Department of Civil Engineering

A SEMINAR REPORT ON

GREEN ROOFS

Submitted in partial fulfillment of the requirements for the award of the degree of BACHELOR OF TECHNOLOGY In CIVIL ENGINEERING

Submitted by

AJAY V JOSEPH Register No:10001913 Seventh Semester

Department of Civil Engineering Amal Jyothi College of Engineering Kanjirappally, Kerala – 686518 Month & Year

Affiliated to Mahatma Gandhi University

DEPARTMENT OF CIVIL ENGINEERING AMAL JYOTHI COLLEGEOF ENGINEERING KANJIRAPPALLY

CERTIFICATE

This is to certify that the seminar report titled “ GREEN ROOFS” submitted by AJAY V JOSEPH to Department of Civil Engineering, Amal Jyothi College of Engineering, Kanjirappally, as partial fulfillment for the award of degree B.Tech in Civil Engineering is a bonafide work undertaken under my supervision.

HOD

Guide

Prof. Sr. Claramma Rosary

Name: Libi P Markose

Date:

ABSTRACT

Green roof infrastructure promises to become an increasingly important option for building owners and community planners. As we move into the 21st century, green roofs can address many of the challenges facing urban residents. Life cycle costing indicates that green roofs cost the same or less than conventional roofing and they are an investment which provides a significant number of social, environmental and economic benefits that are both public and private in nature. This seminar report is an attempt to explain about green roof, it’s types, systems, components, looks at costs, and benefits that could result out of it.

ACKNOWLEDGEMENT

I take this opportunity to express my deep sense of gratitude and sincere thanks to all who helped me to complete the work successfully .My first and foremost thanks goes to God Almighty who showered his immense blessings on my effort. I would like to express my sincere gratitude to Sr. Claramma Rosary (Head of the department), for her support and co-operation. I am deeply indebted to my guide, Ms. Libi P Markose (Asst. Professor, Department of Civil Engineering) for her excellent guidance, constant encouragement, suggestions and constructive feedback in the completion of the seminar. I also thank Mrs. Mini Mathew (Asst. Professor, Department of Civil Engineering) for extending her valuable support for the seminar. I wish to express my sincere gratitude towards the staff members of our Department and Department Library. Finally I thank my parents, all my friends, near and dear ones who directly and indirectly contributed to the successful completion of this work.

AJAY V JOSEPH

Department of Civil Engineering 2013

CONTENTS

Page No.

1. Introduction

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2. Green Roof Types and Systems

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2.1. Green Roof Types

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2.1.1 Extensive Green Roof

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2.1.2 Intensive Green Roof

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2.2. Green Roof Systems

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2.2.1 Modular Systems

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2.2.2 Loose Laid / Built-Up Systems

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3. Green Roof Components

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3.1. Waterproofing Membrane

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3.2. Root Barrier

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3.3. Drainage

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3.4. Filter Fabric

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3.5. Growth Media

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3.6. Plants

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4. Green roof maintenance

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4.1. Membrane Maintenance

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4.2. Drain Inspection

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4.3. Surrounds and Rooftop Structures

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4.4. Plants and Growing Medium

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4.5. Irrigation

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5. Cost

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6. The Benefits of Green Roof

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6.1. Reduce Urban Heat Island Effect

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6.2. Energy Efficiency

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6.3. Improved Air Quality

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6.4. Aesthetics and New Amenity

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6.5. Storm Water Management

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6.6. Fire Prevention

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6.7. Biodiversity and Habitat Preservation

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6.8. Urban Agriculture

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6.9. Noise Attenuation

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7. Disadvantages

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8. Green Roof Buildings

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8.1. CII Sohrabji Godrej Green Business Centre, Hyderabad 16 8.2. Millennium Park, Chicago

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8.3. Vancouver Convention Centre, Canada

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9. Case Study: City Hall, Chicago

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9.1. Introduction

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9.2. Planning the Green Roof

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9.3. Conclusions from the study

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10. Summary

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References Appendix: Questions and Answers Amal Jyothi College of Engineering

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LIST OF FIGURES Sl no.

TITLE

Page No.

Figure.1.

Extensive Green Roof

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Figure.2

Intensive Green Roof

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Figure.3.

Components of Green Roof

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Figure.4.

CII Sohrabji Godrej Green Business Centre

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Figure.5.

Millennium Park

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Figure.6.

Vancouver Convention Centre, Canada

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Figure.7.

City Hall, Chicago

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Figure.8.

