How Green Roofs Can Improve the Urban Environment In Uptown Waterloo

Transcription

1 How Green Roofs Can Improve the Urban Environment In Uptown Waterloo Photos: Top left-hamilton Apartments, Portland; Middle-Seattle Municipal Courthouse; Right-Hamilton Apartments, Portland; bottom-uptown Waterloo. Top photos by authour, bottom photo from KW Film Society. Nada Sutic April, 2003 Nada Sutic Integrating Natural and Urban Environments (519)

2 Table of Contents Table of Contents... i List of Figures...iii Acknowledgements... iv Executive Summary... v CHAPTER 1 INTRODUCTION STUDY OBJECTIVES RATIONALE METHODOLOGY ORGANIZATION OF STUDY... 5 CHAPTER 2 GREEN ROOFS OVERVIEW WHAT ARE GREEN ROOFS? CONVENTIONAL FLAT ROOFS GREEN ROOF SYSTEMS BUILDING GREEN ROOFS GREEN ROOF INDUSTRY GREEN ROOF BENEFITS THAT IMPROVE THE URBAN ENVIRONMENT Stormwater Management Urban Heat Island Reduction Air Quality Improvements Community Greenspace and Aesthetic Value Urban Agriculture PRIVATE BENEFITS OF GREEN ROOFS Energy Efficiency Roof Durability and Life Extension Private Amenity Space Horticultural Therapy Sound Insulation Food Production SUMMARY OF GREEN ROOF BENEFITS BARRIERS TO GREEN ROOF IMPLEMENTATION IN CANADA MOTIVATIONS AND TRENDS CHAPTER 3 THE CITY OF WATERLOO URBAN STRUCTURE PROJECTED GROWTH WATERLOO S ENVIRONMENTAL STRATEGIC PLAN STUDY AREA ROOFSCAPE CHAPTER 4: GREEN ROOFS IN UPTOWN WATERLOO STORMWATER MANAGEMENT Current Situation i

3 4.1.2 Current Responses Improving Stormwater Management in Uptown Waterloo with Green Roofs Alternatives for Stormwater Management URBAN HEAT ISLAND EFFECT Current Situation Current Responses Potential for Green Roofs to Mitigate Waterloo s Urban Heat Island Alternatives For Reducing the Urban Heat Island AIR QUALITY AND SMOG Current Situation Current Responses Potential for Green Roofs to Improve Waterloo s Air Quality Alternatives for Improving Urban Air Quality and Reducing Smog COMMUNITY GREENSPACE AND AESTHETIC VALUE Current Situation Current Responses Green Roofs Providing Community Greenspace and Improving Aesthetics Alternatives for Providing Community Greenspace and Improving Aesthetics URBAN AGRICULTURE Current Situation Current Responses The Role of Green Roofs in Urban Agriculture in Waterloo Alternatives for Urban Agriculture in Uptown Waterloo ENERGY EFFICIENCY Current Situation Current Responses Green Roof Potential to Improve Energy Efficiency in Waterloo Alternatives for Improving Energy Efficiency SUMMARY OF GREEN ROOF BENEFITS IN UPTOWN WATERLOO CHAPTER 5 OVERALL ANALYSIS GREEN ROOF BENEFITS IN WATERLOO CHALLENGES FACING IMPLEMENTATION OF GREEN ROOFS IMPLICATIONS CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS REFERENCES ii

