Application of Green Roofs in Cairo

By: Mahmoud Sherif Saad

December, 2010

Cairo University Faculty of Engineering AET/Fall 2010 Independent Studies

Abstract:

Green Roofs have become a very important component of sustainable urban

development within the last 30 years in developed countries. Green Roofs have many

benefits on urban development including environmental, energy and economic

advantages. The focus of this research is to study the environmental and energy

impact of green roofs in Cairo which is now considered to be one of the most air

polluted cities in the world.

The World Health Organization reports that the Air Pollution in

Downtown Cairo is 10 to 20 times what is considered a safe limit. The US

environmental Protection Agency states that above the safe limit, the risk of

developing serious respiratory diseases and cancer from inhaling particulates in air is:

2 for every 1000 persons. (

The main aim of this research is to prove that green roofs can move the Air

Pollution in Cairo towards the safe limit stated by the World Health Organization and

reducing energy consumption thus protecting Cairo inhabitants from the threats facing

them.

KEYWORDS: Green Roofs; Air pollution; Cairo; World Health Organization;

Environment; Landscape

PART 1: LITERATURE REVIEW

1.1. Definitions

1.1.1. Air pollution

1.1.2. Causes of Air Pollution

1.1.3. Smog

1.1.4. Air pollution in Cairo

1.2. Benefits of Green Roofs

1.2.1. Private Benefits

1.2.2. Public Benefits

1.3. Types of Green Roofs

1.3.1. Extensive Green Roof

1.3.2. Semi-Intensive Green Roof

1.3.3. Intensive Green Roof

1.4. Green Roof Engineering

Basic Green Roof Planning

1.4.1.1. Checklist

1.4.1.1.1. Roof substructure 1.4.1.1.2. Waterproofing 1.4.1.1.3. Roof parapets, roof penetrations and adjacent building parts 1.4.1.1.4. Roof slope 1.4.1.1.5. Roof construction 1.4.1.1.6. Assumed load 1.4.1.1.7. Roof Drainage 1.4.1.1.8. Irrigation 1.4.1.1.9. Access to the roof 1.4.1.1.10. Additional functions

PART 2: CASE STUDY

2.1. International case study

2.1.1. City Scale, Chicago

2.1.2. Building Scale, Seattle City Hall

PART 3: GUIDELINES AND RECOMMENDATIONS

PART 4: APPLICATION OF THE GUIDELINES ON A LOCAL CASE

PART 1: THEORETICAL BACKGROUND

1.1. Definitions

1.1.1. Air Pollution

Every day, the average person inhales about 20,000 liters of air. Every time we

breathe, we risk inhaling dangerous chemicals that have found their way into the

air. Air pollution includes all contaminants found in the atmosphere. These

dangerous substances can be either in the form of gases or particles. The sources

of air pollution are both natural and human-based. As one might expect, humans

have been producing increasing amounts of pollution as time has progressed, and

they now account for the majority of pollutants released into the air. The effects of

air pollution are diverse and numerous. Air pollution can have serious

consequences for the health of human beings, and also severely affects natural

ecosystems. (5)

1.1.2. Causes of Air Pollution

There are many different chemical substances that contribute to air pollution.

Among the many types of air pollutants are NO2, SO2, O3, PM10 and organic

compounds that can evaporate and enter the atmosphere. The biggest causes are

the operation of fossil fuel-burning power plants and automobiles that combust

fuel. (6)

1.1.3. Smog

Smog is caused by many factors. The smog that enters the atmosphere consists of

over 100 chemicals, many coming from different sources. Particulates present in

smog include carbon monoxide, dirt, soot, dust, and ozone. To really create the

smog effect, sunlight, hydrocarbons, and nitrogen oxides have to mix together.

Major producers of smog include automobiles, fires, waste treatment, oil

production, industrial solvents, paints, coatings and the operation of fossil fuel-

burning power plants. (7)

1.1.4. Air pollution in Cairo

Cairo is one of the most air polluted cities in the world like Mexico City,

Bangkok, San Paulo, Delhi and Tokyo. The sky color in Cairo is not blue but gray

and theres a haze over Cairo. If we assume that Cairo population is 18 million, a

simple risk calculation comes to the conclusion that half a million will develop

serious health problems (respiratory and cancer) which will result in premature

death in a period of 5-25 years, that is one person for every twenty four persons.(1)

1.2. Benefits of Green Roofs

Until today the benefits of Green Roofs are still underestimated. The "natural

look" is only one obvious benefit within the broad range of arguments for

Green Roofs. The benefits can be classified into Private and Public benefits as

follows:

1.2.1. Private Benefits

Green Roofs has many private advantages like the increased roof life, reduced

noise levels, thermal insulation, heat shield and the use of space.

