As cities become more densely populated, the demand for fresh produce is expected to increase. However, with high demands for real estate the land for gardens and farms is likely to decrease. A potential solution is using city rooftop space for green roofs and gardens. Green roofs could contribute to water sustainability in several ways: 1) significantly reducing the distance food must travel for delivery; 2) reducing CO2 levels and urban heat islands; and 3) assisting stormwater management by incorporating rainwater harvesting and water absorption from plants as storms and flooding become more severe and less predictable.
Atop the 9 story Engineering Teaching Center (ETC) at UT Austin is the Solar Water Energy and Thermal Lab (S.W.E.A.T. Lab) with a complete weather station, rainwater collection system and rooftop garden. The SWEAT Lab was original a Green Fee Sponsored Project to build a weather station on UT campus to measure solar radiation, windspeed, wind direction and rainfall in the downtown Austin area. The rainwater collection system, rooftop garden and drip irrigation system was added in 2015 and 2016 by UT undergraduate research assistants Heather Rose and Yuval Edrey and Postdoctoral Fellow Dr. Charlie Upshaw in the Webber Energy Group.
The SWEAT Lab is currently being used as a weather data station. Weather data for the downtown Austin area can be downloaded by anyone on the SWEAT Lab website. The 330 gallon cistern collects rainwater that is used to water the rooftop garden via a solar powered drip irrigation system. Plants grown include organic edibles, flowers, succulents, and little bluestem grass grown for the UT Fire Research Group.
Green roofs present unique constraints that engineers must consider in their designs. For structural safety, plant beds had to be placed in accordance with the support beams built into the roof. Water containment was also key to prevent any damage to the roof. Built into the rainwater harvesting system was an overflow drainage that is directed into a plant bed supported by a support beam if the cistern were to ever overflow in the occurrence of unexpected heavy rain.
Wind speeds are very high atop a 9 story buildings. Because of this, a wind shield was built around pants that are more sensitive to wind. All structures on the roof had to be either heavy enough to withstand high wind speeds, or strapped down to the steel overhead structure.
There is no elevator that goes to the roof of the ETC building. All items on the roof had to be carried up 4 flights of stairs by students. Items that were too large to be carried up the stairwell, such as the steel welded overhead structure, had to be craned in. As you can imagine, this was extremely difficult and very expensive. For future green roof projects, we highly recommend incorporating a freight elevator that will go to the roof level and designing equipment that can be assembled on the roof while still being heavy and sturdy enough to withstand high wind speeds.
Building the Rooftop Garden was an excellent learning experience. We reap the rewards of our labor every time we climb up to the garden and see the plants flourishing, the bees and butterflies, and the spectacular views of the UT campus and downtown Austin.
The Webber Energy Group plans on adding a aquaponics system to the rooftop garden. This will be a space where students can learn about aquaponics growing systems and where they can experiment with designs to optimize water and energy efficiency. The group also plans to work with other research groups across campus to dedicate part of the space to research in areas of biology, horticultural and agriculture.
*This project, along with the building of the Solar Water Energy and Thermal Lab, will be featured in the ASEE Gulf-Southwest Conference in April 2018 and will be published in the Conference Proceedings.