Arizona State University researchers conducted a two-year trial with simulated test rooftops using the materials that would go onto the new Tempe Transportation Center building, and exposed it to summer heat and the amounts of water produced by heavy monsoon rains. In 2005, a research team was formed at ASU to test appropriate desert plants on living roofs, with Vidar Lerum as Principal Investigator. Professor David Tait conducted the experiment at the Solar Lab, with Hemant Thakare as research assistant. “The test was conducted during the summer and fall of 2005. The main purpose of this research project was to produce new knowledge about the thermal performance of a roof garden in the hot and dry climate of Tempe, Arizona at 33 degrees Northern latitude. Findings from the study represent insight that widen the knowledge upon which decisions will be made regarding the construction of a roof garden on the new Tempe Transportation Center building.Five 3′ x 3′ test boxes were used, with one as the control, non-greened roof. Each test box contained “a soil depth of 12 inches. Over structure Soil Mix was used as distributed by Western Organics with 40% fine sand without silt, 40% moisture light (2mm-8mm size), 10% Black Bottom mulch, and 10% Omni soil amendment. The soil was placed on top of a Hydrotech prototype green roof system,” (Lerum, 2006).

“Test box #1 was used as a reference case with a white waterproof roofing membrane and no soil or plants. The four remaining test boxes were configured as follows (from left to right, see above). Plants were provided by Mountain States Wholesale Nursery.#2: Dalea frutescens – Black/Loose-Flowered Dalea – irrigated with 3 gallons of water per week.#3: Nolina microcarpa – Bear Grass – irrigated with 1/2 gallon of water twice a day for three days – 3 gallons per week.#4: Muhlenbergia rigens – Deer Grass – irrigated with 1/2 gallon of water four days – 2 gallons per week.#5: Malephora lutea – Rocky Point Ice Plant – irrigated with 2 gallons of water per week,” (Lerum, 2006). The study was conducted with partial funding from OTAK/ARCHITEKTON, the transportation center design team.