Top view of City Hall, Chicago

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Figure.9.

Components of Green Roof

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1. Introduction

If buildings sprang up suddenly out of the ground like mushrooms, their rooftops would be covered with a layer of soil and plants. That’s not how humans build, of course. Instead we scrape away the earth, erect the structure itself, and cap it with a rainproof, presumably forgettable, roof. It’s tempting to say that the roofscape of every city on this planet is a man-made desert, except that a desert is a living habitat. The truth is harsher. The urban roofscape is a little like hell—a lifeless place of bituminous surfaces, violent temperature contrasts, bitter winds, and an antipathy to water. Green roofs are defined as a living system that is an extension of a roof. This green space can be below, at or above grade involving systems where plants are not planted in the ‘ground’. A green roof system contains a high quality waterproofing membrane and root barrier system, drainage system, filter fabric, a lightweight growing medium, and plants. Green roof systems can be modular layered systems already prepared in trays, including drainage layers, growing media and plants, or, each component of the system can be installed separately on top of the structure.


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2. Green Roof Types and Systems 2.1

Green Roof types

2.1.1 Extensive Green Roof Extensive green roofs mimic nature and require very little external input for either maintenance or propagation. The plants, normally mosses, succulents, herbaceous plants and grasses, are carefully chosen to be able to regenerate and maintain themselves over long periods of time, as well as to withstand the harsh conditions on rooftops such as exposure to extreme cold, heat, drought and wind. Extensive green roofs have a relatively shallow layer of lightweight growing medium that is low in organic material and high in mineral substrate. In general, the growing medium is about 2 – 15 cm thick with a saturated system pressure of 0.5 – 3.0 kPa. Because of the low structural capacity required, extensive systems may not require structural upgrades and therefore are particularly suited for retrofits. They typically do not require irrigation, and are usually inaccessible to the public. (Fig.1)

Figure 1. Extensive Green Roof

2.1.1 Intensive Green Roof Intensive green roofs in comparison to extensive are usually constructed where public access and recreational use are a primary function. These roofs have a deeper growing medium than extensive roofs, with a higher organic content, and can support lawns, large plants, trees and outdoor furnishings. The growing medium depth ranges from 20 cm to 100 cm or more, with saturated system pressures of over 4 kPa. Because of the high structural capacity involved, intensive green roofs are almost always incorporated in the Amal Jyothi College of Engineering

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Department of Civil Engineering 2013 building plan at the design stage as structural upgrade afterwards can be expensive and impractical. Like gardens on the ground, intensive systems require ongoing maintenance, including regular irrigation, weeding and fertilization. (Fig 2)

Figure 2. Intensive Green Roof

2.2 Green Roof Systems Green roofs are typically modular (trays or continuous mat) or loose laid/built-up.

2.2.1 Modular Systems

Modular system consist of typically readymade flexible (vegetative mats into a woven fabric) or firm (metal or recycled plastic) trays or modules. These ready-made modules typically have the essential components of the system already combined (except irrigation), including: Drainage, Growing medium, Root barrier layer, Borders, Plants.

2.2.2 Loose Laid / Built-Up Systems

Loose laid systems are separate installation of green roof components. These increase design opportunities, biodiversity and experience. These typically use various subcontractors for design and installation.


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3. Green Roof Components A green roof is a complex system of layers that work in conjunction to provide aesthetic and performance goals. When designing a green roof, it is critical to make educated and informed decisions about the inclusion or exclusion of certain layers of the system. Although sometimes not composed, designed and built in this particular order for various reasons such as performance, site constraints or cost, this section of the document will expand on each layer in the following order:

Fig.3. Components of Green Roof

3.1. Waterproofing Membrane The most critical component of a green roof, or any roof, is its ability to prevent water from entering the building. The waterproofing membrane prohibits water from penetrating the building while also facilitating run-off. It is comprised of a material able to withstand hydrostatic pressure (ponding water) for extended periods of time.

Common choices for waterproofing material are modified bitumen, rubberized asphalt, polyvinyl chloride (PVC), ethylene propylene diene monomer (EPDM, a water resistant rubber, and thermoplastic polyolefin (TPO).


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3.2. Root Barrier The root barrier protects the integrity of the waterproofing membrane by preventing unwanted plant roots from reaching the layer and the supporting structure. Because root systems in semi-arid and arid climates tend to be aggressive for the purpose of survival, this layer is extremely important for any green roof.

