- Category: Green Buildings
03 Sep 2012
- Published on Monday, 03 September 2012 10:15
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An aerial view of the Jiutian International Square mall in Zhuzhou, Hunan province in China will reveal some interesting structures sprouting on its roof.
Four two-story houses surrounded by living green gardens have been built on the mall’s roof. The villa-style houses, fully outfitted with electricity and plumbing, will serve as offices for mall employees.
The structures, developed by local developer Zhuzhou Jiutian Real Estate, are an interesting example of how to maximize the use of existing property space. It’s also an example of a sustainable building technique known as the green roof.
A green roof is a building roof that is either partially or completely covered with vegetation. Aside from the aesthetic value of having a roof covered in green living things, a green roof shades surfaces and removes heat from the air, reducing the temperature of the building and of the surrounding areas.
For its efforts, Zhuzhou was named one of 34 national level garden cities in 2008, and it wants to keep that reputation.
Growing your own cooling system
According to the United States Environmental Protection Agency, by naturally cooling and shading a building, green roofs can help reduce urban heat islands and cool the air. A building with a green roof can also reduce its energy use and decrease its emissions as there is less need for heating and cooling mechanisms.
The growing plants are key to the green roof’s ability to regulate the temperature of the building through what is called evapotranspiration. Evapotranspiration refers to two processes – evaporation and plant transpiration – which occur in vegetated areas.
In transpiration, the plants absorb water through their roots and emit it as water vapor though their leaves. Evaporation converts water in the soil around the plants to gas. The two processes contribute to the lowering of temperature by using heat from the air to evaporate water.
A green roof can contribute to human health and comfort, remove pollutants from the air and rain, reduce and slow storm water runoff and even provide habitats for other species.
A green roof can be as simple as patches of grassy, hardy, ground cover or an elaborate and ornamental park, as long as the vegetation covers a good part of the surface area of the building.
Growing the shade
Japanese company Kyocera uses vegetation cover in many of their facilities to bring down their temperature control costs through what they call their “Green Curtain” program.
Instead of growing plants on the roof, Kyocera grows climbing plants such as goya or morning glory as a natural shade over the outside of building windows and parts of the building’s façade. These literal green curtains block out the direct rays of the sun, preventing temperature from rising inside the rooms and on the surface of buildings.
The evapotranspiration of the hanging plants also result in cooler temperatures, allowing them to reduce their use of air-conditioning and reduce their emissions.
An additional benefit of the Green Curtains is the production of edible material that can be harvested by the employees. Green Curtains utilize cucumber and pea vines as well as a traditional summer Japanese vegetable called the goya or bitter gourd.
Kyocera first started growing their Green Curtains at their Okaya Plant in Nagano Prefecture in 2007 as part of the company’s energy conservation and climate change prevention efforts. As of 2011, the Green Curtains grown at Kyocera Group locations reached 725 meters and covered a total area of 3,043 square meters.
By Kyocera’s calculation, a Green Curtain can decrease the temperature by as much as 15 degrees. It can also absorb carbon dioxide removing it from the atmosphere. The rate of carbon absorbed by a Green Curtain is said to be 3.5 kilograms of carbon dioxide a year for every 1 meter square of foliage.
The company is decidedly proud of the Green Curtain initiative, which has now spread to their facilities in Thailand and Brazil. For 2012, the company plans to have 28 more Green Curtains installed.
Kyocera is also not stingy about sharing the idea behind the program with the Kyocera Group Green Curtain Activities Web site providing a complete and step-by-step instruction for planting your own Green Curtain.
Planting and caring for a green roof or green curtain may strike some as labor intensive but there are significant benefits.
According to the E.P.A., the estimated costs of installing a green roof would come to around $10 per square foot to $25 per square foot, with annual maintenance costs at around $0.75-$1.5 per square foot.
While this may seem daunting, a full life-cycle analysis shows that a green roof would eventually earn back its keep in energy savings as well as other benefits.
A University of Michigan study compared the expected costs of conventional roofs with the cost of a 21,000 square foot green roof and placed the green roofs installation cost at $464,000 while the conventional roof cost $335,000. However, over its lifespan, a green roof would net its owner about $200,000 in savings with nearly two-third of this coming from reduced energy use.
A green roof is also recognized and credited by the United States Green Building Council’s Leadership in energy and Environmental Design Rating System and other sustainable building initiatives.
Either way you look at it, a green roof is cool. Not just a cooling solution but a cool way to make a building more appealing to those seeking a greener lifestyle and a lower-carbon environment to work, play and live in. (Katrice R. Jalbuena)