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Sustainable development & Eco – Roof
( a) Dr.Hossam Elborombaly (b) Dr. Luis Fernando Molina-Prieto (b)
(a)Prof. Department of Architecture, Effat University, Jeddah, Kingdom of Saudi Arabia
helborombaly@effatuniversity.edu.sa Tel: +966 562745117, Fax +966126377447
(b) Department of Architecture, Universidad de América, Bogotá, Colombia
Abstract:
The analytical preview of the elements, definitions and historical background for the research.
It started with identifying the global problems and methods of solution through sustainability
concepts and the method of applying these concepts in building roof design.
Then it continues with the study of the building and its elements, and the study of historical
development of the sustainable cities. The research focuses on types of buildings roofs, and studies
comprehensive definition of Eco-roof and accompanying theories and systems.
The many acres of flat rooftop space in most cities can become additional green spaces while
also mimicking the natural environment in a way that restores ecosystems, combats the urban heat
island effect, controls storm water runoff, and conserves energy.
There should now be enough evidence and successful examples worldwide to be able to
convince more legislators, planners, architects, landscape architects, engineers, developers and
builders that green roofs have real benefits, at local and city-wide scales. It is predictable that
attitudes towards green roofs will change and that they will become more commonplace and
mainstream following further adoption of new guidelines on urban design by central and local
government. Green roofs will make the cities, homes, and workplaces of the future, greener,
cleaner, cooler, and more tranquil, with people sharing space with nature.
Problems
Sustainable roofing design presents a feasible design strategy for microclimate amelioration
and energy conservation in buildings which in return will build sustainable cities. Previous field
and modeling studies in various climatic zones indicate that an individual Sustainable roof can
reduce roof surface temperature by 15–45 °C, near-surface air temperature by 2–5 °C and building
energy consumption by up to 80%.
In an extremely compact tropical city such as Cairo with severe shortage of ground-level
green spaces and intense UHI effects, Sustainable roof could bring significant benefits. Large-
scale installation of greenery on the spatially concentrated roofs and podiums & passive roof
cooling solutions forming an elevated sustainable network could compensate for the green-space
deficit, mitigate urban climate and improve quality of life.
Objectives
i- The Research aim at reaching a practical design strategy for building roof
design as a step for sustainable & environmental building developments for
improving building performance & energy efficiency, which in return will
affect the indoor air quality creating a comfort atmosphere for the building
uses.
Research Contents
History & Origin of Roof ideas
Concepts related to environmental treatments to the building roof Building
Envelope
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Sustainable Roofing Systems
Energy efficiency
Result and Recommendation
KEY WORDS:, Eco-roof, global energy, green roofs , Passive cooling ,Sustainable roofs,
This chapter is concerned with the theoretical study, definitions and historical background for
the thesis subject. It starts with identifying the global problems and methods of solution through
sustainability concepts and the method of applying these concepts in buildings roof design. Then
it continues with the study of the building envelope and its elements, and the study of historical
development of the building envelope. The chapter focuses on residential and commercial
buildings as an urban design element, and studies their relations with other city elements, and
studies comprehensive definition of Eco-roof and accompanying theories. Then the chapter is
concerned with the evaluation and assessment methods, first through rating systems, second,
through computer simulation, and finally, through equipment monitoring. This chapter is the
theoretical study sector which is the basic foundation for the coming chapters.
1.1 Background
Cities have become major contributors to global energy consumption and greenhouse gas
(GHG) emissions. The urbanization process causes local climate change through excessive
anthropogenic heat release and modification of land biophysical properties. The resultant urban
heat island (UHI) effects and aggravating human heat stress have become key environmental issues
in city management. Cities can be designed to be climate-conscious and energy-efficient to
contribute to urban sustainability and address global climate-change issues at the local level.
Sustainable roofs present a feasible design strategy for microclimate amelioration and energy
conservation in cities. Previous field and modeling studies in various climatic zones indicate that
an individual Sustainable roof can reduce roof surface temperature by 15–45 °C, near-surface air
temperature by 2–5 °C and building energy consumption by up to 80%. In an extremely compact
tropical city such as Cairo with severe shortage of ground-level green spaces and intense UHI
effects, Sustainable roof could bring significant benefits. Large-scale installation of greenery on
the spatially concentrated roofs and podiums forming an elevated green network could compensate
for the green-space deficit, mitigate urban climate and improve quality of life.
Previous assessments of sustainable-roof thermal effects are largely restricted to the
individual building scale.(23)
Fig (1) Hanging Gardens of Babylon
Fig (2) Turf roof - Iceland
Source : Sustainable roofs
Research by David Stater -
Online document
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Sustainable roofs are not a new phenomenon. They have been standard construction practice
in many countries for hundreds, if not thousands, of years, mainly due to the excellent isolative
qualities of the combined plant and soil layers.
Two modern advocates of Sustainable roof technology were the architects Le Corbusier and
Frank Lloyd Wright. Although Le Corbusier encouraged rooftops as another location for urban
green space, and Wright used Sustainable roofs as a tool to integrate his buildings more closely
with the landscape, neither was aware of the profound environmental and economic impact that
this technology could have on the urban landscape. Until the mid-20th century, Sustainable roofs
were viewed mainly as a vernacular building practice. However in the 1960’s, rising concerns
about the degraded quality of the urban environment and the rapid decline of green space in urban
areas, renewed interest in Sustainable roofs as a "green solution" was sparked in Northern Europe.
New technical research was carried out, ranging from studies on root-repelling agents, membranes,
drainage, lightweight growing media, to plant suitability.(3)
1.2 History & Origin of Roof ideas
The earliest known Sustainable roofs were turf roofs, a Nordic tradition still practiced today
in many parts of Norway and Iceland. Turf was a durable and readily available building material
known to have an insulating effect. There are several remaining examples of relatively
sophisticated earth-sheltered and turf-roofed structures dating as far back as the Bronze Age, 3,000
years ago.
Sustainable roofs are not a new phenomenon. They have been standard construction practice
in many countries for hundreds, if not thousands, of years, mainly due to the excellent isolative
qualities of the combined plant and soil layers.
Sustainable roofs date back to thousands of years. Despite the recorded existence of roof
gardens, little physical evidence has survived but history reveals the purposes of vegetated roofs
were diverse. These purposes include the insulating qualities, and an escape from the stress of the
urban environment.
The origins of Sustainable roofs began thousands of years ago. The most famous Sustainable
roofs were the Hanging Gardens of Babylon. They were considered as one of the Seven Wonders
of the Ancient World, were constructed around 500 B.C. They were built over arched stone beams
and waterproofed with layers of reeds and thick tar.