Types of root barriers include High density polyethylene (HDPE) (various thicknesses) Impregnated copper hydroxide, Impervious concrete, Poly Vinyl Chloride.

3.3. Drainage The drainage layer is a network of sheets, pipes and drains intended to remove additional water that might find its way to the waterproofing layer. It allows enough moisture to remain and sustain plant life. Additional functions may be to act as an additional layer to the root barrier or membrane and augment the compressive strength and thermal capacity of the insulation layer.

Aggregate choices include various granular media, such as gravel. Synthetic types include high-density plastics, rigid and non-rigid foam boards, and modular units of plastic or metal. A non biodegradable filter fabric is placed on top of the drainage material to prevent fine growth media particles from clogging the drains.

3.4. Filter Fabric Filter fabric is a lightweight and durable material that prevents the infiltration of particulates into the drainage layer and behaves as a protective barrier to prevent clogging in the drainage system. Types of filter fabric include Landscape fabric, non-woven, non-biodegradable, Polyester fiber matting, Polypropylene-polyethylene matting.


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3.5. Growth Media This layer is critical to the long-term success of a living roof. Growth media consists of extremely lightweight engineered soil substrate that has as a high ratio of inorganic minerals to organic material. The properties necessary for growth media include good drainage and aeration; water holding capacity; and nutrient holding or cation exchange capacity (CEC). The growth media must not settle (lose volume) or blow away, and must provide stability for the plants. Inorganic components in the growth media could include materials such as expanded slate and shale, extruded clay, crushed recycled bricks and concrete rubble, lava, rock wool, and perlite. Much smaller percentages of organic matter may be added, such as well-rotted humus material (e.g., hen manure, guano, or mushroom compost). This can be augmented with organic fibrous material and a small amount of clay particles.

3.6. Plants The vegetation layer is the most vital and exciting part of the green roof, and judicious research into each project’s appropriate plant material selection is essential. After assessing geographic and climatic considerations (such as cold and heat tolerances, rainfall, humidity, wind, and sun/shade exposure), the depth of the growth substrate will actually determine the choice of plants.

A much larger variety of plant selections is available for intensive roofscapes. For extensive green roofs, appropriate plants are types that can grow in harsh environmental conditions with very thin growing substrates like those found in crevices and rocks, dry meadows, edges of woods, and steppes.


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4. Green roof maintenance A maintenance plan should be established prior to the completion of all new green roofs. Both plant maintenance and inspection of membrane flashing points and various roof structural elements are regularly required. Green roof plants require regular attention and care including irrigation, weeding, fertilizing, pruning and replanting. Some maintenance procedures should be scheduled after events (such as floods and storms) while others can be scheduled according to seasonal events (such as germination period, season for certain invasive and unwanted species and in the fall after leaf fall).

4.1. Membrane Maintenance The waterproofing roof membrane is the most vital aspect of green roof longevity and success. There are areas where regular inspections are advised at least three times per year. These include all joints, borders or other features penetrating the roof, such as all abutting vertical walls, roof vent pipes, outlets, air conditioning units and perimeter areas.

4.2. Drain Inspection Plants are susceptible to insufficient drainage in the soil. If too much water is present and unable to drain, the plants will drown or rot. Regular inspections of drains should take place approximately three times per year, with additional inspections advised after major weather events. All drains must remain free of vegetation and foreign objects. Inspection of drainage flow paths is crucial because of the severe consequences of drainage backups. In order to allow for regular inspections and maintenance, every drain on a green roof must remain permanently accessible. Roof outlets, drains, interior gutters, and emergency overflows should be kept free from obstruction by either providing a drainage barrier (e.g., a gravel barrier between the green roof and the emergency overflows) or they should be equipped with an inspection shaft. Amal Jyothi College of Engineering

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Department of Civil Engineering 2013 If an under-drain system is used, provide a clean-out for both inspection and maintenance. There is potential over the long term for the roof under-drain system to become clogged and the ability to access the under drain system for clean-out is imperative.

4.3. Surrounds and Rooftop Structures Surrounds must be designed and installed with consideration for the structural integrity of the roof membrane and for water drainage. Drainage outlets may be installed at the foot of the surrounds, depending on layout of the roof regarding paved and vegetated areas. Vertical components rising from the main structure such as walls, vents, HVAC systems and electrical boxes should not generate pressure on any part of the roof membrane, which could potentially over time compromise the membrane and cause water ponding or leaks. Regular inspections should take place around these vertical components to keep them clear of debris. These inspections may be scheduled at the same time as drain inspections.

