An-Najah National University 

Faculty of Graduate Studies 
 

 

 

 

 

 

 
Towards Green Palestinian Cities the 

Feasibility of Using Roof Gardens in 

Nablus as a Case Study 
 

 

 

By 

Dua "Mohamad Rayeq" Ahmad Mallah 

 

 

Supervisor 

Dr. Mouhammad Ata Yousef 

 

 

Co- Supervisor 

Dr. Haithem Ratrout 

 
This Thesis is Submitted in Partial Fulfillment of the Requirements for 

the Degree of Master of Engineering Architectural, Faculty of 

Graduate Studies, An-Najah National University, Nablus, Palestine. 

2017 



II 

 

 

 
 
 

Towards Green Palestinian Cities The Feasibility of 

Using Roof Gardens in Nablus as a case study 

 
By 

Dua "Mohamad Rayeq" Ahmad Mallah 

 
This Thesis was defended successfully on 19/02/2017 and approved by: 

Defense Committee Members         Signature 

 Dr. Mouhammad Ata Yousef /Supervisor        ……………… 

 Dr. Haithem Ratrout /Co-supervisor         ……………… 

 Dr. Jamal Amro /External Examiner         ……………… 

 Dr. Khaled Qamhieh /Internal Examiner         ……………… 



III 

 

Dedication 
To my parents, my brothers and sister. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



IV 

 

Acknowledgment 
I wish to express my gratitude to my supervisors Dr. Mouhammad Ata 

Yousef and Dr. Haithem Ratrout. Appreciation for Dr. Muhannad Haj 

Hussein for his help. Dr. Erik Henry, Dr. Hafida Boulekbache ,and Dr. 

Patrizia Laudati from Université de Valenciennes for their hospitality and 

support. Mr. Rick I am much obliged. 

My family both at home and in the department of architecture thank you 

all, teachers ,and colleagues. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



V 

 

 قراراإل

Towards Green Palestinian Cities the Feasibility of 

Using Roof Gardens in Nablus as a Case Study 

Declaration 

The work provided in this thesis, unless otherwise referenced, is the 

researcher’s own work, and has not been submitted elsewhere for any other 

degree or qualification. 

 
 :Student's Name :                                                                           الطالب اسم

 :Signature "        "محمد شعيب                                                              :التوقيع

 :Date                                                                                                 التاريخ

 

 

 

 

 

 



VI 

 

Table of Contents 
 

Dedication ................................................................................................... III 

Acknowledgment ........................................................................................ IV 

Declaration ................................................................................................... V 

Table of Contents ........................................................................................ VI 

List of Figures ............................................................................................. IX 

List of Tables ............................................................................................ XIV 

Abstract .................................................................................................... XVI 

Chapter One ................................................................................................... 1 

1.1. Introduction....................... .................................................................. 2 

1.2. Problem Statement:.................. ........................................................... 3 

1.3. Aims and Objectives................ ........................................................... 4 

1.4. The importance of the study:................... ........................................... 4 

1.5. Literature review.............. ................................................................... 5 

1.6. Methodology................ ....................................................................... 8 

1.7. Research Outline:.......... ...................................................................... 9 

Chapter Two ................................................................................................ 10 

Green Roofs Conceptual and Theoretical Background .............................. 10 

2.1. Introduction: ...................................................................................... 11 

2.2. Green roof definition ......................................................................... 12 

2.3. Historical Development of Green Roofs: ......................................... 13 

2.3.1. Ancient Green Roofs .................................................................. 13 

2.3.2. Islamic roof garden ..................................................................... 15 

2.3.3. Renaissance green roofs.............................................................. 16 

2.3.4. Sod (turf) roofs ............................................................................ 16 

2.3.5. Modern green roofs. .................................................................... 17 

2.4. Green Roofs building types, Technologies, and components. ......... 20 

2.4.1. Green roof types: Structural Load .............................................. 21 

2.4.2. Other green roof constructing technology, Modular Green Roof 

Systems (Green grid) ............................................................................ 27 

2.4.3. Green roof components. .............................................................. 27 

2.5. Green roof benefits............................................................................ 35 

2.5. 1. Storm water management. (Reduce water runoff)..................... 36 

2.5. 2. Mitigate city heat island effect .................................................. 41 

2.5. 3. Reduce energy budget for building ............................................ 45 

2.5. 4. Aesthetic value (for both the building and the city) .................. 47 

2.5. 5. Social benefits: Green amenity space and improving citizens' 

health. .................................................................................................... 51 

2.5. 6. Air Quality ................................................................................. 54 

2.5.7. Improve property value ............................................................... 55 

2.5.8. Extend roof structure life ............................................................ 56 



VII 

 

2.6. Worldwide cities experience ............................................................. 56 

2.7. Summary ........................................................................................... 61 

Chapter Three .............................................................................................. 62 

City of Nablus ............................................................................................. 62 

3.1. City of Nablus Physical Profile......................................................... 63 

3.1.1. City location ................................................................................ 63 

3.1.2. City expansion and urban development: .................................... 64 

3.1.3. Topography and morphology ..................................................... 66 

3.1.4. Land use ...................................................................................... 67 

3.1.5. Green areas in the city ................................................................ 68 

3.1.6. Weather data ............................................................................... 70 

3.1.7. Problems in the City of Nablus that could be addressed by using 

green roofs. ........................................................................................... 72 

3.1.8. Obstacles restraining the application of green roofs in the City of 

Nablus. .................................................................................................. 74 

3.2. Building technology .......................................................................... 74 

3.2.1. Structural design ......................................................................... 76 

3.2.2. Extra weight ................................................................................ 77 

3.2.3. Current use of the roof. ............................................................... 78 

3.2.4. Cost of green roof ....................................................................... 80 

peat moss ..................................................................................................... 81 

3.3.Summary ............................................................................................ 82 

Chapter Four ................................................................................................ 83 

People of The City of Nablus and The Use of Green Roofs, Questionnaire.83 

4.1. Introduction. ...................................................................................... 84 

4.2. General information .......................................................................... 84 

4.3. Plant and Garden Preferences ........................................................... 88 

4.4. Green Roof Knowledge .................................................................... 90 

4.5. Green roof preferences ...................................................................... 92 

4.6. Summary ........................................................................................... 97 

Chapter Five ................................................................................................ 98 

Green Roof Simulation and Environmental Comfort ................................. 98 

5.1. Autodesk Ecotect .............................................................................. 99 

5.2. Climate .............................................................................................. 99 

5.2.1. Solar Radiation ............................................................................. 100 

5.2.2. A psychrometric Chart .............................................................. 101 

5.2.3. Wind Analyzing ........................................................................ 102 

5.2.4. Conclusion of Climate Analyzing ............................................ 102 

5.3. Building Simulation ........................................................................ 103 

5.3.1. Results and analysis: ................................................................. 105 

5.3.2. Direct solar radiation ................................................................ 106 

5.3.3. Fabric gain ................................................................................ 112 



VIII 

 

5.3.4. Indirect solar heat gain .............................................................. 121 

5.3.5. Passive gains breakdown .......................................................... 130 

5.3.6. Energy consumption ................................................................. 133 

5.3.6. Thermal computation ................................................................ 135 

5.4.Summary .......................................................................................... 146 

Chapter six ................................................................................................. 147 

Conclusion and Recommendations ........................................................... 147 

6.1. Conclusion ...................................................................................... 148 

6.2 Recommendations ............................................................................ 150 

References ................................................................................................. 152 

Appendix ................................................................................................... 171 

Appendix 1 ................................................................................................ 172 

Appendix 2 ................................................................................................ 178 

Appendix 3 ................................................................................................ 179 

Appendix 4 ................................................................................................ 180 

Appendix 5 ................................................................................................ 181 

Appendix 6 ................................................................................................ 182 

Appendix 7 ................................................................................................ 183 

 ب ........................................................................................................... الملخص

 

 

 

 

 

 

 

 

 

 

 

 

 

 



IX 

 

List of Figures 
Page Figure NO. 

7 

 Number of publications per country (between 

2001 and 2012) overlaid on terrestrial ecoregions 

map.  

Figure (1) 

14 Sketch of the ziggurat of Ur.  Figure (2)      

14 Sketch for the Hanging Gardens of Babylon. Figure (3)      

15 
Reconstruction of Villa of Mysteries, near Pompeii, 

Italy 
Figure (4)      

15 Image of Villa of Mysteries roof garden. Figure (5)     

16 
Garden loggia atop the Palazzo in Poccolomini, 

Pienza overlooking the Val D’Oria. 
Figure (6)    

17 Norwegian sod roof Figure (7)     

17 The Casino Theatre, 1909.   Figure (8)    

18 Images of Villa Savoy  Figure (9)    

19 

Image of Stuttgart, Germany, since 1989, municipal 

regulations require green cover for all new flat-roof 

buildings. 

Figure(10)    

21 
Section in green roof types from Extensive (left) 

to Intensive (right)  
Figure (11)   

23 Mat based system Figure (12)  

23 Substrate based system Figure (13)    

24 Intensive green roof, Namba Parks, Japan. Figure (14)    

25 Semi-Extensive green roof   Figure (15)    

25 Mixed green roof. Figure (16)  

25 roof top garden Figure (17) 

25 Terrace garden in New York Figure (18) 

27 Green Grid   Figure (19) 

28 Green roof layers (1). Figure (20) 

28 Green roof layers (2). Figure (21) 

33 Comparing types of drainage systems. Figure (22) 

34 
 (A) Granular drainage (B) Drainage plat (C) 

Drainage mat Comparing  
Figure (23) 

39 
Rain event on October 5-6, 2011, green roof runoff 

(in green) and regular roof runoff in blue. 
Figure (24) 

40 
Rain event on 61-17 October, 2011, green roof runoff 

(in green) and regular roof runoff in blue. 
Figure (25) 

40 

Runoff of two rain events (a) light rain (b) heavy rain. 

Showing the difference between green roof runoff (in 

green) and regular roof runoff in blue.  

Figure (26) 



X 

 

42 Sketch of an Urban Heat Island profile. Figure (27) 

44 

Temperature profile of the roofing systems on (July 

16, 2001) indicating the green roof reduction on 

temperature fluctuation within the roofing system. 

