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Bangladesh is country in South Asia. It is bordered by India to its
west, north and east; Myanmar (Burma) to its southeast; and is
separated from Nepal and Bhutan by the Chicken's Neck corridor.
To its south, it faces the Bay of Bengal. The largest city is Dhaka
situated at the center as capital. There are 10 metropolitan cities
having a lot of municipal small towns inside each of them.
Bangladesh is fourth polluted country in the world; Dhaka,
Narayanganj, Gazipur are among top 25 worst polluted cities listed
by WHO. Dhaka is referred as ‘Sick City’ (warm humid tropical
climate getting worse each day).
Unfortunately, urbanization is taking place too quickly in unplanned
approach and thus many municipalities are unable to find the proper
balance necessary for preventing a range of symptoms from
developing, which can leave a city rather sick and in turn impact the
well-being of residents. Bangladesh is a land of tropical climate and
rivers which are ended into the longest sandy seashore of the world;
and therefore has been very well known for its green agricultural
landscape and mangrove forest as well 1 . Recently,
1Simulating Land Cover Changes and Their Impacts on Land Surface Temperature in Dhaka, Bangladesh - Bayes Ahmed, Md. Kamruzzaman, Xuan Zhu, Md. Shahinoor Rahman and Keechoo Choi
2
rapidlyincreasing economy has lifted a rapid growth of urbanization
in Bangladesh. Thus ‘the green’ especially in the cities like the
capital-Dhaka, is fast diminishing (Table 1) and rising urban heat
island (UHI) effects.Tabassum et al reported that the trend of green
space declination in Dhaka city seems to be null within 20202.
Design and application of green landscape on building exterior is
an inhalation demand of time. Though a very few practice of green
application on buildings as a part of leisure activity had been
reported, these small scale practitioners are not sufficient against
the UHI effect. Besides the decorative benefit, green roof or wall
plantings may provide food, temperature control, hydrological
2Tabassum, T &Sharmin, S., 2010. The Impact of Green Space Declination in Dhaka’s Local Thermal Environment, Conference proceeding, URBANIZATION, TRAFFIC JAM AND BANGLADESH ENVIRONMENT, ISBN: 978-984-33-5373-3
Table 1. The trend of green space declining in Dhaka city
Year Total vegetation(ha) Total built-up(ha)
1975 6585 5551
1985 <6250 >9000
1995 5687 >11682
2005 3992 16105
2010 <2225 >16105 (Estimated)
2020 0 (Estimated) >16105(Estimated)
3
benefits, architectural enhancement, habitats or corridors for
wildlife, and recreational opportunities.
To see this plot in a big scale, lack of research interest and
technological knowledge stands like barriers. As a result, the rate
of developmental research is very slow and involves long interval.
Recently, it has become the point of interest among the motivated
researchers to a step toward intensive and extensive green roof
designing as well as green wall designing in Bangladesh3.
On the other side, urban activities generate large quantities of city
wastes including several Biodegradable materials (like vegetables,
how to build a coherent strategy to optimize plastic waste policy. A
second challenge is linked to resources conservation. Nearly 50%
of plastic waste in the EU is still landfilled. Therefore, much energy
and processed raw material is lost instead of being recycled into
new products. Until now there is no comprehensive policy response
to such challenges. Specific aspects are addressed in various
pieces of legislation, like the Waste Framework Directive with its
2015 separate plastic waste collection target or its 50% household
waste collection target by 2020.7
Although there many
approaches are being
developed for waste
management; the plastic
waste management
seems to be uncontrolled
in Bangladesh.
Recycling is processing used materials (waste) into new, useful
products. This is done to reduce the use of raw materials that would
have been used. Recycling also uses less energy and great way of
controlling air, water and land pollution. Effective recycling starts
7Ambitious waste targets and local and regional waste management - Ecologic Institute (Albrecht Gradmann),UmweltbundesamtÖsterreich (Thomas Weissenbach (main author) andHubert Reisinger) and RIMAS (Francesca Montevecchi).