4.4. Plants and Growing Medium Care of the plants on the green roof will require the most attention during the critical establishment phase, which lasts approximately 18-24. New green roofs will succeed with proper plant selection and care.

Watering and weeding is especially important during the first two years of the green roof. The roof requires careful weeding before weed seeds are produced. Sterile plant medium may also contain weed seeds. A certain amount of weed growth is inevitable, as seeds arrive on the roof via wind, birds and shoes. For overall health of the green roof, weeds should be identified and removed early and often.


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4.5. Irrigation The irrigation system needs to be flushed out completely before the first winter freeze. It is recommended to check emitters and spray heads at spring start-up and throughout the season. If you have a drip irrigation system, hand watering can be used during the plant establishing period. Installing or adding a main line hose spicket might be considered for additional hand watering during establishment periods, during dry seasons and during fall and spring, while irrigation is off and for cleaning.


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5. Cost In the past, the cost related to the installation of a green roof has been high. As this industry develops, the initial cost of implementation may be reduced with standardized practices and programs that allow consistent availability of products, suppliers and installers.

Major variables that influence the overall project cost are retrofit versus new construction, potential structural upgrades and/or re-roofing, type of green roof - shallow or deeper (extensive versus intensive), accessibility, maintenance and it’s components.

It has been seen through various studies that initial installation cost of intensive green roof will range from Rs.2500 to Rs.3800 per sqft and for extensive from Rs.800 to Rs.1500 per sqft.


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6. The Benefits of Green Roof Green roofs offer multiple benefits to urban areas. While some of the benefits can be quantified and assigned financial values, other benefits are intangible and their values are difficult to quantify objectively. This section of the report summarizes the major benefits of green roofs regardless of when, to whom, or with what value the benefit accrues.

6.1 Reduce Urban Heat Island Effect The urban heat island (UHI) refers to the higher air temperature in the city centre compared to the surrounding natural landscape. The lack of vegetation cover and natural landscape in the city means the city experiences less evaporative cooling and therefore increases the air temperature. Dark building materials such as rooftops and pavements further absorb and trap solar heat and these factors combine to contribute to the urban heat island.

The inclusion of green roofs can reduce UHI by introducing vegetation onto some of the hottest surfaces in urban areas. By means of evapotranspiration and simply covering the roof with a less absorbing surface, temperatures can be reduced.

6.2 Energy Efficiency Green roofs increase the energy efficiency of the building envelope and reduce a building’s energy demand on space conditioning and therefore greenhouse gas emissions, through direct shading of the roof, evapotranspiration and improved insulation values.

Green roofs are particularly effective in reducing heat entry into the building in the summer. The plants shade and cool the roof. The insulation value is in both the plants and the growing medium. Water in the plants and the growing medium evaporates and further cools the roof. The growing medium also acts as a thermal mass that stores solar energy


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Department of Civil Engineering 2013 during the day and releases it at night. Green roofs are less effective in preventing heat leaving the building in the winter due to the limits of the same thermal mechanisms.

6.3 Improved Air Quality Plant surfaces adsorb airborne particles and remove them from the air. The particles are washed off the leaves and into the growing substrate during rain events.

Green roofs can reduce summertime peak cooling demand therefore indirectly reducing CO2 emissions from power plants due to lower energy demand. This is particularly important for air quality in regions that generate electricity through coal combustion.

6.4 Aesthetics and New Amenity Rooftops are perhaps the most underutilized space in cities. Green roofs not only make use of this space by providing much needed recreational green space for city dwellers and living space for birds and insects; they often improve the architectural aesthetic of the building, therefore increasing the overall property value. Green roofs help encourage a more thoughtful approach to city planning by increasing amenity and green space, encouraging community gardens and food production and extending commercial and recreational space. The introduction of a green roof into the standard building palette creates a unique and desired quality of visual significance. It has been suggested that including greenery in the cityscape reduces stress and patient recovery time, increases property values and has been linked to a reduction in crime.

6.5 Storm Water Management The amount of impermeable surfaces in an urban environment is directly linked to volume and quality of storm water run-off. Because urban environments tend to have a low percentage of permeable surfaces, a larger volume of storm water is sent through Amal Jyothi College of Engineering

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Department of Civil Engineering 2013 various management components (e.g. pipes, ditches and tunnels) that eventually lead to rivers, streams and lakes. This increase of runoff volume as well as the increased frequency of runoff causes pollution and erosion in our rivers and streams. Green roofs can convert impervious rooftops into pervious surfaces that absorb water and release it slowly over a period of time. Some of the water is taken up by the vegetation and released back to the atmosphere through evapotranspiration. Excess water is discharged from the system to the roof drain.