Figure (28) 

45 Infra-red image of a roof in Singapore. Figure (29) 

48 Scenes shown to participants  Figure (30) 

49 
Houses in different vegetation conditions shown to 

participants  
Figure (31) 

50 
Images of Beirut (a) with green roofs and (b) the 

current image of the city.  
Figure (32) 

56 Sketch of the difference in roof temperature Figure (33) 

56 Reduction heat fluctuation Figure (34) 

63 

(1) Governorates of West bank and Gaza showing 

Nablus Governorate in red 
(2) Population in Nablus 

Governorate at Mid Year by Locality 2011 , City of 

Nablus is shown in cyan 

 Figure(35) 

64 
Satellite image of Nablus showing in red the city 

boarders 
Figure (36) 

65 Historical expansion of the city  Figure (37) 

65 Nablus political areas  Figure (38) 

66 
The geopolitical divisions of Nablus city 

according to Oslo agreement 1995 
Figure (39) 

66 Photo of the city between the two mountains. Figure (40) 

67 Population projection (1997-2025) Figure (41) 

68 Land use percentage  Figure (42) 

69 

Map of the city of Nablus showing the contour 

lines of the mountains with the building density 

and distribution. 

Figure (43) 

72 Difference in world mean temperature 1986-2005 Figure (44) 

72 
Minimum temperature from 1997 to 2010 in 

Nablus 
Figure (45) 

73 
Maximum temperature from 1997 to 2010 in 

Nablus  
Figure (46) 

73 
Images of the city streets flooding with water in 

winter. 
Figure (47) 

75 
Percentage distribution of households in Nablus 

Governorate by type of housing unit 
Figure (48) 

76 
Images of the city building taken from different 

locations. 
Figure (49) 

77 
The difference in support between one-way slab 

and two-way slab 
Figure (50) 



XI 

 

77 Section of a conventional ribbed roof structure Figure (51) 

77 Image of a conventional ribbed roof structure Figure (52) 

78 

Extra loads added by the different types of green 

roofs in blue, yellow is the standard extra weight 

the roofs in the city designed to sustain and green 

representing the intersection.   

Figure (53) 

79 
Images of the city roofs showing the current use 

for roofs  
Figure (54) 

79 

Images of the city roofs showing the current use 

for roof to the left, and the same building with 

green roof to the right 

Figure (55) 

80 
Site plan of building used in the simulation multi 

storey building 
Figure (56) 

85 Male and female percentage. Figure (57) 

85 Age groups percentage. Figure (58) 

86 City districts percentage. Figure (59) 

86 Academic levels percentage. Figure (60) 

86 Property ownership  percentage Figure (61) 

87 Type of residence Figure (62) 

87 Floor level for residence of multi storey building Figure (63) 

87 
comparing accessibility to a private ground level 

garden and accessibility to the building roof 
Figure (64) 

88 Accessibility to a private ground level garden Figure (65) 

88 Accessibility to the building roof Figure (66) 

88 

Comparing accessibility to a private ground level 

garden and accessibility to the building roof for both 

building types.  

Figure (67) 

89 The existence of plants in homes. Figure (68) 

89 
The availability of public green spaces on the 

respondent district 
Figure (69) 

90 The availability of gardens. Figure (70) 

90 Green roof knowledge. Figure (71) 

91 Green roof benefits. Figure (72) 

92 
First example of before and after adding green 

roof images(a) Before(b) After 
Figure (73) 

93 
Second  example of before and after adding green 

roof images(a) Before(b) After 
Figure (74) 

94 
Third example of before and after adding green 

roof images. (a) Before(b) After 
Figure (75) 

95 Adding green roofs to buildings. Figure (76) 

96 Comparing answers to adding green roof to the Figure (77) 



XII 

 

building for both building types.  

96 
Comparing answers to adding green roof to the 

building for owned and rented property. 
Figure (78) 

97 
Comparing answers of the building ownership for the 

two building types. 
Figure (79) 

100 The best orientation of the buildings.  Figure (80) 

101 Solar radiation.   Figure (81) 

102 Psychrometric Chart (A) summer (B) winter Figure (82) 

102 Wind rose (A) summer (B) winter Figure (83) 

103 Climate analyses  Figure (84) 

103 
Images of building used in the simulation (A) 

individual house (villa) (B) multi storey building 
Figure (85) 

104 
Site plan of building used in the simulation multi 

storey building 
Figure (86) 

105 Site plan of building used in the simulation villa  Figure (87) 

106 

Comparison between direct solar radiation for a green 

roof, a regular roof on the villa and multi storey 

building. 

Figure (88) 

112 

Comparison between internal solar gain for a green 

roof, a regular roof on the (a) villa and (b) multi 

storey building. 

Figure (89) 

119 

Comparison between fabric gains for a green roof, 

a regular roof and an insulated green roof in 

January on the villa. 

Figure (90) 

119 

Comparison between fabric gains for a green roof, 

a regular roof and an insulated green roof in 

January on the multi storey building. 

Figure (91) 

120 

Comparison between fabric gains for a green roof, a 

regular roof and an insulated green roof in June on 

the villa. 

Figure (92) 

120 

Comparison between fabric gains for a green roof, a 

regular roof and an insulated green roof in June on 

the multi storey building. 

Figure (93) 

128 

Comparison between indirect solar gains for a green 

roof, a regular roof and an insulated green roof in 

June on the villa. 

Figure (94) 

128 

Comparison between indirect solar gains for a green 

roof, a regular roof and an insulated green roof in 

June on the multi storey building. 

Figure (95) 

129 
Comparison between indirect solar gains for a green 

roof, a regular roof and an insulated green roof in 
Figure (96) 



XIII 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

June on the villa. 

129 

Comparison between indirect solar gains for a green 

roof, a regular roof and an insulated green roof in 

June on the multi storey building. 

Figure (97) 

131 

Comparison between losses of passive gain 

breakdown for a green roof, a regular roof and an 

insulated green roof in June on the villa. 

Figure (98) 

132 

Comparison between losses of passive gain 

breakdown for a green roof, a regular roof and an 

insulated green roof in June on the multi storey 

building. 

Figure (99) 

132 

Comparison between gains of passive gain 

breakdown for a green roof, a regular roof and an 

insulated green roof in June on the villa. 

Figure (100) 

132 

Comparison between gains of passive gain 

breakdown for a green roof, a regular roof and an 

insulated green roof in June on the multi storey 

building. 

Figure (101) 

135 

Comparison between heating loads for a green 

roof, a regular roof and an insulated green roof for 

villa and multi storey building 

Figure (102) 

135 

Comparison between cooling loads for a green roof, a 

regular roof and an insulated green roof for villa and 

multi storey building. 

Figure (103) 



XIV 

 

List of Tables 
Page Table name No. 

26 Green roof types comparison Table (1)              

58 
Policies of cities worldwide regarding the 

application of green roofs 
Table (2) 

69 Green area in the city Table (3)          

70 
The mean monthly temperature in Nablus in the 

year 2104 
Table (4)                   

71 

 

The mean monthly wind speed in Nablus in the 

year 2104 
Table (5)                   

71 
The mean monthly Relative Humidity (%) in 

Nablus in the year 2104 
Table (6)                   

71 
The mean monthly Evaporation (mm) in Nablus 

in the year 2104 
Table (7)                   

71 
The of the mean monthly rainfall in Nablus in 

the year 2104 
Table (8)                   

81 Estimated green roof cost Table (9) 

82 Structural reinforcement Table (10) 

85 Age groups Table (11) 

85 districts of the city Table (12) 

105 roof materials and types Table (13)   

107 Villa: Regular roof. Table (14) 

108 Villa: Green roof results. Table (15) 

109 Multi story building: Regular roof. Table (16) 

110 Multi story building: Green roof. Table (17) 

111 
Results of average direct solar radiation  for the 

regular roof  
Table (18) 

111 
Results of average direct solar radiation  for the 

green roof  
Table (19) 

111 Internal solar gain Wh/m2 Table (20) 

113 Villa Fabric gain for Regular roof Table (21) 

114 Villa Fabric gain for Green roof Table (22) 

115 Villa Fabric gain for Insulated green roof Table (23) 

116 Multi-storey building Fabric gain for Regular roof Table (24) 

117 Multi-storey building Fabric gain for Green roof Table (25) 

118 
Multi-storey building Fabric gain for Insulated 

green roof  
Table (26) 

122 Villa Indirect Solar Gains for Regular roof  Table (27) 

123 Villa Indirect Solar Gains for Green roof Table (28) 

124 Villa Indirect Solar Gains for Insulated green roof Table (29) 



XV 

 

125 
Multi-storey building Indirect Solar Gains for 

Regular roof 
Table (30) 

126 
Multi-storey building Indirect Solar Gains for Green 

roof 
Table (31) 

127 
Multi-storey building Indirect Solar Gains for 

Insulated green roof 
Table (32) 

130 Villa gains breakdown Table (33) 

131 Multi storey building gains breakdown Table (34) 

133 Villa energy consumption Table (35) 

134 Multi-storey building energy consumption Table (36) 

135 Energy consumption reduction Table (37)  

137 
Energy saving in the HVAC through the roof for 

villa  
Table (38) 

138 
Energy consumption by the HVAC for the walls 

(villa) 
Table (39) 

139 
Energy consumption by the HVAC for the windows 

(villa) 
Table (40) 

140 Heat infiltration through the cracks. (villa) Table (41) 

141 
The entire energy savings for the whole building for 

villa. 
Table (42) 

142 
Energy saving in the HVAC through the roof for 

multi storey building   
Table (43) 

143 
Energy consumption by the HVAC for the walls for 

multi storey building   
Table (44) 

144 
Energy consumption by the HVAC for the windows 

for multi storey building   
Table (45) 

14lht5 
Heat loss around windows and doors cracks 

area=110ft for multi storey building   
Table (46) 

146 
The entire energy savings for the whole building for 

multi storey building. 
Table (47) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



XVI 

 

Towards Green Palestinian Cities The Feasibility of Using Roof 

Gardens in Nablus as a case study 

By 

Dua "Mohamad Rayeq" Ahmad Mallah 

Supervisor 

Dr. Mouhammad Ata Yousef 

Co-Supervisor 

Dr. Haithem Ratrout 

Abstract  

Urban greening is considered to be a very important issue in many cities, 

just like the city of Nablus where the topography and the political situation 

restrict the establishment of new green spaces.  

In this study, the feasibility of green roofs in the city of Nablus was tested, 

after displaying the background of green roofs and the benefits could be 

provided by green roofs, and how cities encourage the application of green 

roofs to take advantage of these benefits. Then the physical and 

environmental profile of the city was clarified, to determine if the city's 

buildings could accommodate green roofs, after studying the common 

construction method in the city and the building structure it is clear that the 

city existing buildings can sustain extra load added by the lighter types of 

green roof without structural reinforcement. Also the added cost of the 

green roof was calculated to be 37.5%. 