Figure 1 Waste plastic causing pollution in Dhaka
10
with household (or the place where the waste was created). In many
serious countries, the authorities help households with bin bags
with labels on them. Households then sort out the waste themselves
and place them in the right bags for collection. This makes the work
less difficult. Paper waste items include books, newspapers,
magazines, cardboard boxes and envelopes. Items include plastic
bags, water bottles, rubber bags and plastic wrappers. All glass
products like broken bottles, beer and wine bottles can be recycled.
Cans from soda drink, tomato, fruit cans and all other cans can be
recycled.
Plastic use in road construction is another recycling option Recent
studies in this direction have shown some hope in terms of using
plastic-waste in road construction i.e., Plastic roads. Plastic roads
mainly use plastic carry-bags, disposable cups and PET bottles that
are collected from garbage dumps as an important ingredient of the
construction material. When mixed with hot bitumen, plastics melt
to form an oily coat over the aggregate and the mixture is laid on
the road surface like a normal tar road. Use of the innovative
technology not only strengthened the road construction but also
increased the road life. Rainwater will not seep through because of
the plastic in the tar. So, this technology will result in lesser road
repairs. Plastic will increase the melting point of the bitumen. Roads
laid with plastic waste mix are found to be better than the
11
conventional ones. Plastic road would be a boon for India’s hot and
extremely humid climate where durable and eco-friendly roads
which will relive the earth from all type of plastic waste. Help to
improve the environment. Use of the innovative technology not only
strengthened the road construction but also increased the road life.
The idea of using recycled materials in green roof construction site
will be very exciting and needed to be studied in perspective of
Bangladesh.
The tradit ional way of potted planting in Bangladesh is not yet
effect ively researched for f ight ing against UHI and micro
climate of Dhaka city occurred by pollut ion . Shortage of
experts and no off icial guideline for roof top garden design
using recycled materials . Here, I report a standard roof top
garden design guidelines wh ich can minimize the gap between
the current status of green roof in Bangladesh and a model
green roof designed by research based guidelines using
recycled waste materials .
12
1.2 Goal & Objective
This study is designed to create a single solut ion to shot out
these major two problems i.e. green reduction and plast ic
mediated pollut ion by with install ing roof top garden with
recycled waste plast ic material around the Dhaka city.
The goal is to upgrade the roof top garden concept of
Bangladesh more functionally as well as aesthetically using
recycled waste materials to improve the city condit ion)
The object ive of the study is to make a guidebook with sample
roof top garden design based on the context of Dhaka city.
I I. Scope & Method
2.1 Scope
2.1.1 Contexts
Manufacturing is a sunset industry in west. Because of the low
costs it could be quite rewarding to start a plast ic recycling
factory in Bangladesh. The main prospects are below:
Affordabil i ty of the labor cost and the fast developing
recycling industry of post -consumer plast ic wastes in
Bangladesh are the great advantages to compete in the global
market. The consumption rate of plast ic in Bangladesh is
5kg/year as compared of world consumption rate 30kg/year,
13
there is a huge potential for the domestic growth of the plast ic
industry in Bangladesh. The populat ion growth in Bangladesh
is high and therefore the consumption rate wil l increase and
if the plast ic industry can take the consumers of lower &
middle class, the business should be prof itable 8. Thus, the
concept of ut i l izing plast ic in the rod/ construct ion or in the
roof top can easily be manipulated in Bangladesh.
2.1.2 Time
Bangladesh has three major seasons: summer, winter and
rainy season. W inter is very short and suitable for all the
construct ion works and for plantat ion e nd of rainy season wil l
be the best choice to avoid heavy rainfall. Pract ically it wil l
take almost a year to install such a well-planned green roof.
However, theoretically, it is already studied and surveyed in
my study and hopefully the continuation of s tudy in very detail
wil l not take longer period of t ime.
8A Report on Plastic Industry of Bangladesh Mansur Ahamed (Ph. D) Research Department, JBBC Corporation.
14
2.1.3 Site
Bangladesh is located in the Indomalaya ecozone. Its ecology
includes a long sea coastl ine, numerous rivers and tributaries ,
hil l forests, moist deciduous forests , f reshwater swamp
forests and f lat land with tall grass. The Bangladesh Plain is
famous for its fert i le alluvial soil which supports extensive
cult ivat ion. The country is dominated by lush vegetat ion, with
vil lages of ten buried in groves of mango, jackf ruit ,
bamboo, betel nut , coconut and date palm 9. There are 6000
species of plant l i fe, including 5000 f lowering plants 10. Water
bodies and wetland systems provide a habitat for many
aquatic plants. Water l i l ies and lotuses grow vividly during
the monsoon. The country has 50 wildlife sanctuaries. Beside,
having all these plantat ion f riendly features, Bangladesh is my
native country and so it is very convenient for me to gather all
necessary information for my study, therefore it is selected as
the site of study.