1.2.1.1. Increased Roof Life

Due to physical, chemical and biological stress on the roof skin, the life

expectancy of a normal flat roof is only 15 to 25 years. The temperature

differences are about 100 C during the year and 60 C over 24 hours. Green

Roofs protect the waterproofing, buffers the temperature during summer and

winter, and the temperature differences are about 35 C during the year and 15

C over 24 hours. (2)

1.2.1.2. Reduced Noise Levels

Green Roofs reduce sound reflection by up to 3 dB and

improve sound insulation by up to 8 dB. This is

important for people who live near airports or noisy

roads. Moreover, electromagnetic waves from

transmitting stations can be shielded by the vegetation (2)

1.2.1.3. Thermal Insulation

Green Roofs can be regarded as an additional thermal

insulation which reduces the use of primary energy thus

reducing the economic cost. An amount of about 1-2

L/m2 of oil can be saved with this additional thermal

insulation. (2)

1.2.1.4. Heat Shield

During the summer months Green Roofs reduce indoor

temperatures through transpiration. According to tests

from Drefahl (1995), the microclimate of an apartment

underneath a Green Roof is comparable with one on the base floor. This

means decreasing the use of air conditioning and energy consumption. (2)

Figure 1, Green roofs reduces sound reflection for people living near airports, http://www.igra-world.com/images/red_noise.jpg

Figure 2, Green roofs is an additional thermal insulation, http://www.igra-world.com/images/thermal_ins.jpg

1.2.2. Public Benefits

Green Roofs has also many public benefits like the reduction of dust and smog

levels, urban heat island effect, natural habitat for animals and plants, and the

visual effect of cities and landscape.

1.2.2.1. Reduction of Dust and Smog Levels

Air pollution causes serious adverse health effects, which has been proven by

numerous studies over the last years. Plants are able to enhance the quality of

the air. One square meter of Green Roof can filter approximately 0.2 kg

aerosol dust and smog particles per year. In addition, nitrates and other

harmful materials in the air and from rainfall are deposited in the growing

medium. (2)

1.2.2.2. Urban Heat Island

Global warming, excess heat from residential buildings,

industry and traffic are leading to rising temperatures

within urban spaces. The difference in temperature

between a city and a surrounding countryside is called

the urban heat island effect. In summer this effect can

reach 10 C. Natural "air conditioners" such as green

areas and parks can absorb up to 80% of the energy

input. (2)

1.2.2.3. Natural habitat for animals and plants

Green Roofs can compensate for lost green areas. They

create lively places and connect isolated refuges for flora and fauna within city

centers. Low maintenance extensive Green Roofs promote biodiversity, as

wild bees, butterflies, and beetles find food and shelter there. The natural cycle

of plant growth and self-seeding lends to ecological systems with unique

character. (2)

1.2.2.4. Cities and landscapes

Green Roofs are visually enhancing the quality of life in the cities. Green

Roofs are able to interrupt the monotony of the grey, dismal city centers and

thus having better peoples mental and physical

health. (2)

1.3. Types of Green Roofs

1.3.1. Extensive Green Roof

Figure 3, the urban heat island effect, http://www.igra-world.com/images/urban_heat.jpg

Extensive Green Roof has low maintenance, no irrigation, build-up height of

60-200mm, weight 60-150 kg/m2, low cost and can be used as an ecological

protection layer. Moss-Sedum-Herbs and Grasses can be planted here. (3)

1.3.2. Semi-Intensive Green Roof

Semi-Intensive Green Roof must have periodical

maintenance, periodical irrigation, build-up height of

120-250mm, weight 120-200 kg/m2, middle cost and

can be used as a designed Green Roof. Grass-Herbs

and Shrubs can be planted here. (3)

1.3.3. Intensive Green Roof

Intensive Green Roof must have high maintenance,

regular irrigation, build-up height of 150-400mm,

weight 180-500 kg/m2, high cost and can be used as

a park like garden. Lawn or Perennials, Shrubs and

Trees can be planted here. (3)