After exploring the city's buildings ability to sustain green roofs and the 

availability of construction materials, the citizens knowledge regarding 

green roofs and their willingness to apply green roofs to their building was 

measured by qualitative and quantitative approach, questionnaire results 

shows that the participants were willing to add green roofs to their 



XVII 

 

buildings but have concerns over the cost of green roofs, further more the 

participants linked the benefits of green roofs with the benefits provided by 

plants and green areas in general, but not to the reduction of energy used in 

heating and cooling, or reducing urban heat. So in the last part of this 

research calculation of the actual reduction of direct solar radiation on the 

roof was conducted using Ecotect, About 50% reduction on the total all 

year direct solar radiation in the villa and 62% reduction is achieved in the 

multi storey building, also reduction in the energy used for cooling and 

heating was also calculated. The Ecotect results indicate that insulated 

green roof have the lowest energy consumption rate, reducing 

approximately 10% for the villa total year consumption and 18% for multi 

storey building. Where green roof provide about 9% and 17% reduction for 

the villa and multi storey building. Thermal computation resulting from 

different U-value, calculations showed total saving up to 26% of total 

energy consumption by green roof, and 37% by adding insulation to the 

green roof layers.  

These results show that green roofs can be cost effective on the long term 

as the increase of building construction cost is to be returned in the 

reduction of energy loads. 
 



1 

 

 

 

 

 

 

 

 

 

 

Chapter One  
 

Introduction 

 

 

 

 

 

 

 

 

 

 

 



2 

 

1.1. Introduction 

Like other cultures worldwide, plants and gardens are considered important 

in Islamic culture and religion. This is due to their benefits to humans’ 

physical and psychological health. These aspects have sparked the interest 

of many people who have established gardens in their houses, both inside 

and outside. This concept can easily be applied with the help of some 

architectural elements, such as balconies, window ledges and some roofs. 

In the Arab and Islamic traditional cities, gardens were widely used. The 

Courtyard garden is the main example where it became the living core of 

buildings. However, in the contemporary new, crowded high-rise building 

style, there is, unfortunately, little space left for gardens.  

People generally enjoy being surrounded by greenery," the belief that 

contact with nature is good or beneficial for people, is an old and 

widespread notion" (Kellert & Wilson, 1993). Historically, this was highly 

considered by planners and designers. Wilson (1984) stated that there is a 

genetic basis for humans’ positive response to nature, which is called 

Biophilia (Kellert & Wilson, 1993). This is "an innate and genetically 

determined affinity of human beings with the natural world". (oxford 

dictionaries, 2014) 

Regrettably, the lack of gardens in Palestine in general and the city of 

Nablus in particular, may be due to its topography as it slopes steeply and 

severely. This generates problems in developing new city gardens due to 

the difficult nature of the city of Nablus, especially, with the current urban 

sprawl.  



3 

 

This research explores and develops ways of creating more green areas and 

spaces in the city of Nablus by implementing the concept of roof gardens. 

The reason behind suggesting the concept of green roofs is due to the fact 

that it will improve greatly the air quality, outdoor environment and 

eventually the health of the city's residents as a whole. 

1.2. Problem Statement:  

In the Palestinian cities; especially the city of Nablus, there is not enough 

landscape or in some areas no green spaces at all. This is due to the 

increasing population and existing land use, therefore, it is hard to create 

new green spaces; however, there is a possibility to provide new green 

areas without confiscation of land or even demolishing buildings. This can 

be achieved by providing green roofs or roof gardens on the unused roofs 

of city buildings. 

Like other Palestinian cities, the steep slope of the mountains demarcates 

the city of Nablus. This topographical characteristic presents an excellent 

panoramic city view, regrettably, green space and landscape are very 

meager, and so to improve the urban appearance of the city and human 

comfort, there is a need to establish roof gardens. This would be in contrast 

to what can be viewed at present Nablus city roofs; i.e. water tanks and 

solar water-heating panels. By implementing the green roof concept, the 

citizens of the city of Nablus will have garden view and private garden on 

their roof. Indeed, instead of going to the gardens they all would live in 

gardens.  



4 

 

Recently the weather in Palestinian cities have changed, one can notice the 

hotter summer and colder winter temperature, this climate change can be 

reduced by increasing the green surfaces in the city. The use of green roofs 

will also increase the area of the city covered with plants and at the same 

time, the roof will not be directly exposed to the different weather 

conditions, which will reduce the heat gain and loss of the building. 

1.3. Aims and Objectives 

This research presents the concept of green roofs for the city of Nablus. 

This will improve the physical environment of Palestinians and provide 

outdoor human comfort, in addition to escape from the summer heat and to 

make gardens accessible to everyone.  

It may be the best way to increase green areas in the city of Nablus by 

making roof gardens on the city of Nablus roofs. This study clarifies the 

feasibility and benefits of roof gardens in the city. 

Green roofs are considered a multidisciplinary field of study. This study 

will not investigate all aspects regarding green roofs application in the city 

of Nablus. The environmental and economical aspects, along with the 

residents opinion regarding green roofs will be studied. 

1.4. The importance of the study:  

Roof gardens are a growing research field, which is multidisciplinary and 

new research area. According to a bibliometric study on the directions in 

green roof research, "the number of publications in this field increased in 

the last two decades. Papers on green roofs were classified into 32 



5 

 

research areas. The percentages of plant sciences, forestry, marine and 

freshwater biology and biodiversity conservation of the total research 

areas classifications used each year increased significantly with time, 

while architecture decreased significantly with time signifying an increased 

interest in environmental issues and less focus on architectural issues." 

(Lior, et al., 2013) 

Statistics of publications throughout the world indicated that the USA and 

the EU conducting 66% of the research, However, there has been a sharp 

increase in the number of countries that conduct green roof research. (Lior, et 

al., 2013) 

Yet, this area of research has not received much attention in Palestine. This 

research draws attention to the benefits of roof gardens. Starting with this 

research on the city of Nablus it is hoped to encourage Palestinian 

universities, cities, and neighboring countries to develop gardens on the 

roofs of their buildings.  

1.5. Literature review   

In the last decade of the twentieth century, green roofs in European 

countries received increasing amount of attention. Germany considered to 

be one of the leading countries in the number of publications and 

application of green roofs.  

The German FLL (FOERSCHUNGSGELLSCHAFT 

LANDSCHAFTSENTWICKLUNG LANDSCHAFTSBAU, Landscaping and 

Landscape Research Society), issued roof greening guidelines (guidelines for 



6 

 

planning execution and upkeep of green-roof sites) (FLL, 2002). This 

publication was widely accepted not only in Germany but also in other 

countries. These guidelines "set out the basic principles and requirements 

which apply in the general terms to the planning, execution and 

maintenance of such green schemes, taking into account the present 

scientific knowledge and the most advanced technology. " (FLL, 2002). FLL 

intended for the guidelines to be used by professionals and craftsmen 

working in relevant green sectors and trades. FLL and other researchers, 

such as GREEN ROOF SYSTEM (Weiler & Scholz-Barth, 2009), and GREEN ROOF 

CONSTRUCTION AND MAINTENANCE (LUCKETT, 2009), focus only on the 

technical aspects of constructing green roofs such as drainage and materials 

for constructing green roofs. Although such aspects are extremely 

important for green roofs research, other aspects have to be tackled, such as 

the effect of roof gardens on the urban appearance of the city physically 

and environmentally.  

The USA and EU are leading countries in the contribution to the 

publications regarding green roofs. For example, the available publications 

on the topic are 34% for the USA, and the EU about 33% (Lior, et al., 2013). 

The results of this concentration of research are having almost no reliable 

data on green roofs environmental effect in the Mediterranean climate 

including Palestine.  



7 

 

 
Fig.1 Number of publications per country (between 2001 and 2012) overlaid on 

terrestrial ecoregions map.  

Source:   (Lior, et al., 2013) 

As shown in the previous figure, the largest number of publications was in 

temperate countries. It is focusing on information regarding green roof 

environmental benefits including improved storm-water management, 

better regulation of the buildings' temperature, a reduced urban heat-island 

effect, and increased urban wildlife habitat.  

Growing interest in researching green roof effects in tropical, semi-tropical, 

and tropical island climates. However, green roof research is to be 

encouraged particularly with reference to Mediterranean climate and in 

Middle Eastern countries. This research may well be the starting point for 

filling the gap in information on green roof behaviors in Palestine, taking 

the city of Nablus as a case study. (OBERNDORFER, et al., 2007)) ( (Bau-

Show Lin, 2013) 



8 

 

Green roof technology is attractive, but still untested in the high-rise 

buildings of Palestine. Due to the lightweight nature of some green roofs, it 

can potentially be used to green up many existing roofs. These could be 

made without structural alteration to accommodate extra load on the roofs. 

Indeed, there is room and large potential for this technology in Palestinian 

cities.  

1.6.  Methodology 

This research is based on interdisciplinary and multidisciplinary 

approaches. It is divided into three stages; the first stage is theoretical. It 

involves data collection relevant to Green Roofs and Roof Gardens from 

different sources. Examples of technology and construction roof gardens 

worldwide have been studied. This section will demonstrate the benefits of 

roof gardens.  

The second stage includes an analysis of the current structure of the city's 

roofs and Green roof. It elaborates on studying the current use of roofs and 

to what extent that will be affected and need restructuring when the green 

roofs are constructed. It also determines to what extent people will be 

satisfied and comfortable. This part of the research will employ qualitative 

and quantitative approaches for a set of numbers and indicators resulting 

from questionnaires.  

The third stage is a practical one, using an experimental approach to 

explore the effect of green roof on the city of Nablus by comparing two 

main building types using computer simulation to clarify the difference in 



9 

 

thermal behavior between regular roof and green roof. This will generate 

answers to the question of; to what extent green roof will improve human 

comfort and environmental conditions. 

1.7. Research Outline: 

The research is divided into six chapters; Chapter one presents research 

introduction and Methodology. Chapter two involves a theoretical 

background to the study. Chapter three investigates green areas in the city 

of Nablus and the Current roofs of the city of Nablus, their construction 

technology, maintenance and cost. Chapter four contains the 

questionnaire analysis. Chapter five is the computer simulation. The 

conclusions and recommendations are presented in chapter six. 

 

 

 

 

 

 

 

 

 

 



10 

 

 

 

 

 

 

 

 

 

Chapter Two 

 Green Roofs Conceptual and Theoretical 

Background 

 

 
 

 

 

 

 

 

 

 

 



11 

 

This chapter demonstrates the wide use of green roofs through history, up 

to the present use of green roofs in modern societies, shows peoples' 

interest and knowledge regarding green roofs.   

