[Expert
Article] Green Roofs
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| 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
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| 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.
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| 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
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| 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.
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| 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