Plants and trees were then planted. In more recent times, people used sod to cover their roof
tops for the purpose of insulation, it kept their homes cool in summer and warm in winter. Modern
Sustainable roofs may have had their "roots" in ancient times but technological advances have
made them far more efficient and expensive than their ancient counterparts. (58)
Modern green roofs are made of a system of layers placed over the roof to support soil medium
and vegetation. This is a relatively new phenomenon and was developed in Germany in the 1960s,
and has spread to many countries, since then. Sustainable roofs are also becoming increasingly
popular in the United States, although they are not as common as in Europe.
Currently, Sustainable roofs are becoming more common in the United States, although other
countries are farther along in the adoption of Sustainable roof systems. In Germany for example,
it is estimated that 14% of all flat roofs are green .Before human development began causing wide
scale disturbance, soil and vegetation managed storm water and solar energy effectively . Since
that is no longer the case, Sustainable roofs have become one aspect of effective storm water and
solar energy management. The introduction into the U.S. urban environment only occurred
recently, gaining popularity in the last few decades. (58)
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Further advancements came from Germany in the 1960’s where still new materials were
developed to create the Sustainable roof we still use today.
1.3 Problems
Here are two global events converging to create the most significant crisis of modern times.
The first of these is global warming. The second major event threatening our planet is the
escalating consumption of energy and resulting depletion of fossil-fuel resources.
1.3.1 Global warming
There is considerable scientific evidence that the earth's temperature is rising and will
continue to do so as a result of human activities. These activities include particularly the burning
of fossil fuels- coal, oil and gas- for our buildings and our transportation, manufacturing and
agricultural systems and they result in increased greenhouse gases (GHG), which contributes to
global warming, see Fig. (1.4).
Climate change affects us all- we should act to reduce its impact by changing from fossil-fuel-
based systems to renewable-energy-based ones.
- The likely negative impacts of global warming include:
1- Disastrous sudden results like increased storms, flooding, droughts, and the probable
destruction of the ecosystems,
2- Slow rate results, as the spread of diseases affecting human health, impairment of crops and
plants, also affecting the living environment of human beings. In urban areas, there is a "heat
island" effect resulting from the production and accumulation of heat in the urban mass. Cities
can be several degrees warmer than their surroundings. The heat island effect will lead to
temperature rises being more marked; air pollution in cities may increase; drainage systems
may need to be altered to cope with periods of higher rainfall.
Global warming will probably lead to social, political and economic disturbance. It seems
wise to stand for what is known as the "precautionary principle" , which maintains that we should
take action now to avoid possible serious environmental damage even if the scientific evidence for
Fig (1.3) Guinigi Tower, Lucca, Italy
Source : Sustainable roofs Research by
David Stater - Online document - Accessed
February 2014
Fig. (1.4) Worldwide GHG emissions by sector
in 2004
source: 4th IPCC assessment report , climate
change mitigation, 2007.
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action is inconclusive, and design our cities to reduce their CO2 production significantly despite
the welfare caused by the over emissions. (101)
There will naturally be environmental costs if the standards of the wealthy are maintained
while at the same time meeting the basic needs of the poor. These environmental costs,
furthermore, will increase dramatically if the living conditions in developing countries improve. It
is one earth that we inhabit, and its environmental, social, economic and political problems have
no borders.(102)
The technology to reduce climate change is largely available. We need more solutions, more
government support and more individual initiative.
1.3.2 Urban heat island effect (UHI)
An urban heat island (UHI) is a metropolitan area that is significantly warmer than its
surrounding rural areas due to human activities. The phenomenon was first investigated and
described by Luke in the 1810s, although he was not the one to name the phenomenon.
The temperature difference usually is larger at night than during the day, and is most apparent
when winds are weak. UHI is most noticeable during the summer and winter. The main cause of
the urban heat island effect is from the modification of land surfaces, which use materials that
effectively store short-wave radiation.
Waste heat generated by energy usage is a secondary contributor. As a population center
grows, it tends to expand its area and increase its average temperature. The less-used term heat
island refers to any area, populated or not, which is consistently hotter than the surrounding area.
Monthly rainfall is greater downwind of cities, partially due to the UHI. Increases in heat
within urban centers increases the length of growing seasons, and decreases the occurrence of
weak tornadoes.
The UHI decreases air quality by increasing the production of pollutants such as ozone, and
decreases water quality as warmer waters flow into area streams and put stress on their ecosystems.
Not all cities have a distinct urban heat island. Mitigation of the urban heat island effect can
be accomplished through the use of Sustainable roofs and the use of lighter-colored surfaces in
urban areas, which reflect more sunlight and absorb less heat.
Despite concerns raised about its possible contribution to global warming, comparisons
between urban and rural areas show that the urban heat island effects have little influence on global
mean temperature trends.
Causes
There are several causes of an urban heat island (UHI). The principal reason for the nighttime
warming is that the short-wave radiation is still within the concrete, asphalt, and buildings that was
absorbed during the day, unlike suburban and rural areas. This energy is then slowly released
during the night as long-wave radiation, making cooling a slow process. Two other reasons are
changes in the thermal properties of surface materials and lack of evapotranspiration (for example
through lack of vegetation) in urban areas. With a decreased amount of vegetation, cities also lose
the shade and cooling effect of trees, the low albedo of their leaves, and the removal of carbon
dioxide.
Materials commonly used in urban areas for pavement and roofs, such
as concrete and asphalt, have significantly different thermal bulk properties (including heat
capacity and thermal conductivity) and surface radiative properties (albedo and emissivity) than
the surrounding rural areas. This causes a change in the energy balance of the urban area, often
leading to higher temperatures than surrounding rural areas.
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Other causes of a UHI are due to geometric effects. The tall buildings within many urban
areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the
efficiency with which urban areas are heated. This is called the "urban canyon effect". Another
effect of buildings is the blocking of wind, which also inhibits cooling by convection and pollution
from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also
contributes to the UHI. High levels of pollution in urban areas can also increase the UHI, as many
forms of pollution change the radiative properties of the atmosphere. As UHI raises the
temperature of cities, it will also increase the concentration of ozone in the air, which is a
greenhouse gas. Ozone concentrations will increase because it is a secondary gas, aided by an
increase in temperature and sunlight.
Some cities exhibit a heat island effect, largest at night. Seasonally, UHI shows up both in
summer and winter. The typical temperature difference is several degrees between the center of
the city and surrounding fields. The difference in temperature between an inner city and its
surrounding suburbs is frequently mentioned in weather reports, as in "68 °F (20 °C) downtown,
64 °F (18 °C) in the suburbs". Black surfaces absorb significantly more electromagnetic radiation,
and causes the surfaces of asphalt roads and highways to heat. "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).
Why Do We Care About Heat Islands?
Elevated temperature from urban heat islands, particularly during the summer, can affect a
community's environment and quality of life. While some heat island impacts seem positive, such
as lengthening the plant-growing season, most impacts are negative and include:
Increased energy consumption: Higher temperatures in summer increase energy demand for cooling
and add pressure to the electricity grid during peak periods of demand. One study estimates that the
heat island effect is responsible for 5–10% of peak electricity demand for cooling buildings in cities.