1.4. Green Roof Engineering

1.4.1. Basic Green Roof Planning

1.4.1.1. Checklist

1.4.1.1.1. Roof substructure

Green Roofs can be realized on different types of roofs. Wooden

constructions, metal sheeting as well as reinforced concrete can be

considered as appropriate roof substructures. The base for the Green

Roof is a waterproof roof construction with appropriate load bearing

capacity. (4)

1.4.1.1.2. Waterproofing

Over a period of time roots can damage the waterproofing and roof

construction if there have been no corresponding protection measures

taken. If the waterproofing is not root resistant an additional root

barrier has to be installed. Aside from the roof surface, the upstands,

perimeters, joints and roof edges also have to be protected against root

penetration. (4)

1.4.1.1.3. Roof parapets, roof penetrations and adjacent building parts

Figure 4, Extensive Green Roof, IGRA

Figure 5, Semi-Intensive Green Roof, IGRA

Figure 6, Intensive Green Roof, IGRA

Figure 7, Roof substructure, IGRA

Figure 8, Waterproofing, IGRA

Figure 9, Roof parapets, roof penetrations and adjacent building parts, IGRA

For Green Roofs, the following upstand and perimeter heights have to be considered:

Upstand height for adjacent building parts and penetrations: minimum of 150

mm (6 in).

Upstand height for roof edges: minimum of 100 mm (4 in).

Important: The upstand height is always measured from the upper surface of the

Green Roof system build up or gravel strip. Clamping profiles guarantee reliable

protection and a tight connection of the upstand areas. In special cases ("Wheelchair

accessible apartments", for example) reduced upstand heights are possible, in this case

special constructions are necessary. Roof penetrations (e.g. water connections,

building parts for the usage of the roof area, etc.), when possible, should be grouped

in order to keep roof penetration to a minimum. (4)

1.4.1.1.4. Roof slope

Using modern technologies it is possible to install a reliable Green

Roof system build up not only on conventional flat roofs, but also on

saddle roofs, shed roofs and barrel roofs. Special technical precautions

for the mitigation of existing shear forces and erosion are only

necessary for a roof slope over 10. Roofs with a slope of more than

45 are normally not suitable for a Green Roof system build-up. Roofs

with a slope of less than 2% are special roof constructions on which

puddles often develop. In order to avoid Extensive Green Roofs from

being damaged by water retention, specific arrangements for the roof

drainage are necessary. In contrast, it can be beneficial for Intensive Green Roofs to

design the roof construction without slope to allow for dam up irrigation. (4)

1.4.1.1.5. Roof construction

a- Roofs without thermal insulation On roofs without thermal insulation, above non-heated rooms

(e.g. garage roofs, porch roofs, etc.) all types of Green Roof

system build-ups are possible. (4)

b- Roofs with thermal insulation

Depending on the roof construction, specific criteria are to be considered

when planning and installing a roof with thermal insulation. Generally,

the installed thermal insulation must show a sufficient compression

resistance to bear the load of the Green Roof system build-up. (4)

o Non ventilated roof ("warm roof"): Depending on the design load, different types

of Green Roofs are possible. A high-quality vapour barrier should be emphasised

right from the design or planning stage.

o ventilated roof ("cold-roof"): The low load bearing capacity of the upper layer

allows for low weight Green Roof constructions. The cooling effect of the Green Roof

system build-up influences the aeration between the layers of the roof construction.

o Inverted Roof: The thermal insulation for inverted roofs is installed above the

waterproofing, and therefore in an area with variable moisture levels. The sheets and

Figure 10, Roof slope, IGRA

Figure 11, Roof construction, IGRA

layers used for the Green Roof build-up must not prevent vapour diffusion processes

from the insulation.

o DUO roofs: DUO roofs are roof constructions with additional thermal layers which

act as a drainage element and are credited as thermal insulation. This build-up

combines the advantages of the "warm roof" with those of the inverted roof (4)

1.4.1.1.6. Assumed load

The maximum load bearing capacity of the roof construction

must be considered when installing Green Roof system build-

ups. Simple Extensive Green Roofs weigh between 60-150

kg/m2 depending on the thickness of the Green Roof system

build-up. On most gravel roofs, once the gravel has been

removed, Extensive Green Roof system build-ups can be

installed without increasing the assumed load. (4)

Trees, bushes and construction elements such as pergolas

and walkways cause high point loads and, therefore, have to be

calculated accordingly. (4)

1.4.1.1.7. Wind uplift

A Green Roof must be tight to the roof, especially in cases of strong wind. When

designing and installing the Green Roof, safety measures against wind uplift are to be

considered. (4)

1.4.1.1.8. Roof Drainage

Green Roof systems store a major part of the annual

precipitation and release it to the atmosphere by transpiration.

