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 Green Roofs
Cool and Insulate Buildings
Hectares of New Space
 Frequently,
city roofs are black They are covered with waterproofing material
to make sure they don't leak. Like our city streets, they offer
a black surface to the sun's heat. Black is a heat-absorbing surface
colour. The combination of black pavement and black building roofs
makes downtown areas absorb a great deal of heat during hot summer
days. This heat absorption often makes temperatures in the urban
core rise higher than those of the surrounding countryside. The
higher temperatures in the city are sometimes referred to as "urban
heat islands."
As global temperatures warm with the effects of climate change,
the "heat island effect" in some cities is becoming stronger.
This temperature effect is clear in Toronto. It is also particularly
notable in Tokyo, where every summer dating back to the Edo period,
Tokyo has been attacked by a fierce heat wave. Tokyo's average
summer temperature has risen by an amazing 3oC over those of 100
years ago, five times faster than the rate of global warming. This
excess heat absorption has become a serious problem to the health
and comfort of residents.
To mitigate their heat island problem, Tokyo's government has
mandated that roof space on top of new buildings larger than 1,000
square meters must feature at least 20 percent green roof. A flat,
black tar rooftop can get as hot as 185oF on a summer day. The
same roof covered with vegetation, would register a mere 75oF.
In Germany, a estimated 10% of buildings have green or "eco-roofs," totaling
more than 13 million square metres (2004). Some cities in Germany
now require green roofs on flat-roofed buildings. In Shanghai,
China, the largest roof top garden in the city was recently completed
on top of a slaughterhouse. The greenery was added to help deal
with the smell from the installation, and to make the environment
more beautiful. The Shanghai roof garden includes the creative
feature of a fish pond installed on a glass ceiling, that allows
people working inside the slaughterhouse to enjoy a shadowy view
of fish moving about right above their heads.
The green roof approach to buildings is still quite a new trend
in North America, but is catching on quickly. The city of Portland,
Oregon, has encouraged eco roof projects since 1994, in large part
due to concern over storm water runoff The city of Toronto has
added an experimental green roof to its City Hall, that is open
to the public. It's known as the Green Roof Infrastructure Demonstration
Project.
From Babylon to High Tech
 Putting
plant materials on roofs is not a new idea. Some experts believe
that the custom of planting hanging gardens on arches or roofs
evolved in the Orient. As early as 900 BC there are reports of
roof gardens in the Orient. In the 6th century BC, the
legendary Hanging Gardens of Babylon were built by Nebuchadnezzar.
His magnificent roof garden was considered to be one of the seven
wonders of the ancient world. The roofs of wealthy patrician Roman
houses were also sometimes lavishly decorated with plants.
The more practical roots of roof greening in our northern latitudes
can be said to be based on the positive effects of spontaneous
vegetation that grows on roofs without cultivation. Scandinavian
and Icelandic earth houses featured roofs covered with grass sod,
or "grass roofs." These traditional grass-covered roofs
provided highly effective insulation and heat storage for their
occupants during the harsh northern winters. They are still used
today, with a more modern under-layer to hold up the soil and sod.
Governments, architects, businesses, horticulturalists and engineers
are recognizing the potential of vegetated roofs for the 21st century.
They are joining forces to update an old technology into a new
one that they call "green infrastructure:" using soil
and living things to increase energy efficiency and healthier city
living.
The Green Roof Advantage
 The benefits from putting vegetation on top of buildings are
impressive. Members of the growing green roof industry educate
about the many modern advantages from the incorporation of plant
material into roofing. What can these "green roofs" do
that normal roofs can't? Their promoters list the following benefits:
- beautification of the environment and increased social well-being
- reduction of city "heat island effect"
- improved
air quality
- temperature regulation reduction of air conditioning and
winter heating costs and energy consumption
- reduction of carbon dioxide impacts
- lessens nitrogen pollution in rain
- lengthened roof life
- water storage and filtration (reducing runoff to sewer systems)
- new habitat and space for biodiversity
- safe, protected green spaces in cities
. Green roofs are very practical and durable: they can last up
to twice as long as conventional roofs, providing savings of both
money and materials. Studies have found that they also reduce the
energy and heating and air-conditioning equipment requirements
needed. With today's rising energy costs, this is a major advantage
for owners of both new and renovated buildings. Environment Canada
research showed that a one-storey building with 10 centimetres
of growing medium topped with grass could reduce summer cooling
needs by as much as 25%.