9Bangladesh | history – geography: Plant and animal life. Encyclopædia Britannica. 10Jump up^ "Flora and Fauna – Bangladesh high commission in India". Bangladesh High
15
2.2 Method
Mostly my study material includes reviewing the related
l iteratures and theoretical analysis as well as a bit of survey
study. Methodology is to applying the knowledge theoretically
to establish a proper guideline o f a green roof project based
on recycled materials.
Dhaka, the capital city of Bangladesh
Polluted city with waste materials
diminished green space
Rooftop garden with recycled waste materials
Rooftop garden design guideline
Figure 2 Research Flowchart
16
I I I. Literature Review
3.1 From Babylon to Dhaka: The History of
Rooftop Gardens
At present, in Dhaka the roof garden has been quite popular.
Just looking at the dif ferent types of roof gardens can be s een
in most container based system. However, most of the roof top
garden has been developed in an unplanned way. The planned
init iat ives on the roof of the plant, even vegetables can be
grown. The collect ive love of nature in the clouds h as existed
since the beginning of recorded t ime.
The f irst known roof
gardens are thought to be
the ziggurats of ancient
Mesopotamia, the most
famous of which is the
Hanging Gardens of
Babylon, one of the Seven
Wonders of the Ancient
World. Usually located in
the courtyards of major
cit ies, these enormous
pyramid towers had
Figure 3: Reconstruction of the Hanging Gardens of Babylon, 1924, from the Collection of the New York Public Library
17
stairways that spiraled along their outer edges, with trees on
the staircase landings to provide some respite f rom the harsh
desert sun. Our only proof of their existence is classical
writ ings based on ora l histories; no archeological proof has
ever been found (although, recently a Brit ish academic
claimed to have identif ied the true location of the Hanging
Gardens of Babylon.)
Fast forward to The Renaissance, when Italians were crazy
for their gardens the more symmetrical and ordered in design,
the better. The oldest and best preserved roof garden is f rom
this t ime, located in the town of Pienza in Sienna, Italy. Pienza
was the birthplace of Aeneas SilviusPiccolomini, who had a
palace built for himself the re when he later became Pope Pius.
On the roof , a formal garden was erected for him to hold
audiences. The entire town of Pienza, now a UNESCO World
Heritage site and its place have remained virtually untouched
since the 15th century.
The tradit ional roof garden in Bangladesh started f rom the
very early unspecif ied t ime with pot planting in residential
buildings as a hobby. Then it started to transform gradually
since 1989 by developing the terrace garden and 1994 as
thermal comfort for urban area.
18
But the concept started to renovate as urban agriculture faster
than any other signif icances. Now it is playing an important
role in economic sector because there are many people who
sell vegetables in the market af ter fulf i ll ing the household
demand.
3.2 Present condit ion of Dhaka
In Bangladesh, the pract ice of roof top garden is ancient but
it is very small scale and a malnourished sector due to lack of
awareness and extensive research. However, here some of
the developmental steps are mentioned which are done b y a
few researchers in Bangladesh.
Overall, the approach of green roof top development in
Bangladesh summarized in f rame (Table 2)
Figure 4 Traditional Rooftop Garden with Pot Planting in Dhaka
19
Table 2: The developmental steps of green roof top of
Bangladesh
Year Scientif ic or non-scientif ic reports
Strategic Procedure
Unspe
cif ied
Pot plants in
residential buildings
of Bangladesh
Just as hobby11.
1989 Terrace Housing Natural venti lat ion and
effect of air well on air f low
and air velocity12.
2004 Residential
Vegetat ion
Financial and
environmental benef it13.
2005 Roof Gardening Impact on built
construct ion14.
2007 Roof gardening Important aspects of roof
gardening 1 1
2009 Green roof concept
in Residential
apartment building
Green roof in context of
Dhaka city apartment15.