Depending on the thickness of the Green Roof system build-up

and rain intensity, surplus water may accumulate at certain

times and must be drained off the roof area. The number of

roof outlets and the penetrability factor, or more precisely, the

water retaining capacity of the Green Roof system build-up,

has to be adjusted to the average local precipitation. Roof

outlets are to be kept free of substrate and vegetation and have

to be controllable at all times. For this purpose "inspection

chambers" are installed over the roof outlets. Due to safety precautions, roof areas

with inlayed drainage must always have two drainage outlets or one outlet and one

safety overflow. (4)

1.4.1.1.9. Irrigation

Simple Extensive Green Roofs with drought resistant plant species have to be

irrigated only during planting and installation maintenance over the first year. After

its establishment, the annual rainfall is sufficient to sustain the vegetation. In contrast,

the requirements are more involved for Intensive Green Roofs with lawn, shrubs,

bushes or trees. An adequate number of precisely dimensioned hoses with automatic

irrigation units make plant maintenance during drought periods more manageable. In

Figure 12, Assumed load, IGRA

Figure 13, Roof Drainage, IGRA

order to lower the consumption of drinking water, roof gardens can also be irrigated

with cistern water. (4)

1.4.1.1.10. Access to the roof

Access to the roof has to be guaranteed throughout the installation

and for annual maintenance and service of the Green Roof. (4)

1.4.1.1.11. Additional functions

Green Roof system build-ups can improve the environmental and

energy balances of the roof:

Green Roof system-build ups with thermal insulating

properties (according to building approval) can be used for energy saving

purposes.

The combination of Green Roofs and solar power leads to a higher efficiency

of the solar module.

Rainwater run-off from Green Roofs can be stored in cisterns for additional

use. In cases where the water is used within the building, the colouring of the

water, due to the system substrate, has to be taken into account.

Green Roofs can also be applied for various uses if the structural engineering

and the accident prevention measures allow for it. The roofs can be used for

crop growing, recreational gardens, roof cafs or leisure and sporting facilities. (4)

PART 2: CASE STUDY

2.1. International Case Studies

2.1.1. City Scale: Quantifying air pollution removal by green roofs in

Chicago

2.1.1.1. Abstract

The level of air pollution removal by green roofs in Chicago was quantified

using a dry deposition model. The result showed that a total of 1675 kg of air

pollutants was removed by 19.8 ha (198,000 sq.m) of green roofs in one year

with O3 accounting for 52% of the total, NO2 (27%), PM10 (14%), and SO2

(7%). The highest level of air pollution removal occurred in May and the lowest

in February. The annual removal per hectare of green roof was 85 kg 1 1. The amount of pollutants removed would increase to 2046.89 metric ton if all

rooftops in Chicago were covered with intensive green roofs. Although costly,

the installation of green roofs could be justified in the long run if the

environmental benefits were considered. The green roof can be used to

supplement the use of urban trees in air pollution control, especially in situations

where land and public funds are not readily available. (9)

2.1.1.2. Study Site

Figure 14, Access to the roof, IGRA

This study took place in Chicago, Illinois, which is located along the

southwest shore of Lake Michigan. The total area of the city is 588.3 sq. km.

Chicago is the third most populous city in the U.S with a population of 2.9

million in 2000. According to American Lung Association (ALA 2007), over 2

million people in Chicago were at heightened risk for health problems resulting

from acute exposure to O3 and particulate matters. (9)

Chicago is ranked number one in terms of total area of installed green roofs

among North American cities. According to Taylor (2007), green roofs were

installed on 300 buildings resulting in a total area of 27.87 ha by June 2007. (9)

2.1.1.3. Survey of green roofs in Chicago A request for information was submitted to Chicagos Department of

Environment for a list of green roofs resulting in a list of 170 green roofs. Two

steps were taken to verify the list. First, information including the address of the

green roof, type of the green roof, size, and the date it was completed was

gathered from various sources. We then searched the address of each green roof

through an image database hosted by Pictometry International Crop.

Digital aerial photographs covering Chicago were taken by Pictometry

International Corp in July 2006. Because the photographs have a ground

resolution of 16 cm and were taken from multiple angles, the location, size, type

of the green roof, and the type of building could be clearly interpreted.