6.6 Fire Prevention A well designed green roof can be successful in preventing the spread of fire. Though some plants may be less fire resistant than others (such as succulents retaining significant amounts of water versus grasses that seasonally dry out), layers of organic matter and even minimal moisture can be effective in preventing the spread of fire. It is important to maintain and provide appropriate fire breaks to limit flammability on all roofs. All green roofs should be in compliance with local fire codes.

6.7 Biodiversity and Habitat Preservation Urban sprawl has affected the health of ecologic systems by disrupting migration corridors and manipulating the resources and vegetation in natural environments. Green roofs can behave as an intermediate link for migration for species of insects and birds, using the urban environment as stepping stones for wildlife movement. The potential for biodiversity depends on plant species and height, surface variation, food sources and building height.

Extensive green roofs, with their lack of human intervention, are more protected and can become home to sensitive plants that are easily damaged by walking, and to birds species that only nest on the ground. Since the soil on an inaccessible green roof is also less likely to be disturbed, it becomes a safer habitat for insects as well. The deeper the soil the more insect diversity the green roof will support.


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6.8. Urban Agriculture Green roofs can provide secured growing space for gardening and agriculture in urban areas. They have the potential to address the balance between urban spaces for living and growing – an essential component of improving living quality in high density urban areas. Green roofs for food production require little alteration from the standardized system, but a few issues need to be considered such as: - The depth of the growing medium needs to be sufficient for anchoring and sustaining food plants - Waterproofing membrane needs to be sufficiently protected from frequent use of gardening tools - Fertilization may be required to sustain nutrient availability in heavily used growing medium - Safety and quality of produce must be considered

6.9. Noise Attenuation A green roof (and green walls) can reduce the noise level within the building by 40-60 decibels. The thickness, plant type, growing medium and plant coverage can influence the effectiveness of the green roof (and green wall / vertical garden) to reduce noise levels.


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7. Disadvantages Green roof has a higher initial cost. Depending upon the type of green roof, maintenance will be higher. Green roofs also require stronger roof beams to support the layers of the green roof, mostly the soil. One more disadvantage of a green roof is that when they are built in places susceptible to bad weather, such as seismic zones or windy places there is a great chance of the plants not surviving.


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8. Green Roof Buildings 8.1. CII Sohrabji Godrej Green Business Centre, Hyderabad The CII-Sohrabji Godrej Green Business Centre (also known as CII or CIIGBC) earned a LEED® rating of 56 credits and became certified LEED Platinum for New Construction (NC) v 2.0 in 2003 - the first in India and the first outside of the U.S. Vegetated roofs cover 55-60% of the building's roofs, and the remaining portion of the roof is covered by solar photo voltaic with a 24 KW capacity. The 100 to 120 units of power generated per day is fed into the grid meeting 20% of the total energy cost of the building.

Project

Name:

CII-Sohrabji

Godrej

Green Business Centre (CIIGBC) Year: 2003 Owner: Confederation of Indian Industry (CII) Location: Hyderabad, India Building Type: Corporate Type: Extensive System: Custom

Figure 4. CII-Sohrabji Godrej Green

Business Centre (CIIGBC) Size: 11000 sq.ft. Slope: 6% Access: Accessible, Private

"The green roofs on the curvey building are divided into parcels that are separated by parapets. On top of a concrete roof, the green roof system begins its build-up with three layers of waterproofing. The green roof system comprises 2” of sandy soil topped with the same pervious paver blocks used at grade, and overlain with a uniform grass sod. In Amal Jyothi College of Engineering

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Department of Civil Engineering 2013 their appearance and composition, the green roofs are identical to the grassy pedestrian and parking areas at grade.

"All wastewater and runoff generated by the building is recycled by "root zone treatment" where specially selected plants purify and filter the water that irrigates them. Water leaving the “root zone treatment” is directed to one of three ponds, thereafter to be used for domestic purposes. The building achieves a 35 percent reduction of municipally supplied potable water, in part through the use of low-flush toilets and waterless urinals. As part of the zero discharge design, recycled water from the building is used for irrigation and any runoff is directed to percolate at grade. During the dry season, the green roofs are irrigated daily." (Christine Thuring, 2009).

