by decision-makers in various fields. A well-known graphic language is utilized to make the decision-making process both transparent to these users and adaptable to new and changing information regarding green roofs. A computer program called PrecisionTree 1.0 for Excel, by Palisade, is employed to generate influence diagrams and corresponding decision trees. The influence diagram at left includes all currently identified parameters as calculation nodes (rounded rectangles) connected by influence arcs (arrows) to the CBA Scoring-Sheet Method, a tabulation of the importance of the advantages identified among eight generic green roof types. The importance of these advantages is determined by the framework’s user, as shown with a decision node (green square). Cost is considered as a special factor, affected by the project’s budget (a decision node) and life cycle cost analysis when conducted (a calculation node). The CBA process includes a Reconsideration Phase that assists the designer in revisiting the system selection, shown as the final, or payoff, node (blue diamond) in the diagram. Left: Value functions for Parameter A1. Top right: Influence diagram for Parameter A1. Bottom right: Decision tree for Parameter A1 Identified Parameters To develop a workable list of factors for green roofing system selection, it is necessary to sort the pertinent parameters into a manageable number of categories. Six such categories are identified, along with their constituent parameters, as shown in the table above. Items in gray indicate parameters for which no adequate evaluative criteria currently exist. Future research beyond the scope of this project will be necessary to fill in these blanks. College of Architecture & Urban Studies School of Architecture + Design


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