Economic Benefits of a Green Roof
Written on August 11, 2010
Some of the Economic Benefits of a Green Roof:
Increases the Life Expectancy of the roofing system to 40 yrs or more
- Reduces the weathering/damage from extreme heat and freezing
- Reduces the UV exposure and degradation
- Reduces the stress from expansion/contraction in the building
Lowers the Surface Temperature of the Roof by 70 degrees
Conventional roofs store radiation from the sun and re-radiate it back into the atmosphere as heat. But plants convert that radiation through photosynthesis and evapotranspiration into biologically useful energy, and don’t store it as heat. So, rather than being a blistering 170 degrees on a hot summer day, the green roof temperature will be about the same as the ambient air temperature. (see attached drawings illustrating Urban Heat Island Effect)
Improves Air Quality at the Outside Air Intakes
Because of the plant growth on the roof, makeup air inside the building contains more oxygen and less carbon dioxide than air taken off a convention, hard surfaced roof. (see illustrations)
Reduces the Energy Used for Air Conditioning by 75%
In a study done at the Field Roof Facility in Ottawa, a roof was divided equally, and one part was covered with an extensive green roof, while the other remained a standard modified bitumen membrane. The green roof showed a decrease in daily energy demand for air conditioning of over 70%. (see graph sheet)
Increases the Efficiency of AC Systems in Hot Weather
HVAC systems are designed to be most efficient when air temperatures at the Outside Air intakes are 90 degrees or less. Since OA intakes are generally only about 30” above the roof surface, the temperature of the intake air is directly related to the surface temperature of the roof. Studies have shown that when the intake air temperature reaches 115 degrees, the energy required to cool the coils rises by 12%, and the cooling capacity of the system drops by 10%. In summer, conventional roof surface temperatures in Georgia regularly reach 170 degrees.
Reduces Stormwater Runoff Quantity while Improving Quality
85% of the first 1” of rainfall is retained by a Green Roof, and all the runoff is filtered for pollutants such as rainwater pollutants and roof surface contaminants.
Green Roofing – Not just for Hippies and Hobbits Anymore
Written on July 23, 2010
Green Roofing – Not just for Hippies and Hobbits Anymore
A local businessman a few weeks ago said to me “I love doing things to improve the environment – especially when I can afford it.” No one wants to see the environment we depend on ruined, but we do have to be able to pay for what we do. Wouldn’t it be nice to be able to combine “going green” with saving money? Green roofing, after decades of development, may now be able to offer us that very combination.
Commercial Roof Management Services held its first Green Roofing Seminar recently at the Holiday Inn downtown to demonstrate the reality of just such an idea. It was attended by numerous local, forward-thinking decision makers including representatives of local hospitals, Athens Clarke County Unified Government and surrounding government agencies, architects and engineers, as well as contractors and business leaders. The discussion was guided by Tim Carter, PhD, Odum School of Ecology, UGA, and speakers included Tammy Andros, grad student at Odum, and the writer, Garry Todd, President of Commercial Roof, a local roofing contractor. Let me highlight some of the reasons so many people got together to talk about installing green roofs..
First, a “green roof” is simply a roof covered with plants. Once we use it to form a green environment, we change it from a hard, impervious surface to one that more closely resembles the forests and meadows that were in that spot before it was developed. Lots of “green changes” start when the roof becomes organic again.
Conventional roofs store radiation from the sun and re-radiate it into the atmosphere as heat. Green roofs, which use plants to transform that heat, are cooler. And here in the South, heat is our number one issue. On a blistering day in August, we can see temperatures of 170 degrees on a roof. But surface temperatures on a green roof drop down to about the same as the ambient air temperature. That can be a reduction of 70 to 80 degrees. And studies have shown that a building’s interior can be over 10 degrees cooler simply by adding a green roof.
This temperature reduction can then naturally reduce the energy usage in the building. In one example recently in Canada, half the roof had a standard roof installed and the other half had a green roof installed. The study concluded that the green roof decreased the demand for energy required for air conditioning by over 70%.
Then, as the surface of the roof cools off, the Air Conditioning system becomes more efficient, allowing it to cool the building better. HVAC systems are designed to be most efficient when the ambient air temperature is 90 degrees or less. When the unit sits on the roof or the outside air intake is near the roof surface, lower efficiency results from high roof temperatures. Studies have shown that when the temperature at the outside air intake reaches 115 degrees, the energy needed to cool the coils rises by 12%, while the ability of the unit to cool drops by 10%.
And the list of benefits goes on and on. One particularly important benefit for Athens-Clarke County is better storm water runoff quality and quantity due to retention and filtering by the system. Another is an improvement in the quality of air brought into the building due to the plant life. Perhaps another important to residents is noise reduction, as the dirt and plants muffle sounds both inside and outside of the building. By the way, it should also be noted that the green system can easily make the roof last twice as long as it would have, by shielding it from the harmful effects of UV rays and temperature extremes.
But perhaps the best reason is the most economic reason of all: aesthetics. Instead of trying to avoid looking at the roof, we could instead be seeing growing plants in a beautiful array of colors, showcasing something that’s living and renewing, that is actually contributing to our health and well-being, as well as to that of the environment. Maybe now is the time. If you would like to explore this idea further, check out the green roof section of our website, and perhaps even sign up for a future seminar at www.commercialroof.com.