2010 Natural green
technology
The effect of Green roof in
urban l i fe16.
2013 Applicat ion of
extensive and
intensive green roofs
Comparison and contrast
between two major types of
green roof in Dhaka city17.
11Natural Green Application technology on Building in Dense Dhaka City is provide a sustainable, energy saving, comfortable and healthy environment. RumanaRashid ,Mohd. Hamdan Bin Ahmed , Md. Sayem Khan 12Mallick F.H. PhD thesis (unpublished), AA school of Architecture. 13SudiptaBarua, Sarah Bashir, Study of the effect of residential vegetation on built environment; 2005 14Sajjaduzzaman; Analytical study on cultural and financial aspects of roof garden. 15 Shad, Sheikh DibyaPorkash, Dhaka,2007 16 Hossain MM, effects of green roof concept on residential apartment in the context of Dhaka city. (Unpublished) 17Rumana Rashid, Green roof and its impact on urban environment and sustainability, World Journal of Management, Vol 2
20
From the upper table it is clear that almost st i l l now green roof
is a pract ice among the rich and upper middle class society.
This pract ice is not studied well enough to be available for
general and mass people, ult imately result ing ineffect ive
approach against UHI effect.
Markov model simulated land cover maps of Dhaka area
shows the land cover changes for 2019 and 2029; and the
impacts on Land Surface Temperatures in respective periods.
Simulat ion results show that if the current trend continues, at
the year of 2019 and 2029, 56% and 87% area of Dhaka
respectively wil l face more than 30°C tempera ture.
Nevertheless, with a great loss of vegetat ion replaced by
buildup area18.
18Simulating Land Cover Changes and Their Impacts on Land Surface Temperature in Dhaka, Bangladesh - Bayes Ahmed, Md. Kamruzzaman, Xuan Zhu, Md. Shahinoor Rahman and Keechoo Choi
21
Green roofs have many benef its as presented above, but
green roofs also have negative aspects. Based on various
Figure 5 MLP Markov model simulated land cover maps of DMP area (2019 and 2029).
22
researches, the following issues requiring attention of th e
designers are identif ied:
• Green roofs have more demanding structural standards.
Some exist ing buildings cannot be retrof it ted with a green roof
because of the load of the soil and vegetat ion. Depending on
what kind of roof it is, the maintenance costs could be higher.
• Green roofs also place higher demands on the
waterproof ing system of the structure both because water is
retained on the roof and due to the possibil i ty of roots
penetrat ing the waterproof membrane. Install ing adequate
waterproof ing systems and root barriers can increase the cost
of the roof .
• However, for those l iving in increasingly tall buildings
the roof gardens are offering doorstep recreation spaces and
contacts with nature in the vert icality.
Thus, poor installat ion, wrong material choices, negligent
maintenance has played an impactful role as barriers in this
sector.
Green inf rastructure establishment can immediately be
applied to the governmental organizations, public places,
educational inst itutes, off ices etc. compared to any personally
owned building as we can see f rom the well -established
23
examples because this message can be f irst adopted by this
type of powerful, well known and scattered organizations to
create example in a growing city. Nature is gett ing sensit ive
day by day by changing its climates, features, weather,
productivity etc. It changes its face at dif ferent places of the
earth. Thus it is possible that green inf rastructure is needed
to be studied at the place where it is going to be applied
considering the climate, plant resources, weather and other
necessary parameters of that specif ic place. Bangladesh is
allowing one of the fastest growths of urbanization thus Dhaka
is one of the fastest growing cit ies. There are many reputed
universit ies in Dhaka, which are al so an example of
urbanization.
Being a concrete jungle by grabbing huge amount of vegetated
surfaces under rapid urbanization and housing process,
Dhaka as well as residential areas is facing several extensive
environmental problems. So, the importance of vegetat ion
should be analyzed for the betterment of the city’s existence .
Home owners of ten want to avoid this solut ion thinking about
the extra load of evenly distributed substrate on the roof as
they are familiar only with vegetat ion l ike - f lower or f rui t trees
in planter boxes in very l imited space with a poor water
irr igat ion system also not aware of the weight of the garden.
