Lightweight Green Roof Water Retention System

EPA Grant Number: SU835066
Title: Lightweight Green Roof Water Retention System
Investigators: Spatari, Sabrina
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 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 Challenge Area - Built Environment , P3 Challenge Area - Water , P3 Awards , Sustainability


Throughout the second development phase the potential sustainability benefits can be demonstrated with long-term analysis, further data collection, and application tests. Longevity tests, evaluation of durability, and performance will indicate how the LGR system may fulfill the objectives over a period of years existing on a roof and exposed to the elements.


Several field tests will be installed on small roof locations in order to begin our field testing. These tests will be small scale and will serve to collect data necessary to make informed decisions prior to deploying our system in the field. Once installed, temperature data will be gathered from thermocouples and heat flux sensors which will then be used for calculating insulating factors as well as the LGR’s contribution to reduction of heat island effect. Weight data will be gathered using load cells to evaluate the dead and live loads, water retention, drainage, and evapotranspiration rates. As a control metric, a conventional vegetative roof system simultaneously gathering data will be installed at each field test location in order to serve as a comparison to the LGR system. Results and conclusions will be used to prove the proficiency and performance of the LGR system a side-by-side comparison with existing vegetative roof systems. In addition to several smaller field tests, smaller in-house lab testing as well as progressively scaled up system deployment and installation plans will be performed during Phase II. The lab tests will continue to improve the substrate formula and system performance through ‘soil’ tests as well as nutrient assessment. Freeze-thaw tests will be performed to simulate seasonal changes longer than our allotted 2 years. A basis formula has been developed using all natural renewable and recyclable supplements such as used coffee grounds, seashells, and wood ash and has already provided proper amounts of phosphorous and potassium as well as nearing the required amount of nitrogen to supply the system for at least the first six months. To provide as close to a naturally occurring cyclical nutrient release system, clovers will be added to a test cell to serve as a nitrogen fixer. Working with one of our partners, Roofmeadows, we have been informed that these are an invasive species; thus we plan to impregnate several cells with their seeds and monitor their relation to the existing sedum plants. If this test yields successful results, we will have solidified clovers as a continuous source of nitrogen for our system, serving to begin regulating our balance of NPK.

Expected Results:

During Phase I, we have forged numerous necessary partnerships, which will allow us to begin our implementation tests. Working with the Philadelphia Water Department (PWD) and Drexel Smart House (DSH) we have 3 to 4 prime test sites for our system. We plan to execute our installation on a small-scale basis initially, and then work toward bigger projects depending on our progress and collected data. We see this as the most strategic way to deploy our LGR system while maintaining a well-informed collection of data for analysis. Our first installation will be a bus shelter in Center City Philadelphia, in collaboration with PWD. Our goal is to deploy our system, with help from our academic community, in a busy transportation spot. This will serve to raise awareness of both the problem as well as a solution. We will monitor the progress of our system visually and routinely inspect its installation method in order to validate our plans. If all is successful, the system will be deployed on the roofs of the Drexel Smart House. This is an old Victorian Twin house dating back to 1870 and thus is our perfect site for installing our system. It is what we are targeting as a typical house, and our partnership 20 with DSH will allow us the ability to continually monitor it via load sensors, thermocouples, and lysimeters. Based on the results of application here, we have several more sites, including a commercial location from PWD and another carefully selected location the LGR system will be installed next to a typical green roof giving us a control sample from which to gauge our own progress. In Phase I we aimed to achieve a 1 inch water retention capability without exceeding 10 lb/sf and we accomplished that. In Phase II we aim to work out a do-it-yourself deployment plan and implement it on our available sites, going through successive evolutions each time.

Supplemental Keywords:

building envelope, insulation, water retention, carbon reduction, carbon sequestration, heat island effect, sustainable water management, storm water management, green roof, energy conservation,

Progress and Final Reports:

  • 2012
  • 2013
  • 2014
  • 2015
  • Final

  • P3 Phase I:

    Lightweight Green Roof Systems  | Final Report