In a test done by Environment Canada on two "greened" roofs
on Toronto buildings during the summer of 2002, it was discovered
that a six and a half million square metre greened space led to
a reduction of 1-2 degrees C in urban heat island. A 1% reduction
in temperature allows for a 5% reduction in cooling and refrigeration
needs for all the buildings saving on energy generation and green
house gases. The study stated that, "Green roofs insulate
buildings resulting in additional energy conservation totaling
an estimated $1 million in annual energy cost savings and a reduction
of 2.18 Mega Tonnes of greenhouse gas (GHG) emissions." http://www.greenroofs.ca/grhcc/background.pdf.
An impressive action victory for climate change!
Green roof insulation helps to make city buildings more sound-proof,
reducing noise inside the building. They can also provide attractive
new spaces for building residents. Green roofs are being discovered
as delightful new outdoor spaces for daycares, meetings and recreation.
About Green Roofs
 There are two main types of green roofs. One is designed primarily
for environmental and insulation purposes, rather than for access.
This type, called "extensive" by experts, typically only
has two to ten centimeters of soil, and does not add much weight
to the building. It is likely to be covered with grasses and low-lying
herbs, and is largely self-maintaining.
A
second type, designed to allow for larger plants such as trees
and shrubs, needs a greater depth of soil, adds more weight to
the building, and requires more maintenance. These "intensive" green
roofs are designed to be accessible to the people in the building.
They may be penthouse gardens for apartment buildings, new green
spaces for civic buildings, or school roof gardens. Urban schools
with limited space on the ground are discovering the advantages
of gardening on the roof: plenty of sunshine, a secure space and
new "learning grounds" and a living laboratory for urban
ecology, biology, and a whole exciting range of evolving "green
technologies."
A green roof requires a specially designed waterproof, root repelling
membrane and a drainage system. In northern climates, thermal insulation
to keep heat in the building in the winter and out in summer may
be added above this layer. Then a lightweight growing medium (rather
than heavy soil which can pose a weight problem on a rood) is added,
followed by plants appropriate for the size and depth of the green
roof.
Moving Ahead
The many advantages of green roofs have made the transformation
of building tops into a growing industry. Turning a roof from black
to green can involve the skills of a wide variety of professionals,
including architects, engineers, manufacturers of green roof systems
and accessories, roofing and landscaping contractors and consultants,
energy experts, landscape architects, horticulturalists, governments,
non-profit organizations, and educators. This new use of existing
space is one example of how new "green" jobs can be created.
And as enthusiasm grows for the many kinds of learning that green
roofs can provide, educational institutions are also looking for
ways to invest in making turning their roofs into valuable new
resources.
Dealing with climate change is brining new players on board
to seek constructive solutions to reduce greenhouse gases, increase
energy efficiency, protect biodiversity and invest in healthy,
sustainable communities. Green roofs promise to be an important
contribution to climate change solutions in the 21st century.
Resources
What do Green Roofs Have to Offer?
www.greenroofs.org/index.php?page=publicbenefits
Eco-Design Resource Society Green Roofs for Healthy Cities
www.vcn.bc.ca/edrs/resources/greenroofs.html
Images - Green Roofs Before & After, and the dramatic "heat-island
effect" of urbanized areas on hot summer days.
www.greenroofs.ca/grhcc/image%20bank.pdf
A History of EcoRoofing
www.ecoroofsystems.com/history_files/c_historycont.html
ACTIVITY 1
- a) What are the contributing factors
that cause the 'heat island
effect' in cities?
b) Why is this a problem? Hint: See 3.2.6
- Describe some of the advantages of 'Green Roofs'.
Name 3 buildings
and their locations in Ontario that have a green roof.
- Explain the difference between an 'extensive' green roof and 'intensive
green roof.
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