24
But, intensive or extensive type of roof ing is more convenient
and recommended as substrate depth and load can be
balanced and easy to maintain compared to vegetat ion in the
planter box. As the intensive green roof is almost a new idea
in the context of Dhaka, people are not aware of its importance
and benef its and don’t know exactly whom to contact with for
more details. There is lack of technical information - standards
about the whole system and technical expert ise in this f ield to
support interested owners and developers. There are many
added benef its for owners such as long l ife span of the roof ,
energy savings to the building, increases tenancy. Besides,
storm water management, reduced water logging and air
temperature at the micro level are benef its for developers and
community as a whole. Occupants of buildings also get
benef ited by low outdoor and indoor temperature, more air
f low, less air and noise pollut ion.
25
Figure 6: Current rooftop garden system of Dhaka
26
Very inspiring news is, now a days, the government of
Bangladesh is highly focusing on encouraging the mass
people about roof gardening as a part of that they took a lot
of init iat ives as follows 19:
The mayor of South Dhaka city corporat ion,
SayeedKhokon announced that 10% of holding tax wil l
be reduced who has green roof on top of their building.
Clarifying the misconception that roof gets wors e af ter
gardening.
Educating people about most effect ive and safe roof
gardening.
Spreading the idea and sense of “Green Dhaka - Clean
Dhaka” among all.
A professor of dept. of Geography and Environmental
sciences of Dhaka University named Dr. Humayun Kabir
also providing motivat ional speech l ike, green roof wil l
not only for beautif icat ion, it wil l make a balance in the
environment which has high UHI effect.
A lot of owner has diminished a lot of tree in last 20
Recycling is processing used materials (waste) into new,
useful products. This is done to reduce the use of raw
materials that would have been used. Recycling also uses less
energy and great way of controll ing air, water and land
pollut ion. Effect ive recycling starts with household (or the
place where the waste was created). In many serious
countries, the authorit ies help households with bin bags with
labels on them. Households then sort out the waste
themselves and place them in the right bags for collect ion.
This makes the work less dif f icult . Paper waste items include
books, newspapers, magazines, cardboard boxes and
envelopes. Items include plast ic bags, water bott les, rubber
bags and plast ic wrappers. All glass products l ike broken
bott les, beer and wine bott les can be recycled. Cans f ro m
soda drink, tomato, f ruit and all other cans can be recycled.
Plast ic use in road construct ion is not new. Recent studies in
this direct ion have shown some hope in terms of using plast ic -
waste in road construct ion i.e., Plast ic roads. Plast ic roads
mainly use plast ic carry -bags, disposable cups and PET
bott les that are collected f rom garbage dumps as an important
28
ingredient of the construct ion material. When mixed with hot
bitumen, plast ics melt to form an oi ly coat over the aggregate
and the mixture is laid on the road surface l ike a normal tar
road. Use of the innovative technology not only strengthened
the road construct ion but also increased the road l ife.
Rainwater wil l not seep through because of the pla st ic in the
tar. So, this technology wil l result in lesser road repairs.
Plast ic wil l increase the melt ing point of the bitumen. Roads
laid with plast ic waste mix are found to be better than the
conventional ones. Plast ic road would be a boon for India’s
hot and extremely humid climate where durable and eco -
f riendly roads which wil l relive the earth f rom all type of plast ic
waste. Help to improve the environment. Use of the innovative
technology not only strengthened the road construct ion but
also increased the road l ife.
Considering the current overpopulated and polluted situation
of small city Dhaka, it is reasonable wise to pay attention in
increasing the green roof . Because it improves thermal
performance, cleaning the air-cooling a city, decreases urban
heat island effect, creates & preserves of habitat & ecological
biodiversity. Moreover, it increases property value and other
benef its for building owners effect ive for managing storm
29
water. Last but not the least, it opens the door of aesthetics,
offers open space and urban food production.
3.4 Plantation in Bangladesh
3.4.1 Effects of Seasons
Bangladesh has a tropical monsoon climate. There are
basically four seasons in a year: winter (December -February),
summer (March-May), monsoon (June-September) and
autumn (October November). The average temperature across
the country usually ranges between 11°C and 29°C in winter
months and between 21°C and 34°C during summer months.
Annual rainfall varies f rom 160 cm to 200 cm in the west, 200
cm to 400 cm in the Southeast and 250 cm to 400 cm in the
Northeast.
