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rooftop gardens. project overview.
You're reading: What is a roof top garden
joseph kurland ev. 421 sharon hall, steve harris
in the hopes of producing better air quality, lower urban temperatures, and better storm water management gardens or green spaces will be installed upon the roof spaces of buildings in colorado springs. initiated by interested members of the colorado springs community, this project works to increase the standard of living for all members of the city, in addition to increasing property values, and the sustainability of the city. ultimately, i foresee tax breaks, and other financial incentives that will encourage all members of the community to green at least twenty percent of all available roof space in colorado springs.
project promotion and implementation
courtesy chicago doe
ev. 421 sustainable cities
sharon hall, steve harris; professors
what is a roof top garden?
rooftop gardens are man-made green spaces on the topmost levels of industrial, commercial, and residential structures. they may be designed to grow produce, provide play space, give shade and shelter, or simply be there as a living, green area.
two main divisions of garden types exist: extensive and intensive. extensive gardens require minimal maintenance and behave as another from of roofing material. they are not intended for heavy foot traffic nor do they need to meet any additional safety standards.
the other extreme includes intensive gardens created with the intent of active human use. these gardens require landscaping and regular upkeep. in some cases, the roof structure must be reinforced through the addition of decking or additional bracing to accommodate the combined weight of soil, plants, and precipitation. furthermore, intensive gardens may also need to comply with safety regulations regarding decks and public areas on raised structures. these regulations may require some kind of fencing or barrier to be installed with the intent of preventing people from slipping over the edge of the roofline.
i propose that rooftop gardens be studied as a feasible option to improve the air quality, urban temperature, and drainage management in the downtown region of colorado springs. such a proposal would be taken in several steps that would include:
- a testing phase,
- a policy making phase,
- and a final implementation phase where incentives would be added to offset the cost and further encourage development.
a suitable rooftop will be acquired through donation or lease. this space may be anywhere in the downtown vicinity upon some private or public building, although this is not meant to be a limitation. other possible locations for donated roofs include academy boulevard, or one of the dealerships in motor city. the structure must be assessed and cleared by a local engineering firm to make sure the roof will support the weight of a drainage system, growing medium, plants, rocks, people, other landscaping materials, and the accumulation of extreme precipitation in the form of hail, rain, and/or snow.
ideally, the chosen roof will not require any modifications, as that will incur additional expenses.
once the space has been acquired and asserted, a test bed will be installed. this will be a moderately sized space created with the cooperation of local landscapers, engineering firms, and nursery. the primary goals of this test are as follows:
- determine actual cost of production
- gain experience using and modifying available technologies
- perfect construction methods
- raise community interest and awareness of garden benefits
- study flora most suited to semi-arid climate xeriscaping
several different firms can produce cost estimates, however, final costs can only be decided through the physical construction of such a garden.
after construction is complete, regular observation and maintenance will be performed for at least a year to determine the feasibility of the project in this semi-arid climate. during this time community education and outreach will be developed in the form of garden tours, handouts, and local school educational programs. the first phase will be considered a success when there is such an increase in community interest as to warrant a demand for more widespread production of green space.
here, public demand and interest has brought the topic of roof top gardens to the forefront of city government. viewing the benefits, which we will see shortly, the local government will assert that such construction is in the best interest of the general public and that a motion be made to amend the building code requirements. i believe that this top-down control method is necessary as private profit-maximizing industries and commercial businesses would not take such actions on their own.
one regulatory practice, modeled after a program in switzerland, involves requiring the relocation of green space from grade to the roof of any new industrial complex constructed within the city limits1. however, as this applies only to newly developed industry buildings, it affects only a small portion of the total possible surface area in colorado springs. thus regulations must be made to involve most of the buildings in the area of colorado springs.
having the majority of the space taken up by greenery is very important. a few hundred square feet distributed over an entire city does not produce any measurable level of the desired effects upon the surrounding environment. thus, we must have a joint effort from the whole community to improve air, temperature and drainage systems. currently, a rooftop garden demonstration test is being performed in the city of chicago, il and it has been determined that the extent of their action does not produce the air, and urban temperature improvements that are desired. however, a weston design consultants study of the city determined that by greening all available roof space, chicago could save in excess of $100 million annually in energy expenses. furthermore, the study reported that the city could cut peak power consumption by 720 megawatts2.
