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student guest articles

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Read our occasional articles about projects, research, ideas, experiences and more submitted by students from around the world.  Submit your article, too!

(Past Guest Feature Articles)

september 2006
guest feature and student guest article

ENVISIONING A “GREENROOF” POLICY FOR THE DISTRICT OF COLUMBIA - Implementing Strategies to Encourage Alternative Stormwater Best Management Practices

 Storm Water Management on the Lafayette River

Image Courtesy of Building Logics (read about this project in
The Greenroof Projects Database here).

By Gregory C. Long, R.L.A.
All photos used with permission from Greg Long

Publisher's Note: 
This paper was prepared for a Virginia Tech public policy class on 12.8.05.  Greg's thesis is similar in content but he continues to collect more data and expects to have that paper finalized in the spring of 2007.  A follow-up PowerPoint version was presented to the National Building Museum as part of a symposium designed to raise awareness about vegetated roof design in January, 2006.

Abstract -
Recognizing a need to improve the quality of our local watersheds

The District of Columbia is home to 572,000 residents¹ and covers approximately 61.4 square miles of land and like many older cities, collects much of its sanitary sewer effluent and storm water runoff in a combined sewer system.  Approximately 1/3 of the District’s land (12,478 acres)² is served by these combined sewer systems (see figure 1).  It wasn’t until the early 1900’s that city planners decided to split the two systems but by then it proved too costly to replace the existing and aging infrastructure.

Figure prepared by Limno-Tech, Inc.

Figure 1-Combined Sewer Systems, Watersheds, & CSO outfalls

These combined sewers generally function properly during dry weather, however, during rain events the capacity of these systems are often exceeded.  During major “wet weather" events these combined sewer overflows (CSO’s) discharge millions of gallons of untreated pollutants and raw sewage directly into the Potomac, Anacostia, and Rock Creek watersheds, causing unsafe and unhealthy living conditions for us and the environment.  In the District, there are 60 such CSO outfalls which need to be re-designed in order to meet the Environmental Protection Agency’s (EPA) Clean Water Act (CWA)³ of 1972.

The District of Columbia’s Water and Sewer Authority (WASA) has been working to bring the Combined Sewer System back into compliance with the CWA and in doing so has to prepared a Long Term Control Plan (LTCP) to manage its CSO’s.

WASA’s LTCP promises to invest over $1.2 billion to get this problem under control and to meet current development conditions and also provide for another 14 million square feet of additional building footprints over the next 20 years.  The funding for the LTCP is pledged to go directly into infrastructure improvements which will satisfy the EPA requirements.

In order to protect our water resources the District of Columbia needs to take a more holistic and comprehensive approach and implement some alternative methods and strategies towards managing D.C.’s watersheds.  This report outlines several regional and local policies that could be initiated by both the District of Columbia and WASA to ensure that the quality of our water is protected without placing an unreasonable economic burden on taxpayers.  This report will also address ways to implement, administer, and enforce these policies.  Some of the regional policies and local ordinances and mitigation measures which I will cover include:

• Implementing a watershed based zoning overlay district
• Creating a storm water management utility fee
• Providing a tax credit and other financial incentives for developers and homeowners
• Developing performance based codes and a land use development matrix
• Using LEED and green building and LID practices to manage rooftop runoff

The paper will conclude that instituting a “greenroof” policy is an inexpensive low impact development technique and a system wide control alternative that could have a significant impact on our watershed quality over the next 20 years.  This section will lend additional credibility to these theories by providing calculations based on storm water modeling depicting various development scenarios.4

A proposed future look at D.C.

Source: Casey Tree Foundation

....  To continue reading and learn more about Greg's recommendations for a Long Term Control Plan and Greenroof Policy for the District of Columbia, download the complete report in his 22-page PDF...

The Recommended Control Program

Figure 2: Combined Sewer Over flow Long Term Control Plan

Gregory C. Long holds a Masters of Urban and Regional Planning from Virginia Tech, 2001-present and a BSLA from Pennsylvania State University, 1996.  In addition to continuing his education, Greg is a Project Manager in Bowman Consulting’s Alexandria office.  He has been with the firm since August 2003 as a registered landscape architect to help complement the land planning department.

Greg has been actively involved in issues pertaining to regional stormwater management policy/planning issues in and around the Washington D.C. metropolitan area. He has been assigned to a task force/advisory group to assist the District of Columbia’s newly formed Department of Environment on developing a newly proposed green building ordinance. This legislation and incentive based program would recommend the use of greenroofs and other low impact development (LID) practices to manage on site runoff for new construction and existing buildings. He has recently been asked to prepare workshops and lectures on the subject of greenroof and LID design for various trade organizations. In 2005, Mr. Long teamed up with Building Logics and a local non-profit “Lands and Waters” to win an award of excellence for the renovation of Yorktowne Condominiums in Falls Church, VA.

Contact Greg at:  Gregory Long, R.L.A., Bowman Consulting Group, Phone: 703.548.2188; Fax: 703.683.5781 or

may 2006
student guest article
The Urban Ecology: The Tri-dimensional Approach
By Colin Manasse

Publisher's Note:  The following paper was written for and presented at the First Urban Environment Congress, which took place in Brasilia, Brazil in September 2005.  Colin Manasse wrote the paper last summer 2005 in between college and graduate school.

Key Words: urban development, ecological modernization, tri-dimensional agriculture.


Problems abound when considering the environmental challenges of an increasingly urban society. Among these are a decreasing vegetation cover of the soil, water absorption capacity, shade and temperature regulating vegetation, and an increasing level of air, noise, water and light pollution. While many have attributed these problems to a plethora of factors; the main cause remains the properties of the materials used in the urbanization process. This is itself a result of economic circumstances that favor the use of cheap and inorganic materials. It is counterintuitive, therefore, that these very same materials could be used further in the provision of a solution to the problems associated with the urban environment, especially in the case of countries in the “southern cone,” especially Brazil.

Solving the environmental problems associated with urbanization requires lateral thinking, or rather vertical thinking. The surface area of vegetation that is displaced by the urbanization of an area, for example a city block, removes the services that are usually provided by that area of vegetation: heat energy absorption by plant leaves, temperature cooling from plant evapotranspiration, air filtration from plant respiration and the carbon cycle, noise reduction from plant asymmetries, etc.... The solution lies in the utilization of the surface area that is created by the vertical expansion of the buildings; in other words, the sides and roof tops. These are areas on which vegetation could grow, and further provide its services, only to the urban environment. The use of plants on rooftops is slowly emerging as a technique for reducing excessive temperature regulating energy, as well as for treating water. Ford Motor Company installed one on the top of one of their buildings in Dearborn, Michigan. The use of rooftops could help to restore approximately 60 to 90 percent of the vegetation area that has been eliminated, and vines on the sides of the buildings could actually increase this percentage beyond the original surface area.

The problems associated with the urban environment are of increasing importance in the realm of global environmental concern. This can be related to the fact that urbanization is a steadily growing trend globally, and the problems associated therewith are correspondingly of greater concern to societies around the world. Until the nineteenth century, less than 5% of the world’s population lived in cities, and by 1950 a third of the world’s population had urbanized. This trend did not slow down, even in the post industrial economies, which has led to today’s urban population reaching almost 50%, or 3 billion people. This number is projected to grow to 6 of 9 billion, or a swing to an urban ratio of two to one. The ever increasing urban population requires sustainable solutions to the many environmental, social, and economic consequences of this urban migration. (TIBAIJUKA 2005)

The global consequences of solving the problems of the urban environment are best depicted in Our Urban Future:

    A country’s global success rests on its cities’ shoulders. In a rapidly urbanizing world, it is the city that increasingly contains the social, economic, and political details of a country…Governments are the watchdogs that can ensure that environmental standards are being met and ecosystems are not being dismantled, that local services are not arbitrarily withheld from the poor, that citizens have the opportunity to participate in decisions that affect them, that safety nets are in place in case of emergency, and that norms of integrity are upheld by local officials. Therefore, one of the most urgent tasks facing governments everywhere is the formulation of a coherent set of policies that enables cities to take their place at the centre of national economic and social development. (TIBAIJUKA 2005)

The welfare of a city’s and the rest of the country’s population are intimately linked. The cities not only contain a significant portion of the country’s population, but also portray the image of that country to much of the rest of the world, since the economic centers of most of the countries around the world lie in their cities. It is therefore of utmost importance that the quality of life within the cities rise so as to elevate the quality of life within the entire country, if only by attracting foreign investment, and creating a demand for their city.