The climate is tropical in Dhaka. The summers here have a
good deal of rainfall, while the winters have very l i t t le. The
Köppen-Geiger climate classif icat ion is Aw. The average
temperature in Dhaka is 25.9 °C. In a year , the average
rainfall is 2022 mm The driest month is January. There is 6
mm of precipitat ion in January. Most of the precipitat ion here
falls in July, averaging 377 mm. 20
20https://en.climate-data.org/location/1062098/
30
Figure 7 Climate Graph of Dhaka
Figure 8 Temperature Graph of Dhaka
31
3.4.2 Soil and water for Plantation
Bangladesh has three broad types of soil, namely, Flood Plain
Soils (79%), Brown Hil l Soils (13%), and Terrace Soils (8%).
Soil scientists further classify "Flood Plain Soils" of
Bangladesh into 14 subtypes varying f rom calcareous to non -
calcareous, acid basin to acid sulphate, grey to brown
Piedmont, peat and Terai soils.
The "Brown Hil l Soils" are located in the hil ly regions of
Chittagong, CHTs, and Dhaka and Sylhet districts and vary
f rom brown sandy loam to clay loam.
The "Terrace Soils" exist in the "Barind" and "Madhupur"
tracts of Bangladesh and consist of brown to grey clays and
loams. The country has f ive major river systems: the Ganges
or Padma and its deltaic streams, the Meghna and the Surma
river systems, the Jamuna and its adjoining channels, the
North Bengal rivers, and the rivers of the Chittagong Hil l
Tracts and the adjoining plains.
The Ganges River system is divided into two segments, the
Ganges and the Padma. The Meghna River is the union of the
Sylhet-Surma and Kusiyara rivers. The Jamuna and its
adjoining channels span a large area f rom North Central
32
Bangladesh to the Meghna River in the Southeast. The Tista
is the most important water carrier of Northwestern
Bangladesh that meets the Jamuna. The Feni, the Karnaphuli,
the Sangu, and the Matamuhari are the four main rivers that
const itute the river system of the CHTs and the adjoining
plains of Bangladesh. Overall, the soil and water source are
very suitable for plantat ion in Bangladesh.
3.4.3 Plant types
The area under agricultural use is subdivided into three
categories, namely the net cropped area, current fallow, and
cult ivable waste which is a fallow for more than a year.
Agriculture land use has been able to maintain its share at
about 66% of the total area of the country during the 1970s
and 1980s but its share has fallen to about 59% during the
1990s. The share of land under "other uses" l ike sett lements,
homestead, rivers, etc. has consistentl y risen over the past
period21. Bangladesh is the world’s largest producer of jute.
Rice being the principle staple food, its production is of m ajor
importance. Rice production stood at 20.3 mil l ion tons in the
1996-97 f iscal years.
21Bangladesh | history – geography :: Plant and animal life. Encyclopædia Britannica.
33
Crop diversif icat ion programs, credit , extension and research,
and input distribut ion policies pursued by the government are
yielding posit ive results. The country is now at the threshold
of attaining self -suff iciency in food grain production. Forest
areas of Bangladesh vary considerably from one source to
another, and there is a general need of reliable information in
this regard, e.g. the total forest area is 2.56 mi ll ion ha (FMP,
1993), 2.25 mill ion ha (BBS, 1999) and 1.47 mill ion ha (World
Bank, 1997. However, in Bangladesh, of the total area
agricultural land makes up 65% of the geographic surface,
forest lands account for almost 17.5% (2.53 mill ion ha) (FD,
2004), while urban areas cover 8% of the land. Water and
other land uses account for the remaining 10%. The total
forest land includes classif ied and unclassif ied state lands,
homestead forests and tea and rubber gardens.
34
22
22Simulating Land Cover Changes and Their Impacts on Land Surface Temperature in Dhaka, Bangladesh - Bayes Ahmed, Md. Kamruzzaman, Xuan Zhu, Md. Shahinoor Rahman and Keechoo Choi
1 2
3 4
Figure 7 Present Land cover Map of Dhaka: (1) Buildup Area, (2) Green Area, (3) Water body, (4) Bare land
35
3.5 Review of the Rooftop Garden Design Techniques
3.5.1 Rooftop Garden design
In Bangladesh, the pract ice of roof top garden is ancient but
it is very small scale and a malnourished sector due to lack of
awareness and extensive research. However, here some of
the developmental steps are mentioned which are done by a
few researchers in Bangladesh.