Elevated emissions of air pollutants and greenhouse gases: Increasing energy demand
generally results in greater emissions of air pollutants and greenhouse gas emissions from
power plants. Higher air temperatures also promote the formation of ground-level ozone.
Compromised human health and comfort: Warmer days and nights, along with higher air
pollution levels, can contribute to general discomfort, respiratory difficulties, heat cramps and
exhaustion, non-fatal heat stroke, and heat-related mortality.
Impaired water quality: Hot pavement and rooftop surfaces transfer their excess heat to storm
water, which then drains into storm sewers and raises water temperatures as it is released into
streams, rivers, ponds, and lakes. Rapid temperature changes can be stressful to aquatic
ecosystems.
What Can Be Done?
Communities can take a number of steps to reduce the heat island effect, using four main
strategies:
Increasing tree and vegetative cover
Creating Sustainable roofs(called "rooftop gardens" or "eco-roofs")
Installing cool—mainly reflective—roofs
Using cool pavements.
Typically heat island mitigation is part of a community's energy, air quality, water, or
sustainability effort. Activities to reduce heat islands range from voluntary initiatives, such as cool
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pavement demonstration projects, to policy actions, such as requiring cool roofs via building
codes. Most mitigation activities have multiple benefits, including cleaner air, improved human
health and comfort, reduced energy costs, and lower greenhouse gas emissions.
1.3.3 Energy crisis
Fossil fuels are currently the most economically available source of power for both personal
and commercial uses. In 2005, more than 3/4 of total world energy consumption was through the
use of fossil fuels. Petroleum led with over 43.4 percent of the world's total energy consumption,
followed by natural gas (15.6 percent) and coal (8.3 percent). Long thought to be inexhaustible,
fossil fuels have been used extensively since the Industrial revolution.
However, many believe that the world is using fossil fuels at a non-regenerative rate (See Fig
1.5). Some experts believe that the world has already reached its peak for oil extraction and
production, and that it is only a matter of time before natural gas and coal vanish.(103)
Fig. (1.9) Inverse relation between rate of oil discovery and production.
Source : http://seekingalpha.com/article/310502-getting-ready-for-peak-oill
Accessed February 2014
Fig. (1.10) GHG emissions in Egypt by sector.
Source : Emissions Summary for Egypt - Online document
Accessed February 2014
1. 3.4 Environmental problems in Egypt
Egypt had a good share of these problems being part of the world.
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These problems are a share from other countries, plus the contribution Egypt shares as a
polluting country.
Fig. (1.11) Breakdown of GHG emissions in Egypt within the energy sector.
Source : Emissions Summary for Egypt - Online document
Accessed February 2014
A) Climate change and rising sea level
Climate change poses significant risks through sea level rise on the coastal zone, which is
already subsiding at approximately 3-5mm/year around the Nile delta. Analyses of current climatic
trends reveal a warming trend in recent decades with country averaged mean temperature increases
of 1.0°C, 1.4°C and 2.5°C projected by 2030, 2050 and 2100.
Higher temperatures in the semi-arid regions with resulting evaporative losses coupled with
increasing water demands will likely result in decreasing water availability from the Nile. There
is also some possibility of significant decline in Nile stream flow under climate change as a result
of changes in precipitation. Coastal zone and water resource impacts have also serious implications
for agriculture: sea level rise will adversely impact prime agricultural land in the Nile delta, while
the intensive irrigated agriculture upstream would suffer from any reductions in Nile water
availability. Therefore, climate change is a serious development concern for Egypt. Given that
Egypt’s population, land-use and agriculture, as well as its economic activity are all constrained
along a narrow T-shaped strip of land along the Nile and the deltaic coast, it is extremely vulnerable
to any adverse impacts on its coastal zones and water availability from the Nile.(32)
B) GHG emissions
Egypt ranks 31st in total emissions with 221.1 million tons of CO2 emitted yearly making
Egypt responsible for 0.59% of global emissions.
Egypt ranks 94th in terms of per capita emissions with 3 tons of CO2 per person.
C) Water Crisis
Water resources in Egypt are becoming scarce. Surface-water resources originating from the
Nile are now fully exploited, while groundwater sources are being brought into full production.
Egypt is facing increasing water needs, demanded by a rapidly growing population, by increased
urbanization, by higher standards of living and by an agricultural policy which emphasizes
expanded production in order to feed the growing population.
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The per capita water resources is expected to drop from a current value of about 922 m3 per
year to about 337 m3 per year in 2025, this could mean that up to 60 per cent of the agricultural
land will not be irrigated. (34)
1.4 Concepts related to environmental treatments to the building roof Building Envelope
The building envelope is defined in this context as those elements of the building that form
the boundary between the indoor environment of a building and the external environment in which
it is located for example, the floor, walls, roof, windows, etc.
1.4.1 Building envelope and energy performance
The building envelope is in a sense a filter between the internal and external environments. It
serves to protect the indoor spaces from undesirable impacts such as excessive cold, heat, radiation,
and wind, while allowing desirable impacts to pass through such as cool breezes on a hot day,
warmth from the sun on a cold day, daylight, etc.
The building envelope directly influences the energy performance of a building in the
following ways:
Resisting undesirable heat transfer.
Allowing desirable heat transfer.
Providing heat storage (delayed heat transfer).
Allowing daylight penetration.
Preventing undesirable light penetration (glare).
Allowing desirable ventilation.
Preventing undesirable ventilation.
There are two different approaches to envelope design in relation to building energy
performance.
One approach seeks to isolate the interior of the building as much as possible from the external
environment. Insulation is used extensively in all the envelope elements to reduce heat transfer as
far as possible. Such buildings rely entirely on air conditioning systems to provide heating or
cooling to maintain comfort conditions. This is often referred to as an ‘active’ approach to building
energy design.
Another approach to building energy design is referred to as “passive” design. This seeks to
encourage beneficial interactions between the building and the outside environment, while
reducing as far as possible the undesirable interactions. In climates such as that of Botswana, where
the average daily temperature is generally close to indoor comfort conditions, this approach tends
to make use of thermal mass to reduce the extremes of day and night temperature. Careful use of
both insulating and conductive materials as appropriate for different elements of the building
prevent or encourage heat transfer when it is useful, and controlled ventilation allows air
movement through the building to provide fresh air and help to keep the temperature in the comfort
zone.
When successful, this approach can allow the external environment to address some or all of
the internal loads, reducing the energy required by mechanical systems.
Cooling of the building takes place when heavy elements such as walls absorb heat from the
building during the day and release it to outside at night. Ventilation of the building when the
outdoor air is cool can also help to cool the building. In winter heat from the sun can be stored in
the walls and released into the building at night when heating is needed. When it fails, this
approach can lead to high energy consumption if mechanical systems are required to pump heat
into or out of thermal mass elements that conflict with the desired internal temperature. Generally
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buildings such as residential houses with relatively low levels of internal heat gain from occupants,
lights and equipment, can be designed using passive principles to achieve comfort conditions for
most of the year with little or no mechanical heating or cooling.
