Grantee Research Project Results
2013 Progress Report: Lightweight Green Roof Water Retention System
EPA Grant Number: SU835066Title: Lightweight Green Roof Water Retention System
Investigators: Spatari, Sabrina , Mickute, Monika , Magee, Michael
Current Investigators: Spatari, Sabrina , Mickute, Monika , Zakutny, Matthew J
Institution: Drexel University
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2011 through August 14, 2013 (Extended to December 31, 2015)
Project Period Covered by this Report: August 15, 2012 through August 14,2013
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2011) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Challenge Area - Sustainable and Healthy Communities , Sustainable and Healthy Communities
Objective:
Typical North American vegetated roof systems consist of an expanded clay-based growing medium. The bulk density of these dry mixes ranges from 25 to 56 lb/cf (Wark, 2003). Depending on the structural conditions of an existing structure, installation of a conventional vegetated roof can be cost prohibitive. Providing a reliable modular vegetated roof system weighing less than 10 lb/sf will minimize the affordability concerns for the average homeowner and facilitate the introduction of green roofs on buildings across North America. The widespread application of more vegetated roofs in urban areas will result in benefits, including heat island effect mitigation, carbon sequestration, providing heating and cooling energy savings, and most importantly managing stormwater runoff by reducing impervious surface coverage while delaying peak runoff.
Progress Summary:
Sedum Plant Stock
The team worked with the Drexel Biology department to get permission to use a large greenhouse on campus as our laboratory. We were granted space to only grow the plants in a specific section of the greenhouse. The greenhouse was prepared and ready for use from the University in February 2013. A collection of stock plants was started in preparation for the Spring 2013 large-scale prototype installations. This collection of plants was utilized for investigating how well various species survived in the LGR formula, and to generate clippings for the large-scale installations.
Figure 1. Photo taken in May 2013
North Creek Nurseries advised the team to allow the plants to get acclimated to the LGR medium to reduce plant shock during the transition to large-scale installations. The team purchased several species native to the MidAtlantic region, which were known to do well in shallow soil and transplanted them into the LGR medium in February 2013. The greenhouse allowed the plants to grow to adult stage in the LGR medium with natural sunlight as advised by North Creek Nurseries by May 2013. The plant stock generated clippings for prototype installations. The plants grown to adult stage is shown in Figure 1. Two trays in the greenhouse were filled with LGR medium to a depth of 2 in. to simulate the LGR cell medium depth and clippings were spread over top in Figure 2. The investigation revealed how well the plant clippings root into the soil and which plants would survive well in the LGR medium. Species that rooted and spread particularly well are (all sedum) reflexum “blue spruce”, rupestre “angelina”, and spurium “red carpet”. Other species such as sedum floriferum “weihenstephaner gold”, sexangulare, and spurium “john creech” rooted fairly well, but did not spread as quickly as the latter species. Sedum cauticolum “lidakense” and sieboldii do not root well from clippings and would be better inserted as plugs rather than clippings, as seen in Figure 3. 
Figure 2. Clippings spread in May 2013
Figure 3. Plant growth in November 2013
Phase II Installations
Three separate large-scale prototype installations were originally planned to collect quantitative and qualitative data over a period of at least two years while continuously improving upon the system based on real-time performance. The team has been proposing since 2011 to install a prototype LGR system on the roof of the Drexel Smart House at 3425 Race St., however it is still pending approval due to rehabilitation of the house and liability concerns. It has been expressed from the University we may be able to move forward with this installation by Spring 2014 depending on conditional requirements.
Another planned prototype installation was on the roof of a corner row house located in South Philadelphia, a home belonging to a Drexel alumnus and Adjunct Professor. The house was once used as a sustainable demonstration model for the Mid Atlantic Solar Energy Association in the 70s and 80s. The owners expressed interest in restoring the legacy of the historically experimental home for future sustainable projects, starting with the installation of our prototype lightweight green roof. However, after learning more about the materials that make up the LGR soil medium, the owner opted not to move forward until the formula was refined to have a reduced environmental impact from the mined materials of vermiculite and perlite, and the nonbiodegradable EPS. The owner was also concerned with the EPS blowing away and spreading throughout the neighborhood. This further prompted a callout to focus on re-thinking the material make-up of the Phase I formula.
An installation was successful at a company located in Wilmington, DE called Brandywine CAD (BCAD). In 2010, BCAD purchased an old Post Office Building, saving it from destruction and committing to a sustainable transformation and LEED Platinum certification. Their progress to date includes an organic vegetable garden, four large rainwater cisterns for the garden and flushing toilets and a 28 kW solar PV array. The LGR prototype installation is their latest addition. Materials were ordered and cells were manufactured starting in late April 2013, in anticipation for the clippings to be ready in late May 2013. The first cells were installed in late May 2013 and the entire roof installation of 104 cells was completed by mid-June shown in Figure 4.
Figure 4. BCAD installation June 2013.
