Green Roofs - Living Architecture Monitor - Spring 2009 - (Page 24)

FEATURE PUSHING THE ENVELOPE ON COMMUNITY-SCALE RESEARCH TOWARDS AN APPROACH FOR QUANTIFYING BIG PICTURE BENEFITS OF GREEN ROOF INFRASTRUCTURE By Jordan Richie & Steven W. Peck n the From Sites to Communities workshop being held on June 3, 2009, at Green Roofs for Healthy Cities’ 7th Annual Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show in Atlanta, we are planning to bring together researchers and policymakers to explore and advance the art and science of community-scale green roof cost and benefit research. While the growing body of green roof research cuts a wide path across a number of disciplines, most of the research completed to date has focused on understanding the performance characteristics of green roofs at various levels including: • The product scale (e.g. a particular growing medium) • The system scale (e.g. how much stormwater a particular configuration of elements retains); or • The building/site scale (e.g. how a green roof will impact cooling demand within a building). Fewer studies have sought to quantify the community- or regional-scale benefits of widespread green roof implementation. This scale of research is critical, however, toward elevating green roofs into the vaunted realm of “infrastructure,” and to justify multimillion dollar public investment in greening the rooftops of our cities. Community-scale research requires that we model a future scenario I INVENTORY OF BUILDINGS IN TORONTO AVAILABLE FOR EXTENSIVE GREEN ROOF RETROFITS AS DEFINED BY DOSHI ET AL where biophysical impacts of green roof implementation allow us to quantify the big picture socioeconomic benefits that can inform a more rigorous cost-benefit analysis. An essential part of any community-scale study is “scenario construction,” where issues of scale and scope are defined with regard to the fundamental objectives of the research. Spatially, the geographic area for a study is often determined by the principal funding agency, and may represent a watershed, sewershed, airshed or neighbourhood, city and state. Within the region, an analysis of rooftop area available for greening should take into account slope, load-bearing capacity, size and spatial distribution of existing roofs, as well as proposed new construction and the build-out plan for the region, if warranted. It is important to bear in mind that some biophysical benefits can only be achieved with certain types of green roofs. For example, an analysis of food production on green roofs should consider only existing and planned buildings that have (or will have) the load-bearing capacity to support deeper growing media and human access. Furthermore, the benefits offered by intensive green roofs, i.e. those with a deeper growing medium that will support a wider variety of vegetation, will differ from those offered by extensive green roofs. One approach, employed in a 2005 cost-benefit analysis for the City of Toronto1, is to use minimum performance data reported for extensive green roof systems, thus maximizing the hypothetical area available for green roofs (see image). Another 2005 study2 which assessed stormwater and air quality impacts for Washington, D.C., assumed 80 percent extensive green roof coverage and 20 percent intensive, recognizing the different performance values associated with each. Temporally, study periods of 25 to 40 years tend to be most informative. Most existing roofs need to be replaced every 15 to 20 years, and recent studies (including a 2008 cost-benefit analysis for the City of Portland3) have shown that for developers and building owners, benefits do not appear to exceed costs until the avoided cost of conventional roof replacement is accrued. The next step is to model the different biophysical impacts of community-scale green roof implementation. The Green Roofs Tree of Knowledge (, an online database containing detailed summaries of research and policy studies related to green roof infrastructure, features several reports that address one or more community-scale benefits. Some studies, such as the New York State Energy Research and Development Authority’s investigation of urban heat island mitigation strategies4, rely on regional modeling techniques, while others use sitelevel performance research to infer regional impacts. One consideration at this stage is whether or not your methodology will need to support multiple coverage scenarios. Once community-scale biophysical impacts can be quantified, valuation of these benefits will be required to generate big picture socioeconomic benefits. 24 LIVING ARCHITECTURE MONITOR SPRING

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Spring 2009

Green Roofs - Living Architecture Monitor - Spring 2009
From the Founder
Opportunity Knocks
New Green Roof Incentive for Toronto
The Role of Structural Engineer
On the Roof With...
Roots of Learning
Urban Farming
Pushing the Envelope on Community-Scale Research
Raising a Green Roof for Eco-Literacy
Soft-Benefit Valuation
What's New for Atlanta
GHRC Professional Development Calendar
Accreditation Milestone
Welcome New Corporate Members
Moving On

Green Roofs - Living Architecture Monitor - Spring 2009