A Green Roof?

April 30, 2003
Spring is here and for those of us in the Northeast, not a moment too soon!

The first buds on the trees and the tulips poking up out of the newly-thawed ground remind me that there's never been a better time to address one very practical, but under-used, application for green building materials and systems. I'm talking of course about "green roofs."

Now before you hit the "delete" key or write me off as having suffered from a serious case of cabin fever, you should know that the roof you sit under offers tremendous untapped potential for energy savings. A three-to-seven degree temperature drop on the surface of a roof can equal a 10 percent reduction in air conditioning requirements, which in turn can cut cooling costs by up to 30 percent. Still with me?Think about it - roofs are nothing but heat islands that absorb or give off heat, depending on the season and level of insulation. Heat islands are created when sunlight combines with dark building materials, pavement and a lack of vegetation. Surface temperatures increase, as do the average summer temperatures in the city. Increasing vegetation in urban areas is one solution to this problem. According to the Canadian publication CONSTRUCTION INNOVATION (Vol. 5 No. 1, Winter 2000), vegetation provides shading, which reduces the use of air conditioning, while "evapotranspiration," a process in which water is released through the plant's leaves, draws heat from the air. In addition, replacing impermeable surfaces with vegetation intercepts water that would otherwise become storm water run-off. Given the limited space available for trees in many cities, new adaptation strategies such as placing the vegetation directly on building roofs, in rooftop gardens, become especially attractive.
Cities such as Chicago, major corporations and universities are just a few of the growing number of municipalities and organizations to discover that energy-saving roof technologies deserve significant attention due to their natural thermal insulation properties, which result in structures that are dramatically cooler in the summer and warmer in the winter. In fact, a recent study by Weston Solutions, Inc. estimates that greening the rooftops of all city buildings in Chicago would result in nearly $100 million of annual energy savings. Peak demand would be cut by 720 megawatts, which is the equivalent of 16 small turbines or one nuclear power plant.

The Institute for Research in Construction, in a consortium with Environment Canada, the Climate Change Action Fund and members of the Canadian roofing industry, is conducting a study of rooftop gardens to identify sensitivities to climate variability and to quantify their benefits and impacts in different parts of Canada. IRC has constructed a field roofing facility on the National Research Center Canada campus in Ottawa. If you're interested in the results of this study, click here.
Ford Motor Company is undertaking a major redevelopment at its 600-acre, $2 billion Ford Rouge Center - it's flagship plant opened by Henry Ford in 1917 - near Dearborn, Mich. Included in the redevelopment is a new assembly plant with the nation's largest ecologically inspired living roof on an industrial building. About 454,000 sq. ft of assembly plant roofing has been covered with sedum, a succulent groundcover, and other plants. The roof will reduce stormwater runoff by holding an inch of rainfall. Also the living plants absorb carbon dioxide as part of photosynthesis, so oxygen is emitted and greenhouse gases are reduced.Stormwater management is a critical economic and environmental issue for building owners and cities alike. Excess rain and melting snow often reek havoc with flash flooding and erosion, but more commonly overburden storm water and sewer systems with precipitation that has no where else to go. One solution to these issues has been to expand the stormwater infrastructure, which is often costly and disruptive. Green roofs eliminate the previously non-porous surface of the roof and on average absorb 75 percent of all precipitation that falls on them. Building owners and developers are also interested in making more space available for development rather than reserving open space for water percolation or stormwater retention ponds.But green roofs - sometimes called Ecoroofs - are not a new phenomenon. Due to the excellent insulation properties of the combined plant and soil layer they have been considered standard construction practice in many countries for hundreds of years. Green roofs have increasingly become part of the European landscape since the 1970s where there are more than 100 million sq. ft of planted roofs today.Though the original green roofs were time-consuming and expensive to install, there are green roof systems available today, such as the GREENGRID© green roof system, that offer a flexible, modular design roofing product.