The cities contained within the scope of this paper are those which could be qualified as “global cities”. Saskia Sassen, of the University of Chicago, describes these cities as “expanded central urban areas”, “business nodes…that are strategic sites in the global economy” (SASSEN 2005). To better understand these global cities and their function in future social development, Sassen continues to describe this concept by saying: “global cities concentrate both the leading sectors of global capital and a growing share of disadvantaged populations (immigrants, many of the disadvantaged women, people of color generally, and, in the megacities of developing countries, masses of shanty dwellers).” Sassen has here described the concept of he global city, but has also touched on one of the important dimensions of the urban environment: the center-periphery divide.

On an international scale, the center-periphery divide depicts the separation of the rich and poor, not only as access to economic relief and possibilities, but as physical location from the economic centers. As one’s position is more removed from the center, the quality of life and the potential for improvement decrease. This can be seen in the urban sprawl phenomenon in many of the global cities, where the shanty towns referred to above are located on the outskirts of the city, and the greater the number of people migrate the more official the inner shanties become, which will lead to their development by the city, and continue to force the poor and disadvantaged further away. This kind of development leads to a growing mass of disadvantaged, whose problems include pollution and the spread of diseases, as well as increasing casualties and damage during rains or other disasters. The increased casualties are mostly due to the lack of physical structure of the developments, as well as the lack of flora which physically holds the top layers of soil in place during these rains, leading to landslides during heavy rains. The population of slum dwellers is expected to rise from 1 to 3 billion by 2050 (UN-HABITAT 2005), and is therefore a pressing concern when considering the urban environment.

Sassen concludes that it is through this point of view that we can now understand the global cities as locations for “a whole series of conflicts and contradictions.” (SASSEN 2005) This reiterates the link between the many problems associated with the urban environment: social, economic, and environmental. The cities are the new frontiers where national efforts and policies protecting the environment may lead to international treaties that are ratified, and whose enforcement is unnecessary. These cities are the gateway for establishing environmental primacy simultaneously by the international and local communities.

The natural environment should be thought of as an industrial process, which is the most complex regulating system known to us. It provides many services, including filtering the air and water on which we are so dependant, but also provides nutrition and sources of income by transforming our waste and the energy from the sun into natural resources. This is a closed loop system of which we are a part, and the greater the inefficiency of our development, the worse human health can be expected to get. It is this point of view which will allow for understanding the solutions that are needed to provide a cleaner urban environment, as well as solutions to social and economic problems associated with the urban migration.

The most widely publicized problem particular to the urban environment is that known as the Heat Island Effect. This refers to the phenomenon where the temperatures within urban areas reach higher daily levels than those in less developed areas. This has been attributed to the fact that cities are mainly comprised of concrete and asphalt, which absorb the heat from the sun during the day, and continue to radiate that same heat at night. The heat pollution can be linked to the incidents in Paris and London a few years ago in which older members of the population, with no air conditioning, died from heat exhaustion. This heat pollution also leads to increased energy use through artificially high needs for cooling loads of buildings, which contributes directly to increased air and water pollution, acid rain, and the plethora of problems associated with the use of fossil fuels. Therefore, this is a starting point in the reduction of urban pollution and the cleaning of the urban environment. The solution that many cities in the developed world are turning to is known as “Green Roofs.”

The footprint of urban development on a physical level is the area that is taken from nature, and replaced with a building or paved streets. In most cases, buildings allow for an increase in density of people or services by vertically developing the space used. The area of flora that is transformed can be understood as a corresponding loss in ecosystem services that were provided by that area (this is the loss of possible air and water filtration, heat absorption, etc…). The surface area that replaces it, from a bird’s eye view, is often left unused, as only a mere asphalt shingled roof that serves only one purpose, to separate those inside from “the elements.” It is this surface area that provides the opportunity for restoring those ecosystem services that have been so undervalued by developers and planners so far. These roofs can be used to plant gardens and restore some vegetation to the urban environment which would help to restore some of the services provided by nature.

The vegetation could help to filter the air polluted by the internal combustion transportation systems so prevalent in urban areas. This would help to reduce the incidents of health problems such as asthma and respiratory diseases that are strongly correlated with high levels of air pollution. Also, acid rain which causes great harm to national monuments, buildings, and the environment in which it is released would be filtered, and the amounts of urban runoff would be mitigated during heavy rains since much of that rain could be absorbed by the soils and plants on the roofs of the buildings. In addition, the cooling load of buildings would be greatly reduced for two reasons: the soil would provide an extra layer of insulation, which reduces the excess cooling load attributed to leaks, and the heat attributed to sunlight would be absorbed by the plants and other vegetation on the roof by fueling their photosynthetic processes. The shear number of services that would be provided by a citywide implementation of these roofs far outweigh the possible costs.

The tri-dimensional approach mentioned in the title, and heretofore left unexplained takes the concept of the green roof one step further. Since buildings are used to increase the amount of people that can fit onto an area by expanding that area into three dimensional space (elevating that area far above ground), the same development could be applied to the vegetation associated with a building. The soil on the roof of the building can be used to house the roots of vines, which can be allowed to grow along the vertical surfaces of the buildings. This would directly increase the vegetation of a surface area beyond that which was originally possible without any development. The use of vines would provide greater temperature regulation by providing the green roof cover to the sides of the buildings, and an extra epidermal layer of insulation in cold climates. This would also increase the services that were provided by the vegetation, such as air filtration and water absorption and filtration to meet the needs of a population that lives in three dimensional space.

The vines on the sides of the buildings would help to provide not only the same ecosystem services that are provided by the green roofs, but could potentially provide for the mitigation of other forms of pollution that are specific to urban areas: light and noise pollution. The increased density of populations in urban areas, as well as the diverse nature of the urban economy has meant that services and lifestyles have also diversified: people are awake at all hours of the night, traders must be awake to start trading on foreign financial markets…These varied lifestyles correspond to more light being used in densely populated areas, whose buildings have windows and other reflective surfaces which create light corridors that promulgate a single light to many different buildings, and therefore to many different people. The vegetation on the sides of buildings would help to mitigate such effects by reducing the corridor down which the light can travel, as well as by reducing the reflective surface area. The concept being similar for sound waves as it is for light, this absorptive capacity should therefore also apply to noise pollution. In urban areas, sound waves propagate and reverberate by bouncing off the hard surfaces of concrete and glass that are usually uncovered. The very flexible and malleable nature of vines, and vegetation in general, should also help to reduce the noise pollution attributed to cars, buses, and general activity which takes place at all hours of the day or night in global cities. The capacity of vegetation to absorb and transform are the keys to future urban development, and to that development being associated with a high quality of life.

The choice of vegetation used in the provision of urban ecosystem surfaces will vary depending on many environmental factors, as well as economic and social ones. The environmental factors that will affect which vines are used include: yearly temperatures, climate, latitude, and all other factors having to do with the geographical location of a specific city. In this regard, it provides an opportunity for that global city to reconnect to its region. This should help to mitigate some of the social problem associated with urban development, as it would provide ties for the migrant urban poor who migrated from the rural areas to their place of origin, and to something familiar. This might help to reduce the social division between the rich and poor, and help to ease the transition from rural to urban life on a psychological level.

The choice of vegetation will also affect the city on an economic basis, since much of the vines that can be chosen provide sources of revenue for the cultivators. Tomatoes, raisins, and grapes are just some of the choices that will affect the economic interests of the city, and those of its citizens. The increased urban production of produce or flowers will have disseminating economic effects, since there will be an increased demand for the services associated with the agricultural sector, and those linked to it. The cultivation and collection of the fruit and vines will require agricultural knowledge, mostly associated with rural settings, so the immigrating rural poor will have greater opportunity for employment, thereby reducing poverty, and the increase in food availability will help to raise the quality of life. The organization of the cultivating and collecting activities will help to provide management level employment in the private companies or cooperatives formed to efficiently collect the produce. Associated with this, is the need for constantly clearing the windows from obstruction, and therefore vine trimmers should develop as a profession, much like high altitude window cleaners. These are all constant employment opportunities, unlike construction projects which only last as long as the project itself takes to complete.

The nutrients that would be required for the continued growth of the vines and agricultural production associated with it would have to be organic in nature, since the widespread application of chemical fertilizers and pesticides in urban areas would constitute unfathomable health risks. To that end, a city wide organic waste recycling program could be implemented. This waste could be composted on the roofs of the buildings, which would localize the waste to nutrient transformation. Since it is likely that the rate of organic waste production would outpace its absorption as nutrients, the recycling of the waste into nutrients should be accelerated, probably using earthworms (class Oligochaeta) since they both till he soil and their castings improve its texture, although experts should be consulted, and specificities determined. The recycling program, from collection to compost, would again help to provide permanent employment opportunities for the increasing numbers of urban poor.

