Grantee Research Project Results
Final Report: Optimizing Green Roof Technologies in the Midwest
EPA Grant Number: SU833189Title: Optimizing Green Roof Technologies in the Midwest
Investigators: Morgan, Susan , Wackerly, Abby , Noble, Brad , Hise, Crystal , Richey, David , Gaffney, Debbie , Woods, Emily , Luckie, Heather , Gibbons, Joe , Gibbs, Julie , Forrester, Krista , Bhusa, Kusumakar , Richter, Lane , Swearingin, Lauren , Sydow, Mariellen , Sachdev, Rahul , Basham, Rakesh , Lucas, Ray , Watson, Richard , Kaufman, Sam , Hu, Shunfu , Yan, Terry , Retzlaff, William
Institution: Southern Illinois University - Edwardsville
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 30, 2006 through May 30, 2007
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2006) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Sustainable and Healthy Communities , Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities
Objective:
The Phase I project addressed three important issues concerning green roofs—quantifying atmospheric stormwater loss, stormwater quality (specifically nitrate concentration), and thermal effects—for green roof technologies in the Midwest. It built on continuing research at Southern Illinois University Edwardsville and was designed with replicated trials to provide statistically sound data. The project was interdisciplinary—involving biologists, engineers, horticulturalists, environmental scientists, and business people. Undergraduate and graduate students from multiple disciplines collected, analyzed, and presented the data as part of their individual senior assignments, masters research requirements, and course assignments. In addition, the project provided a platform for educating others about green roofs.
Summary/Accomplishments (Outputs/Outcomes):
There was no difference in water loss among any of the unplanted green roof models (i.e., the growth media had no impact). However, there was a difference between the unplanted and the planted systems, indicating that the plants had an impact on water loss. Similarly, no difference was found in the four growth media types among the planted Green Roof Blocks™, a modular system. However, this result may have been influenced by the structure of the module, of which the major evaporative surface is the surface of the media. Conversely, there is a difference in water loss between the different growth media in planted Green Paks™, a modular system that is porous on all surfaces. Planted Green Paks™ with lava growth medium (80% lava and 20% composted pine bark) evaporated/evapotranspirated the greatest amount of water, about 25% more than the other media in Green Paks™ and about 50% more than any of the Green Roof Blocks™. There was also a difference in water loss between drainage layer orientation in the planted Green Paks™ system. This difference is likely due to the fact that with “cups up” more water is retained and, therefore, there is more potential for evaporative water losses.
There were no differences in nitrate concentration or pH over the storage time studied (2 days). Similarly, there were no differences between the first flush from the control roofs and composite samples from overnight. However, the results clearly indicate that nitrate levels in stormwater runoff, regardless of medium depth or type, are elevated above those of a control (conventional EPDM membrane) roof. For the built-in-place green roof models using an 80% Arkalyte and 20% composted pine bark growing media, a shallow planted green roof medium depth of 5 cm leached the most nitrate. There were large differences in nitrate leached from different growing media (generally 80% inorganic material and 20% composted pine bark) in Green Roof Blocks™ containing 10 cm of media. The greatest concentration of nitrate, which was more than twice the others, was leached from a commercial growing medium mix from a collaborator.
Over 45% more nitrate leached from the 10-cm Arkalyte Green Roof Block™ than the 10-cm Arkalyte built-in-place green roof. In fact, all the 10-cm Green Roof Blocks™ leached more nitrate than all but the 5-cm built-in-place green roof. This result may be attributable to the built-in-place models having more established plants, even though all the green roof systems had vigorous plant growth. All had been fertilized with granular isobutylidene-diurea (IBDU, a water-released nitrogen fertilizer) that may be contributing to the nitrate concentration.
Based on ground-level field site data, the results clearly indicate that the built-in-place green roofs studied will provide a thermal benefit to the roof membrane after installation. Examining data from control roofs and green roofs with varying growing media depths (all 80% Arkalyte and 20% composted pine bark) in January 2006 indicated that the average monthly temperature of the roof membrane of the control roof models was at least 0.5 °C colder than the same roof membrane under any green roof models. Conversely, in August 2006, the average monthly temperature of the roof membrane of the control roof models was at least 3 °C hotter than the same roof membrane under any of the green roof models in this study.
Conclusions:
Based on the Phase I results, the following preliminary conclusions were drawn.
- Weighing modular green roof systems can accurately determine water loss from evaporation and evapotranspiration.
- Differences in water loss exist between two modular systems, between growing mediums in one modular system, and between drainage layer orientation.
- Over time, the stormwater retention capacity of green roof systems can be optimized by continuing the water loss monitoring efforts.
- The nitrate concentrations leaching from green roof systems with different growing medium depths and types were quantifiable.
- Nitrate concentrations in runoff from green roof systems were greater than from control roof systems.
- Over time, the nitrate concentrations leaching from green roof systems will likely decrease as plants become more established. In addition, the concentrations can be reduced by utilizing different fertilizer types, different plants, and different growing medium types.
- The thermal benefits of green roof models at the ground-level field site compared to a standard control roof membrane in cold and hot months were quantifiable.
- Green roofs reduced the temperature of the roof membrane in hot months and increased the temperature of the roof membrane in cold months. In both cases, the temperature of the roof membrane under a green roof system is less variable than the roof membrane of a standard roof.
- Over time, the characteristics of green roofs that will contribute to their thermal effectiveness—both for reducing the heat island effect and for reducing energy demand—can be characterized. These characteristics may include the growing medium, plant species, and roof system.
Proposed Phase II Objectives and Strategies: Despite Phase I’s success, more work is needed to optimize the performance of green roofs, including the evaporation/evapotranspiration capabilities and the effects on stormwater quality. The research also needs to be expanded from flat roofs, which are primarily commercial applications, to sloped roofs for residential applications. Additional data is still needed to develop models of the thermal effects of green roofs to lead to calculating the potential energy savings associated with installing green roofs.
Therefore, Phase II will build on Phase I by (1) developing a theoretically-based model of the thermal effects of green roofs and determining insulation values, or R values, to compare with conventional insulation and roofs, (2) continuing to study the effects of green roofs on stormwater quantity and quality but with more established plants and expanding the analysis from Phase I to include nitrate and phosphorus, both important nutrients in runoff, and (3) expanding the overall research from flat to sloped roofs, which represent adding the substantial residential market. The size of scale buildings needed to develop an accurate empirical model of the thermal effects of green roofs will also be calculated for future research to quantify the energy savings potential of green roofs. All the objectives are directly related to understanding and improving the performance of green roofs, especially in the Midwest. Improved performance and knowledge will increase the likelihood of increased use of green roofs nationwide, resulting in realization of the numerous environmental benefits—reduced stormwater runoff, improved insulation of buildings, increased lifespan of roofs, improved air quality, increased biodiversity, and reduced heat island effect.
Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
alternative building, ecological design, energy efficiency, energy conservation, environmentally conscious construction, environmentally conscious design, environmental engineering, EPA Region 5, green building, LEED, modeling, monitoring, nitrate, phosphorus, pollution prevention, precipitation, runoff, stormwater, storm water, sustainable development, thermal effects, US Green Building Council, vegetated roofs,, RFA, Scientific Discipline, Sustainable Industry/Business, POLLUTION PREVENTION, Sustainable Environment, Energy, Technology for Sustainable Environment, Environmental Engineering, clean energy, green building design requirements, sustainable development, green design, alternative building technology, environmental conscious construction, environmental sustainability, green roof, energy efficiencyRelevant Websites:
http://www.green-siue.com Exit
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.