2.1. Introduction:  

Roof gardens existed in human culture and architecture ever since the 

hanging gardens of Babylon, and it is not hard to imagine that these 

gardens were considered paradise on earth for those people living in the 

desert where the day is very hot and the night is cold. The first known 

example is the ziggurats of ancient Mesopotamia, built in the fourth 

millennium (about 600 BC) roof gardens evolved through the centuries and 

in different civilizations and they were an essential element in vernacular 

architecture such as the Scandinavian sod roofs, the sod stripped from 

grassy meadows covers the heavy timber structure. "The combination of 

ground and plants rooted on the roofs prepared it potential to take out 

roofs insulate comparatively healthy, tight to the air and water, 

challenging to the wind and fire." (Almusaed, 2011) 

In modern time, people use green roofs developed from the sod roofs, 

which are lighter, more effective and mass-marketed industry. 

As the green roofing technology developed, the reasons for its use and 

benefits evolved. For example, they were used to escape summer heat, as 

an extension of living rooms, protection from weather changes, planting 

food, a way of flood control and in some cultures to show wealth and status 

in the community, on the other hand modern green roofs are being used to 



12 

 

deal with almost the same problems in addition of recent problems created 

by the urbanism such as the heat island effect, water runoff, bad air quality, 

and a need for increasing green spaces. 

2.2. Green roof definition  

The vast majority of researchers and authorities identified the green roofs, 

as "Green roofs are vegetated layers that sit on top of the conventional 

waterproofed roof surfaces of a building. Whilst green roofs come in many 

different forms and types, usually a distinction is made between extensive, 

intensive and biodiverse or wildlife roofs." (the green roof centre, 2014). Another 

definition was presented by the Green Roof Guide to be "A green or living 

roof is a roof or deck onto which vegetation is intentionally grown or 

habitats for wildlife are established." (green roof guide, 2014) 

Karen Liu, who researches in National Research Council, defines the green 

roofs in her research "the engineering performance of rooftop gardens 

through field evaluation". According to her, "Green roofs or rooftop 

gardens are roofs planted with vegetation". (Liu, 2003) 

In 2009, the Indianapolis city published a manual for Storm-water design 

and Specification. It identified roof gardens to be "A green roof (vegetated 

roof/eco roof/roof garden)". It was also defined as "a system consisting of 

waterproofing material, growing medium, and vegetation. A green roof can 

be used in place of a traditional roof as a way to limit impervious site area 

and manage storm-water runoff ". (City of Indianapolis, 2009) 



13 

 

2.3. Historical Development of Green Roofs: 

Green roofs have evolved throughout the years since ancient Mesopotamia 

to present day green roofs.   

2.3.1. Ancient Green Roofs  

2.3.1.1. The ziggurats of ancient Mesopotamia  

The earliest record shows that these massive pyramids were built between 

4000-600 BC. And were considered to be one of the seven wonders of the 

ancient world. The ziggurats were huge stepped structure of stone, the 

landings of these steps were planted with trees and shrubs that softened the 

climb and offered refuge from the Babylon heat (Magill, Midden, Grouninger, & 

Therrell, 2011). The planted terraces are accessed by stairs, as these ziggurats 

had no interior rooms the plants offers shading and cool place for visitors to 

rest. (Shimmin, Heather Shimmin Photography, 2012) (OBERNDORFER, 

et al., 2007) 

The great ziggurat of Ur is one of the best-preserved ziggurats; its base area 

is about 2000m2, constructed with watertight foundation, asphalt panels, 

bricks, and mortar. Historians believe that the gardens were constructed for 

aesthetic purposes because of the choice of trees, blooming bushes, 

climbing plants, and spice gardens. (Pearen, Dinsdale, & Wilson, 2006) 



14 

 

 

 
Fig. 2     Sketch of the ziggurat of Ur.  

Source  : (Shimmin, Heather Shimmin 

Photography, 2012) 

 
 

Fig. 3    Sketch for the Hanging 

Gardens of Babylon. 

Source  : (Christopher Klein, 2013) 

 

It may be that the best-known roof gardens in the world were the hanging 

garden of Babylon, built by the king Nebuchadnezzar. "The hanging 

garden" phrase came from the vegetation which hung over the walls to the 

lower level terrace. The engineering of the building was spectacular; the 

weight was supported by arcades with about 5 meters thickness and a 

square base of 120m x120m. (Shimmin, Heather Shimmin Photography, 2012) (Pearen, 

Dinsdale, & Wilson, 2006) (Magill, Midden, Grouninger, & Therrell, 2011)  

2.3.1.2 Roman roof garden 

Romans planted trees on the top of their buildings especially in many 

municipal buildings. Historical evidence indicates that roof gardens 

existed on the mausoleums of Augustus and Hadrian (Magill, Midden, 

Grouninger, & Therrell, 2011). The discovery of Pompeii in 1749 under the ashes 

of the volcano eruption which preserved almost the entire roman lifestyle, 

which revealed many roof garden, the roof garden was an important 

element of roman lifestyle, as a place for social activities and dine, 

external living room, and to escape summer heat. 



15 

 

 

Fig.5  Image of Villa of Mysteries roof 

garden. 

Source:     (Shimmin, Heather 

Shimmin Photography, 2012) 

Fig.4  Reconstruction of Villa of 

Mysteries, near Pompeii, Italy. 

Source:     (Shimmin, Heather 

Shimmin Photography, 

2012)

An example of roman roof gardens is the Villa of Mysteries, located on the 

road to Herculaneum, close to the northwest gate of the city. Vegetation 

was grown on the U-shaped terrace arcade. (Shimmin, Heather Shimmin 

Photography, 2012) 

2.3.2. Islamic roof garden  

Little is known about the use of roof gardens in the Islamic period but the 

traveler "Nasir Khusraw" in his book "Safarnama" described Cairo in the 

10th century "in the city orchards and trees between castles irrigated by 

well water. And in the sultan castle an orchard's no other orchard 

resembles it, water mill used to irrigate it. Trees are planted above roofs 

and became parks". (Khusraw, Safar Namah, 1993) 

Also, describing the buildings in Egypt "in Egypt houses of 14 floors, and 

houses of seven floors. And heard from a trusted person that a man 

planted a garden on the top of seven floor house, and planted on this roof 

trees orange and banana and planted roses and other type of flowers". 

(Khusraw, Safar Namah, 1993) 

http://www.heathershimmin.com/wp-content/uploads/2012/07/Villa-of-Mysteries.jpg


16 

 

2.3.3. Renaissance green roofs  

Roof gardens at that time were owned by the rich and Benedictine monks. 

Although the steeply terraced gardens were widespread in Genoa, but the 

first known roof garden or controlled landscape (manmade landscape) on 

top of a structure was in Pienza where Pope Pius II, in 1463, asked 

Bernardo Rossellino to design his private summer residence "The Palazzo 

Piccolomini" on top of the palazzo a roof garden designed with trees in a 

formal organization.  (Shimmin, Heather Shimmin Photography, 2012) 

  
Fig.6 Garden loggia atop the Palazzo in Poccolomini, Pienza overlooking the Val 

D’Oria. 

Source:                (“Gardens in Tuscany,” n.d.) 

2.3.4. Sod (turf) roofs  

Some researchers believe that turf roofs are first known green roofs dated 

back to the Bronze Age (3000 years) (STATER, 2008). The sod or turf roofs 

were used in cold Scandinavian countries, especially in Norwegian 

vernacular architecture (1600-1800). These roofs were not designed to 

impress or for esthetical value but mainly for their benefits in insulation, 

water proofing, and increasing roof life (protect the roof from rain and 

prevent it from rooting, while the root system gave the roof structure more 

strength) figure (7). The roof was built using local materials and covered 



17 

 

with birch bark for waterproofing and a layer of twigs was added for 

drainage. This roofing technique arrived to the United States and Canada 

by the immigrants that continued to use sod (turf) to cover the new houses 

they built in late 1800. (Shimmin, Heather Shimmin Photography, 2012) 

(Donnell -Kilmer, 2013) 

 
Fig. 7  Norwegian sod roof 

Source :            (Kamta, 2012) 

 
Fig.8 The Casino Theatre, 1909.   

Source:          (Miller, 2013) 

2.3.5. Modern green roofs. 

The roof gardens developed as the building materials improved, to support 

more weight and with better waterproofing. 1890s roof top gardens were 

popular in New York, in 1882 the first roof garden was constructed, 

Rudolph Aronson a musician and artist visited Paris in the summer and he 

was charmed by the theater gardens, but the land prices in New York city 

made it impossible to duplicate the Parisian summer theater gardens on the 

ground level, to solve this problem he proposed to elevate the theater 

garden to the roof (with the stage surrounded by plants) of the casino 

theater at 39th and Broadway, figure (8). This summer theater became 

very successful in New York, which encouraged other theaters to add 



18 

 

gardens to their roofs. The most famous summer theater, Madison Square 

Garden's and Winter Gardens got their names from the roof gardens.  

Modern architecture changed the entire architectural principles in early 

20th century. Architects like Frank Lloyd Wright and Le Corbusier started 

a new way of thinking about architecture, presenting new theories for 

architectural design. 

 Le Corburiser’s Cinq Points de l’Architecture Moderne became principles 

of design and theory. The five points are freestanding support pillars, Open 

floor plan independent from the supports, Vertical facade free from 

supports, long horizontal sliding windows, and Roof gardens.  

These five points of architecture were demonstrated in the design of 

houses in the Weissenhof settlement, Stuttgart, 1927, but the best-known 

example to clarify the five points of architecture is Villa Savoye1929–31 

designed by Le Corburiser. (le-corbusier, 1931) 

Le Corburiser has been credited for bringing the roof gardens back to life 

after being almost forgotten. Le Corbusier explained the benefits of using 

a roof garden to restore the area occupied by the building, in general, roof 

gardens mean to a city the recovery of all the built-up area (le-corbusier, 

1931),according to him; "it became the most favored place in the 

building". 

 

Fig.9 Images of Villa Savoy  

Source:                (Glynn, 2001) 

http://www.bc.edu/bc_org/avp/cas/fnart/Corbu.html
http://www.bc.edu/bc_org/avp/cas/fnart/Corbu.html


19 

 

Today Germany is the leading country in present green roof research 

materials regarding green roof benefits starting in 1960s, new building 

materials is still been developed to create green roofs ever since. In 1970s, 

two parallel groups worked on the development of roof gardens 

researchers for technical evaluating the ecological benefits of green roofs, 

and citizen concerned for the environment. 

Accidental plants growing (late 70s) on the “rental barracks” in 

Berlin (working class housing roof constructed with tar, gravel, 

and sand). Lead the researchers to study the roof ecological value. 

The FLL (the Research Society for Landscape Development and 

Construction) was launched in 1975 and started to write down 

guidelines and standards for the construction of green roofs with 

high quality. 

 

Fig. 10  image of Stuttgart, Germany, since 1989, municipal regulations require 

green cover for all new flat-roof buildings. 

Source:             (“design you trust.com,” n.d.) 