There are some problems that may be associated with the increase in flora in urban areas; most obvious is the corresponding increase in fauna. The increased vegetation is likely to bring into the city some of the pests and insects that are commonly associated with farms, and they are likely to bring some of the diseases and health problems with which they are linked. This could reduce the overall health benefits of urban agriculture in the short term, though not significantly. In the long-term, as with much of ecology and evolution, increased exposure will increase the population’s resistance, so human vulnerability to such diseases and insects will decrease over time.

More pertinent to the agricultural vine developments, is the possibility of bioaccumulation. The vines that grow the produce and filter the air do so in part by absorbing the toxins that are in the air. There is therefore a possibility that these toxins may accumulate in the fruit that they produce, and could therefore pollute some of the fruit. While this is unlikely, its possibility must be investigated before deciding which vines should be grown, since it will have effects on human health as well as the economy, and possibly international political relations since the fruit would be available for export. It would therefore be prudent that the first few vines be floral in nature, to avoid compromising the citywide implementation of this solution.

This solution addresses mostly the center of the urban center-periphery division of the city. The solutions for the periphery require that financing be taken into account before any further questions may be addressed, since the global city already has financing and infrastructural services at its disposal, these can be assumed, which is not the case for the periphery. The solution for the periphery is much the same as for the center. Vines would help clean up the air and the general environment, as well as provide increased quality of life by providing alternate sources of food for those who cannot afford it. If the vines are planted in the ground, which is uncovered in shanty towns, and allowed to grow atop the shanties they would provide “anchors” for the top soil, which will help to mitigate the disastrous landslide effects of rains, as well as shade and cooler temperatures for the shanty residents.

The problems arises when the financing of the vines and associated costs are being considered. We must here link the center to the periphery on a political level, since only proper political financing structures will help provide the necessary incentives. The vegetation cover that is lacking due to window clearance provides a financing opportunity in a tax/trade structure for the center to provide the means of growing these vines to the periphery. If tax deductions are provided for growing vines on the sides of buildings, it could be reduced accordingly by the lack of vegetation in the windows. The proprietors could therefore be offered the opportunity to compensate for this lack of vegetation by increasing the vegetation cover in the periphery. The incentive would arise from a tax reduction, but also in the overall lowered costs associated with landslides and generally on the social benefit of having a higher quality of life for all city residents, such as reduced crime. The incentive would have to be provided according to those services, such as a reduction in health care taxes for those participating members, though limited only to the surface area covered by the windows of the buildings so as not to remove incentive for central urban solution implementation. This addresses a major flaw depicted by Blair Ruble when considering past development plans: “master plans proved too inflexible to respond to the rapid growth of informal settlements” (RUBLE 2005).

The tri-dimensional approach applies on a physical, as well as on a conceptual level. The approach calls for floral development in three physical dimensions (height, width, length). The implementation of this approach provides solutions in three dimensions as well: the social, the economic, and the environmental. Raw data still needs to be generated, collected, and analyzed so that more accurate cost benefit analyses may be carried out. However, on a theoretical basis, vines and green roofs seem to provide many solutions to the problems within the urban environment, and should therefore be seriously considered by all global cities as a means to move past the limits of urban development provided by physical limitations, and into the development of their populations by increasing the employment, the ties to the region, and the quality of life for its citizens generally.

Profile of an Urban Heat Island

Source:  EPA

Participants of the International Congress on Environmental Planning and Management –
Environmental Challenges of Urbanization
, held in Brasilia, Brazil, from September 11th to
15th, 2005, decided to adopt the following Charter of Brasília, inspired by the presentations and the papers submitted, and by the outcomes of the discussions that took place during the event: Charter of Brasília in PDF.

Bibliographic References

1. SASSEN, S.; The Global City: Introducing a Concept, Brown Journal of World Affairs Volume XI, Issue 2, Providence, Brown University Press, 2005, 14 p.
2. TIBAIJUKA, A.K., MASELAND J., and MOOR J., Our Urban Future: Making a Home for Homo Urbanus, Brown Journal of World Affairs Volume XI, Issue 2, Providence, Brown University Press, 2005, 11 p.
3. RUBLE, B. A., TULCHIN, J. S., and HANLEY, L. M., Moving Towards Inclusive Cities, Brown Journal of World Affairs Volume XI, Issue 2, Providence, Brown University Press, 2005, 8 p.
4. CAMPBELL N. A., Biology, 4th ed., Menlo Park, The Benjamin/Cummings Publishing Company Inc., 1996, 1206 p.
5. ATLANTA CITY HALL, March 2004,
6. United States Environmental Protection Agency

Colin Manasse is currently studying International Environmental Policy at the Monterey Institute of International Studies, in Monterey California, specializing his studies in renewable energy development in Asia and Africa.  I am therefore conducting most of my research in those areas, both topical and geographic, but enjoy researching and studying urban and sustainable development.  Colin is currently working at the Transportation Agency for Monterey County, which is a transportation planning agency. He will be interning at the United Nations Statistics Division this summer, which he looks forward to with great anticipation.

Contact Colin at:


march 2006
student guest article
Preliminary Survey of the Plant Species on Carleton’s Green Roof
(Fall 2005)

By Sonja Mae Langton-Yanowitz ’06
with help from Mark McKone, Phil Camil, Miranda Fix, Jennifer See, Jason Lord & Richard Strong
All Photos Courtesy
Sonja Mae Langton-Yanowitz

Publisher's Note:  Sonja-Mae is providing an update to the July 2005 Student Guest Article "The Carleton College Green Roof Project" by David Holman, Jason Lord, Jake Gold, and Andrew Kaplan of Carleton College.  The students conducted a survey of the plants growing on the green roof last fall and they wrote the following report of their findings.  As the lengthy report features extensive charts, please download the entire survey in PDF form below. See the Carleton College Green Roof Project in the Greenroof Projects Database here.


In the spring of 2005, a team of Carleton College students built the first student-designed green roof in Minnesota at Carleton College. Consisting of 666 sq. ft., it was planted with 75 species of plants native to Minnesota prairies, and has given the building an aesthetic and environmental function. However, besides adding to beauty of our campus, one of the primary reasons to build the green roof was so that we could conduct research.

Our research interests are three-fold: We are curious about 1) the additional insulation value (R-value) that a green roof provides to an existing roof, 2) how a green roof affects water-runoff quality, and 3) how the unique environment of a green roof affects the colonization and survival of prairie plants native to Minnesota. This article addresses question number three and presents the findings of our first plant survey, which was conducted during the fall of 2005. The primary leader of this survey was Sonja Mae Langton-Yanowitz, a senior biology major, who became involved with the project because of her interest in plant identification.

During our design process, we thought that the unique conditions of our green roof, which the prairie plants would have to adapt to, would be a shallow soil depth, and a dry and hot environment. Prairie plants typically have deep root systems. However, the soil depth of our green roof ranges from 6” to 2”. We predicted that the green roof conditions would be dry because the plants would not have an underlying water table to draw water from in times of low precipitation. Also, because of the exposed position on top of a roof, we predicted that the green roof environment would be hot as compared to a typical prairie system. With these conditions in mind, we were curious to see which plants would grow during the first season. The following survey explains what we found.

Planting the Roof

During the spring of 2005, root stock was hand planted in sections on the roof and a seed mixture was spread all over the roof. During fall, 2005, we noticed that species not present in the root stock or seed mixture were also growing on the roof; these plants will be referred to as colonists from this point forward.

Survey Method

The Daubenmeyer vegetation plot survey method was used to estimate the percent cover of each plant species on the roof. The roof was subdivided into 10 plots (Figure 1), and within each plot, each species was estimated as covering: 0, 0-1, 2-5, 6-25, 26-50, 51-75, 76-90, or 91-100 percent of the plot. For example, a person could look at a plot and estimate that dandelions are covering 6-25% of the plot, 6-25% of the plot is barren (no plants are growing), and clover is covering 51-75% of the plot. The data that we collected is presented in the tables following Figure 1.

I was not able to identify all plants growing on the roof because not all plants were in flower, and it can be difficult to identify a plant without the flower. For this same reason, some plants were only identified to family. It is likely that the identifiable species composition will evolve as the years pass because some prairie species require a period of dormancy (sometimes ranging up to a few years) before they are able to send up a flower stalk and can be identified.


Overall, 75 species were planted on the roof; of these species 9 were found growing on the roof. Twenty-eight colonist species, which were not planted on the roof, were also found growing on the roof.

