Scot Livingstone
BIO 1010
Prof Cannon
25 July 2012
Green Roofs to Save Our Cities
Introduction:
From the Hanging Gardens of Babylon to the old Scandinavian sod roofs, people
have been incorporating living biomass into construction of homes and other structures for
thousands of years. The Scandinavians did it because it kept their homes warm in the
winter and cool in the summer. In modern society we use heat when it’s cold, and air
conditioning when it is hot. Who cares what the roof is made out of? The answer is, we all
should care. The difference in temperature, water management, and oxygen gas
production when comparing industrial roofing to green roofing is astonishing.
The practicality of living roofs has been overlooked through recent history but the
concept is coming back with a vengeance. There is a movement to bring green roofs back
into the mainstream. Advocates of the green roof system cite numerous environmental,
economic, and aesthetic benefits. Cities are now incorporating more green space into their
ground level to help address the issues of storm runoff, air quality, and even temperature in
the city. Since roof space goes mostly unused, and makes up such a significant portion of
the horizontal surface area of all cities, we
should encourage every building to incorporate a
green roof system.
Is There a Problem?
Storm Water Runoff
Rain is an inevitability. Even in a dry
climate like Utah, we rely heavily on rain for
drinking water, agricultural prosperity, and fire
protection. When we get rain here in the
summer, people generally consider it to be a
Photo: Little Norway
good thing. “I guess I don’t have to water the lawn
tonight!” The truth is that storm runoff is the
leading contributor to water contamination. “Rainwater and snowmelt run off streets,
lawns, farms, and construction and industrial sites and pick up fertilizers, dirt, pesticides,
oil and grease, and many other pollutants on the way to our rivers, lakes, and coastal
waters (cfpub.epa.gov).” Limiting exposure to toxic chemicals is something we should all
strive for. When storm water is run through vegetation, the soil and plants absorb the
water, preventing it from reaching sewers, rivers, lakes, or streams. Plants are natural
filters that can convert toxins back into biomass and oxygen gas.
Heat Island Effect
The “Heat Island effect” is a well-known phenomenon where the temperature in a
large city is significantly higher than the surrounding suburbs. This is mostly due to the
solar heating of streets and restricted wind velocity from tall buildings. Streets are dark
and absorb most of the solar radiation they are exposed to. According to the EPA, “The
annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–
3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F
(12°C). (epa.gov)” With summertime high temperatures in cities becoming artificially
warmer, and the streets and sidewalks retaining heat so that it takes longer to cool in the
evening. People are using their air conditioners more often, and longer into the night.
Green roofs actually cool buildings when it’s hot out thanks to evaporation of the water
they retained during the last rainstorm.
Air Pollution
It’s common knowledge that air quality in cities is far worse than outside city limits.
Adding green space in the city is a cost effective way to bring the quality of the air back up
to a reasonable. Photosynthesis is something that all plants do. Basically, a plant can pull
CO2 from the atmosphere and with a little water from the ground and energy from the sun,
it converts the CO2 and water into stored sugar (biomass) and oxygen gas. Every blade of
grass, every tree, even the weeds in the
garden photosynthesize. Obviously, by
increasing the amount of plants in a city,
we can improve the air quality. Since
most cities lack extra space to convert to
green areas, roofs are perfect places to
add vegetation. They are mostly unused
space, and make up a huge percentage of
horizontal surface area in the city, so it
makes perfect sense to use them for
vegetation.
Source: Chicago Dpt. Of Environment
Green Roofs
There are two main types of green roofs, Intensive
and Extensive. Both are similar in design, with the main
difference being soil depth and structural load capacity.
Both types of roof start at the original roof. Next, there is
a vapor barrier, insulation, an added support panel,
waterproof membrane, drainage material, filter
membrane, and finally growing medium or soil.
Intensive Green Roofs are typically set up to be
accessed by people. They are built to accommodate more
weight. This allows Intensive roofs to have deeper soil so
they can grow larger more diverse plants, shrubs, and trees. Intensive roofs require more
maintenance but can transform a roof into an urban oasis where one can go and enjoy its
beauty.
Extensive Green Roofs are usually either built for private use, or for no access at
all. They have a thinner soil medium (6 inches or less) and a lower structural load capacity.
They are characterized by the types of plants in them, usually grasses and other selfsustaining plants, and also by their low to zero required maintenance, and their lack of a
permanent irrigation system. Extensive green roofs are a less expensive option which have
a similar environmental benefit, but they lack the beauty and diversity of the larger
Intensive roofs.
Conclusion
Air and water pollution is a growing problem. All over the world, we’re seeing the
consequences of living and building beyond our means. It’s time to take a step back and
think about how much we should really be alienating ourselves from the nature that we
come from. There is a delicate
balance on this earth, and we do
more than our fare share of
manipulation of that balance. How
far can we push it? I for one would
prefer not to find out. Lets act on
some of our most pressing issues,
not by using mass amounts of
taxpayer dollars to attack the
problem with technology and
American brawn, but by giving
back to the environment, by
allowing it a few extra square feet
to thrive on. We will find that
nature doesn’t hold a grudge, it’s
not mad that we took the space in
the first place. We will find that the
Source: Inhabitat.com
leaves continue to photosynthesize and
purify our air, and that the soil and root
system will happily take up our dirty water and use it without complaint. Our future
depends on our rekindled relationship with nature. It’s a partnership, for the overall good
of both humans and all other living things on the planet. It’s time to go green.
Works Cited
"Extensive Green Roofs." Green Roof Technology, n.d. Web. 25 July 2012.
<http://www.greenrooftechnology.com/extensive-green-roof>.
GRHC1. "Green Roofs for Healthy Cities." YouTube. YouTube, 25 Nov. 2008. Web. 25 July
2012. <http://www.youtube.com/watch?v=7UA1rjnPZtU>.
"Heat Island Effect." EPA. Environmental Protection Agency, n.d. Web. 26 July 2012.
<http://www.epa.gov/hiri/>.
"Stormwater Outreach Materials and Reference Documents." EPA -. N.p., n.d. Web. 25 July
2012. <http://cfpub.epa.gov/npdes/stormwatermonth.cfm>.
"Stormwater." Stormwater. State of Washington, n.d. Web. 25 July 2012.
<http://www.ecy.wa.gov/programs/wq/stormwater/index.html>.