returning to the policy requirements, the majority of available space must be involved to produce any of the desired environmental effects. thus, the second portion of the building code is amended to require twenty percent all roof space, new and old, to be developed with some form of greenery. for buildings with less support, the highly extensive systems may be adopted, and buildings with stronger tops the intensive gardens should be encouraged. these programs have already been adopted in parts of tokyo, japan and in various cities in switzerland as well as other countries in europe. this is not something new, but we would be the first to develop such a plan in a high desert climate.
understanding that construction of gardens is not cheap, local and state government should work to develop financial assistance plans in the form of subsidies, grants, and tax breaks. seeing as how production of a garden in an urban setting can work to the publics benefit, we see the need for city and state support. however, government need not work alone. i plan that local environmental groups also embrace such practices and actively seek out finical assistance for those who cannot afford to develop gardens on their own.
if such a program costs a lot and requires so much effort, why bother? the answer is literally all around us. such gardens help the environment and better the standard of living. the production of gardens can work to improve the following points:
- urban island heat affect phenomenon
- overall air quality
- storm water removal system overload
- building efficiency
i will be discussing each of these in greater detail in a moment however; we must also consider the emotional and psychological benefits each human receives with the ability of interacting with or simply viewing open, greened spaces. some hospitals have reported that between patients recovering from similar operations, those with views of landscaped courtyards had fewer post-operative days, required fewer strong and medium level painkillers, and complained less than those looking at a brick wall3. this appears to be one of many benefits of the developing field known as “horticultural therapy” whereby patients gain exposure to living plants and thus are able to remove themselves from their injury4. lets then look at what measurable, physical benefits gardens have in urban settings.
the urban island heat effect phenomenon is characterized by city centers commonly having temperatures six degrees higher than that of the surrounding environment. most of this temperature increase is due to the natural landscape having been paved over with darker materials that tend to absorb sunlight and radiate off energy in the form of heat. a study performed by the takenaka corporation to determine to what extent plant life can reduce the temperature on man-made structures. to do so, they built this south facing structure, grew plants on the steps, and analyzed radiant heat through thermal imaging. the results were impressive. according to the infrared imaging data as seen above, green spaces can be as much as 15° c or 60° f cooler than the neighboring concerete5.
such levels of heat radiation may explain the nature of urban island heat effect. other reports have stated that while grassy surfaces rarely become warmer than 77° f, flat, gravel rooftops can reach as high as 140° f6. this increase in urban temperatures begins a vicious cycle where greater levels of energy are required to cool the internal environment of buildings, requiring a higher output of energy from the power plants, which then produce higher levels of pollution. this pollution can form haze and smog trapping in more heat and further increasing the need for cooling energy. with the existence of various chemicals and particles in the citys air, elevated temperatures work to expedite the production of smog. here, rooftop gardens can have multiple benefits.
canadian sources have calculated that, on average, eleven square feet of grass can remove one-half pound of air particles each year7. this may not sound like a lot, but consider how much material there is in a half pound of dust! furthermore, they calculated that sixteen square feet of grass could produce enough oxygen to supply one human with his yearly need8. these filtering actions combined with the temperature reducing nature of plants will go a long way in improving the air quality in urban centers.
another aid for the colorado springs community involves the water retention nature of plants and their growing medium. studies are currently being performed in portland, or and toronto canada to analyze the benefits rooftop gardens can have in storm water removal system overloads. during a heavy downpour, sewer and water removal systems in large cities become overburdened, the excess water pours out of the waste water retention centers and into the neighboring streams and ponds. at high enough levels, this pollutes the rivers and lakes killing plant and animal life and makes them unsafe for human use. green roofs can help by moderating the level of runoff, thus delaying or minimizing the water removal systems overload. seeing as how a recent tax initiative to improve the storm water systems in colorado springs failed, this may become a creative, multi-purpose answer.
additional benefits from rooftop gardens exist for the buildings, themselves in the form of insulation, lower energy expenses, and extended lifespan of roofing materials. fifteen inches of grass and growing medium can have the same insulating effects as six inches of standard fiber building insulation9. this can save the building operator hundreds of dollars in cooling and heating expenses. it has also been estimated that a roof top gardens can also help retain as much as fifty percent of the heat that is normally lost through the movement of cold air across a typical roof10. finally, even greater cost reductions exist by the extended life span for roofing the materials that do not experience as great a change in temperature due to the protecting effects of the garden11.