Suggestions for the Future

I would recommend surveying the roof during the summer, because more plants will be in bloom and identification will be easier. If anything, this survey underestimates the species richness on the roof, but at least it is a good preliminary survey. During this project, it was suggested by Myles Bakke (Carleton Arboretum Manager) that since many prairie species thrive under periodic burns, it may be worthwhile to simulate the effects of a burn. He suggested mowing the roof in the spring, burning the mulch, and then spreading the burnt mulch over the roof. This would give a competitive advantage to the prairie species by eliminating their competitors and would reintroduce nutrients back into the soil.

Also, Mark McKone (Biology Professor) suggested the possibility of growing vines on top of the roof. He said that vines are often a hardy species that can grow in little soil and are not very bothered by dry or wet conditions. Also, he said that the leaves of the vines would probably be good at absorbing heat, just like the other roof-top plants...

Carleton College Test Greenroof, Fall 2005.

The green roof as viewed from Plot I (see Figure 1
in PDF).  The red flags pictured help mark the
plot boundaries.

                                    >>more (Download the 27-page PDF)

Please visit the new Carlton College Green Roof Project website.  For more information about our Carleton College building and design process, see the July 2005 Student Guest Article "The Carleton College Green Roof Project" below by David Holman, Jason Lord, Jake Gold, and Andrew Kaplan of Carleton College.

Sonja Mae Langton-Yanowitz is a senior Biology major at Carleton College.  Her interest in plant identification began when she worked as a Naturalist for the Superior National Forest Service during the summer of 2004.  She will be attending Dental School at the University of Minnesota in the fall of 2006.  Contact Sonja Mae at:

july 2005
student guest article
The Carleton College Green Roof Project
By David Holman, Jason Lord, Jake Gold, and Andrew Kaplan
Carleton College
All Photos by and Courtesy of Jason Lord and Dave Holman

Carleton Test Greenroof

The Carleton College Test  Green Roof Project


On May 18 of this year five Carleton College students completed building the first green roof to test 78 varieties of prairie plants native to Minnesota for their viability to the green roofing industry.  This 666 sq ft roof on part of the Olin Science Building at Carleton College is also the first student-designed and built green roof in Minnesota.

The roof will provide structural, functional, environmental and aesthetic benefits to the building.  The project will provide plant growth data, water monitoring and temperature data that will be used for further roof construction at Carleton and by green roof contractors.  The roof can be easily viewed from the glass breezeway connecting the Olin and Mudd Science Buildings at Carleton College.

The Carleton College Green Roof Project was formed last September 2004 by David Holman ('06), Jason Lord ('06), and Jake Gold ('07) as an independent study at Carleton College in Northfield, MN.  The project is advised by green architect and Carleton Director of Facilities Richard Strong, and was inspired by his class "Building the Eco-House" taught in the spring of 2004.

Student on Gravel RoofThe vegetation is coming in
Before Left: The Olin Science Building at Carleton College; Right: Greenroof After Three Weeks

The fall of 2004 was spent studying green roof design and planning where green roofs could be made at Carleton.  In our independent study, we set out to conduct some of our own research. To determine energy savings, we calculated the additional insulation value (R-value) that a green roof provides to an existing roof.  We calculated R-values with our soil mixture saturated and dry.  The team did R-value testing on various soil types during the fall and winter finding many case studies demonstrating the energy savings green roofs provide in the summer, but like other research has shown, green roofs do not contribute very significantly to a roof's R-value or energy savings in the winter.  We will continue to do further testing next year.

R-Value Testing at Carleton

Last winter we planned where to build a small test roof on campus and decided what materials and plants to use.  This Spring Mandi Fix ('08) and Andrew Kaplan ('08) joined the project.  The team decided to try testing only prairie plants native to Minnesota.  Prairies are typically so draught resistant because of extremely deep root systems, so we expect many of our species to suffer under the low soil conditions of our green roof.

The crane does all the heavy lifting!The three volunteers

Getting the materials up and then taking a needed break!


Separating the materials

Staging area for materials

The group chose a 666 square foot roof connected to the Olin Science building.  The roof is highly visible via an elevated glass walkway on the West side and is one of the strongest roofs on campus because chemicals are stored underneath.  The soil substrate consists of two layers: the bottom layer is a 4" mix of 36.5% Perlite, 36.5% Vermiculite, 12% Clay Particles (a product called Turface), and 15% compost from Carleton's yard waste pile.

Growth Media Mix

Left: 4-Mix Bottom Layer Growth Media; Right: Top Layer

This bottom layer is designed to be extremely lightweight, water absorptive, and inorganic. The top layer 2" of pure compost is then slightly mixed into the bottom layer to create a heavier, more organic top layer for seed germination and prevention of soil loss via wind. The 6" mixture weighs 16.1 lbs/sq ft dry and 24.9 lbs/sq ft saturated. This unusually organic soil mixture was used to provide more lush plant growth. This compares favorably to the existing ballast, weighing 11 lbs/sf.

Mixing up the media ingredients

Spreading the media

Left: Mixing the specified growth media; Right: Spreading it is hard work, too!

Our Goal in this project was to design a green roof using as many native prairie plants
as possible.  We used a large seed mixture of hardy prairie plants from this area. We
chose species that we thought would best survive thin the hot, dry and shallow soil

Root Stocks from Prairie Moon NurseriesGrasses and Cactus

Root stocks

Native grasses and cactus sprouting

We planted: 54 species of prairie forbs, three types of shrub/vine species, 19
species of grasses, sedges, and rushes, and a cover crop of oats was seeded.  This mix was provided by Prairie Moon nurseries of Winona, MN.  To provide faster plant establishment for this highly visible roof, 250 root stocks from Prairie Moon of various prairie plants were also planted.  We selected our plants with the help of Ron Bowen of Prairie Restorations, Prairie Moon Nursery and Carleton Biology and Arab faculty.

The drainage layer beneath that soil is a DBR-50 Rootbloc product manufactured and generously donated by American Wick Drain.  This drainage layer provides a grid of small plastic cups to retain water while any overflow drains away.

The American Wick Drain DBR-50 Rootbloc

American Wick Drain donated 1,000 sq ft of their 1/2” drainage layer DBR-50 Rootbloc

Thanks to donation of materials and student labor, the cost of the current project was around $2.07 per square foot. The total project cost of our green roof (with free labor and drainage layer) was $1,375.  We would like to thank American Wick Drain for their generous donation of
1,000 sq ft of their 1/2” drainage layer for this project!   We would also like to thank Carleton’s facilities and grounds departments for their great support for this project!

This season the team will be constructing another test roof which will compare plant growth using three different drainage techniques over two different soil depths.  The team will be measuring plant establishment and survival over the next couple years and planning to construct a much larger project that would provide cooling benefits to a dorm.  A hydrologist from Carleton will be testing the water runoff quality over time.  The team will be publishing all the specifics of our materials, design and testing on our website (which is still under development) at:

See our PDF of The Carleton Green Roof Project here.

Growth after three weeksGrasses

Plant growth will be monitored at the Carleton Test  Green Roof Project over the next couple of years

Construction began on Friday, May 13 and the roof was finished and planted by Thursday, May 19.  In the three weeks following the construction thousands of seeds germinated and the rootstocks seemed to be taking hold and growing.  The team expected a much slower growth rate but the roof already looks truly green with plants several inches high covering its surface.

Jake, David, and Jason's fields of study in greenroofs at Carleton College are thermal performance, specifically R-value of different substrate materials, and cost benefit analysis.  They are experimenting with native prairie plantings.

Jake Gold is a geology major at Carleton College graduating in 2007.  He runs
the Farm House garden and is the Carleton Green Roof's biology expert.
 Jake can be reached at:

David Holman is a Latin American Studies major and Environment and Technology
studies concentrator at Carleton College graduating in 2006.  He is on the
Environmental Advisory Committee at Carleton and oversaw the logistics of the
Reach David at:; Phone: 507.646.5479.

Jason Lord is a Studio Art and Economics major at Carleton graduating
in 2006.  He is an expert builder and handled many of the technical
issues of the green roof. 
Jason can be reached at:

Andrew Kaplan joined the Carleton Green Roof Project this Spring, and he
will be graduating in 2008.


may 2005
student guest article
Elevating Greywater Filtration to New Heights
By Keith Ardron, BLA student
University of Guelph

The average human can survive for around four minutes without air and only about four days without water. Why then are we so wasteful of these most precious resources?

