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Greenroofs have been tested by the FLL and many others in Europe for decades, and now the United States with the creation of the ASTM Green Roof Standards Task Force (see the ASTM Updates column by Ralph Velasquez here).

Why Not Have a Test Greenroof at Your School, Business, or Local Government Building?

Numerous studies involving heavily instrumented test greenroofs are presently in place or planned for future research and documentation across North America including Toronto, Ottawa, Portland, University Park, PA and Chicago.  Sponsored by city governments, university research, and/or a combination of public and private coalitions, test parameters are in place to measure thermal analysis and comparison, stormwater retention qualities, soil substrates and various plant species.  These studies hope to explore, measure, and analyze greenroofing benefits to ultimately promote greenroofs as a new type of infrastructure.  Below are a couple of examples of research areas and suggestions for a test greenroof:

Thermal Analysis and Comparison

Continuing their study of the urban heat island effect on major U.S. cities, NASA took aerial photos over Atlanta in May 1997.  The photos below illustrate the cooler temperatures of greenspace versus the absorbed heat from the mostly impervious developed areas.  The left photo is a color aerial, and the right is a color thermal image.

Color Photo of Atlanta, 1997, by NASA Thermal Color Photo of Atlanta, 1997, by NASA

                                             Thermal Images Courtesy of Dr. Jeffrey C. Luvall, NASA

Thermal analysis and comparison can be achieved between a greenroof and regular impervious roof.  It is important to capture the energy flux through the two roof systems in order to understand their functioning.  The simplest way is to take temperature profiles through a cross section of each roof.  Using a minimum of seven fine wire thermocouples, air temperature, middle layer of roof surface, underside of roof, pelitum air temperature, inside ceiling upper surface temperature and building air temperature can be measured, as well as incoming solar radiation (albedo), wind speed and direction, and relative humidity.  In addition, it would be useful to have net radiation and a ‘soil’ heat flux plate to measure flux.  These instruments can be monitored and data recorded using Campbell data loggers (model cr10x), see www.campbellsci.com.  Approximate cost is $5,000 per roof.”  (Personal communications, Dr. Jeffrey C. Luvall, NASA’s Global Hydrology and Climate Center, April 2000).

If a "real" greenroof is not an option at the moment, how about experimenting with a smaller test greenroof?  Just like a trial garden, a test greenroof can offer a myriad of learning opportunities for children and adults alike.  Schools can demonstrate the potential for helping the environment through the construction of a small greenroof for both fun and educational purposes.  Perhaps the low roof of a playhouse, fort, or garden shed can be covered in a simple do-it-yourself vegetated cover.  Tom Liptan, ASLA, suggests using inexpensive and easily accessible materials such as plastic lining, local native soils (to reduce the weight and increase drainage, add some locally available inorganic material such as expanded slate or shale, recycled crushed bricks, or small pieces of concrete to the mix) and a mixture of the proven Alpine-type plants such as sedums and other succulents and some native plants.

Scandinavian Play Fort from Mike Lawrence

Photo of a Scandinavian-style play greenhouse from The Step-by-Step Outdoor Woodworking Guide by Mike Lawrence.

 

Greenroof Test Panels from ReNatur
                                         Source:  ReNatur

Stormwater Monitoring

By observing cause and effect, kids can sharpen their observation and experimental skills.  Botany and other science classes can experiment with the natural processes related to this technology by using simple monitoring equipment to measure water runoff amounts and temperature differences between vegetated covers and any standard non-porous surface.  All you need is a small barrel to catch unabsorbed rain water, a plastic rain gauge, a temperature gauge, a test greenroof area and control panel, and the time required to monitor daily rainfall events and temperature fluctuations.  Keeping a daily track record and then compiling the results into charts and graphs could be a great learning experience.  Different plant species, including both proven alpine-type and native plants could also be observed for their heat and drought tolerances in each of our climate areas.

A more precise, complete, and therefore expensive upgraded system for easy stormwater monitoring would include using a tipping-bucket rain gauge with data logger, and a mechanical (cable-and-pulley) level recorder to measure levels in the barrel (Charlie Miller, April, 2000).

ReNatur Birdhouse

Optima Birdhouse on Intensive Greenroof

Top Photo Source:  ReNatur; Below:  LSV

Another easy and fun learning project, especially for younger children, would be to build a simple birdhouse greenroof of sedums and place it in a garden designed for wildlife, such as birds or butterflies.  I took the above picture at the Optima Headquarters near Hamburg, Germany, in March 1999.

 

 

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