Buildings with high levels of internal heat gain such as office blocks will generally require
mechanical systems to maintain comfort conditions, but there are significant opportunities to
reduce the energy consumption with careful design.
In the design of energy efficient buildings dominated by internal heat gains particular attention
should be given to matching the mechanical systems to the internal loads, and to ensure that control
systems are designed and operated to avoid conflict between the mechanical systems and the
thermal mass elements of the envelope and internal structure. (29)
1.4.2 Passive cooling approaches
Passive cooling is considered an alternative to mechanical cooling that requires complicated
refrigeration systems. The building envelope is a critical component of any facility since it both
protects the building occupants and plays a major role in regulating the indoor environment.
Consisting of the building's roof, walls, windows, doors, construction details and ground surfaces
the envelope controls the flow of energy between the interior and exterior of the building.
The building envelope can be considered the selective pathway for a building to work with
the climate- responding to heating, cooling, ventilating, and natural lighting needs. (U.S.
Department of Energy, 2004)
There are four key approaches for achieving thermal comfort in cooling applications:
envelope design, natural cooling sources, hybrid cooling systems, and adapting lifestyle.
Envelope design as a means of passive cooling is the integrated design of building form and
materials as a total system to achieve optimum comfort and energy savings. An optimal design of
the building envelope may provide significant reductions in cooling loads-which in turn can allow
downsizing of mechanical equipment Natural cooling sources including air movements,
evaporative cooling, and earth coupled thermal mass can also provide thermal comfort. Hybrid
cooling systems are whole building cooling solutions employing a variety of cooling options
(including air-conditioning) in the most efficient and effective way. They take maximum
advantage of passive cooling when available and make efficient use of mechanical cooling systems
during extreme periods. Adapting lifestyle involves adopting living, sleeping, cooking and activity
patterns to adapt to and work with the climate rather than using mechanical cooling to emulate an
alternative climate. The general design principles of passive cooling are the reduction or
elimination of external heat gains during the day with sound envelope design, and allow lower
nighttime temperatures and air movement to cool the building and its occupants.
They take maximum advantage of passive cooling when available and make efficient use of
mechanical cooling systems during extreme periods.
Adapting lifestyle involves adopting living, sleeping, cooking and activity patterns to adapt
to and work with the climate rather than using mechanical cooling to emulate an alternative
climate.
The general design principles of passive cooling are the reduction or elimination of external
heat gains during the day with sound envelope design, and allow lower nighttime temperatures and
air movement to cool the building and its occupants. (30)
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1.4.2.1 Development of a passive cooling strategy
Passive cooling techniques can reduce the peak cooling load in buildings, thus reducing the
size of the air conditioning equipment and the period for which it is generally required. The
important cooling concepts like shading are discussed in details:
A) Solar shading
Among all other solar passive cooling techniques solar shading is relevant to thermal cooling
of buildings especially in a developing country owing to their cost effectiveness and easy to
implement.
Rural India and developing countries in Middle-east region has witnessed a steep rise masonry
houses with RCC roofs. However the availability of electric power in the villages especially during
summer is limited. These RCC roofs tend to make the indoor temperature very high around 41°C:
This is due to high roof top temperature of around 65°C in arid regions. Solar shading with
locally available materials like terracotta tiles, hay, inverted earthen pots, date palm branches etc.
can reduce this temperature significantly.
Scientists in India evaluated the performance of solar passive cooling techniques such as solar
shading, insulation of building components and air exchange rate. In their study they found that a
decrease in the indoor temperature by about 2.5°C to 4.5°C is noticed for solar shading. Results
modified with insulation and controlled air exchange rate showed a further decrease of 4.4°C to
6.8°C in room temperature. The analysis suggested that solar shading is quite useful to
development of passive cooling system to maintain indoor room air temperature lower than the
conventional building without shade. (106) Shading by overhangs, louvers and awnings.
Well-designed sun control and shading devices, either as parts of a building or separately
placed from a building facade, can dramatically reduce building peak heat gain and cooling
requirements and improve the natural lighting quality of building interiors. The design of effective
shading devices will depend on the solar
orientation of a particular building
facade. For example, simple fixed
overhangs are very effective at shading
south-facing windows in the summer
when sun angles are high.
Fig (1.4) Different types of shading
- Shading of roof
Shading the roof is a very important method of reducing heat gain. Roofs can be shaded by
providing roof cover of concrete or plants or canvas or earthen pots etc. Shading provided by
external means should not interfere with night-time cooling.
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A cover over the roof, made of concrete
or galvanized iron sheets, provides protection from direct radiation. Disadvantage of this system
is that it does not permit escaping
of heat to the sky at night-time .
Fig (1.5) Roof Shading by solid cover
A cover of deciduous plants
and creepers is a better
alternative. Evaporation from the
leaf surfaces brings down the
temperature of the roof to a level
than that of the daytime air temperature. At night, it
is even lower than the sky temperature.
Fig (1.6) Roof Shading by plant cover
Covering of the entire surface area with the closely packed inverted earthen pots, as was being
done in traditional buildings, increases the surface area for radiative emission. Insulating cover
over the roof impedes heat flow into the building. However, it renders the roof unusable and
maintenance difficult. Broken china mosaic or ceramic tiles can also be used as top most layer in
roof for reflection of incident radiation.
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Fig (1.6) Roof Shading by earthen pots
Another inexpensive and effective device is a removable canvas cover mounted close to the
roof. During daytime it prevents entry of heat and its removal at night, radiative cooling. Fig. 1.7
shows the working principle of removable roof shades. Painting of the canvas white minimizes the
radiative and conductive heat gain. Ref. (107)
B) Radiative cooling
The roof of a building can be used both as a nocturnal radiator and also as a cold store. It is
often a cost-effective solution. During the night the roof is exposed to the night sky, losing heat by
long-wave radiation and also by convection. During the day, the roof is externally insulated in
order to minimize the heat gains from solar radiation and the ambient air. The roof then absorbs
the heat from the room below.
- Diode roof
The diode roof eliminates the water loss by evaporation and reduces heat gains without the
need for movable insulation. It is a pipe system, consisting of a corrugated sheet-metal roof on
which are placed polyethylene bags coated with white titanium oxide each containing a layer of
pebbles wetted with water. The roof loses heat by long-wave heat radiation to the sky and by the
evaporation of water which condenses on the inside surface of the bags and drops back onto the
pebbles. By this means, it is possible to cool the roof to 4°C below the minimum air temperature .
(67)
- Roof pond
In this system a shallow water pond is provided over highly conductive flat roof with fixed
side thermal insulation. The top thermal insulation is movable. The pond is covered in day hours
to prevent heating of pond from solar radiation. The use of roof pond can lower room temperature
by about 20°C. While keeping the pond open during night the water is cooled by nocturnal cooling.