20 

 

(Bürgerinitiativen) citizen movement shed the light on urban areas 

environmental concerns such as growing urbanization and scarce green 

spaces. This movement led to the creation of political party the Greens 

(Die Grünen). In 1980s, many municipalities and stats started programs to 

greening the cities. The programs engorged many greening methods such 

as green roofs, green walls, and courtyard, by funding 50 to 100 per cent 

of the expenses. By 1983 more than 24 cities granted subsidies for urban 

greening. In addition to federal building codes and regulations, which was 

submitted to support greening the city that encouraged the use of green 

roofs systems. Today Germany possesses the largest number of green 

roofs. Other European and western countries are adopting green roof 

technology to help mitigate the effects of urbanization. (Lawlor, Currie, Doshi, 

& Wieditz, 2006) (STATER, 2008) 

2.4. Green Roofs building types, Technologies, and components. 

Modern green roofs concepts are basically divided into two main types; 

intensive and extensive. Between these two types, there are a number of 

green roof technologies derived from these two main types, including 

semi-intensive and semi-extensive. All of these types present various 

benefits to the urban environment, as well as, having various methods of 

construction. This part will explain these technologies and their 

components. 

Dividing green roofs to intensive and extensive is a general way or the 

most common way for spotting the differences between green roofs types, 



21 

 

manufacturers usually list the green roof technology after construction 

method, mat based systems or substrate based systems, pre-vegetated or 

vegetated after application, also different drainage technologies used in the 

drainage layer; drainage plates, granular media or drainage mats, many 

other factors play a role in defining the green roof type; flat roof or sloped 

roof, built in layered-style or modular vegetative grid. 

All green roofs must contain the following layers: plant layer, growing 

media (soil), filter layer, drainage layer, root barrier, waterproofing, vapor 

control and in some thermal insulation.   

2.4.1. Green roof types: Structural Load  

Plant type and design controls substrate depth, which affects the weight of 

the green roof components, different types of roofing have different 

substrate depth, therefore different added weight to the structure.  

 

Fig. 11  Section in green roof types from Extensive (left) to Intensive (right)  

Source:  (“Green Roof Systems | Green Roofing Solutions | Products, Materials,” 2006) 



22 

 

2.4.1.1 Extensive Green Roof (Climatic Skin Roof) 

This type of green roofs have shallow growing media, range between 5 to 

15 cm substrate, hence the growing media is shallow small plants only 

used in this type of green roofs such as grass, sedums (low laying ground 

covers), and herbs plant, their height doesn't exceed 25 cm, therefore, 

extensive green roofs requires little or no maintenance and irrigation, the 

plants are watered and fertilized in the first year, after that the roof is to be 

inspected three times a year. (Townshend, 2007) 

As these roofs are not designed to be accessed by the public or the users of 

the buildings only basic access is needed for maintenance (weeding or 

mowing). The extra load added by extensive green roofs range between 60 

to 150 kg/m2 and the added cost range from 100$ to 200$ / m2. (Lawlor, 

Currie, Doshi, & Wieditz, 2006) 

This type of roofing is purely functional as for storm-water management, 

thermal insulation, fire proofing and other environmental aspects of a 

green roof, but it offer limited benefits for living space or a garden. 

(OBERNDORFER, et al., 2007)  

This type of roofing is less likely to provide amenity space, but it is more 

appropriate for high levels and retrofitting.  

Extensive Green Roof have two ways of constructing 1st mat based 

system which are pre-grown with mostly sedum species, and a very 

shallow growing media 20-40 mm, this mat system retain less rainfall and 

have lower thermal mass. The 2nd is substrate based systems this system 

have more depth 75-150mm, a wider variety of species could be planted, 



23 

 

higher thermal mass and could retain more rainfall, although it have more 

advantages than mat based system but it takes more time to have full 

vegetation cover and higher weight. (Gedge, et al., 2008)  

 
Fig. 13  Substrate based system 

Source:  (“Green Roof Report | ZinCo,” 

2012) 

Fig. 12 Mat based system 

Source:            (Dorsey, 2013)

2.4.1.2 Semi-Intensive. 

Is a way of bridging the gap between intensive and extensive roofing 

system (hybrid of the two systems) with substrate depth ranging between 

12 to 25 cm, and 120-200 kg/m2 weight. This system can sustain grass, 

herbs and shrubs figure (15). Therefore, seasonal maintenance is needed. 

The cost of this system is medium (more than the extensive and less than 

the intensive). (International Green Roof Association (IGRA), 2008) 

2.4.1.3 Intensive green roof. (Garden roof, sky garden) 

Garden roofs are very similar to the landscape on earth. Consequently 

requires more substrate depth than extensive roofs, the substrate depth 

varies according to the type of plants used, but the depth growing media 

depth more than 20 cm, or 30 cm, up to 200 cm for tree planting, therefore 

the added weight to this type of green roofs is higher, between 180 to 900 

kg/m2 added cost more than 200$ /m2. (OBERNDORFER, et al., 2007) 



24 

 

 
Fig. 14  Intensive green roof, Namba Parks, Japan. 

Source:             (Yuka Yoneda, 2014) 

Although the intensive roof considered expensive, needs more 

maintenances and a complicated irrigation system, but it will be used and 

accessed as a garden in the same way as a garden at ground level, so it will 

provide more than just functional environmental value for the building and 

users, as an escape, outdoor living room and adds aesthetic value as an 

amenity or recreational space to the building and the city. (Townshend, 2007) 

(Lawlor, Currie, Doshi, & Wieditz, 2006) 

2.4.1.4 Mixed green roof 

Using different roofing type on different locations on the roof, the design 

of this roof combines intensive and extensive areas, figure (16), the 

substrate depth can range from five to 200 cm, growing vast diversity of 

plants, grass, shrubs, and trees. So mixed green roofs needs a mixed 

maintenance and irrigation as the roof garden type differ, as well as, 

uneven weight distribution from 30 to 500 kg/m2. (Velazquez, 2005) 

(Almusaed, 2011) 



25 

 

 
Fig. 15  Semi-Extensive green roof   

Source:             (“Roof Systems 

Consultants,” n.d.)  

 
Fig. 16   Mixed green roof. 

Source: (“Highlighting Baltimore 

Green Roofs!,” 2013) 

2.4.1.5 Rooftop gardens 

"Rooftop gardens consist of movable growers strategically placed on 

existing rooftops that do not always require structural reinforcement". 

(Ayalon, 2006) 

This system is simpler than the extensive and intensive roofing systems 

where the garden can be a group of planted pots or containers distributed 

on the accessible roofs. 

 
Fig.18  Terrace garden in New York 

Source: (“Garden, Gardens Apartments,” 

n.d.) 

Fig.17  roof top garden  

Source: (“ InteriorHolic.com,” 2012)

Table (1) demonstrates a comparison between different characteristics of 

green roof types, obtained after reviewing green roofs guidelines, 

manufacturers' details, and published research. As the preceding part of this 



26 

 

chapter explained these characteristic in detail; table (1) surmise the green 

roof type's information, to extract the needed information easily, for 

example, one can see that extensive green roofs are lighter but intensive 

green roof can support wider range of plants. 

Table (1): green roof types comparison  

characteristic  Extensive 

Green Roof  

semi-

intensive 

Green Roof 

Intensive 

Green Roof  

mix green 

roof  

Rooftop 

Garden  

Substrate depth 5 to 15 cm  12 to 25 cm 20 to 200 cm  vary  vary 

according to 

the planting 

container  

weight  light (30 to 

150kglm2) 

medium 120-

200kg/m2 

high 180-970 

kg/m2 

30-500 

kg/m2 

vary 

according to 

the planting 

container  

cost  low ($100 to 

200/m²) 

medium  high(more 

than $200-

2000/m²) 

high low 

Plants utilized  sedum-herbs 

and grass 

grass-herbs 

and shrubs  

shrubs and 

trees  

grass-herbs 

shrubs and 

trees 

grass and 

shrubs 

plant diversity  low  medium high high medium 

accessibility often  may be 

partially 

accessible  

usually 

accessible  

partial 

accessible 

accessible 

energy 

efficiency 

low  middle high over middle  low 

thermal 

insulation  

middle  middle high high low(no 

thermal 

insulation ) 

Maintenance  low  periodically high special  special  

Irrigation  low  periodically frequently  periodically  frequently 

Source (Almusaed, 2011) (Townshend, 2007) (ZinCo, 2014) (OBERNDORFER, et al., 

2007) (Gedge, et al., 2008) (Weiler & Scholz-Barth, 2009) (FLL, 2002) (Lawlor, 

Currie, Doshi, & Wieditz, 2006) 



27 

 

2.4.2. Other green roof constructing technology, Modular Green Roof 

Systems (Green grid) 

As the green roof technology is developing every day, there is new, easier, 

less expensive and improved way of constructing green roofs, 

such as (Green grid) in this method pre-planted grid of plastic trays, boxes, 

like flowerpots, installed directly on the insulated roof. These boxes or grid 

comes in all sizes and with wild variety of plants. It is easier to replace and 

repair than the non-modular green roofs.(Dineen & Woodward, 2013) 

 
Fig. 19 Green Grid   

Source:                 (“Greenroofs.com Projects” 2015) 

2.4.3. Green roof components. 

Green roofs usually constructed with layers, which may differ between the 

types of green roof listed in the previous part of this chapter, the following 

images, demonstrate the layers used to construct a green roof. The most 

important layers of green roofs are waterproofing and soil (growing media). 



28 

 

 
Fig. 20   Green roof layers (1). 

Source:       (“Hardscaping 101: Green Roofs: Gardenista” 2015) 

Fig. 21  Green roof layers(2). 

Source:                 (Dineen and Woodward 2014) 

As noted in figure (21), some roof need structural support to sustain a green 

roof, but if the roof structure could sustain a green roof without the addition 

of support this layer is no longer needed. Also the thermal insulation layer 

as its not considered essential component for green roofs but it is usually 

added to improve the thermal fluctuation of the roof. This layer could be 

added bellow the roof structure (inside the building), or above roof 

structure. It is preferred to place this layer above roof structure and above 



29 

 

waterproofing membrane. When applying thermal insulation under 

waterproofing it is needed to add vapor barrier to avoid having water or 

vapor reaching the roof structure, and also a protection, cover board may be 

added to protect the thermal insulation layer from cracking or deforming 

causing the waterproofing layer to rupture.  

2.4.3.1. Membrane, waterproofing membrane, Waterproofing Layer 

(A Seal) 

The waterproof membrane is applied to the roof directly; it is one of the 

most important layers in green roof construction for it prevents moisture 

from leaking through the roof. Concern over the roof leakage is one of the 

main reasons drive people to hesitate about applying green roofs. And as 

this membrane the bottom layer of the green roof system, it's not easily 

maintained. 