Each GREENGRID© System module contains a drainage/root retardant layer, and is pre-planted with lightweight soil media and plants recommended by horticulturalists for plant hardiness, zone, size and color. The system can be installed within several days depending on the size of the roof, and is designed for placement directly atop the existing roof membrane system or other media, assuming structural capacity is present. Modules are locked together and can be unlocked individually to rearrange the look of the green roof, and for roof maintenance.
Another green roof provider is American Hydrotech, a global leader in the development of waterproofing and roofing technology, and a single source supplier of green roof systems. Hydrotech is associated with ZinCo GmbH of Germany, their partner in the development of the Garden Roof™ Assembly. Hydrotech claims green roofs "add beauty to the once forgotten area of a building, reclaiming this neglected 'fifth elevation' for both man and nature by integrating the building and surrounding landscape." Hydrotech has numerous completed greenroof projects within the U.S., including the Gap Headquarters outside of San Francisco.According to Sandra McCullough, vice president, GreenGrid, green roofs offer several other well-documented economic, environmental and aesthetic benefits such as: Energy: When the outside air temperature reaches 95 F, rooftop surface temperatures can be as high as 175 F. These temperatures impact not only the temperature within the building, but also the amount of energy necessary to heat and cool the building to the desired temperature. Green roofs have been consistently shown to save up to 50 percent of the heating and cooling costs for the floor directly below the green roof, due to superior insulating properties.
Longevity of roof membrane: Green roofs have been proven to protect the exterior roofing membrane against ultra-violet radiation, extreme temperature fluctuations, and puncture or physical damage from recreation or maintenance.

Storm Water Reduction: Green roofs can retain up to 100 percent of a one-inch rainfall. Excess runoff is reduced and is stretched out over several hours, thereby reducing the risk of flash flooding and combined sewer overflows. Their use can offset the need for storm water management ponds, thereby making more land available for development.

Noise Reduction: Tests have shown that green roofs can reduce machine, traffic and airplane sound by 40 dB, thereby mitigating the effects of noise on building occupants and increasing the value of those structures

Efficient Use of Undeveloped Space: Green roofs provide the opportunity to turn undeveloped roof space into usable space for relaxation, informal meetings, events and games suitable especially for residential apartments/condos and hotels.
Aesthetic Appeal: A green roof can enhance a building and provide an oasis of green in the urban environment. The plants can soften industrial and commercial properties, and facilitate their blending into suburban or rural areas.

Air Quality: Buildings with green roofs require less heating and cooling, resulting in a net reduction in the amount of energy required. This in turn results in fewer green house emissions from the burning of fossil fuels for energy. Additionally, plants are known to trap airborne particulates, and absorb gaseous pollutants through photosynthesis.Urban Heat Island Effect Mitigation: Urban areas are significantly warmer and produce more harmful ozone than surrounding suburban areas due to the prevalence of heat absorbing buildings, dark surfaced pavements and hot air vented through cooling systems. Green roofs assist in the insulating and shading of buildings that in turn reduces this effect.
Use of Recycled and Natural Materials: Systems such as GREENGRIDÔ make extensive use of recycled materials such as HDPE for modules and edge elements and automobile tires for pavers.
Another tangible, fiscal payoff in the implementation of a green roof system lies in the increased longevity of the roof membrane. It has been proven that green roofs protect the exterior roofing membrane against ultra-violet radiation, extreme temperature fluctuations, and puncture or physical damage. Whereas the normal life cycle of a roof membrane is 10 to 15 years, green roofs can increase the life expectancy of the membrane up to the life of the building. This nullifies the need for costly replacements and maintenance, resulting in real savings for the building's owners in addition to the various other economic, social, and environmental benefits.
As energy demands continue to threaten the supply of the power grid and smog maintains its stifling stranglehold on cities, more and more states and cities are propagating the use of green building technologies and in particular green roof systems. For example, the city of Portland, Ore. is heading up an aggressive incentive program nationally providing financial, technical, and educational incentives to willing participants in the green roof initiative. California and Maryland all have existing incentive structures to offset costs, implement tax credits and avoid fees for impervious surface cover. Both Massachusetts and Pennsylvania currently have legislation in the works to establish incentives for green building structures. In all 39 out of the 50 states have some method of incentive structure in place for sustainable technologies, alluding to an inevitable increase in tax breaks and program benefits as public reception and recognition of green roof technologies increase.While the theory behind green roofs traces its roots to the ancient Middle East cultures, modern materials and technology have combined to create a great, untapped wealth of building energy savings and enhanced comfort.

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