I have spent the past few years researching and designing green roofs in North America. During this time, I’ve never really questioned the use of city supplied drinking water for irrigating green roofs in arid climates. It seemed like what was needed to be done. Where else would you find a source of irrigation water in today’s cities? It’s not just the green roof that uses drinking water for irrigation, but almost all outdoor landscapes use this water source. Why? Clean drinking water is one of our most valuable natural resources, second only to air. There simply must be a better way.

Greywater (used wash water from sinks, showers, and basins) is looking like it holds the key to the future of irrigation, with many states changing their laws to allow for the use of this more sustainable water source. Filtered greywater can be safely used as toilet flush water and ornamental landscape irrigation. The problem is that many conventional greywater filtration systems require some space on the ground for a constructed wetland or similar type of filter. In today’s dense urban environments this is not always possible due largely to the cost of land and the lack of it. The roof’s surface is looking like it may hold the solution to this dilemma.

For many years, several European countries have used this idea successfully. The Possmann Cider Company in Frankfurt, Germany has been using the warm greywater from its cider production operation to irrigate its marsh-like green roof. The plants, in turn, filter out impurities from both the used cooling water and rain, while cooling the warm water before it is reused inside the building again. This greywater filtration system saves the company $6,000 annually in cooling costs. (Earth Pledge, 2005)

Another company that may have the solution for making this technology more obtainable for commercial use is Water Works UK. This company is working to develop a kit from of its GROW (Green Roof Water Recycling) system. The system has been installed on the roof of Cranfield University in London, England where it filters much of the greywater from the student residence for reuse as toilet flush water. Another ingenious feature of this system is that it dyes the water slightly green to distinguish the filtered greywater from the potable drinking water supply. (Shirley-Smith, 2004)

I think that greywater filtration on green roofs is the future for many cities in arid regions. The benefits would be widely felt including reduced water use by as much as 40% when greywater is reused in the same building for toilets and landscape irrigation. But, most importantly, it would make green roofs a much more sustainable solution in the hot and arid regions that could benefit most from their use. The increased benefits of an irrigated green roof have been shown most notably in an energy model of the City of Toronto done by Brad Bass and Bas Baskaran (2002) which indicates that irrigated green roofs are 400% more effective at reducing the urban heat island effect than non-irrigated ones.

I would like to see this technology implemented on pilot projects throughout North America to assess its feasibility for larger scale use. I think that to ignore the soon to be severe shortage of the world’s second most valuable resource would be a very grave mistake, the effects of which will be felt by generations to come.

Works Cited

Bass, B., Baskaran, B. (2002) Modeling the impact of green roof infrastructure on the urban heat island in Toronto. [Electronic Version], Green Roofs Infrastructure Monitor. (Vol. 3(1), p10-12): Green Roofs for Healthy Cities.

Earth Pledge (2005). Green Roofs: Ecological Design and Construction. Atglen: Schiffer Books.

Shirley-Smith, C. (2004) Water Works UK. Retrieved March 20, 2005, from

Keith Ardron will be graduating from the Bachelor of Landscape Architecture program at the University of Guelph this summer. Keith is also a graduate of the Landscape Design Diploma program at Fanshawe College in London, ON where he first began his research into green roofs four years ago. He has been working for Elevated Landscape Technologies for two years now, helping to develop and market their innovative new ELT Easy Green™ roofing system.

For more information about
Elevated Landscape Technologies or their new ELT Easy Green Product visit or for specific green roof questions contact Keith at

january 2005
student forum editorial
Reflections and a Look Ahead from the Student Editor

By Christine E. Thuring, MSc Student, Centre for Green Roof Research
College of Agricultural Sciences, Penn State University

What a fantastic year was 2004 in the world of rooftop greening!  As a graduate student playing the balancing acts of time management with crafty prioritization, or cerebral overload with joie-de-vivre, the advances made in the North American green roof market add a sweet dash of big-picture motivation and excitement that brings it all together.

A special Happy New Year to each of the 40 students registered in the Student Directory!  If you scroll through the Directory, you'll see that the fields of study covered by our Student Forum covers rooftop greening's broad scope: environmental (energy, air, ecology, water); social (urban agriculture, community education); economic (landscape management, sustainable construction, modeling).

For 2005, Linda and I look forward to more Student Guest Articles, from which we can all learn, not to mention inspire and encourage each other.  While it may seem impossible to allocate time and energy to on-line extra curriculum, the unanticipated benefits from committing yourself to a wee article can be truly rewarding.  Whether you've just finished your project proposal, or have just graduated with your degree, we'd love to hear what you have up your sleeve!

Also lighting up 2005 are the international conferences that offer an actual forum for networking and information exchange.  I'm so looking forward to seeing familiar and new faces during D.C's cherry-blossom time!  And word has it that Basel, Switzerland, will be hosting a Kongress sometime in 2005, too!

Happy New Year, best of luck with your endeavours, and keep in touch!


august 2004
student forum update

Christine Thuring, MSc student at Penn State University, is the new Student Editor at  She hopes to build a network of students involved in green roof research and will contact those listed in The Student Directory and others.  Email her your thoughts on what you wish the Forum to offer, and share your endeavors with the Student Forum.

Christine's interests in rooftop greening are supported by her academic background (BSc Environmental Science & Biology) and work experiences (field botany/ ecology, rooftop greening).  Rooftop greening satisfies her devotion to both the environment and to the improvement of humanity's relationship with the natural world.

Her mission is to help advance rooftop greening in America (North, Central, South).  Sustainable development of this new industry is vital, and she hopes to pursue this aspect in the future. Her Swiss-Canadian roots will always pull her to her home - and motherland, where high quality of life inspire her further.  She believes that the Future is green.

september 2004
student guest article
Encompassing the Whole Program: Michigan State University
By Angie Durhman, Masters in Horticulture student
Michigan State University

Photos courtesy Angie Durhman, unless otherwise noted.

MSU Logo

Just as green roofs provide a unique environment for plants and wildlife to live, they also provide a unique environment to study, collect research, and receive advanced degrees.  My pursuit of an advanced degree was finalized when I realized I could combine my love of plants with a practical application that was interesting, beneficial to the environment, and mostly, sustainable.  Once again, green roofs answer each of these demands.

About Me

I received my B.S. in Horticultural Science from North Carolina State University, where I also minored in Technical Writing and Botany. I accepted a job immediately after graduation, and I worked for a year in the private industry.  I decided to return to school in pursuit of a Masters degree at Michigan State University in the department of Horticulture when I was offered an assistantship researching horticultural aspects of green roof technology.  In addition to my research, I wanted further experience in the plant sciences and learn about sustainable systems.

The Research

My research focuses on increasing plant diversity on extensive green roof systems and evaluating plant performance over time.  I think it is important to observe what plants are successful in different regions of the country so the green roof industry can be ready with successful planting systems.  What we know grows well in Germany, and the east coast of the United States, may not be hardy in the Michigan climate.  Our research program is located in the USDA hardiness zone 4-5.

MSU Plot in the Beginning!

Test MSU Greenroof Plot Planted on June 12, 2003

Data collection methods in the field included measuring growth rates of 25 different succulent species (established from un-rooted cuttings) using image analysis.  To measure competition among those species, I used a point frame transect with a vertical needle to accurately record species presence or absence over time.  Evaluations also included documenting rooting and over-wintering successes.  The 24 research plots were randomly assigned three substrate depths of 2.5 cm, 5.0 cm, and 7.5 cm.

Michigan State University Test Greenroof, Photo by Angie Durhman

Transect Method, 1-Year Growth

The field plots host several plant life form types - meaning, morphological/physiological response during the stressful winter season.  Specifically, retaining vegetation (evergreen), protecting the regenerative buds in the soil (deciduous), or by spreading seeds (annuals).  Documenting their flower time and vegetative changes has been exciting each week I collect data.

Additionally, a greenhouse experiment allowed us to control watering regimes to measure drought stress by chlorophyll fluorescence.  Several plants in this study were also used in my field plots.

Research Conducted by Angie Durhman

MSU Test Greenroof Field Plots on the Farm, June 23, 2004

More details and photos can be found at The Michigan State University Greenroof Research Program.

Consequently, doing green roof research without a rooftop has its limitations.  The research program I entered into had simulated roofing platforms that were built just like a conventional roof, without the actual building underneath it.  The obvious criticism is that the building structure does change the microenvironment for plant growth.  To which I must reply, sure - but if anything, it creates a more harsh environment that forces plant performance to the extreme.  However, benefits of working on simulated roof platforms is the ease of data collection because it is raised only three feet from the ground, problems can be more easily solved, observations can be more detailed, and it is cheaper to construct.