8.2. Millennium Park, Chicago Project Name: Millennium Park Year: 2004 Owner: City of Chicago Location: Chicago, IL, USA Building Type: Park Type: Intensive System: Custom Size: 1067220 sq.ft.

Figure 5. Millennium Park, Chicago

Slope: 1% Access: Accessible, Open to Public

At 24.5 acres, Millennium Park is considered either the largest or one of the largest intensive green roof projects in the world. As it sits at grade over a parking garage, it is considered a


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Department of Civil Engineering 2013 green roof. At a total project cost of $475 million, it incorporates landscape art, full-size trees and a skating rink, the roof covers two parking garages, a transit center and a 1,525seat indoor performance center.

8.3. Vancouver Convention Centre, Canada Project Name: Vancouver Convention Centre Expansion Project Year: 2008 Owner: BC Pavilion Corporation, a Crown corporation Location: Vancouver, B.C., Canada Building Type: Municipal/Government Type: Intensive

Figure 6. Vancouver Convention Centre, Canada

System: Custom Size: 261360 sq.ft. Slope: 56% Access: Inaccessible, Private

The Vancouver Convention Centre is LEED® Platinum certified for new construction by the Canada Green Building Council, the first convention center in the world to receive this highest level of LEED® certification. Built over land and water on some 1,000 piles, the Vancouver Convention Centre Expansion Project was completed in late 2008. In order to ensure that the expansion and existing facility are fully integrated, a glass-walled connector links the facilities, providing delegates with exceptional harbor views as well as a seamless transition. Featuring floor-to-ceiling glass throughout the expansion, the green roof is landscaped with more than 400,000 indigenous plants and grasses from the Gulf Islands, providing natural habitat to birds, insects and small mammals. This unique ecosystem is planted over 12" of growing media, and the vegetated roof is just one of many environmental innovations included in the expansion. Amal Jyothi College of Engineering

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9. Case Study: City Hall, Chicago 9.1 Introduction Chicago is the third largest city in the United States, with a population exceeding 2.8 million. It sits on the shores of Lake Michigan. This green roof is one of the most photographed and publicized green roofs ever. Initiated by Mayor Daley as part of Chicago City Hall Urban Heat Island Initiative project. After extensive planning, construction on the 20,000 square-foot garden began in April 2000. The landscape design followed a formal garden plan instead of the more common meadow-like environment. The project is the first of its kind in the City of Chicago and will be a showcase of the possibilities that can grow out of plans for a green roof. The design includes both extensive and intensive systems.

Figure.7.City Hall, Chicago

Thousands will be able to enjoy the green roof from the many taller buildings that surround City Hall. Scientists are monitoring City Hall’s rooftop garden for its air quality benefits. This includes energy use within the building and temperature readings on top of Amal Jyothi College of Engineering

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Department of Civil Engineering 2013 the roof. For comparison, the adjacent Cook County building, which is the same height and area as City Hall but which has a black tar roof, is monitored. The City also will monitor temperature, rainfall, wind speed, and wind direction. This data will help evaluate the garden itself and help the City advise other rooftop gardeners about what works best. The City Hall green roof is currently, on average year-round, 7 degrees cooler than the surrounding roofs and as much as 30 degrees cooler in the summer. Cooling is done in many ways, the first of which is the reflective property of the plants. In addition the plants help cool the air by evapotranspiration, which happens when the plants release moisture from their leaves. In addition to cooling, the plants serve to filter pollutants from the air and greatly reduce the strain on the stormwater system by holding the water on the roof.

Figure 8.Top view of City Hall, Chicago Roof of the building shared by Chicago City Council and Cook County Council.


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9.2 Planning the GreenRoof Following are the steps in planning the GreenRoof: 9.2.1 Considering the condition of the roof

The most cost-effective time to construct a green roof is when the roof needs to be replaced or newly constructed. This way you can make features, such as a waterproof membrane, a root-resistant layer, or certain containers, part of the new roof. Working with an existing, intact roof is not impossible, but it will mean taking into account the roof’s faults, such as existing leaks, damage, and inability to resist roots and standing water.

Prior to designing and constructing the green roof, first determine if the roof can support the additional weight of soil and plants. A licensed structural engineer or architect is hired to conduct a structural analysis. The purpose is to determine the amount of weight the roof can support at different locations on the roof. The structural capacity largely will dictate the type of green roof that you can build.

