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
Thermal Analysis and Comparison
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.
Thermal Images Courtesy of Dr. Jeffrey C. Luvall, NASA
analysis and comparison can be achieved between a greenroof and regular
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
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, NASAs 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.
Photo of a Scandinavian-style play greenhouse from The
Step-by-Step Outdoor Woodworking Guide by Mike Lawrence.
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
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).
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
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