The waterproof layer should have been used to cover the roofs of existing 

buildings, never the less not all roofs in the city are covered with such 

layer. Commonly Bitumen sheets is used as a water proofing material in 

Palestine, but in the case of green roofs bituminous roofing material is not 

the best choice of material for green roofs, other water proofing materials 

are more efficient such as rubberized asphalt, polyolefin (cartouche 

ethylene propylene  polypropylene), PVC, or compounded thermoplastic 

composition. In Europe, mainly use PVC-covered polyester fabric and 

polyolefin-covered fiberglass fabric. (Almusaed, 2011) (Donnell -Kilmer, 

2013) (Pearen, Dinsdale, & Wilson, 2006)  



30 

 

The application of this membrane depends on the type of waterproofing 

used according to the book (green roofs systems, a guide to the planning, 

design, and construction of landscape over structure) there are three main 

types:  

 Built-up membrane 

 Single-ply membrane (includes hybrid or combined membrane 

types) 

 Fluid-applied membrane 

Built-up membrane: This type of membrane is assembled on the roof a 

sequent of layers "felts" and a kind of molten bitumen. The felts made of 

fibers such as fiberglass ,providing strength , and the molten bitumen is the 

water resistant(coal tar or asphalt).In this type of membrane the molten 

bitumen is hot-applied or in some cases can be cold-applied, in either ways 

the bitumen is mopped or brushed and harden when dries. The final 

membrane is composed of three or four layers, and needs protection from 

damage and ultraviolet radiation. 

Single-ply Membrane: One layer of this type provide the required water 

proofing, that is by using of thermosetting (elastomeric) or thermoplastic 

sheets. 

Fluid-Applied Membrane: This type of roofing membrane is used when 

the form is complex or for vertical elements, compounds like asphalt 

emulsions, silicones and neoprene is used and applied with rollers or 

sprayers. (Weiler & Scholz-Barth, 2009)  



31 

 

2.4.3.2. Root-protection layer, root barrier  

The root barrier layer or root-protection layer is used to keep the membrane 

intact from the plants roots, the material used in this layer can be copper 

sheeting or thick polyester coating. Although it may not be needed if the 

membrane is single-play membrane (synthetic roof materials) because the 

roots cannot easily penetrate this type of membrane, it is necessary to be 

used in all asphalt-based membrane plants can easily damage the layer and 

use the asphalt organic materials as food. However, it is still advised to use 

the protection layer to avoid future problems. 

The root protection layer is very important to cover the membrane at seams 

and along perimeters and wall connection where it is most likely to crack 

and leak. 

Simple polyethylene (plastic) sheets is considered one of the most efficient 

primary root barriers, it's applied over the water proofing membrane, a 

separation layer can be added to ensure the absence of chemical reaction . 

Polypropylene geotextile fabrics can be applied as a secondary root barrier 

over the drainage board to keep plants root from blocking the drainage 

core. Root barriers usually made as rolls whether it is incorporated with 

waterproofing or lose-laid, the seams must overlap for minimum 30 cm. 

The placement of root barrier depends on the type used whether it is 

directly applied over the membrane or over a protection layer. (Weiler & 

Scholz-Barth, 2009) (Donnell -Kilmer, 2013) 



32 

 

2.4.3.3. Protection Board  

After installation of the waterproofing layer, it is important to protect it 

from damage caused by construction activity and maintenance after 

construction is complete. In order to protect water proofing layer the 

protection board supposed to be durable and do not deteriorate in water, 

such as Semi-rigid sheets of cement board, pressure-laminated fiberglass or 

mineral-reinforced asphaltic core that is part of the waterproofing system. 

Typically, protection boards are 1/8 inch (0.3175cm) to 1/4 inch (0.635cm) 

thick. 

For reducing the cost temporary protection layer can be installed but it is 

not recommended, or rely on the drainage layer or insulation board. These 

material increase protection but will not provide the required protection 

under if heavy construction is needed. (Weiler & Scholz-Barth, 2009) 

2.4.3.4. Drainage layer 

This layer remove excess water after filtration, using channels, Drainage 

plat or Drainage mat, with angle of 1.5 degree if the slope of the roof is 

greater drainage layer may not be necessary, but still highly recommended 

in order of removing water quickly. (Donnell -Kilmer, 2013) 

It is preferred to use natural material for drainage layer, but using rubber, 

polyethylene and expanded polystyrene is suitable for the production of 

drainage elements. (Almusaed, 2011) 



33 

 

2.4.3.4.1. Drainage layer types  

When classifying green roofs after the drainage technology used to 

construct it, there are three main types of green roof drainage technology.1st 

granular drainage 2nd drainage plates 3rd drainage mats.  

Drainage plates are waffled plastic sheets (characteristically of an egg 

carton style configuration) their work mechanism is to store water above 

and drain water below. Drainage plates have the advantages of lightweight, 

easy to installation, and availability of sizes.  

Granular drainage system is also lightweight but can sustain a heavier 

media, but this system of drainage, needs more work to install the slotted 

plastic triangular drainage conduit covered with inorganic granular media. 

This can be a layer of 4–8 cm of expanded clay or similar aggregate of 4–8 

mm diameter. 

Drainage mat is a multi-layer fabric mat that combines soil separation, 

drainage, and protection functions. The fastest system to install and the 

thinnest and lightest green roof assembly. Nevertheless, it has limited water 

storage and drainage capacity, therefore it is mainly used for sloped roofs. 

(Conservation Technology, Inc.) 

 

Fig.22 Comparing types of drainage systems 

Source:                (Conservation Technology, Inc.) 



34 

 

 (A)   (B)  (C)  
Fig.23     (A) Granular drainage (B) Drainage plat (C) Drainage mat Comparing  

Source:   (Conservation Technology, Inc.) 

2.4.3.5. Filter layer 

This layer retain soil media, while allowing only water through to the drain 

layer, the importance of this layer is retaining the soil and maintaining the 

drain unclogged.  

The filter layer is a special fabric made of strong materials, made from a 

lightweight polyester geo textile. Non-woven, non-biodegradable, and non-

fabric, engineered to retain a specific grain size from passing through, but 

still passes water easily.  

The entire area planted or the plant bed must be lined with filter layer and 

covering up to 8 inches (20.32cm) the plant container to stop soil from 

slipping through. (Donnell -Kilmer, 2013) (Pearen, Dinsdale, & Wilson, 2006) (Almusaed, 

2011) 

2.4.3.6. Planting Media 

Substrate, Growing Medium or Soil Medium are other names for the soil 

used in green roofs, soil is considered the most important part of any 

garden. Yet green roof soil must have particular characteristics ranging 

from, heavy clay and light sandy soil, clay soil are very heavy due to its 



35 

 

water retaining capacity, while, sand soil are very light do not retain water 

it is very poor for growing plants and reducing storm water runoff. 

Engineered soil (slightly sandy loam) is used in green roof, where a balance 

is needed between weight and nutritious. (Donnell -Kilmer, 2013) 

The green roof soil is have to be mixed with lightweight aggregates, slag, 

expanded slate, or expanded clay; sand and gravel can also be used. 

Synthetic soil mixes are commonly used. The soil mix is preferred to be 

just about 75–80% inorganic to 20–25% organic. It is not recommended to 

use highly organic substrate as it will decompose and cause substrate to 

shrink (Almusaed, 2011). "It is important that the soil medium meet the 

demanding physical, chemical, and biological design requirements 

associated with storm water drainage. This includes moisture retention, 

porosity, hydraulic conductivity and maximum water capacities 

properties." (Pearen, Dinsdale, & Wilson, 2006) 

The type of plants, climate, and area of planting and green roof type 

determines thickness of the substrate layer. 

2.5. Green roof benefits  

This section of the research explores the benefits of green roofs, although 

the amount of research conducted on green roof technology and benefits in 

the Mediterranean region is increasing, but when compared with the 

research have been done, and being conducted in other climatic regions, the 

number of green roof research in Mediterranean region seems to be limited. 

Mainly because of the little knowledge on the green roofs characteristics 



36 

 

and benefits. (Fernandez-Cañero, Emilsson, Fernandez-Barba, & Herrera 

Machuca, 2013) 

Not only, green roofs can be beneficial for both macro-city and micro-

building level, but also, worldwide benefits can be achieved, as the total 

area of urban roofs estimated to be 3.8*1011 m2. Nevertheless, the urban 

area as assumed by Jacobson in 2007 to be 2.26 times above the estimated 

area calculated by analyzing satellite data (White & Gatersleben, 2011), 

about 25% of urban areas are roofs (Akbari, Menon, & Rosenfeld, 2009). 

By adding greenery to the roofs of urban areas global environmental 

improvement can be achieved.  

The application of green roofs to the urban roofs considered less expensive 

than constructing a garden on available ground level area, as well as, 

providing additional benefits (Kolokotsa, Santamouris, & Zerefos, 2013). On the 

macro-city level, reducing storm-water runoff, reducing the heat island 

effect, reduction of pollution particulate, the potential for urban food 

ecology, improving city appearance and citizens' health, and the return of 

wildlife to the city, and on a micro-building level, reducing heating and 

cooling costs, extending roof surface life, and having easy access to 

gardens. (Donnell -Kilmer, 2013)  

2.5. 1. Storm water management. (Reduce water runoff) 

The roof garden concept have been used worldwide to mitigate water 

runoff, cities like New York, Vancouver, Toronto, Waterloo, Portland and 

several cities in Germany. 



37 

 

 As the majority of the cities surfaces are impervious, man-made hard 

surfaces, (buildings roofs and walls, sidewalks, streets, paved parking lots). 

Consequently, about 75% of rain in urban area is lost directly to run-off, 

when compared with 5% in a forest where 95% of rainwater infiltrates into 

the ground or captured by vegetation. (Lawlor, Currie, Doshi, & Wieditz, 

2006) (Townshend, 2007)  

In the urban areas (cities) rainwater is directed to sewer systems. These 

systems may be different from a country to another. There are two main 

types of storm water and sewage system, the first system contains separated 

lines of channels (storm water line and sewage line), the other have 

combined infrastructure, which is the case in the city of Nablus, in this 

system the sewers reach maximum capacity rapidly and discharge a mix of 

rain water and untreated sewage to the city streets. 