The covered pond during the day provides cooling due to the effect of nocturnally cooled water
pond and on other side the thermal insulation cuts off the solar radiation from the roof. The system
can be used for heating during the winter by operating the system just reverse. The movable
insulation is taken away during day so the water of pond gets heated up by solar radiation and
heating the building. The pond is covered in night to reduce the thermal losses from the roof and
the hot water in the pond transfers heat into building .(67)
1.4.2.2 Walls and Roofs
The building envelope is a critical component of any facility since it both protects the building
occupants and plays a major role in regulating the indoor environment. Consisting of the building's
roof, walls, windows, doors, construction details and ground surfaces the envelope controls the
flow of energy between the interior and exterior of the building.
The building envelope can be considered the selective pathway for a building to work with
the climate- responding to heating, cooling, ventilating, and natural lighting needs.
For buildings dominated by cooling loads, it makes sense to provide exterior finishes with
light colors and high reflectivity or wall-shading devices that reduce solar gain considering the
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impact of decisions upon neighboring buildings. A highly reflective envelope may result in a
smaller cooling load, but glare from the surface can significantly increase loads on and complaints
from adjacent building occupants. Reflective roofing products help reduce cooling loads because
the roof is exposed to the sun for the entire operating day.
Wall shading can reduce solar heat gain significantly using roof overhangs, window shades,
awnings, a canopy of mature trees, or other vegetative plantings, such as trellises with deciduous
vines.
In new construction, providing architectural features that shade walls and glazing should be
considered. In existing buildings, vegetative shading options are generally more feasible. Building
walls, roofs, and floors of adequate thermal resistance is essential to provide human comfort and
energy efficiency. Passive evaporative cooling design can also be used on roofs through roof spray
or roof ponds, and Insulating materials in walls and roofs are very beneficial for energy saving and
efficiency. Incorporating solar controls on the building exterior can also have a significant impact
to reduce heat gain which will studies in chapter two.
1.4.3 Sustainable roofs as a key step in climate change mitigation
A Sustainable roof is either a vegetated landscape built up from a series of layers that are
installed on the roof surface as ‘loose laid’ sheets or modular blocks or a passive "cool roof"
approach, where the roof is designed to absorb less of the sun's heat and therefore stay at a cooler
temperature . This approach will always benefit in hot climates, but will also benefit in any climate
where summer heat gain on the roof outweighs winter heat loss.
Sustainable roofs are constructed for a number of reasons - as a space for people to visit, as
an architectural feature, to add value to the property or to achieve particular environmental benefits
(e.g. storm water management, biodiversity, thermal insulation).
Vegetation on Sustainable roofs as one approach is planted in a growing substrate (a specially
designed soil-like medium) that may range from 50mm to over a meter in depth, depending on the
weight capacity of the building’s roof and the aims of the design. Sustainable roofs will do best if
they have some irrigation, although it is possible to create a Sustainable roof that survives lives
without any irrigation (but be aware that there will be periods of die back).
The cool roof approach to creating a cool roof is to use light colored roofing, but beware that
light colored composition (asphalt) roofing isn't generally as reflective as light colored metal
roofing.4 An even more effective approach in hot climates would be to use a roofing that is coated
with a material that has high emissivity and low absorption (high reflectance) essentially building
a solar collector in reverse. High emissivity coatings will increase winter heat loss, so usually
don't make sense in cold climates.
Not only are Sustainable roofs a key climate change mitigation strategy, they also help with
energy consumption. Sustainable roofs help maintain a buildings temperature by regulating
temperature variability –insulating it from cold weather in the winter and absorbing the heat in
summer. This reduces central heating and air-conditioning costs.
Often known as roof gardens, they break up the monotonous grey jungle of cities, creating green
spaces, and encouraging biodiversity.
Since the industrial revolution, smog and heat levels – known as the urban heat island effect –
have increased in major cities. Sustainable roofs, with their intense vegetation, help control the rise in
temperature and make the air cleaner.
Sustainable roofs have traditionally been categorized as extensive or intensive. Extensive
Sustainable roofs are lightweight with a layer of growing substrate that is usually less than 200mm
15
deep. Extensive Sustainable roofs generally have lower water requirements and grow smaller sized
plants. Intensive Sustainable roofs are generally heavier, with a deeper layer of growing substrate
that can support a wider variety of plants. Because of this they can have greater needs for irrigation
and maintenance, compared to extensive roofs. Traditionally extensive Sustainable roofs were seen
as light weight, non-publicly accessible, spaces whilst intensive Sustainable roofs were designed
as amenity spaces for people. Over time the Sustainable roof at Council House , Little Collins
Street, Melbourne boundaries between these types of roofs have blurred, and terms like semi-
intensive or semi-extensive have been introduced to describe roofs that are a blend of both
categories.
Other descriptions of Sustainable roofs include Brown roof or Eco-roof, which are generally
lightweight, with shallow, substrate and minimal access and maintenance. They are typically
associated with low growing plants - generally succulents. Biodiversity roof - lightweight roof,
with a focus on using native vegetation. May be designed for a particular species of invertebrate,
bird, mammal, or plant. Roof garden or Podium roof - heavier, deep substrate, designed for access
by people, and requires regular maintenance and are built directly on a structure with considerable
weight loading capacity, such as a car park.(18)
Fig (1.7) Sustainable roof at Council House 2, Little Collins Street, Melbourne
Source : Victoria’s Guide to Sustainable roofs, walls & facades - Online document
Accessed February 2014
1.5 Sustainable Roofing Systems
1.5.1 Green Roofs (Living roofs)
1.5.1.1 Origin
Green roofs involve growing plants on rooftops, thus replacing the vegetated footprint that
was destroyed when the building was constructed (Getter and Rowe 2006). The earliest
documented roof gardens were the Hanging Gardens of Semiramis in what is now Syria,
considered one of the seven wonders of the ancient world. In the 1600s to 1800s, Norwegians
covered roofs with soil for insulation and then planted grasses and other species for stability.
Germany is recognized as the place of origin for modern-day green roofs (Getter and Rowe 2006).
16
These were developed to help with protection for radiation on the roof, and even used as fire
protection.
In the 1970s, growing environmental concern, especially in urban areas, created opportunities
to introduce progressive environmental thought, policy, and technology in Germany . These
innovations and technologies were quickly embraced. The use and understanding of green roofs
have allowed the formation of building laws that now require construction of green roofs in many
urban centers. Green-roof coverage in Germany alone now increases by approximately 13.5
million square meters (m2) per year. Today, similarly elaborate garden projects are designed for
high-profile international hotels, business centers, and private homes.
Greens roofs are classified into two categories, intensive and extensive. Intensive green roofs
involve intense maintenance and include shrubs, trees, and deeper planting medium. Extensive
green roofs have less maintenance and usually consist of shallower soil media, different plants
such as herbs, grasses, mosses, and drought tolerant succulents such as sedum (Getter and Rowe
2006). The creation of green roofs, whether they are intensive or extensive, has beneficial effects
to the environment and on the UHI.