The Plant and Soil Sciences Building (PSSB)

Now MSU has its own green roof to boast about!  On May 21, 2004, we installed an extensive green roof.  The intent is to serve as a demonstration/education roof for the general public and students while providing data to the campus wide master planners.  As with many campuses and cities, MSU is concerned with storm water runoff and energy conservation within buildings.  Providing data collected in the local environment will support the claims already associated with green roof benefits, in hopes to serve as a practical alternative when replacing rooftops on existing buildings or designing them on new buildings on campus.

Laying the Vegetated Mats

Volunteers Helping with Installation, May 21, 2004


MSU Rooftop Before Greenroof, Photo by Dr. Bradley Rowe

Pre-existing PSSB Rooftop; Photo Courtesy Dr. Brad Rowe

The Plant and Soil Sciences Building (PSSB) is surrounded by public horticultural gardens, which beckons over 200,000 visitors a year (500,000 projected within five years!).

To view the 3500 sf vegetative roof, visitors can easily enter the second floor break room where the view is less than 100 feet away.

People can see the changing vegetation year round and become aware that it is more than “green” but could be better described as “living.”

The PSSB green roof has a scientific component.  The pre-existing roof (gravel) section will be compared to the new vegetative surface.  Instrumentation includes: heat flux sensors (measures heat transfer of the building), time domain reflectometry (TDR) soil moisture probes, relative humidity probes, thermocouples measuring temperatures at various levels in the green roof system and surrounding air, and a complete weather station.  Eventually, we will have a web camera for images and real-time data posted on the internet so anyone, anywhere can see a working, evolving, green roof!  The process of installing and maintaining a green roof, and programming the monitoring equipment has been an invaluable learning experience.

MSU's PSSB Rooftop, 5th Floor, Immediately After Installation, May 21, 2004

As in the “real-world industry” setting, collaborations are essential in creating a successful green roof.  Inter-departmental collaborations has strengthened the MSU Green Roof Research Program.  Professors and students come from the following departments to bring forth their expertise in: Horticulture, Crop and Soil Sciences, Plant Biology, Agricultural Engineering, Mechanical Engineering, and Climatology.

Response to the PSSB Green Roof

Our green roof has provided the local community with a new buzz word.  Television crews documented the installation.  Several newspapers, magazines, and trade journals published articles.  Garden clubs and conference attendees wander the halls in search of the green roof.  To answer inquiries from inhabitants of the building and visitors, a poster was written to explain the benefits and describe the ecological reasons why it is not always “green.”  The governor of Michigan is considering implementing a state-wide green roof initiative and is using our research program as a perfect learning tool!

Currently, my biggest struggle is to convince people that the roof is living and changing, and that it will not always be the color green.  I explain that with a variety of species comes different times in which plants flower, retain the dried seed heads, and change leaf color due to drought stress.

Holistically Acting

Fellow graduate students constantly tell me (with a bit of jealousy in their tone) I have a completely interesting and beneficial research project - and I think I am finally believing the truth in those statements!  Although taking the necessary courses to finish my degree, continuing to collect data, and writing my thesis, I have found another important responsibility as “a student researching green roofs.”

As interest in green roofs increases, I get emails and phone calls with questions.  Promotion is a big component that I welcome, though feared at one point!  My background in technical writing has helped me prepare posters, papers, and talks for a variety of audiences.  One thing that I am going to continue to do is promote living roofs: the good, the bad, the ugly, the successful!  When I graduate this December (2004), I hope to continue in this dynamic industry, using my horticultural experience and overall excitement and belief in the technology to establish my own sustainable career!

Angie Durhman, Graduate Research Assistant in the MSU Department of Horticulture, welcomes your comments and can be reached at or 517.230.2229.


june 2004
student guest article
Center for Green Roof Research, Penn State University
The effects of different media, depths, plants and drought on green roof plant performance
By Christine Thuring, MSc student
Penn State University - Updated 6.19.04

Photos courtesy Christine Thuring

The Center for Green Roof Research at the Pennsylvania State University (PSU) is working steadily to advance rooftop greening in North America. Public outreach is initiated through exhibits, presentations and posters, and research is being conducted at all academic levels.

In Spring 2004, for example, several student groups in Horticulture 315 chose green roof topics for their semester research projects. For 6 weeks, students observed the responses of green roof plants to different stimuli. One group studied photoperiodic responses of green roof plants, and another observed the effects of different storage periods on root production by cuttings. The effect of slope on plant water availability was also studied, as well as growth rates and competition dynamics of plants growing at different locations on a slope.

Currently pursuing my MSc, I came to PSU in Fall 2003 with a BSc in Environmental Science and Plant Biology (Trent University, Ontario), as well as an internship experience in the German rooftop greening industry (Bienger GmbH). Under the mentorship of Drs. David Beattie and Robert Berghage, I am studying the influence of growing medium type and depth on green roof plant performance in face of different drought treatments. The experiment will run for the summer of 2004, after which it will be harvested and analyzed. Results and discussion will be posted on the PSU Green Roof website.

The Study
Two growing medium types were selected – expanded-shale and -clay – to be studied for variations in water holding capacity and, consequently, plant support. Each of the medium types is being tested at three depths – 3, 6, and 12cm (1.18, 2.36, and 4.72 inches). The limit imposed by growing medium depth on plant water availability will be evaluated by examining plant responses such as percent cover, root-to-shoot ratio, photosynthetic rate and biomass.

PSU Greenroof Study Plant; Photo by Christine Thuring

Sedum album in expanded shale

Three drought treatments were designed to evaluate the effect of drought during green roof plant establishment. Plants in the “no drought” treatment will receive weekly irrigation. Plants in the “early drought” treatment will be watered at planting but then won’t receive any water for three weeks (they will have weekly irrigations thereafter).

Plants in the “late drought” treatment will receive weekly irrigation until late August when they will be droughted for three weeks.

The Center for Green Roof Research, PSU

Plant Testing at PSU

Left: Sedum sexangulare in expanded clay; Right: Delosperma nubigenum

Five plant species will be studied, including three succulents and 2 perennial forbs. Based on the different water relations and rooting systems, as well as common experience, it is expected that the succulents (Sedum album, S. sexangulare, Delosperma nubigenum) will perform better in the shallow depths than the forbs (Dianthus deltoides, Petrorhagia saxifraga). The plants will be studied in monoculture and in community.

PSU Greenroof Plant; Study by Christine Thuring

Christine's Greenroof Plant Testing at PSU

Left: Dianthus deltoides; Right: Petrorhagia saxifraga in flower

Experimental Test Tunnel, PSU Green Roof Research Center

The tunnel. Note the door vent and hanging irrigation system.

The experimental units are arranged in a randomized complete block design in a temporary greenhouse, or tunnel, at Potter's Mills, PA.

This way, plants receive water solely from the irrigation treatments.

Air circulation and temperature regulation inside the tunnel are achieved by rolling up the sides and door vents.


Christine's PSU Greenroof Plant Study Site

PSU's Kacee Wheeland in The Tunnel

Left: The sides of the tunnel are rolled up enough to keep water off the study while promoting air circulation. The tunnel sits on a well-drained bed of shale, which prevents puddling.

Right: Summer student, Kacee Wheeland, keeps things in order; what a gal. The study comprises 6 blocks, which are flagged and marked by concrete slabs.

Future Applications
This research may help to identify the effective balance between green roof depth, function and weight. In terms of planning, this could relate existing roof construction with potential green roof type. Results may facilitate the planning and application of extensive green roofs in North America.

For instance, knowing the plants and communities that perform well in certain growing medium depths can serve to establish guidelines for roofs of different weight capacities. Also, results may show that medium type should be considered when planning for certain green roof types. Since this experiment is controlled for drought treatments, future trials might be located outdoors and exposed to actual climatic conditions.

Check the PSU Green Roof Research website soon for updates.

Christine Thuring is the new Student Editor, and she will be contacting students listed in The Student Directory and others to see how we can encourage, support and network all students involved in green roof research.  Share your projects with the Student Forum and your thoughts on what you wish the Forum to offer.

Christine Thuring is a MSc student in Penn State's Department of Horticulture's Centre for Green Roof Research, graduating in Spring 2005. Her project will study the effect of different medium depths on plant performance, seeking a balance between depth and effective green roof function (stormwater retention, persistent plant community).

Or, you can also contact Christine at; 814.574.1711.

march 2004
student guest article

Research Survey for Rooftop Landscapes
By Emily Drake, MLA student
University of Texas @ Arlington

I cannot recall the moments in which I first became interested in roof top gardens.  In 1996, I received a Bachelor of Arts in Theater from the University of Arkansas in Fayetteville.  After a brief stint of working as a “techie” with local audio-visual companies and theater houses, I moved to Dallas, Texas.  It was in Dallas that I wandered into the field of landscape architecture.  Since starting in the MLA program at the University of Texas @ Arlington, I have had an interest in roof top landscapes.  Perhaps it is that they possess some kind of other-worldly power that inspires the collaborative work of great artists.  Or it may be because, when imposed correctly, they enable the magic of illusion to fully captivate their audiences.

