[Final] Green Roofs

[Expert Article] Green Roofs

Via buzzbuzzhome.com

As cities grow rapidly, more buildings are being built in higher altitudes. Buildings are replacing what have once been grasslands and forests, raising the local temperatures of such metropolitan areas. When we take a look at the conventional roof in an urban environment, it is often a barren concrete desert with unfavorable conditions such as high temperature contrasts and harsh winds. To mitigate the various environmental issues we’re facing, we want to make a reverse turn and transform these concrete deserts back into grasslands, this time at elevated levels.

Historically, green roofs have appeared on the prairies in U.S.—sod houses constructed with the sod of thickly-rooted prairie grass. These living roofs were invented because of the lack of other building materials like wood or stones. Nowadays, architects and planners increasingly turn to green roofs not because of shortage of building materials but for aesthetic and environmental reasons. When it comes to energy saving for buildings, instead of setting up solar panels, nourishing a green roof can offer a better use of space.

Benefits of Green Roofs

Via roofmeadow.com

• Reduced energy use and air pollution
• Enhanced human health and comfort
• Improved storm water management
• Revamped look for a lackluster rooftop

It is no news that air pollution has been a problem in cities. Green roofs add layers of insulation to buildings, thereby reducing the energy used for cooling and heating systems.  They also cut down air pollution, since air conditioning is directly linked to greenhouse gas emissions. In addition, vegetation cleans the air by removing air pollutants through dry deposition and carbon sequestration (epa.gov).

Ever walked across an outdoor parking lot on a sizzling hot summer day? If yes, then you have experienced the urban heat island effect. Urban heat island describes the condition in which cities are hotter than the surrounding rural areas. Because cities tend to have a lot more dark surfaces and fewer green covers, more heat is absorbed. According to EPA statistics, the annual mean temperature of a city with one million or more can be 1.8-5.4°F warmer than its surroundings. In New York City’s case, it is 7°F hotter than Westchester suburbs. Green roofs alleviate this issue by providing shade and removing heat through evapotranspiration, a process in which air is cooled by water evaporating from the plant leaves.

Green roofs reduce storm water runoff and filter pollutants from rainfalls. In some cities that rain often, rainwater can overflow the sewer and causes pollution and diseases.

Via Inhabitat.com

In addition, a rooftop garden allows city dwellers quick retreats from the bustling city, being right above their apartment homes or offices. The greeneries can attract birds and butterflies, forming small ecosystems of their own. In contrast to the dreary concrete rooftop, green roofs are like a breeze of fresh air in city dwelling.

There are two main types of green roof systems: extensive and intensive. Extensive green roof system is the more common of the two, weighing 15 to 50 pounds per square foot. Since the plant media are shallow—about 1.6 to 6 inches thick, extensive roofs are not designed for public access or being walked on. These are easy to add onto existing roofs and suitable for single or multi-family residential buildings. With the emergence of modular roof products, people are given the option of instantly installing pre-grown green roofs that fit together like giant puzzles. The downside is that plant choices are limited to those with shallow root systems. Intensive green roofs are relatively complex and can accommodate almost all types of plants as well as walkways and benches. The planting media, usually over a foot, creates a load of up to 150 pounds per square foot. Due to the heavier extra load, it’s more cost-efficient to incorporate the intensive green roof and its irrigation system in the initial building design and construction. An example of green roof in the U.S. that uses both systems is the rooftop meadow at Chicago City Hall.

Taking it to the Next Level: Roof Farming

Via afar.com

What’s even better than having a rooftop garden? Having a garden and a source of fresh food. Rooftop farms offer the same perks as gardens, so why not? With emerging rooftop farms, residents and even grocery stores and restaurants are getting high quality and pesticide-free local produce. It is hard to associate farming with cities, but Gotham Greens, a New York based greenhouse business, have been operating rooftop greenhouses that supply local grocers in New York and Chicago. In 2008, Gotham Greens opened the first commercial-scale rooftop greenhouse in the U.S. It yields 100 tons of fresh produce annually and their Brooklyn location, built on top of Whole Foods Market, brings 200 tons more. Additionally, the newest facility in Chicago aims to produce 500 tons a year. Although greenhouses don’t have all the benefits of open-air green roofs, Gotham Green’s irrigation method helps save resources and eliminate the use of pesticide. The hydroponic technique—growing plants without soil and providing them nutrients through water supply, is ideal for urban environments where land and soil are scarce. Its climate-controlled environment also makes year-round harvests possible.

Via cookjenshel.com

Elevated Park: The High Line, New York 

Besides the rooftops of homes, green roof is a versatile concept that can be carried out on other structures such as abandoned infrastructures. High Line, the green strip that runs across Manhattan is a repurposing of the obsolete railway called the West Side Line. Not so long ago, the West Side Line was just an abandoned remnant of concrete and steel that the city was eager to tear down. Nonprofit organization Friends of High Line sees its potential to be reused as a greenway similar to the Promenade Plantee in Paris, and advocates to preserve it. Turns out that the structure is perfect for elevated public amenities. The black steel columns that formerly supported train tracks now prop up the park that is a combination of a promenade, town square, and botanical garden. An elevated park gives an unique experience, visitors can observe the street life and sceneries while being separated from car traffic. 

Worth the Weight?

People who take interest in growing a green roof are often scared away by the initial costs. More complex green roofs such as ones using the intensive system require design expertise and structural analysis. Even the lower-maintenance extensive roofs start at around $8 per square foot. In the long run, however, environmental and economic benefits outweigh the expenses. Green roofs protect the roof membrane and help them last longer. The planting media provide insulation that minimizes building heat gain, bringing down energy demand as much as 75%. In a wider scale, when installed by many, these roofs improve air quality of cities, making them more livable and ultimately more valuable in terms of real estate. Moreover, some cities such as the City of Chicago’s have been giving incentives and grants for growing green roofs. Sounds like a win-win situation for all. It’s a growing trend that rooftops are no longer an afterthought in building design, and not long from now more luscious greeneries will jazz up cityscapes all over the world.

Works Cited

"Green Roofs." EPA United States Environmental Protection Agency. N.p., n.d. Web. 01 June 2015. <http://www.epa.gov/heatisland/mitigation/greenroofs.htm>

"HIGH LINE." BuroHappold Engineering. N.p., n.d. Web. 01 June 2015. <http://www.burohappold.com/projects/project/high-line-160/>

Klinkenborg, Verlyn. "Green Roofs." — National Geographic Magazine. N.p., May 2009. Web. 10 July 2015. < http://ngm.nationalgeographic.com/2009/05/green-roofs/klinkenborg-text>

"Plant Connection, Long Island NY, Green Roofs: Extensive vs. Intensive."Green Roofs: Extensive vs. Intensive. N.p., n.d. Web. 10 July 2015. <http://www.myplantconnection.com/green-roofs-vs.php>

Elliott, Brianna. "Gotham Greens Is Pushing The Scale Of Urban Agriculture With Their Tasty, Pesticide-Free Veggies." The Huffington Post. TheHuffingtonPost.com, 24 Apr. 2014. Web. 10 July 2015. < http://www.huffingtonpost.com/2014/04/24/gotham-greens-urban-agriculture_n_5175724.html>