1.5.1.2. Types of green roof
The term green roof is used to describe both ornamental roof gardens and roofs with more
naturalistic plantings or self-established vegetation. Green roofs consist of three types of
construction, design, and cost: intensive, simple intensive, and extensive. The intensive roof is
closest to what is known as a roof garden. It has the appearance of a garden or park that you would
see at ground level. Because of the amount of weight needed for a growing medium, plants, water,
and visitors, these gardens are usually constructed over reinforced concrete decks. Because of the
expense of roof structure upgrades these roofs are usually not an option for green roof retrofits, but
if implemented at the design phase they can have a dramatic affect on the architecture of a building
while adding green roof benefits to the structure.
Fig (2.1) The ACROS Building, Fukuoka, Japan is an intensive green roof
The second type is referred to as a simple intensive green roof. This roof is vegetated with
lawns or ground covering plants, and requires regular maintenance, including irrigation, feeding
and cutting. Demands on building structure are much more moderate than that of the intensive
roof, making it much more affordable and a possible choice for retrofit green roofs.
It is, however, more expensive and complex than extensive green roofs. These roofs are
usually not meant to be accessible but they are often designed to be overlooked. A structure with
a tiered roof system would be a great candidate for a roof of this type.
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Fig (2.2) The School of Art and Design in Singapore is an
example of a simple-intensive green roof
The third type is the extensive green roof. This type
requires minimal maintenance and is usually not
irrigated, although in some cases it can be during the
time when plants are being established. The extensive
roof has a very shallow planting media (low weight,
sometimes soil-less) which helps minimize the cost and
the structural load on the roof. This makes it an ideal
candidate for retrofit green roofs. There are also
disadvantages. The low- weight synthetic planting
media is more susceptible to winds, drought, and high
temperatures associated with an elevated surface. With
this in mind, plant selection must consist of hardy, low-
height drought resistant plants like succulents, herbs, and grasses. This roof would only be
accessible for maintenance. (1)
Fig (2.3) Canary Wharf, London, an extensive green roof.
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1.5.1.3 Benefits of green roof
Green roofs have multiple benefits, one of which is shadowing the surfaces of roofs, which
can reduce heat gain by nearly 100 percent. A green roof forms a buffer zone between the roof and
the sun's radiation and shades the roof, preventing its surface from heating up and increasing
outdoor and indoor air temperatures (FEMP 2004). Green roofs provide many other benefits such
as storm-water management, improving roof membrane longevity, summer cooling of interior
space, support of wildlife diversity, improvement in air quality, aesthetic views, and reduction of
the UHI effect.(42)
Fig (2.5) Eco - roof benefits
Source : Green Roofs Research by David Stater - Online document - Accessed February 2014
Green roofs benefits are generally bio-physical, that is they provide ecosystem services like
flood control and temperature moderation. Amenity and having rehabilitative properties are
additional and important social benefits offered by green roofs. Several authors classify specific
benefits offered by green roofs and the commonly mentioned include the following:
Retain storm water and act as possible detention sites.
Reduce pollutant levels in storm water.
Provide insulation, reducing heating and cooling costs for the building.
Influence urban microclimates.
Reduce the urban heat island effect.
Offer noise reduction (as a result of the insulating effects).
Improve urban air quality and absorb greenhouse gases.
Promote biodiversity and increase habitat.
Provide amenity and rehabilitative services.
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Improve aesthetic quality of buildings and the urban environment.
Provide opportunities for urban agriculture.
Life-cycle assessment
Longer roof membrane
Embodied energy and recycled content
Reduce energy costs 10 percent to 30 percent
1.5.2 Cool roofs
1.5.2.1 Ventilation Cooling Strategies
In climates where it regularly cools of during the night, an especially when there is at least a
gentle breeze, the house temperature can be lowered significantly overnight (assuming of course
that you don't have a lot of thermal mass that was heated during the day). Taller buildings (i.e.
two stories or more) can use the stack effect, e.g. by opening a vent high in the building the hot air
in the house will rise up and out. The cooler it is out, and the taller the vent, the stronger the air
movement. If there is not enough stack effect pressure, an attic fan can supply the same pressure.
By designing the house with good cross ventilation, any nighttime breeze will both provide
cooler night air in a horizontal direction, but help force air out any ceiling vents.
Since the ground temperature in most areas stays relatively cool (typically below 60 degrees),
we can use the ground as a thermal mass also by using a pipe under the house to draw cold air out
of the ground. Transferring too much heat will cause heating of the ground around the pipe,
rendering it as ineffective as any other thermal mass, so the usual cautions apply.
1.5.2.2 Evaporative coolers
When the relative humidity is low, passive cooling can be increased by evaporating water
(such as the body's perspiration system, or the cooling towers used in the Middle Eastern
countries), which takes advantage of the additional heat absorbed by the evaporating water.
Depending on the demand, an evaporative cooler can easily use 30-50 gallons of water a
day. Since they work best in dry climates, and water tends to be scarce in dry climates, they're use
it limited to areas where there is plentiful source of water. Their main advantage is that they use
less energy, there disadvantage is the increase in water usage, and sometimes increasing the room
humidity too much.
The typical evaporative cooler used in the US is the "swamp cooler" which usually sits on the
roof, or in a wall and has a fan that blows air over a wet, sponge like material. Water evaporates
into the air, cooling the air, but also increasing its humidity, typically above 70% relative humidity.
1.5.2.3 Reflective roofs:
Reflective roofs involve either laying down a white membrane or spraying a white paint on
top of a roof, which gives roughly the same effect. With the right insulation, white roofs can be a
good investment. Of course, they won’t stay the same white color over time and will lose some of
their reflectivity. You also have to consider neighbors and the effect that a highly reflective roof
can have on them. Otherwise, they can be a very effective way of reversing the heat island effect
at a reasonable cost, and saving some investment on cooling. Storm water runoff, of course, isn’t
addressed by this approach, but there are other water management approaches a building owner
can use instead
20
1.5.2.4Photovoltaic roofs:
Roofs are becoming a hot destination for solar panel installations.
“The cells themselves are more efficient if you have a white membrane because you are
keeping the roof cooler. And by it being cooler you can get more energy from it,” he explains. “On
the other hand, black membranes are more able to handle the high heat, and PVs will generate
heat.”
1.5.2.5 High-performance roofing:
High-performance roofing can best be described as more intelligent design in roofing — using
elements of each type of roofing described above to function in the best possible manner given the
environment in which a building exists. Paroli offers one interesting example — putting white
paint around the air intakes, so you keep that area of the roof cool instead of incurring the overall
expense of putting in a new cool membrane roof.