Many problems occur from water run-off in urban areas such as flooding 

which make significant disruption and financial damage to private and 

public property, contamination of storm-water, combined sewage 

overflows, and increased water temperatures. Run-off from paved areas has 

higher temperatures than in the surrounding natural areas. This will lead to 

drop in local water tables, heavy investment in artificial drainage systems 

and destruction of natural habitat. (Lawlor, Currie, Doshi, & Wieditz, 

2006) (Townshend, 2007) 



38 

 

Adding green roofs to the conventional roofs of the city will reduce the 

impervious surfaces area, as the buildings are usually about 50% of city 

area, in Nablus buildings are about 67% of city area (Nablus Municipality , 

2011), the green roof store rainwater in the growing medium and plants, then 

evaporate the water to the atmosphere. The storing or evaporating of water 

depends on the plants types and growing medium depth. Studies have 

shown that green roof retains 70-90% of rain in summer and 25-40% of 

rain in winter. (Banting, et al., 2005) 

Many cities developed green roof policies and legal recruitments as a 

consequence of water run-off problem. For example, in Germany between 

2000 and 2001, installation 25 million m2 green roofs were recorded 

mainly as a result of water run-off reduction polices. (“Green Roofs - 

Enviromental Advantages,” n.d.)  

The green roofs have two main effects regarding water run-off treatment, 

on one hand reduce the total run-off, absorb water, and return it to the air, 

on the other hand spread the run-off water over a longer time, the water is 

held in the roofing layers for a period before it runs-off. Therefore, reduce 

the likely hood of local flooding. (Townshend, 2007) (Livingroofs.org 

,ecologyconsultancy, 2004) (Banting, et al., 2005) 

A study to measure the effect of a green roof in comparison to a regular 

roof in Canada, the rain incidents and the storm water run-off for the two 

roof sections were monitored over time in fall 2001. Two rain events 



39 

 

occurred the first on October 6, 2001 the following figure shows the 

difference in rain/run-off, (Rain: purple), run-off from the Reference Roof 

(Runoff-R: blue) and runoff from the Green Roof (Runoff-G: green), and 

the orange shows the difference in run-off between the two roofs. While the 

run-off from the reference roof was equal to the rainfall, the green roof 

retained 8mm of the 34mm rain. 

 
Fig.24  Rain event on October 5-6, 2011, green roof runoff (in green) and regular roof 

runoff in blue. 

Source:  (Bass & Baskaran, Evaluating Rooftop and Vertical Gardens as an Adaptation 

Strategy for Urban Areas, 2001) 

On the second event the results showed a run-off delay for 45minutes from 

the start of the first rain event and a lower run-off rate the reference roof 

rate is about 2mm/h while the green roof rate is 0.4mm/h, the green roof 

retained 2 mm before the run-off start and retained 4.5 mm of the 10 mm 

rain that fell, although the growing medium was not dry because of light 

rain the day before. The figure shows the difference between regular roof 

and green roof run-off. 



40 

 

 
Fig.25   Rain event on 61-17 October, 2011, green roof runoff (in green) and regular 

roof runoff in blue. 

Source:  (Bass & Baskaran, Evaluating Rooftop and Vertical Gardens as an Adaptation 

Strategy for Urban Areas, 2001)  

Another study to determine the engineering performance of rooftop gardens 

through field evaluation by Liu in Ottawa, showed the difference in green 

roof run off (in green) and regular roof run off (in blue) in two different 

rain intensity. 

 
Fig.26   Runoff of two rain events (a) light rain (b) heavy rain. Showing the difference 

between green roof runoff (in green) and regular roof runoff in blue.  

Source:               (Liu, 2003) 

In Genoa 2007 a green roof experiment in Mediterranean climate was 

conducted the results shows that green roofs are excellent device to control 

storm water " with an average percent retained volume of 85% and a 

 (a) light rain  (b) heavy rain.  



41 

 

percent peak reduction of 95%. However, in the framework of the 

assessment of the environmental benefits (prevention of flooding 

phenomena and reduction of the impact on waste water treatment plants), 

it is necessary to extend the investigation horizon from the spatial scale of 

the single rooftop to the one of the entire watershed". (Palla, Lanza, & La 

Barbera, 2008) 

2.5. 2. Mitigate city heat island effect  

The urban heat island effect is one of the most recognized negative effects 

of urbanization, resulting the air and surface temperature in urban areas to 

be higher than rural surrounding areas, from 5 to 10°C. The difference in 

temperature caused by the density of asphalt concrete roofs, glass facades, 

combined with air pollution caused by motor vehicles and lake of natural 

elements such as trees. These surfaces absorb sun heat and radiate it to the 

surrounding air causing the temperature in the urbanized area to rise above 

cooler surrounding with an isotherm island like pattern. Where the 

surrounding areas with more vegetation such as rural areas, city park and 

suburban residence, have cooler air temperature due to the cooling effect of 

plants, evaporation and transpiration through the leaves. (Lawlor, Currie, Doshi, 

& Wieditz, 2006) (Banting, et al., 2005) 



42 

 

 
 Fig.27  Sketch of an Urban Heat Island profile  

Source:                 (Paul R. Baumann, 2001) 

Different factors effects the intensity of the urban heat island other than 

density of the urban area, city size and energy consumption, geography of 

the city and its location, weather, the parentage of green spaces, and time 

related factors such as season, month, time of the day. The concern over 

urban heat island effects drive many municipalities and cities to lunch 

programs to reduce it, various strategies was introduced to increase urban 

green spaces and  trim down the surfaces with direct sun exposure, these 

strategies includes cool roofs, streets and public spaces greening and green 

roofs. (Banting, et al., 2005) 

Adding vegetation to the cities proved to be a functional way to lower 

urban heat island also improving aesthetics image of the city, but the 

demand of ground level areas in cities makes adding new green spaces 

more difficult, therefore green roofs considered being a great way to reduce 

the city urban heat island as they add greenery to the existing impermeable 

surfaces. (Banting, et al., 2005) 

The adoption of green roofs on a large scale has the potential for reducing 

urban heat island (Liu, 2003). Green roofs cover the roof surface preventing 



43 

 

the sun from accessing and increasing the roof structure temperature and as 

green roof constructed with materials that do not radiate heat the air 

temperature above the roof is lowered. Also with evapotranspiration, where 

plants release water through their leaves contributes to the cooling factor of 

green roofs, plants provide wide array of benefits including lowering CO2 

percentage. (Donnell -Kilmer, 2013) 

The reduction of urban heat island provided by adding green roofs cannot 

be easily computed (Banting, et al., 2005). A simulation of green roofs added to 

1km in the city of Toronto to calculate the effect of green roof on the urban 

heat island, for 48 hours in June, a Mesoscale Community Compressible 

(MC2) model with conjunction of the ISBA SVAT scheme and an urban 

canyon, with green roof covering 5% of total land area, reduction of 

temperature about 1Co across the city. While the difference between 

irrigated green roof and dry green roof in this simulation showed that 

irrigated green roof reduced the temperature 2Co and maintained the 1oC 

reduction for a longer time. (Bass, Krayenhoff, Martilli, & Stull, 2002) 

A field study of Ottawa campus in 2000 comparing 72m2 roof divided in 

half with 1 meter divider. On one installed extensive green roof with 

150mm growing medium, and the other is a conventional roof assembly 

covered with modified bituminous. And on both roofs instruments 

monitored temperature profile, heat flow, solar reflectance, relative 

humidity, soil moisture content and storm water run-off. The results 

showed a reduction in roof surface temperature from over 70°C of the 

conventional roof to about 30°C under the green roof in summer. And the 



44 

 

daily temperature fluctuation of the Conventional Roof in spring and 

summer ranged from 42 to 47°C, but the temperature fluctuation was 

reduced to 5-7°C by using green roofs. (Liu, 2003) 

 
Fig.28  Temperature profile of the roofing systems on (July 16, 2001) indicating the 

green roof reduction on temperature fluctuation within the roofing system. 

Source:     (Liu, 2003) 

An advanced weather Research and Forecasting Model (ARW) combined 

with an urban canopy model was conducted to determine the green roof 

mitigation effect in Chicago, Illinois. The research concludes that 

"Vegetative rooftops, or green roofs, offer a potentially attractive 

mitigation strategy by increasing equivalent albedo and thereby reducing 

temperatures in the urban environment", and green roofs have the potential 

of reducing the urban environment temperature up to 3°C. (SMITH & 

ROEBBER, 2011) 



45 

 

 
Fig. 29   Infrared image of a roof in Singapore. 

Source:                (Townshend, 2007) 

Yok & Sia in their book "Selection of Plants for Green Roofs in 

Singapore", demonstrated infrared images to show the difference in 

temperature between the concrete roof and roof covered with plants in 

Singapore (Townshend, 2007). As shown in figure (29) the vegetated area has 

lower temperature than the concrete roof. 

A new low in Tokyo, Japan was initiated in order to install green roofs on 

new buildings with roof area more than 1000 m2, to reduce the urban heat 

island effect. (Liu, 2003) 

2.5. 3. Reduce energy budget for building  

By adding an extra layer to the roof the thermal insulation of the roof is 

increased, as well as, decrease the direct exposure of the roof structure to 

the sun. This, on one hand, will reduce heat gain in summer, and on the 

other hand reduce the heat lose in winter.  

The type of green roof applied can affect the added thermal insulation, but 

in general green roofs provides lower U-value than all other roofs. (D’Orazio, 

Di Perna, & Di Giuseppe, 2012) 



46 

 

A research shows that the cooling load in the warmer months was reduced 

by green roof to 1.5(5,100 BTU/day) when compared with the load of the 

reference roof 6.0-7.5 KWh/day 20,500-25,600 BTU/day) (Liu, 2003). In 

Germany Zinco International (German green roof company) estimates, that 

the green roof saves about 2 liters of fuel oil/m2/year, and Possman Cider 

Cooling and Storage Facility in Frankfurt declared the recovering of the 

green roof installation cost after 2-3 years as the heating and cooling costs 

was reduced to save about £4,300 per year. (Livingroofs.org 

,ecologyconsultancy, 2004) 

The monitoring of an extensive green roof during the summer of 2010, 

2011 and 2012, with a different density of vegetation each year, results 

60% reduction of heating gain when the roof is covered with dense 

vegetation when compared with non-vegetated roof. The green roof with 

dense vegetation acts like a passive cooling system, this study demonstrates 

the importance of vegetation density in the cooling effect of the green roof. 

(Olivieri, Di Perna, D’Orazioc, Olivieri, & Neilaa, 2013)  

A study of the effect of green roof technology on energy saving and 

thermal benefits through computer simulation was conducted on an 

apartment building in Amman, Jordan. The analysis of the simulation data 

showed that green roof decrease heat loss by 41% through the roof, and a 

reduction of 17% of total energy consumption was calculated. (Goussous, 

Siam, & Alzoubi, 2014) 

Although green roofs have the greatest effect on the roof directly 

implemented on, but also reduction of cooling loads in the lower floor 



47 

 

levels can be achieved, when implementing the green roof technology on a 

city level, the urban heat island effect is lowered, the overall temperature of 

the city is reduced and therefore the need to use air conditioning or other 

cooling devises. This eventually will reduce energy consumption and 

budget. 