For each green roof, the area of grass, trees, and other surfaces was measured and

the percentage to the total area was calculated. Pictometry software allows users

to directly measure distances and areas on those georeferenced images. The error

margin of the measurement was estimated to be 1% or smaller (Federal

Emergency Management Agency, 2005). (9)

2.1.1.4. Removal of air pollutants by green roofs

In this study, a big-leaf resistance model was used to quantify the dry deposition

of air pollutants. The structure of the model and how the input parameters were

fitted are explained below. (9)

The removal of a particular air pollutant at a given place over a certain time

period was calculated as (Nowak, 1994):

Q = F x L x T (1)

Where Q is the amount of a particular air pollutant removed by certain area of

green roofs in a certain time period (g), F is the pollutant flux ( 21), L is

the total area of green roof (2), and T is the time period (sec). Table 1 shows

different vegetation types with their average heights.

Figure 15 Concentrations of criteria air pollutants in Chicago between August

Hourly air pollution data including NO2, SO2, O3, and PM10 concentration

from an air pollution monitoring station in central Chicago between 8/1/2006 and

7/31/2007 were obtained from the U.S. EPA. Hourly surface meteorology (9)

2.1.1.5. Results

The information about the green roofs is shown in Table 2. Among the 71

green roofs, half had an area larger than 500 m2 and 23 green roofs were larger

than 1000 m2. (9)

Based on the analysis of aerial photographs, the 19.8 ha of green roof

consisted of 63% short grass and other low growing plants, 14% large

herbaceous plants, 11% trees and shrubs, and about 12% various structures and

hard surfaces. The monthly air quality between August 2006 and July 2007 in

Chicago is shown below (Fig. 16).

It can be seen from Fig. 16 that

O3 was the main air pollutant in

Chicago. PM10 ranked second while

the SO2 pollution was low. PM10

and O3 pollution peaked in summer

while SO2 and NO2 peaked in winter. (9)

The monthly mean deposition velocities for air pollutants calculated for

different vegetation types showed a seasonal trend (Table 3). The deposition

velocities for all air pollutants were highest in May and lowest in February. (9)

The modeled monthly uptake of air pollutants by green roofs is shown in

table-3

The total air pollution removal by 19.8

ha of green roofs was 1675 kg between

August 2006 and July 2007. If the reported

27.87 ha of green roofs were all completed

and had the same ratio of extensive vs.

intensive green roofs, the air pollutants

removed could reach 2388 kg. (9)

Among the four air pollutants, the

uptake of O3 was the largest, 52% of the

total uptake followed by NO2 (27%), PM10

(14%), and SO2 (7%). Seasonally, the highest

uptake occurred in May and the lowest in

February. The annual removal rate among different vegetation types is compared in

Table 4. (9)

If all remaining roofs in Chicago were planted with intensive green roofs, the

direct removal of air pollutants could reach as high as 2046.89 metric tons,

assuming the same level of air pollution as

20062007. (9)

2.1.1.6. Conclusion

If this case study proved that a total of 1675 kg

of air pollutants were removed by 198,000 sq.m.

extensive and intensive green roofs in one year;

it can be concluded that for a 200 sq.m. green

roof, 1.66 kg of air pollutants can be removed.

2.1.2. Building Scale: Seattle City Hall, Seattle, WA

2.1.2.1. About the Project

The Seattle City Hall achieved a Gold

LEED rating from the US Green Building Council. The City Hall building is divided into

two components: Council Chambers and

Mayor/Council/Staff offices.

Seattle contains urban habitat of endangered

wild salmon species, and so innovative storm-

water management practices are considered to

be a component of salmon-friendly design. The City Hall green roof was designed to decrease combined sewer overflows,

decrease peak flows, and improve storm-water runoff water quality. Another

ecological function of the green roof is the reduction of solar and heat reflection

on the adjacent taller wall of the buildings north portion. (8)

2.1.2.2. Green Roof Design

The 13,200 sq.ft. roof is planted with 5,600 pots of sedums, including varieties

such as Sedum reflexum and 8,400 pots of fescue and 8,400 pots of June Grass.

