A number of years ago, I became involved in a business project to assess the cost-benefit of green roofs as applied to an industrial facility (Alcoa’s smelter in Finland).  This project offered me insights in the opportunity to build a research and teaching emphasis in this area, considering its relevance to civil (construction, load bearing capacity) and environmental (stormwater, energy, air quality) engineering.

Despite their widely touted benefits to enhance building energy efficiency, stormwater runoff reduction and increased longevity of roofs, the upfront costs of green roofs often deter implementation of the technology by developers and homeowners. This adoption threshold is, in part, due to the lack of quantitative (economic) information to make informed business decisions.

To address this problem, our research used a net present value (NPV) approach to compare the cost of a conventional roof versus a green roof scenario that incorporates a myriad of public and private benefits – as is being increasingly being scientifically proven – including stormwater mitigation, reduced air pollution and building energy savings this technology can provide.

Our goal with this research was to provide an effective cost-benefit-analysis tool that can be applied to a wide range of green roof projects to better enable stakeholders such as building owners, developers and designers to more effectively analyze the *real* cost of green roof technology.   This tool took into account air and water policy frameworks, and applied two modeling tools to quantify the impact of green roofs on air pollutant fate transport and energy use in the building:

1. 1. The DOE Energy Plus Model:  This is a building energy simulation software program supported and made available by the US Department of Energy. It can model building heating, cooling, lighting, ventilating, and other energy flows, based on climate and building use, material, and size inputs. It contains the capability to include a green roof (referred to as ecoroof) on a building which is modeled using 1-dimensional heat transfer
   

2. 2.Sequestering Emissions: a Designable Uptake Model (SEDUM):  This is a custom green roof multimedia model to quantify the contaminant interactions in the air-vegetation-soil- compartments. The model was tested in an uncertainty framework using Monte Carlo specifications using the following variables: roof area, solid matrix properties, regional climate, and atmospheric contaminant concentration data. 
   

For more detail on these models and the application to green roof systems, please check Verdant Concepts, the blog maintained by Dr. Corrie Clark.

Publications:

1. 1. Clark, C.E., P. Adriaens, and B. Talbot.  2008.  Emissions Mitigation Using Green Roofs:  Probabilistic Analysis and Integration in Market-Based Clean Air Policies. Environ. Sci. Technol., 42 (6), 2155–2161.
   

2. 2.Clark, C.E., C.M. Lastoskie, and P. Adriaens. 2007.  Fugacity-Based Model within Green Roof Systems.  Proceed. Green Roofs for Healthy Cities Conference, Minneapolis, MO.
   

3. 3.Clark, C.E., P. Adriaens, F. B. Talbot.  2008. The Big 3 - Researchers quantify the *real* cost of green roofs by including the savings resulting from more energy savings, less stormwater and cleaner air. Living Architecture Monitor, Spring 2008.
   

4. 4.Niu, H., C.E. Clark, J. Zhou, and P. Adriaens.  2010.  Scaling of Economic Benefits from Green Roof Implementation in Washington DC.  Environ. Sci. Technol.  Accepted.
   

5. 5.Clark, C.E., P. Adriaens, and C.M. Lastoskie.  2010.  Fugacity-based Multimedia Model of a Green Roof System. Environ. Toxicol. Chem.  In Review.