In Dhaka, urban dwellers hardly seen any greenery around
them, every inch of land is occupied by concrete structures.
The solut ion l ies in planting as many trees as possible, and
the only place to do that seems to be roof tops. If people can
make vegetable, f ruit , f lower of ornamental gardens, this wil l
supply f resh vegetables for them. Fruits and vegetables
purchased in the city are of ten mixed with chemicals, which
are hazardous for health, but a roof to p garden can be a source
of f resh vegetables for city dwellers, and also be a pleasant
and unusual sight.23
23NogorKrishor (Urban Farmer) Working for The Greenery of Dhaka City - By M.H.M. BorhannuddinBhuyan
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3.5.2 Need for green roof
Considering the current overpopulated and polluted situation
of small city Dhaka, it is reasonable wise to pay attention in
increasing the green roof . Because it improves thermal
performance, cleaning the air, cooling a city, decreases urban
heat island effect, Creates & preserves of habitat & ecological
biodiversity. Moreover, it increases property value and other
benef its for building owners effect ive for managing storm
water. Last but not the least, it opens the door of aesthetics,
offers open space and urban food production.
3.5.3 Use of recycled waste product for roof garden
Pre consumer and postindustrial recycling of products mad e
f rom poly-vinyl chloride (PVC) is already well established in a
variety of industrial segments. With regards to thermoplast ic
PVC roof ing membranes, efforts to reclaim and recycle plant
trimmings go back well over a decade.
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The grinding process is very effect ive at separating scrim, as
well as the polyester felt backing used in some applicat ions,
f rom the polymer matrix. The residual f luff can be used as a
reinforcing f iber in the production of cement blocks for
landscaping and retention wall construc t ion or as feedstock in
waste to energy conversion processes.
Although a signif icant amount, the roughly four mil l ion pounds
of trimmings material produced, processed and recycled
annually by one manufacturer, pales in comparison to the
potential volumes available for post-consumer recycling.
Figure 8 Geo-textile made by recycled plastic
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One of the major problems with creating a roof top garden is
the sheer weight of soil. While a typical rooftop is designed to
handle about 20 to 40 pounds per square foot, some soil can
weigh up to 120 pounds per squa re foot. That means that,
while you may have the space for a roof top garden, it st i l l
might not be feasible. But Gaia Soil, a social venture of Gaia
Inst itute, a non-prof it corporat ion, has found a way around
that part icular problem, using an unexpected pr oduct:
Styrofoam.
Environmentalists have long decried the use of Styrofoam, or
polystyrene, because of its non -sustainabil i ty, health
concerns, hazardous waste, and pollut ing qualit ies. It ’s an
unlikely coupling, to be sure, but it ’s also quite innovative .
Gaia Soil uses recycled Styrofoam and pectin to create a
synthetic soil.
End of Service Life Recycling of Thermoplast ic PVC Roof ing
Membranes By S.P. Graveline, Vice President Technical
Services, SikaSarnaf i l, a Division of Sika Corp.
The nearly weightless Styrofoam is coated with pectin, which
is a gel that “holds every plant and every f ruit and leaf
together,” according to Paul Mankiewicz, creator of the new
soil. A cubic foot of Styrofoam and pectin weighs just 10
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pounds and can hold up to 20 pounds o f water. That’s a big
difference f rom the 120-pound natural product.
Some are concerned about the possible risks associated with
using Styrofoam as soil. Th is is a matter of concern that it
might leech dangerous chemicals into plants, blow off into the
air, or create other environmental concerns. But so far, there
is no indication of any of those problems. It ’s been in use for
years in some locations and there have been no problems.
The soil is also held down by a coconut f iber or burlap cover,
topped with an inch or so of compost, and t ied together with a
root matrix—so there’s no real danger of it blowing off . One of
the best things about this synthetic soil—besides the fact that
it makes roof top gardening far more feasible —is that it ’s
completely sustainable. It uses materials that have already
been made and would otherwise go into our waste system.