The runoff from the roof goes into a 30,000 cubic foot rainwater collection

cistern. This water is then used for toilet flushing and irrigation of other

landscaping. (8)

Figure 16, City Hall Green Roof

2.1.2.3. Green Roof Characteristics

2.1.2.4. Green Roof Cross Section & Details

a) Membrane Base Hot fluidapplied rubberized asphalt membrane, layer of spun-bounded polyester fabric reinforcing

sheet, 60 mm thick uncured

neoprene flashing. (8)

b) Root barrier/ protection course A polyethylene sheet, Root Stop

WSF40, was rolled out over the

assembly as a root barrier. Over

the root barrier, STYROFOAM

closed cell, extruded

polystyrene was applied to

provide the required thermal

value. (8)

c) Rigid Insulation

Extruded polystyrene rigid foam insulation board, compressive strength of

60 psi max., water absorption by volume 0.1%, R-5 per inch and free of

HCFC blowing agents. (8)

d) Water Retention/Drainage Panel

Three-dimensional, 100% recycled polyethylene providing water storage,

drainage, and aeration for soil substrate with non-woven polymeric

geotextile fabric, minimum 0.40 gallons per square foot water

containment. (8)

Existing Roof/ New Roof: New Roof

Green Roof Area 13,200 square feet

Green Roof Type Extensive

Green Roof System American Hydrotech Inc.

Accessibility Maintenance only

Installation season Fall 2003

Establishment Period Six months

Slope of existing Roof Flat

Soil Mix/ depth 6 inches

Plant Type Drought tolerant plants

Irrigation Yes

Structural Load 50 lbs/sq.ft

Cost $2/sqft

Figure 17(Green Roof Cross Section, King County Roof Case Study Reports)

e) Filter fabric Systemfilter SF non-woven, polymeric, geotextile fabric (8)

f) Soil mix

The engineered soil mix used for the City Hall garden roof included

pumice, sand, compost and nutrients. (8)

g) Plants used (8)

Festuca brachyphylla / Pt. Joe Fescue Koeleria macranthe Barkol / June Grass Sedum reflexum

Sedum spectabile Frosty Morn Sedum spurium John Creech Sedum Vera Jamieson

2.1.2.5. Irrigation & Maintenance Procedures

The current irrigation schedule is once a week for 45 minutes during summer.

The irrigation system designed for the project landscape was not adequate to

support the plants during the establishment period. This system was later

supplemented with more sprinkler heads for adequate watering of plants.

The water from the green roof goes into a storage tank and is reused for toilet

flushing. Therefore no fertilizers are being used in order to prevent water

contamination.

Because of the large amount of weeds growing on the roof, regular

maintenance is required. The weeds are wind-blown or dropped by birds.

Several weeds such as clover leaf, dandelion and black berries are pervasive on

the roof. This summer 50 to 60% of the roof was covered with leaf clovers.

Clovers can smother other plants causing them to rot and die. (8)

2.1.2.6. Challenges

a) No operations and maintenance manual exists that describes the

maintenance and irrigation requirements for the roof. (8)

b) The maintenance staff time varies from 12 to 15 hours a week for the green roof on this project. (8)

c) The intent was to irrigate the roof for just the first year. However, certain plant types, such as Blue Fescue, require irrigation in the summers or else

they turn brown. These plants spring up again with the rain, however. The

building visitors and users complain about the aesthetics of the roof if the

roof is brown. (8)

d) Access to the roof is through a small room that has a vertical ladder and a hatch on top that opens onto the roof. It is very difficult for the

maintenance staff to carry tools and weeds through this access. The

gardener had to retrofit a pulley to take things up and down. (8)

e) The project was designed to collect rainwater from the roof and reuse it for flushing toilets. However, the water from the conventional roof and

the green roof go to a single drain and the water is yellow in color

because of the green roof soil. This discolored water resulted in a lot of

complaints from the building occupants. (8)

PART 3: GUIDELINES AND RECOMMENDATIONS 3. 3.1. Guidelines for local Green Roofs

a) Roof substructure Reinforced concrete is most widely used in the residential buildings in

Cairo. A check for load bearing capacity is essential before building the

green roof.

b) Water proofing water proofing must meet the requirements for the root resistance test or else

an extra root barrier has to be installed

c) Upstand height

Upstand height for adjacent building parts and penetrations: minimum of 150 mm (6 in).