Sustainable roofing as a “cradle to gradle” approach — understanding that while much will be
recycled (cradle) in replacing a roof some things will end up in the garbage (grave). The point of
designing a high-performance roof is very similar — to aim for heightened durability and
longevity, while taking into account the environment and energy savings at the same time.
Installing a new, more sustainable roof can add great environmental benefits. And he stresses
that there are many ways to reach that ultimate goal. At the same time, he points out that the
fundamentals are what matter most – keep the building dry and well insulated
1.6 Energy efficiency
Sustainable roofs increase the energy efficiency of the building envelope and reduce a
building’s energy demand on space conditioning and therefore greenhouse gas emissions, through
direct shading of the roof, evapotranspiration and improved insulation values.
Sustainable roofs are particularly effective in reducing heat entry into the building in the
summer. The plants shade and cool the roof. The insulation value is in both the plant and the
growing medium. Water in the plants and the growing medium evaporates and further cools the
roof. The growing medium also acts as a thermal mass that stores solar energy during the day and
releases it at night. Green roofs are less effective in preventing heat leaving the building in the
winter due to the limits of the same thermal mechanisms.
Sustainable roofs have a substantial thermal mass and a moderate insulation value. These
combined properties significantly reduce diurnal temperatures at the boundary between green roof
and building structure (the diurnal temperature being the daily maximum to minimum temperature
range).
The diurnal temperature range for a conventional construction ‘warm-roof’ waterproof layer
can be very large; for example, the surface of a typical bitumen waterproof layer may exceed 50°C
during a sunny summer’s day, whilst falling to just above 0°C at night. A roof with a low level of
insulation below the waterproof layer will allow the space below to heat up quickly in hot, sunny
weather. The increased internal temperatures in the floor below the roof contribute to making the
internal building environment uncomfortable for the building’s occupants.
Overheating can lead to increased use of air-conditioning, which in turn will lead to an
increase in energy consumption. During cold weather, the opposite effect applies, resulting in a
demand for extra heating of the floor directly below the roof and, hence increased energy
21
consumption. The energy used for heating and cooling has a financial as well as an environmental
impact.
The green roof has the same energy providers as a conventional roof, but it has the additional
energy consumers of evapotranspiration and photosynthesis. Unlike a conventional roof, the green
roof is a living system that reacts to the environment in a number of important ways:
Water is stored within the substrate and is used in evapotranspiration by the vegetation layer;
this process utilizes a considerable proportion of the incoming solar radiation in comparison to
a non-green roof the green roof has a large thermal mass, which stores energy and delays the
transfer of heat to or from the building fabric
Plants absorb solar radiation for photosynthesis
Plants have a higher albedo (solar radiation reflectivity) than many standard roof surfaces.
The use of a green roof compared to conventional surfaces can have a significant impact on
the energy balance within a given building and on the immediate environment surrounding the
building. This is particularly relevant if a building has poor insulation and poor ventilation, which
can lead to more use of air conditioning and therefore increased energy use.
Studies have shown that the membrane temperature beneath a green roof can be significantly
lower than where the membrane is exposed. Table 2 shows the average temperatures under the
membrane of a conventional roof and that of membrane under green roofs in a study undertaken
at Nottingham Trent University.
Table 1 : Study of Temperatures Under Membranes of a Conventional and a Green Roof
Source : www.greenroofs.co.uk - Accessed February 2014
Although green roofs do provide potential energy savings by improving building insulation
characteristics, these are often considered difficult to assess due to the varying climatic conditions
throughout the winter months, and will be minimal on already well-insulated buildings.(9)
1.6.1 Storm water management
Many local governments are interested in water sensitive urban design (WSUD) which
embraces a range of measures that are designed to avoid, or minimize, the environmental impacts
of urbanization by reducing the demand for water and the potential pollution of natural waterways
(City of Melbourne 2009). WSUD is based on the idea of treating storm water before it enters a
waterway or before it is re-used for another purpose.
The importance of integrated water cycle management in Victoria has been highlighted by the
recent establishment of the Office of Living Victoria with a $50m commitment from the state
government to support innovative rainwater, storm water and recycled water projects (OLV 2013).
22
Green roofs absorb and retain water and are therefore one strategy for controlling storm water
runoff in urban environments (DDC 2007). Green roofs influence run-off by intercepting and
retaining water from the early part of the storm, and limiting the maximum release rate of run-off
in larger storms (Newton et al. 2007). Water is stored in the substrate, used by the plants, or
retained in plant foliage and on the substrate and evaporates (Oberndorfer et al. 2007, cited in City
of Sydney 2012, Newton et al. 2007 and DDC 2007). Additional water storage capacity is available
in green roof systems which have a drainage layer. In addition to helping slow and reduce storm
water run-off, green roofs can also filter particulates and pollutants (Carter & Jackson 2007 and
Frazer-Williams et al. 2008, cited in Tolderlund 2010). This is important in urban areas where run
off can be polluted from contaminants that are picked up on the way, such as motor oil, animal
droppings and pesticides (Tolderlund 2010).
A number of elements influence the extent to which a green roof or vertical wall can control
the volume of water running off from a site. The vertical depth of the growing medium and
drainage layer, consistency and porosity of the growing medium, structure of the drainage layer,
and slope of the site are all important elements of a rooftop’s ability to slow water. The type of
plant species and type of drainage system are important factors to consider when designing a green
roof system for water treatment .The run off diversion for green roofs is also influenced by the
weather conditions of the region. The length, intensity and frequency of rain events influence a
green roof’s ability to retain water. (7)
1.6.2 Air Quality
Green roofs also filter out fine, airborne particulate matter as the air passes over the plants.
Airborne particulates tend to get trapped in the surface areas of the greenery. Rain washes it into
the growing medium below. Plants also absorb gaseous pollutants through photosynthesis and
sequester them in their leaves (later to become humus). Studies show that treed urban streets have
10-15% fewer dust particles than found than similar streets without trees.
In Frankfurt Germany, for example, a street without trees had an air pollution count of 10-
20,000 dirt particles per liter of air and a treed street in the same neighborhood had an air pollution
count of less than a third of that amount. Based on data from trees, one estimate suggests that a
grass roof with 2,000 m2 of unmown grass (100 m2 of leaf surface per m2 of roof) could cleanse
4,000 kg of dirt from the air per year (2 kg per m2 of roof). This estimate, is probably high since
the lower portion of the grass layer is too dense to be in direct contact with the air. However, even
if the amount were 1/10th of what trees could remove, 10 m2 of grass roof could still take out the
significant amount of 2 kg of dirt every year. (Ref.3) (p. 9)
1.6.3 Noise Attenuation
There are few research studies indicating the benefits of sustainable roofs at muffling and
attenuating urban noise. At the British Columbia Institute of Technology (BCIT), Connelly and
Hodgeson studied the noise attenuation capacity of two 33 m2 extensive green roof reference plots
relative to a control section of conventional flat roof to determine the differences.