After preliminary research, I found myself asking why roof top landscapes are built in the first place.  This question became the basis for a master’s thesis entitled “Development Factors of Roof Landscapes.”  The thesis investigates the historic and current factors that affect the development of roof top landscapes.

Preliminary research showed that these factors included:  desire on the part of wealthy individuals to build roof top landscapes, physical need for protection from the elements, environmental impact, economic incentive, aesthetic appeal, research, and technology.  Through a survey of key contributors to the field, I hope to gain insight into the current relevance of these factors affecting the development of roof top landscapes.

This survey will be available on line beginning 8 am Tuesday February 24, 2004 through 8 am Tuesday, March 9, 2004, and it takes less than 3 minutes to complete. If you would like to participate in this survey, please click here:  Survey

I anticipate research on this subject to be complete beginning April, 2004.  I am extremely interested in the Aesthetic appeal of roof top landscapes and whether or not roof top landscapes in America have any chance of being anything more than a market trend or style with out any real connection to an American aesthetic, and I hope to research this aspect in the future.  I will be graduating in May, 2004 from the University of Texas at Arlington with a Master’s of Landscape Architecture, and I plan to remain in Texas for a few years following.

Emily Drake welcomes your comments and may be contacted further at:  She is also the Student ASLA president 2003-2004 at the University of Texas @ Arlington.

september 2003
student guest article

Green Roofs from a Student Point of View

By Hope Beecher Wright,
B.S. Degree Candidate, City College of New York,
School of Landscape Architecture, NYC

My B.A. degree in Art History led me to explore Europe for a personal "Grand Tour."  Icelandic Airlines was offering low airfares but it meant a stopover in Iceland before landing in Luxembourg -  I wound up spending 6 months in Iceland, exploring the countryside with my tent and working on an Icelandic freighter to see the fjords in all their glory! There is no air or water pollution and they have the highest literacy rate in the entire world.

Much to my amazement, I found GREEN ROOFS dating back a thousand years in an isolated outpost where their first Parliament met.  The buildings were still intact; some were half-buried on the side of an embankment and others were freestanding.  The roofs were GRASS.

What does an art history major know about science?  Not much.  But common sense told me that their green roofs meant wonderful insulation in this rugged, cold climate.  I was impressed with their ingenuity.  What else where they going to use in this land of fire and ice where only 1% is covered with greenery?  The remainder is barren lava fields and glaciers.  The wind is strong all the time.  The sheep outnumber the humans almost three to one and eat anything that grows. Trees find it almost impossible to survive.  These intelligent people used grass and soil instead of a thatched roof and it worked!

Icelanders also tapped into the ground to heat their homes.  While hiking one day near Myvatn in the far North, close to the Arctic Circle, I spotted a HUGE structure looming up in the distance.  I was surrounded by hot sulfur springs, geysers and lava fields and there in the distance was a BUILDING. I felt like I was in Oz.  I walked towards it for what seemed like an eternity.  It was a geothermal power plant!  I walked up to the front door and went in.  Seems they have few visitors up there, so I spent the whole afternoon with the scientists/ engineers and got an in-depth tour as an honored guest.  Eventually I went into the energy management business back in the United States.

About two years ago I found out about an organization in NYC called Earth Pledge which was having a symposium on GREEN ROOFS! Utterly amazed, I immediately signed up!  Green roofs were coming to New York City!  About time!

Earth Pledge has since given two more symposiums. Then the AIA NY Chapter gave a symposium on roofing which I attended and they included a session on green roof design. This spring I attended the 3-day Conference in Chicago sponsored by Green Roofs for Healthy Cities, which had over 450 attendees from around the world. There were exhibitions, lectures, slide shows and tours including the green roof atop City Hall.  Mayor Daly had visited Germany and was so impressed with the green roofs he saw there that he ordered one built on top of his own City Hall.

There is an excellent book, which happens to be the ONLY one in English, called Roof Gardens: History, Design and Construction by Theodore Osmundson, FASLA, who used to teach at Harvard Graduate School of Design. While not focusing on green roofs in particular, he does cover many salient points in detail and his photographs are truly inspirational. Chapter 4, Roof Garden Construction, is of particular interest and is a must-read for anyone contemplating a green roof. The hard-covered 315-page book was published in 1999 by W.W. Norton & Company (ISBN 0-393-73012-3) and can be bought at the New York Botanical Gardens Bookstore, Urban Center Books, or in's MarketPlace.  Other books are now planned on green roofs and we will share details as they become available.

The whole idea of green roofs led me to apply to City College of New York (CCNY) School of Urban Landscape Architecture.  I go back to school on September 2 and, as a transfer student, will receive my B.S degree in two years.

CCNY plans to replace this undergraduate degree with an M.L.A. (Masters of Landscape Architecture) which will be a three-year program, unless you have a previous degree in Landscape Architecture and in that case it will take just one year. This change will not take effect for another two years. They also offer an M.U.P. one-year degree (Masters in Urban Planning).

CCNY's campus is 35-acres and was the nation's first public institution of higher education. Shepard Hall, the neo-Gothic building that is the home of the School of Architecture, was built in 1847. A new building is under construction now; for information you may call the School of Architecture at 212-650-7118. The Admissions number is 212.650.6977 and mailing address is: The City College/CUNY, Convent Avenue at 138th Street, New York 10031.

CCNY is a branch of the City University of New York (CUNY), which has campuses in all five boroughs of the City of New York. It offers an excellent education and one of the lowest tuition rates in the State. It is also one of the few colleges in the United States to offer a degree in Urban Landscape Architecture.

The New York Botanical Gardens in the Bronx is another wonderful resource and this past summer I took several classes in their outstanding Certificate in Landscape Design Program. If you call 718.817.8747 and leave your name and address, they will mail you their brand new 84-page catalog for Fall 2003-Winter 2004 which includes classes, exhibits and lectures.

This fall The New York Botanical Gardens will be offering the following classes:

Create Your Own Green Roof: A Step-by-Step Guide.
Saturday, November 1 from 10 a.m. to 12 noon.
Room P201. NYBG
$23 non-members and $21 members.
"The European style of environmentally sound, low maintenance vegetative roofs is just being introduced to North American cities. Chicago's City Hall has a celebrated large green roof, and the Hudson River Park opened June 2003 with a smaller scale one. THE FUTURE OF THE ROOF GARDEN IS HERE, AND THE TIME IS RIGHT TO LEARN THE METHODS, TECHNOLOGY AND MATERIALS TO BUILD THEM. Class includes a slide presentation of the journey to construct and establish a beautiful green roof on a simple tool shed in Manhattan."
Taught by Lynn Torgerson who specializes in rooftop gardens and urban spaces.

Roof Garden Basics
4 Saturdays Oct 4-25
10-1 p.m.
Cooper Union in Manhattan
"With its dense, varied, and soaring residential architecture, NYC is the ideal place to learn about roof gardens. This course includes visits to two roof gardens of contrasting styles with onsite discussions with contractors and consultants who participated in the designs. Learn about the special requirements of roof garden design and the basic materials and plants for this environment. Please dress for the weather for field trips. THIS CLASS IS A PRE-REQUISITE FOR ROOF GARDEN DESIGN WORKSHOP LAN 432.
Taught by Steven Cantor, Registered Landscape Architect and member of the American Society of Landscape Architects.

Roof Garden Design Workshop (see above prerequisite)
4 Wednesdays, October 8, 15, 22, 29
6:30-9:30 p.m.
Cooper Union, Manhattan
$138 non-members, $125 members
"Learn to apply and expand your design skills to roof gardens and also learn practical information about the basics of green roof design. Work on a design project and focus on specific aspects of roof garden horticulture, maintenance, and technology. Course includes a take-home exam. Students must also be enrolled in Roof Garden Basics, LAN 232, to register for this course. Prerequisites: Graphics I, LAN 301 and Landscape Design I, LAN 401.
Also taught by Steven Cantor, RLA, ASLA.

To register call the New York Botanical Gardens at (718) 817-8747 or go online to their website: They are located in the Bronx and it is convenient to NY, NJ and Connecticut.