there are several limiting factors that would act to prohibit garden production in the city of colorado springs.
problem 1: lack of water. as previously stated, we live in a semi-arid high desert climate, where the annual precipitation does not often exceed sixteen inches. a typical garden requires much higher levels than what is naturally given.
solution 1: several construction, use, and maintenance methods can be employed to minimize the necessary levels of irrigation. firstly, the use of growing mediums that have a high retention level would work to maximize what water is delivered to the garden and thus reduce the need for irrigation. secondly, non-potable water may be used for irrigation, not affecting the drinking water supply. drip method irrigation can be used to minimize the level of water lost to evaporation. finally, xeriscaping, or using plants that flourish in dry environments will aid in water use reduction.
problem 2: current roofs cannot support the weight added by soil and plants.
solution 2: where physical roof reinforcement is impractical or too expensive, roofs may use lighter weight plants such as mosses and seeders along with a thinner layer of growing medium.
problem 3: what about roof damage caused by leaking water?
solution 3: in addition to using drip method of low-level water irrigation, drainage systems would need to be installed between the growing medium and the roof membrane. this system will channel out excess water during rainstorms and snowmelt preventing accumulation of water upon the roof surface. these are currently part of construction and commonly used by rooftop gardeners.
problem 4: this program will be too expensive!
solution 4: if reducing the temperature of the city is the primary goal, then there are other options including the use of lighter colored roofing materials, however this method eliminates all environmental benefits derived from natural plant life. the question really is, which costs more: the complete repair of the storm water removal system, plus the higher temperatures within the city, plus having to live with air polluted by smog and dirt or the construction of green spaces on the majority of building in the springs?
the graph below looks at the average annual temperature in colorado springs over the last fifty-four years. the vertical axis represents temperatures measured in fahrenheit. the blue line represents the average temperature as received from the national oceanic and atmospheric administration. a black trend line was included to study the overall pattern of temperatures. we can see that, this trend line suggests that the average temperature has, overall, increased by one-half a degree over the last fifty years.
this may not seem like all that much, but we know that any deviation from the original environmental conditions can have massive, usually negative effects upon the natural environment. this increase in temperature has been seen across the globe where large cities have averaged an increase of one degree per decade12.
colorado springs will be the most recent addition to cities involved in roof top gardening whose members include: chicago, il, toronto canada, manhattan, ny, and many cities in germany, france, austria, norway, and switzerland where these practices are larger, and more common. germany alone developed ten million square meters of green roofs in 199613. its time we got started.
as taken from proposal above:
Read more: How to Guzzle Your Garden
acquire roof spacefall/winter 2002
find landscapers, builders, nurserywinter/spring 2003
growing seasonspring/summer/fall 2003
building code requirement introduced to agendasummer 2004
develop 20% practice across townwithin 10 years.
raise city government members awarenessongoing
seek tax discounts2003/2004
1.kuhn, monica. “roof greening” http://www.interlog.com/~rooftop/greening.html printed 11/12/01.
2.elston, suzanne. “green rooftop technology saves energy, cools air.” environmental news network. www.enn.com printed 11/14/01.
3.green roofs for healthy cities website http://www.peck.ca/grhcc/about.htm printed 11/13/01.
4. kuhn, monica. “roof greening” http://www.interlog.com/~rooftop/greening.html printed 11/12/01.
5. takenaka corporation. “heat island phenomenon proven to be alleviated by rooftop greening, acros fukuoka step garden creates winds.” printed 11/13/01 http://www.takenaka.co.jp/takenaka_e/news_e/pr0108/m0108_05.htm.
6. elston, suzanne. “green rooftop technology saves energy, cools air.” environmental news network. www.enn.com printed 11/14/01.
7,8,9. green roofs for healthy cities website http://www.peck.ca/grhcc/about.htm
10. kuhn, monica. “roof greening” http://www.interlog.com/~rooftop/greening.html printed 11/12/01.
11. liu, karen ph. d. “a progress report on the environmental benefits and energy efficiency of green roofs.” the green roof infrastructure monitor. 2001 vol.3, no.2 pg. 14.
12. gatland, laura. “chicago rooftops: from gravel and tar to greenery”. christian science monitor. 4/15/99, vol.91 is. 97
13. green roofs for healthy cities website http://www.peck.ca/grhcc/about.htm printed 11/13/01.
mr. ira joseph, colorado springs comprehensive planning committee.
mr. steve harris