While the study had to be performed outside in open air, rather than in an acoustically
controlled environment, the background noise was minimized by careful timing of the testing
during calm periods and at night. The study found that the green roof plots reduced noise
transmission by 5 to 13 decibels (dB) over the low to mid frequency range and by 2 to 8 dB over
the mid to high frequency range.
1.7 Examples & Analysis
1.7.1 International Examples
23
1.7.1.1 Chicago City Hall Building
Chicago’s City Hall shares a 12-story building in downtown Chicago with Cook County’s
administrative offices (FEMP 2004). The overall roof measurements are about 38,800 square feet,
with 22,000 square feet of green roof The first interesting effect, the reduction in heat flow
resulting from the green roof, was observed during the first winter.
The snow lasted for an extended period of time on the green roof, as observed by engineers
in the city’s environment Department, while the snow on the adjacent buildings roof melted in just
two weeks, indicating reduced heat flow on the green roof (FEMP 2004). Actual data have been
collected for this particular rooftop to show temperature reduction.
City Hall along with 12 other public buildings and through a unique combination of mayoral
commitment, policy development and implementation, and incentive, have incorporated more than
300 green roofs that are establishing roots in this densely developed Midwestern city, adding more
than 3 million square feet of vegetation (Berkshire 2007). Through the development of these
projects the city continues to encourage green roof incorporation through a number of activities:
The Building Green/Green Roof Policy
The Green Permit Program
Green Roof Grant Program
Fostering Green Roof Products and Services
The Green Roof web site
The Green Roof Improvement Fund (GRIP)
Streamlining City Effects
The result of these projects and initiatives is to create a well-established, healthy, and vital
green roof market and ultimately make green roofs a more standard building feature, but also to
ensure a healthy future for the city as a whole. As it stands, Chicago currently has the most green
roof space of any city in North America.
Besides Chicago other cities have studied the effects of the UHI and green initiatives but only
on a smaller scale or by computer aided analysis. These studies have helped in understanding the
benefits of green roofs and have helped in defining the purpose and scope for this project, by
creating interest in finding out how the benefits of green roofs have an effect on an entire city and
not just in one or two particular areas.
Fig (3.1) Chicago city hall green roof
Fig (3.2) Chicago city hall green roof
24
1.7.1.2 ACROS Fukuoka Prefectural International Hall
Argentine-born, U.S. architect Emilio Ambasz transposed a nearly 100,000-square-meter
park in the city center onto 15 stepped terraces of the ACROS, "Asian Crossroads Over the Sea,"
Fukuoka Prefectural International Hall. The design for ACROS Fukuoka proposes a powerful new
solution for a common urban problem: reconciling a developer's desire for profitable use of a site
with the public's need for open green space. The plan for Fukuoka fulfills both needs in one
structure by creating an innovative agro-urban model.
The Takenaka Corporation website states, "Emphasizing continuity of the planting zone with
Tenjin Central Park, and to represent the landscape from the park as an image of a mountain instead
of the low vegetation which has a tendency to occur in the vicinity of buildings in city areas, a
staircase-shaped rooftop garden was adopted. Regarding the building as a mountain, and with the
beauties of nature as a theme, a space configuration and vegetation configuration was adopted
which represents the changes of the four seasons.
"Its north face presents an elegant urban facade with a formal entrance appropriate to a
building on the most prestigious street in Fukuoka's financial district. The south side of the Hall
extends an existing park through its series of terraced gardens that climb the full height of the
building, culminating at a magnificent belvedere that offers a breath-taking view of the city's
harbor. Underneath the park's fifteen one-story terraces lies over one million square feet of
multipurpose space containing an exhibition hall, a museum, a 2000-seat proscenium theater,
conference facilities, governmental and private offices, as well as several underground levels of
parking and retail space. The structure is steel-framed reinforced concrete, the building has 14
floors above ground and 4 floors below ground, and the total floor space area is 97,252 m2.
Along the edge of the park, the building steps up, floor-by-floor, in a stratification of low,
landscaped terraces. Each terrace floor contains an array of gardens for meditation, relaxation, and
escape from the congestion of the city, while the top terrace becomes a grand belvedere, providing
an incomparable view of the bay of Fukuoka and the surrounding mountains. Growing media
depths range between 12 and 24".
A stepped series of reflecting pools upon the terraces are connected by upwardly spraying jets
of water, to create a ladder-like climbing waterfall to mask the ambient noise of the city beyond.
These pools lie directly above the central glass atrium within the building, bringing diffused light
to the interior through clerestory glazing separating the pools. Each year during the famous week-
long Don Taku festival, the encircling balconies inside the atrium allow for a panoramic view as
the procession passes through the building, while outside the stepped garden terraces become an
inviting outdoor amphitheater for the entire city.
A large "stone" like wedge at the foot of the terraced park pierces a V-shaped entrance into
the building, revealing rough-hewn stone suggestive of geologic strata underlying the surface
vegetation and likening the building to a massive block cut from the earth. This wedge shaped
element also doubles as ventilation exhaust for the underground floors below and as a raised stage
for performing artists.
The opposite side of the building faces onto the most important financial street of Fukuoka.
Composed of striped glass, with every floor so angled as to reflect the passersby below, it softly
de-materializes the mass of the building. The facade rakes outwardly from the vertical with each
successively higher floor, creating the effect of an awning over the sidewalk. These overhanging
eaves use the building design itself rather than an applied device to provide cover to pedestrians.
25
The final stepped layers at the top create the effect of a large 45° cornice overhang at the
street's edge, defining the public entrance while enhancing the building's urban presence.
Fig (3.3) The ACROS Building, Fukuoka, Japan
is an intensive green roof example
Fig (3.4) The ACROS Building, Fukuoka, Japan
is an intensive green roof example
26
1.7.2 Regional Examples
Green Mat campaign in UAE
Dubai Municipality has teamed up with suppliers to launch a public awareness campaign to
encourage ‘green’ roofs in the Emirate.
1.8 Checklist for considerations before starting a Sustainable roof
27
Refrences
Abeer Mostafa ,Evaluation of Building envelope as a thermal mediator in office buildings
in Egypt. Ain Shams University -2008
Gupta V. A Study of Natural Cooling Systems of Jaisalmer, unpublished Ph.D.
thesis, Indian Institute of Technology, New Delhi, 1984.
http://seekingalpha.com/article/310502-getting-ready-for-peak-oill accessed
February 2014
Moughtin, c., and Peter Shirley. Urban Design: Green Dimensions. Architectural
Press, 2nd edition. (2005). P.9.
Kumar R., Garg S. N. and Kaushik S. C. Performance evaluation of multi-passive
solar applications of a non-air-conditioned building. International Journal of
Environmental Technology and Management, Vol. 5, No.1, pp. 60-75, 2005
Thompson, Mark, Steve Watson, Richard Hyde, and, Wendy Cheshire. The
Environmental Brief: Pathways for Green Design. Uk: Spon Press, 2007. P.84.
2003