An important consideration is access to the roof. In addition to access for the people who will be constructing and enjoying the green roof, you will need to transport materials for construction and maintenance, and may need to consider the need for electricity. Typical access includes stairs or fire escapes. Generally, Chicago’s Building Code requires two separate exit paths. 9.2.2 Determining the weight of the garden and cost

Weight considerations are at the heart of planning a green roof of any type. You must determine the weight of the garden you wish to plant and make sure it does not exceed the structural capacity of the roof. With the structural capacity determined by the licensed architect or structural engineer, an architect or landscape architect


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Department of Civil Engineering 2013 can design the garden. To determine the weight, you must take into account: what system(s) you will use to store water, the growing media and plants you wish to use, the kind of containers you may want, equipment for heating, ventilating and air conditioning, and snow loads. Weight capacity might limit the number of people who may access the roof.

In addition to the cost of the structural analysis and design assistance, your construction budget should include any needed structural or safety improvements, irrigation systems, garden materials, maintenance costs, transportation, and fees associated with any ongoing professional assistance and permits. Green roof systems, cost about 50% more than a conventional roof. An extensive green roof system is generally less costly than an intensive garden. Either kind of green roof system can increase the useful life of your roof by about 50% over a conventional roof because the green roof system layers protect the “hard” roof from exposure to harsh weather.

9.2.3 Designing the Green Roof

Typically, the cross section of a green roof begins (starting from the bottom) with an insulation layer, a waterproof membrane to protect the building from leaks, and a root barrier to prevent roots from penetrating the waterproof membrane. For the waterproof membrane, look for products that can withstand the effects of acids released by some plant roots. A drainage layer, usually made of lightweight gravel, clay, or plastic is next. The drainage layer keeps the growing media aerated in addition to taking care of excess water. Since a green roof system covers the entire roof, drainage points must be accessible from above for maintenance purposes. In some designs, and with certain products, the drainage layer can do double duty, serving to store water for use by the plants at a later time. On top of the drainage layer, a geotextile or filter mat allows water to soak through but prevents erosion of fine soil particles.


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Figure.9. Components of Green Roof Finally, the top layers consist of growing media, plants, and a wind blanket. The growing media is lightweight material that helps with drainage while providing nutrients to the plants. A wind blanket is used to keep the growing media in place until the roots of the plants take hold. The project is irrigated throughout and maintained regularly by crews supervised by horticultural experts from the Chicago Department of Transportation.The City encourages landcaping with native plants as an environmentally beneficial garden design. In addition to providing habitat, native plants usually survive well on rainwater. Still, there may be times during the year when rainfall will be insufficient to supply the water requirements of even drought-tolerant plants. Plans are done to supplement rainfall with irrigation. Examples of irrigation systems include but are not limited to, rainwater storage tanks, drip irrigation systems, moisture sensors to regulate irrigation needs, or hose-bibs for manual watering. The water drainage system is an essential component of any green roof. A key environmental benefit of rooftop gardens is that they absorb rainwater and reduce runoff to sewer systems. Still, any excess water not absorbed by the growing media, used by the Amal Jyothi College of Engineering

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Department of Civil Engineering 2013 plants, or stored by the water storage system must be effectively drained from the rooftop. Failure to do this will create “bathtub” conditions that may cause root rot and disease as well as add significant weight beyond the roof design load. Most gardens should be able to use the existing rooftop drainage system with only minor modifications. Typical drainage systems include gutters, downspouts, drains, and screens or barriers to prevent erosion of the growing media and clogging of the drainage system. Since natural soils are heavy, particularly when wet, rooftop gardeners typically use lightweight growing media consisting of high-quality compost and recycled materials. The purposes of these materials are to be water permeable, to retain water and air, to resist rot, heat, flying sparks, frost and shrinkage, to provide nutrients appropriate to the chosen plants, and to provide a rooting medium. Plants appropriate for extensive green roofs favor poor soils. Generally, the growing media should be as deep and have as great a volume as possible within the constraints of the structural capacity, in order to provide plants with stability in wind and keep the system from becoming too dry. Rooftops can be hostile environments for plants due to the effects of wind, heat, rain, and shadows. Extra insulation may be needed inside and/or outside of planting containers to protect plants from freeze/thaw cycles in winter. A rule of thumb is that wind speed doubles for every ten stories of building height. Windy conditions increase the loss of moisture from growing media and leaves, so drought-tolerant plants often survive best. Many plants, especially native varieties, are suitable and attractive options for rooftop gardeners. Green roofs must be maintained just like any garden, for instance by watering or weeding. The amount of maintenance will depend on the types of plants used and the garden design. Larger plants, shrubs, and trees must be pruned to ensure safety during windy conditions. Drains and gutters must be inspected and cleared more frequently than without a garden, because of the plant material.