Anyone who experienced the August 14th blackout knows what a difference green roofs would have made to lower the ambient temperature of your city (not to mention what a cool place it would have been to sleep on that hot night). New York also has a problem with storm-water runoff and sewer overflow, and green roofs in NYC would help diminish that impact. In fact, the sewage treatment plant on the Hudson has a green roof which was just completed this June.

If I might make a suggestion from experience:  Take advantage of the educational opportunities which are available to you to become an informed voice for the urban green roof movement in your area.

Hope Wright has a B.A. degree in Art History from Marymount College in Tarrytown, New York and did post-graduate studies at the University of Florence, Italy.  Presently, Hope is a third-year B.S. degree candidate at the City College of New York School of Landscape Architecture.  She transferred from SUNY Fashion Institute of Technology in New York City where she was an honor student in the Interior Design Department.  Hope is also enrolled in the New York Botanical Gardens' Certificate in Landscape Design Program.

She may be contacted at

august 2003
student editor feature editorial
Green Roof Research: Academics Over Advocacy
By Tim Carter, The Institute of Ecology,
University of Georgia, Athens, GA

After graduating from the University of Tennessee three years ago, I thought I would never again witness the passion, emotion, and fervor of what many people in the south consider a religious event, but what the rest of the world calls college football. I now find myself at the University of Georgia, which is like going from the frying pan into the fire. On any given football weekend in Athens, GA the town comes to a halt, save anything that supports, promotes, or encourages UGA football. How is it that a game inspires such behavior? More importantly, what do thousands of screaming disciples of the pigskin have to do with green roofs?

It is here where advocacy enters the picture. An advocate, according to Webster’s Dictionary, is “a person who speaks or writes in support of something”. Advocates have been a necessary part of most novel and innovative advances in history, and the green roof industry in America is no exception. It seems to presently overflow with them. Green roofs were the first subject mentioned by the opening speaker at the Sustainable Design + Education conference in Athens in January. Many architects have taken a lead role by incorporating green roofs into their designs, and the U.S. Green Building Council uses green roofs in their LEED rating system. Almost all literature concerning green roofs in North America is written to further the green roof cause and spread the word about the benefits of green roof technology. This advocacy is a necessary part of educating the public on the benefits green roofs can provide.

Advocacy takes a different form for researchers, however. Our aim is to be as objective as possible in our study and examination of green roofs. We must wear the hat of an objective observer without allowing zeal for progress to compromise our study. A recent conference in Chicago highlighted a track that was termed “Research on Technical Performance and Benefits.” While many of the presentations were impeccable studies of green roof benefits, it was clear that the advocacy position was threatening to nudge solid science off the podium through shoddy methodology being passed off as “research”. These studies are sufficient promotional tools, but limited in their academic applicability.

Academic study of green roofs is still young on this continent, and this is all the more reason to build the industry on a solid research footing. The goal of this forum is to provide an open discussion for all aspects of green roofs. We are not here to be advocates; we are here to be academics. Anyone who wants to contribute is welcome and hopefully we can engage in meaningful discussion that will further everyone’s understanding of green roof technology. As years pass and studies commence and conclude, our goal is to have a better picture about how green roofs can (and can’t!) contribute to ecological design and sustainability in the future.

Tim Carter is currently pursuing his Ph.D. at The Institute of Ecology, University of Georgia, focusing on using greenroofs as part of GIS modeling for examining remediation of urban watersheds.  Read about his project here. Tim is also involved in SEEDS - Students and Educators for Ecological Design and Sustainability - an organization created by students from UGA's new College of Environment and Design.

Tim is the former Student Editor here at  Please send comments to Tim at:

july 2003
student guest article

Looking for Green Roofs… in all the right places
By Janet Faust, North Metro Technical College, Atlanta, GA

Several events this past month have had me looking for green roofs and finding them in all the right places.  No surprise, the First North American Green Roof Infrastructure Conference, Awards and  Trade Show in Chicago this May did shape up to be an outstanding event. More than 500 participants from 10 countries converged on Chicago for two days of workshops, awards, trade show, and a breathtaking tour of Chicago City Hall’s 11th-floor green roof.

Chicago City Hall Greenroof, May 31, 2003;
Photo Courtesy Doug Faust

After almost a year of personally researching green roofs, the chance to put names to faces, and hear these pioneers in the industry speak about their own projects and the challenges and rewards they faced was in itself worth the trip to Chicago.  The multi-disciplinary nature of green roofs was truly reflected in the diversity of the attendees.  We each had different stories to tell, but I believe we all shared the same underlying vision of a greener tomorrow.  As I have found over the years, green industry folks are a rare breed, whether it be heirloom seeds, or drainage and irrigation wisdom, we like to share.  And share we did for two days. 

Highlights included practical information.  “Information,” as Theodore Osmundson in his book Roof Gardens, History, Design, and Construction wrote in 1999 ‘is frustratingly lacking’.  Though none of us can or do claim to know it all, what a difference just a few years can make.  We have our heads together and our step is in the right direction.  The ability to learn from those who have gone before us in other countries as well as here in the United States, and share and learn from their successes and mistakes is imperative.  As one spokesperson said, we need to keep talking and sharing notes, what works, and what does not work.  This unique opportunity strengthened my hopes as an environmental horticulture student, and left me very optimistic about the world we will leave to our children and grandchildren.  We’ll see you all and hopefully more, at the Second North American Green Roof Infrastructure Conference in Portland, Oregon in 2004 for more success stories.

Several weeks after the green roof conference in Chicago, I attended the 11th Congress for the New Urbanism conference in Washington D.C.  “New Urbanism” is an urban design movement that burst onto the scene in the late 1980’s and early 1990’s.  New Urbanists aim to reform all aspects of real estate development.  New Urbanist neighborhoods are walkable, and contain a diverse range of housing and jobs.  They also support regional planning for open space, appropriate architecture and planning.  They believe these strategies are the best way to reduce how long people spend in traffic, to increase the supply of affordable housing and to rein in urban sprawl.

What does this have to do with ‘green roofs’?  Green building is the third principle in the Charter for New Urbanism and states that the metropolis has a necessary and fragile relationship to its agrarian hinterland and natural landscapes.  And the relationship is environmental, economic, and cultural.  Farmland and nature are as important to the metropolis as the garden is to the house.  (See for more information.)

Farr Associates Rendering of Normal, Il Plan
Photo Courtesy ©Farr Associates Architecture & Urban Design Website
Redevelopment Plan & Multi-Modal Rail Facility, Normal, IL

Across the country, developers are raising new buildings and neighborhoods that combine New Urbanism with sustainable site design and green building.  I was fascinated to learn of the many techniques already being incorporated into community designs that solve some of the very environmental issues that green roof proponents are trying to solve.  Vegetated roofs are but just one answer.  Here in the United States green roofs is an answer that is still very much in the fledgling stages.  However, after both conferences I got a feeling of momentum and a feeling that there are many concerned voices of people who are willing to take the necessary leap of faith, after they add the extra costs of environmental improvements and making their money work.  I have heard some negative undertones from businesses and planners that these environmental “extras” are being forced upon them.  However, after seeing project presentations this past week from all over the country and the innovative ideas architects and planners are designing and incorporating, the enthusiasm far exceeds the complaints. 

Next year, The Congress for New Urbanism conference will be held in Chicago, June 24 – 27.  Environmentalists, businesspeople, developers, and citizens will come together once again to support the development strategy called New Urbanism.  And if this were not enough, they are looking forward to taking tours on you guessed it, the Chicago City Hall green roof. 

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The National Building Museum in Washington D.C. just completed a six month exhibition titled “Big and Green”: Toward Sustainable Architecture in the 21st Century.  It explored five categories of issues that design and building professionals are addressing in order to reduce the deleterious environmental impact of skyscrapers and other megastructures: Energy; Light and Air; Greenery, Water and Waste; Construction; and Urbanism.  It was a spectacular investigation of the technologies in use and in development of significant green projects worldwide.  The GAP corporate offices in California was just one of the 50 projects highlighting the concept of sustainability and the potential to yield a more vibrant, exciting architecture for the future.

A book illustrating the entire “Big and Green” exhibit can be purchased at the National Building Museum’s home page (, or here by clicking on the picture.

Janet Faust is an Environmental Horticulture student at North Metro Technical College, Atlanta, Georgia.  She researched and prepared an in-depth paper on green roofs as an Independent Study.  She is also fulfilling an Internship requirement as a Landscape Designer/Project Manager for Unique Environmental Concepts, a landscape design/maintenance company in Atlanta.  She has designed a green roof for a residential site in College Station, Texas, and will be assisting the City Hall of Atlanta with their plant installation on their green roof this summer. 

We welcome all your comments and input; please contact:

Christine Thuring, The Student Forum

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