2.5. 4. Aesthetic value (for both the building and the city) 

Although the green roof research area is more focused on the 

environmental benefits of green roofs, the visual improvement of green 

roofs recently have the attention of many architects and researchers, as in 

cities with high building density dominated by the gray concrete and 

modern building materials, the green roofs add new colors and bring life 

back to city (Fernandez-Cañero, Emilsson, Fernandez-Barba, & Herrera Machuca, 2013), 

the city skyline aesthetic appearance can also be enhanced with green roof 

design (Abdul Rahman, Ahmad, Mohammad, & Rosley, 2015). By 

reducing the artificial appearance of urban area, and improving the 

architectural design. (Abdul Rahman & Ahmad, Green Roofs As Urban 

Antidote, 2012) 

A study in Seville, Spain carried out to examine public preconception and 

preferences for green roof design used computerized images (containing 

different types of green roof and one without green roof on the same roof 

structure). Questioned 450 respondents to choose the most aesthetic 

visually in their opinion. The results showed that respondents favored the 

roof garden that has variety of plants and colors and good maintenance, 



48 

 

when the image with no green roof got the lowest rating. Figure (30). 

(Fernandez-Cañero, Emilsson, Fernandez-Barba, & Herrera Machuca, 

2013) 

 

Fig.30    Scenes shown to participants  

Source:  (Fernandez-Cañero, Emilsson, Fernandez-Barba, & Herrera Machuca, 

2013) 

The study indicates "On a daily basis many participants found themselves 

attracted to the green roof almost unconsciously. They would be chatting 

on the phone, or looking out over the cityscape, and would find their eyes 

drawn to the roof". (Loder, 2014) 

Moreover, in a study conducted in the Northeastern United States, seven 

roof gardens was included in questionnaire, to measure the visitor's reaction 

towards green roofs, overall reactions to green roofs were positive. (Jungels, 

Rakow, Broussard Allred, & Skelly, 2013)  

More research were carried out on the same issue such as, a test of the 

visual improvement theory in the UK by adding five different type of 



49 

 

greenery to four sample houses and introduced to the participants of the 

experiment with six different computerized images of the four houses (the 

sixth image of the original houses without any green elements) figure (31). 

This study concludes, "Houses with integrated vegetation are more liked, 

aesthetically pleasing, and restorative than houses without vegetation". 

(White & Gatersleben, 2011) 

 
Fig. 31      Houses in different vegetation conditions shown to participants  

Source:      (White & Gatersleben, 2011) 

Another study in Chicago and Toronto, to explore the relationship between 

aesthetic and green roof among office workers viewing roof gardens in 

both cities. Find that all the participants preferred looking at green roof 

than to look at black tar or gravel roof. (Loder, 2014) 



50 

 

In the Arab world, an initiative in 2012 arises to greening the city of Beirut. 

It was started by architect Wassim Melki due to the lack of green spaces, 

only 3% of Beirut land area is gardens.  

Computerized images were created to show the difference between the city 

image with and without the vegetation to encourage people to add and 

maintain plants on their roofs and balconies, figure (32). To describe the 

project Melki said, "Aside from the major environmental and social 

benefits, it would also be incredibly iconic," he says. "Just imagine: The 

world's first rooftop garden city".(Webster, 2012) 

(a) (b)   

Fig. 32    Images of Beirut (a) with green roofs and (b) the current image of the city.  

Source:    (Webster, 2012) 

Different studies have almost the same results, visitors, or respondents 

agreed on preferring well-designed roof garden with different types and 

colors of vegetation. 

All the studies documented a relationship between childhood memories 

(environmental background, growing up in urban or rural environment) and 

socio-demographic factors effected the preference of green roof or 

vegetation layout options. Still all the studies proven that greenery or 

vegetation visually improve the overall appearance of the building and 



51 

 

were preferred by the population when compared with no green roof 

alternative. 

2.5. 5. Social benefits: Green amenity space and improving citizens' 

health. 

All over the world, the city development and urban sprawl especially in 

cities with improper planning which could be the case in the city of Nablus, 

ends up with the destruction and loss of open spaces and green areas. 

Highly urbanized cities in the world tend to combine the urban structure 

with green elements to replace the lost green areas. (Abdul Rahman, 

Ahmad, Mohammad, & Rosley, 2015)  

Usually citizens benefiting from urbanization do not mind the loss of green 

spaces and do not recognize their need to green spaces until the green 

spaces are very limited. As the urban life have many stressors like traffic, 

noise and jam, pollution, crimes and crowding, but greenery and open 

natural spaces offer opportunity to reduce stress and mental fatigue (van 

den Berg, Hartig, & Staats, 2007). Many researchers suggested that visitors 

go on foot to urban green areas, to places approximately three to five 

minutes from their living place, which is about the time needed for 

residents to reach the roof of their building, green roofs offer a great 

replacement of ground level amenity gardens. (Abdul Rahman & Ahmad, 

Green Roofs As Urban Antidote, 2012)   

Earlier studies demonstrate the human preference of viewing green natural 

spaces rather than built urban environment. And that residents and workers 



52 

 

with access or view of a green roof have better health and greatly value it, a 

study on the tenants at 401 Richmond Ltd, Toronto, revealed that tenants 

consider their green roof as "an oasis in the city" (Banting, et al., 2005). 

Likewise, in a report for the city of Toronto, discuss a study by Bass et al. 

(2004) on graduate students living in Charles Street, Toronto, described the 

viewing of a green roof as it "provides sanity and relief". (Banting, et al., 

2005) 

 Many other studies suggests that human interaction with nature or viewing 

green spaces provide calmness, reduce stress, increase the ability to focus 

(Banting, et al., 2005), and employees who view natural elements were less 

stressed, their blood pressure was lower and reported less sick days (Abdul 

Rahman & Ahmad, Green Roofs As Urban Antidote, 2012), as the natural 

view holds their attention, and drive their awareness to a meditation-like 

state away from their worries and thoughts (Townshend, 2007). Study 

suggests that the increase of  green spaces improve the mental health (Vries 

et al., 2003). While physical access to green space provides benefits such as 

cleaner air, reduction in heart rate and blood pressure and can improve 

overall well-being (Livingroofs.org ,ecologyconsultancy, 2004). For 

instance, people living in high urban density having a garden on their 

balcony or terrace, known to be less subjected to illness, as plants provides 

air filtration, additional oxygen, control of humidity and other not 

measurable benefits such as the movement, sounds, smells and colors. 

(Townshend, 2007) 



53 

 

Providing spaces for recreation and social interaction in the community is 

another benefit could be achieved by adopting green roofs, the building 

tenant can use it for relaxing, dining and meditation (Banting, et al., 2005). 

Green roofs also endorse sense ownership, and bring occupants closer to 

greenery. 80% of Singapore citizens participating in survey voted to 

increase the number of green roofs in the city (Abdul Rahman & Ahmad, 

Green Roofs As Urban Antidote, 2012). Another survey in Malaysia 

indicates that 95% of respondents agreed with the increase of green roofs in 

Malaysia, and 92% were interested in adding green roof to their building. 

This is because they think that green roofs add new dimension to the 

private gardens and they do not find space on the ground to have green area 

(Abdul Rahman, Ahmad, Mohammad, & Rosley, 2015). In Hong Kong 

green roofs are created on podium decks and used as public or private 

gardens, and described as essential for well-being of the population and 

enriching of the urban experience and quality of life. (Townshend, 2007) 

In the report "Green Roofs Benefits and Cost Implications" number of 

studies supporting the positive effect of green roofs on human health was 

presented, such as, study was performed in Texan hospital on post-surgery 

recovery showed that patients with green space view recovered faster and 

had lower relapse rates. As result of this study many hospitals had planned 

to redesign their views to allow the patients to profit from the benefits 

provided by greenery. (Livingroofs.org ,ecologyconsultancy, 2004)  



54 

 

2.5. 6. Air Quality 

Plants and trees are known to improve air quality; in fact, some people 

think that improving air quality is the only benefit provided by trees. The 

trees and greenery contribution to increase the levels of O2 and filter the 

particles in the air have been documented by many researchers. 

The green roof contribution to the air quality improvement have and still 

been studied by researchers, they believe that intensive green roofs might 

have more effect on air quality than extensive green roofs. 

A study Hong Kong conducted by using filed measurements and computer 

simulation to compare green roof CO2 levels absorption in day and CO2 

levels emission in the night. Concludes that on extensive green roof CO2 

concentration could be lowered up to 2%on areas near the green roof.(Li et 

al., 2010) 

Investigation on six scenarios of green roof vegetation and their effect on 

improving air quality. The results point that although grass roofs 

(extensive) contribution to air pollution mitigation could be similar to trees 

and shrubs but planting shrubs on roof (extensive) would have more impact 

in mitigating air pollution (Currie & Bass, 2008).  And adding 109ha of 

green roofs would remove 7.87 tons of air pollutant per year. (Berardi, 

GhaffarianHoseini, & GhaffarianHoseini, 2014). 

The effect of roof greening on air quality in street canyons was calculated 

using computational fluid dynamics; the results shows that the cooling 

effect of the green roof could reduce the concentration of pollutant and 

improve air quality near roads. (Baik et al., 2012) 



55 

 

In Chicago, a study revealed that 19.8 ha of green roof removed 1675 kg of 

air pollutants. And one hectare of green roof annually removes 85 kg ha-1 

yr-1.(Yang et al., 2008) 

Likewise, investigation of the effect of green roof on particular particles 

such as sulphur dioxide, fund that adding green roof reduced its levels by 

37%.(Tan & Sia, 2005) 

Other studies discuss that green roofs contributes to the air pollution 

reduction by reducing urban heat resulting in less use of air conditioning 

and this reduction in consumed energy would decrease the air pollution 

(Berardi et al., 2014). 

2.5.7. Improve property value  

Apartments and office building overlooking greenery such as New York 

central park tends to having higher property value. Researcher's 

documented rented offices with landscape scene have 7% increase in their 

rental rate. (Clements, St Juliana, & Levine, 2013) 

The green roof will improve the value of the building constructed on and 

the building surrounding it, as the owner of the building ask for higher rent 

because of the extra amenity space provided for the residence, and 

surrounding buildings overlooking the green roof can charge higher rent 

(Tomalty, Komorowski, & Doiron, 2010). In a study in Washington, DC, 

buildings with green roofs have 15% higher rental value per square foot 

when compared with similar buildings (Abbott & Lewis, 2013). Similarly, 



56 

 

in New York, rental rates for buildings with green roofs were 16% higher. 

(Ichihara & Cohen, 2011)   

2.5.8. Extend roof structure life  

The roof structure not exposed to UV lig