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9.2.4 Obtaining Permits Before you begin constructing any kind of green roof in the City of Chicago, you will need to have the Chicago Department of Buildings review your plans, and you will need to obtain the proper permits. Terminology is important. A “rooftop garden” is presumed to mean it will be accessible to people. Thus there will be requirements such as ensuring proper barriers at the edge of the roof, raising exhaust stacks on the roof, providing two exits, or calculating a higher garden weight to account for people. A “green roof” means the garden will not be accessible to people except for occasional maintenance. To obtain a permit, you will need drawings that document the design. If your home is a free-standing single-family house, you may draw the plans yourself. If your building has more than one dwelling unit, or if the building is commercial or industrial, the plans must be prepared by an architect licensed in the state of Illinois.

9.3 Conclusions from the study The City Hall green roof includes both extensive and intensive systems. The green roof contains 20,000 plants in all, consisting of more than 100 varieties, including shrubs, vines, and two trees. The plants are mostly low-maintenance perennials, and honeybees on the roof produce more than 150 pounds of honey every year! Scientists are monitoring City Hall’s rooftop garden for its air quality benefits. This includes energy use within the building and temperature readings on top of the roof. For comparison, the adjacent Cook County building, which is the same height and area as City Hall but which has a black tar roof, is monitored. The City also will monitor temperature, rainfall, wind speed, and wind direction. This data will help evaluate the garden itself and help the City advise other rooftop gardeners about what works best. The City Hall green roof is currently, on average year-round, 7 degrees cooler than the surrounding roofs and as much as 30 degrees cooler in the summer.


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10. Summary As urbanization increases, it is critical to find a balance between human development requirements and environmental concerns. The conventional usability of Green Roof has evolved and acquired a more responsible profile in the environment. In the past, roof spaces were not used as relaxation spaces. In present state as land is becoming scarce in urban areas, storm water drainage problem is growing, and energy prices are increasing for building heating and cooling, green roofs are becoming increasingly viable. Consequently Green Roof technology is one of the potentially viable options for countries with tropical climate. There are more advantages than disadvantages of building green roofs to reduce air pollution. ‘Green roof’ is one such method to minimize the impact of construction, thus improving the environment. Incorporation of green roof in both new and existing structures helps in replacing lost eco habitats in urban areas as well as provides other benefits associated with green spaces. It also provides new opportunities for ‘urban agriculture’. In totality it contributes towards creating ‘liveable’ cities.

References Journals Bhavani Balakrishna, Green Roofing Systems: The Need of the Hour!, The Masterbuilder, Vol.14, No.5,2012,144-152. B.Fabricio & H.Kasun, How green are the green roofs?-lifecycle analysis of green roof materials, Building and environment, Vol. 48, 2012, 57-65. H.F. Castleton, V. Stovin, S.B.M. Beck, J.B. Davison, Green roofs; building energy savings and the potential for retrofit, Vol. 42, 2010, 1582-1591. Code for Design and Construction of Green Roofs in Beijing», DB11/T 281-2005 Standards for Test of Soil Moisture Contents»,GB7172-87 Reclaimed Water Quality for Urban Usage»,GB/T18920-2002


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Department of Civil Engineering 2013 Water Supply and Drainage Project Budget ,China architecture & building press, Beijing,1993 Beijing Construction Projects Budget,Beijing municipal construction committee, Beijing,2001 Water Demand and Water-saving Mode of Roof Greening in Beijing. Research report, BUCEA, 2010

Websites www.greenroofs.com www.wbdg.org www.greenrooftechnology.com www.greenroofstoday.co.uk www.cityofchicago.org


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Appendix: Questions and Answers Qn.1. What do u mean by modified bitumen? Ans: Modified bitumen means bitumen modified with styrene or butadiene. Qn 2. What do u mean by light weight engineered soil substrate? Ans: Engineered soil substrate is not the normal soil. It is artificially prepared soil which consists of necessary minerals that boosts the plant growth and prevents rotting of roots. It should have sufficint amount of water holding capacity also. Qn 2. Which material is used for drainage? Ans: High density plastic sheets or natural gravels are used. Qn 3. What are the maintenances to be done on the growing media? Ans: Weeding, watering and fertilizing.


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