Figure 5. BCAD installation October 2013
Activities Planned for January 2014 to August 2014
A weather station was purchased and installed onto the BCAD roof. Observations and data are being collected on a regular basis and photos are taken to be compared with the weather data to note any trends in the qualitative performance of the LGR. Quantitative data on stormwater retention will be evaluated using the electronic rain gauge from the weather station and comparing to measured roof runoff using a PVC pipe and a water level sensor taken from a methodology explained in Voyde et al, 2010. A gutter system will be installed in early 2014 around the LGR roof at BCAD using the remaining budget. Prior to the installation, the structure must be fixed properly to accept the proper attachments for the gutters as required by the property owner, and which could not be completed during the Summer of 2013.
Cell Manufacturing
An ultrasonic welder was purchased to assist in the manufacturing. The team manufactured the prototype cells manually on-site at BCAD, the location of the large-scale installation. The prototype manufacturing procedure was documented to evaluate the mass manufacturing potential and for reference in future installations. It was found to be a very labor and time intensive process that could be improved to avoid manual labor.
Refining Planting Media Formula
During Phase I of our research, we were able to combine several lightweight, water absorptive, natural and synthetic materials to develop a unique planting medium, which sustains vegetation and weighs less than 10 lb/sf when fully saturated. This specially engineered Lightweight Green Roof (LGR) ‘soil’ satisfied all of the required ASTM standards demonstrating an appropriate performance without the added weight, or associated costs. During the continuation of Phase II of the project, the research team concentrated their efforts in making this system more sustainable by reducing its carbon footprint. The team has experienced some issues with the specific materials that make up the current formula that performs well. The Expanded Polystyrene (EPS) component of the planting medium was continuously rising to the top of the formula in between watering periods causing them to be vulnerable to the wind and spreading outside of the green roof. This caused the team to start researching mew materials having similar bulk density and absorptive materials that could replace the EPS component of the mixture. We attempted replacing current micro EPS with recycled 1/8 in EPS, however this attempt was not successful. EPS is the lightest component of the planting medium and when an 1/8 in. size particle was introduced into the mixture, it did not create a well distributed soil mixture. The team discovered a company named Ecovative that produces packaging materials similar to polystyrene from agricultural waste and fungal mycelium. The material can be produced with natural waste resources from the earth and unlike EPS, is biodegradable. Samples of the various materials offered from Ecovative were aquired and tested to compare with EPS, however the material has a bulk density that is much too large compared to the EPS.
The research team still requires additional time to refine the prototype design and planting medium formula to make it durable under ambient testing conditions. The final planting medium will be verified by Turf Diagnostics to meet appropriate ASTM test.
Future Activities:
The installation on the roof of BCAD will provide the team with an evaluation of the qualitative and quantitative characteristics of the initial prototype to consider for an updated future prototype. Observations and data are continuously being recorded and concluding results will be available by August 2014, the project end date determined from the no-cost extension approved by USEPA, after the roof has been in service for one year and three months.
An update to the design of the cell with the purpose of improving the manufacturing process is being considered for future prototype installations. A new high heat resistive Polylactic Acid (PLA) tray design that can be injection molded in a factory is being considered to replace the current cell system. The purpose is to eliminate the need for manual labor, reduce manufacturing costs and increase long term biodegradability.
We are still working in altering the final mixture design to reduce LGR systems carbon footprint and to present a more sustainable product. Currently LGR planting medium contains 90% of mined materials and non-biodegradable EPS. Our goal is to reduce it to less than 50% of mined material and find an EPS replacement that can biodegrade over a period of time comparable to the life expectancy of the LGR system. Once the LGR planting mixture is refined, it will be independently verified by Turf Diagnostics, and a new stock vegetation will be grown in the green house at Drexel University for a second round prototype installations. We are in the process of value engineering the LGR system to make it more competitive in the market and more attractive among homeowners.
Due to several unexpected delays, two expected large-scale prototype installations will not be installed as anticipated. Instead, the team will focus on developing a strategy to improve soil medium and test the existing installation at BCAD Several key team members left the project due to graduation and job commitments, therefore the LGR project remains under the budget with anticipated future refined prototype installations. More team members are currently being recruited to fulfill the understaffed team in order to aid in improving the system and move forward.
References:
- Robert D. Holtz, W. D. (1981). An Introduction to Geotechnical Engineering, 1st edition. Upper Saddle River, NJ: Prentice-Hall, Inc.
- Voyde et al. (2010). Hydrology of an extensive living roof under sub-tropical Climate conditions in Auckland, New Zealand. Retrieved March 8, 2013, from Journal of Hydrology.
- Wark, C. G. (2003). Green Roof Specifications and Standards. The Construction Specifier , pp. Vol. 56, No 8.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
Building envelope, insulation, water retention, carbon reduction, carbon sequestration, heat island effect, sustainable water management, storm water management, green roof, energy conservationProgress and Final Reports:
Original AbstractP3 Phase I:
Lightweight Green Roof Systems | Final ReportThe 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.