Upstand height for roof edges: minimum of 100 mm (4 in).

d) Roof slope Slope must not be greater than 10 degrees

e) Assumed loads Simple extensive green roofs weigh between 60-150 kg/m2. On most gravel

roofs, once the gravel has been removed, Extensive Green Roof can be

installed without increasing the assumed load

f) Roof Drainage Green Roof systems store a major part of the annual precipitation and

release it to the atmosphere by transpiration. Because Cairo has very low

rain intensity, number of roof outlets doesnt have to be much but an inspection chamber has to be placed over them for maintenance.

g) Irrigation Simple Extensive Green Roofs with drought resistant plant species have to

be irrigated only during planting and installation maintenance over the first

year. For Intensive Green Roofs, An adequate number of precisely

dimensioned hoses with automatic irrigation units make plant maintenance

during drought periods more manageable.

h) Fire Prevention 50 cm vegetation free zones at every opening

i) Access to the roof Access to the roof has to be guaranteed throughout the installation and for

annual maintenance and service of the Green Roof

PART 4: APPLICATION OF THE GUIDELINES ON A

LOCAL CASE 4.1. Local Application (Building Scale)

The selected local application is a residential building located in Nasr City, Cairo with a roof area of 400 m2 and will be planted with an extensive Green Roof. Using the above guidelines, the schematic section in figure 19a was drawn for this application.

4.1.1. Before and After

In figure 20, it can be noticed that many modifications were made to the building including:

a) The actual building roof was covered by cement tiles which were removed to reduce the dead load and add the green roof safely.

b) For insurance that the roots will not penetrate the water insulation, an extra protection board was installed on the concrete slab.

c) Insulation and water drainage layers were installed. d) Filter Fabric and soil mix which included sand, compost and nutrients.

e) A roof access room was built and an automatic irrigation system for irrigating the plants for the scarcity of rain in Cairo, short grass, shrubs and small plantings were planted.

Figure 19b (38, Abdullah Ben Taher St., Nasr City) Google Earth Figure 19a(Schematic section)

Figure 20(3D rendering for building no. 38 before and after building green roof using 3ds max)

4.2. Local Application (Urban Scale)

Taking Building no.38 as a prototype for Green Roofs in Cairo, the research will try to repeat this prototype allover a specific land in Nasr City which is red shaded in fig.21. The area is bordered by Abo Dawoud Al-Zahery St., Hassan Mamon St., Mustafa Al-Nahhas St., and Abbas Al-Akkad St.

4.2.1. Before and After

Figure 21(selected Area in Nasr city; 1,300,000 m2) Figure 22 (3d rendering for Building no. 38, the prototype)

Figure 23 (3d rendering showing the buildings in the selected area before and after creating the Green Roofs)

The total area of the selected land is 1,300,000 m2. If it can be assumed that the average area of a single building is 500m2, and the number of buildings is 1400 buildings then: 1400x500=700,000 m2 The total area of green roofs can be assumed to be 80% of total roof areas which can be calculated as: 700,000x0.8= 560,000 m2

4.3. Conclusion As it was concluded from Chicago case study, for every 200m2 of green roofs, 1.66 kg of pollutants are removed. The total removal of pollutants can be calculated as: (560,000/200) x 1.66= 4648kg This means that 4648kg of pollutants can be removed annually by creating extensive green roofs all over the selected area in Cairo.

REFERENCES

(1) Dr. Salah Hassanein, Air Pollution in Cairo - The Cost Arab World Books

Articles 11-2010 http://www.arabworldbooks.com/articles1.html

(2) Green Roofs Benefits, International Green Roof Association

11-2010, http://www.igra-world.com/benefits/index.php

(3) Types of Green Roofs, International Green Roof Association

11-2010, http://www.igra-world.com/types_of_green_roofs/index.php

(4) Green Roofs Engineering, International Green Roof Association

11-2010, http://www.igra-world.com/engineering/index.php

(5) Air Pollution, 12-2010,

http://library.thinkquest.org/26026/Economics/pollution_problems_in_the_

thir.html

(6) Causes of Air Pollution, 12-2010

http://library.thinkquest.org/26026/Environmental_Problems/air_pollution_

-_causes.html

(7) Smog, 12-2010

http://library.thinkquest.org/26026/Environmental_Problems/smog.html

(8) Seattle City Hall, 11-2010

http://www.seattle.gov/dpd/cms/groups/pan/@pan/@sustainableblding/d

ocuments/web_informational/dpdp_020117.pdf

(9) Removal of air pollutants by green roofs, 12-2010

http://www.slrss.cn/download/08_SCI/Quantifying%20air%20pollution%20r

emoval%20by%20green%20roofs%20in%20Chicago.pdf