4 List of Tables TABLE 2.1: COMPARISON OF EXTENSIVE AND INTENSIVE GREEN ROOF SYSTEMS... 9 TABLE 2.2: SUMMARY OF GREEN ROOF BENEFITS TABLE 4.1 STORMWATER REACHING UPTOWN WATERLOO TABLE 4.2: PRECIPITATION DATA FOR WATERLOO TABLE 4.3 MONITORING RESULTS FOR LAUREL CREEK SITES NEAR UPTOWN WATERLOO, TABLE 4.4 EXTREME DAILY RAINFALL TABLE 4.5: SUMMARY OF STORMWATER BENEFITS EXAMPLES TABLE 4.6: URBAN HEAT ISLAND IN KITCHENER TABLE 4.7: SUMMARY OF URBAN HEAT ISLAND REDUCTION EXAMPLES TABLE 4.8: MOE AIR QUALITY DATA FOR KITCHENER TABLE 4.9 SUMMARY OF AIR QUALITY IMPROVEMENT EXAMPLES List of Figures FIGURE 2.1: SOPRANATURE SYSTEM FIGURE 2.2: GREENTECH ITM SYSTEM FIGURE 2.3: EFFECT OF RAINFALL ON GREEN ROOF PERFORMANCE FIGURE 2.4: SKETCH OF AN URBAN HEAT ISLAND PROFILE FIGURE 2.5: HEAT FLOW WINTER, NO SNOW FIGURE 2.6: HEAT FLOW WINTER, SNOW COVER FIGURE 2.7: HEAT FLOW SUMMER FIGURE 2.8: LINKAGES BETWEEN BENEFITS THAT RELATE TO COOLING FIGURE 3.1: CITY OF WATERLOO (MEIS-IMAGERY, 2000) FIGURE 3.2: STUDY AREA FIGURE 4.1 LAUREL CREEK WATERSHED FIGURE 4.2: COMPONENTS OF A CONCRETE GRID PAVEMENT FIGURE 4.3: UNI ECO-STONE PAVING SYSTEM FIGURE 4.4 POROUS PAVEMENT AT THE ECOTRUST CENTRE IN PORTLAND FIGURE 4.5: TEMPERATURES AT NRC FACILITY iii

5 Acknowledgements This research began as a senior honours thesis for my undergraduate degree in Environmental Studies. Eight months later, it has become so much more! Thank you to everyone who has helped me to gather information and data, and to those who have provided tours, expertise and support. Special thanks to: Dr. Robert Gibson for his guidance throughout the project, the Green Roofs Steering Committee at the City of Waterloo for support, encouragement and an avenue to grow with green roofs, and all of my friends and family who have supported me throughout the year and on this project. iv

6 Executive Summary Green roofs are a tool well suited to densely developed urban environments, where they can add to the amount of vegetation and greenspace. They are an encouraging addition to urban environments where people, goods, and resources are concentrated and have numerous environmental impacts that can affect human health through poor water quality, poor air quality, urban heat islands, noise, the amount of available green space, and other less direct avenues. This study investigates the benefits of green roofs to determine how they can improve the urban environment. The aim is to understand how valuable they may be as a tool for environmental problems in Uptown Waterloo. The benefits of green roofs accrue to both the community and the building owner. The focus of this study is on the public benefits, such as improved stormwater management capabilities, reduced urban heat island effects, improved air quality, more community greenspace, improved aesthetics and local food production. Although energy efficiency gain is chiefly a private benefit, it is considered because of its importance in encouraging green roof implementation. Other private benefits discussed in Chapter 2, include roof durability and life extension, private amenity space, horticultural therapy, sound insulation and food production. Some of the benefits of green roofs can fall into both the public and private categories. Their categorization is dependent on how green roofs are used. Waterloo s Environmental Strategic Plan The City of Waterloo developed an Environmental Strategic Plan and Council adopted it in The plan outlines what Waterloo s current environmental issues are, based on the findings of the Mayor s Environmental Task Force, and results of the Imagine! Waterloo community visioning process (City of Waterloo, 2002, iv). Six key environmental areas of importance were identified, and strategic actions were defined for each of them. The six areas of importance are: 1) planning and growth, 2) water resources, 3) air quality, 4) energy and resources, 5) environmental awareness, and 6) green space (City of Waterloo, 2002, v). Green rooftops fit into the environmental strategic plan in a few areas, most notably under planning and growth, and air quality. v

7 Green Roofs in Uptown Waterloo To determine how valuable green roofs could be in Uptown Waterloo, the urban issues associated with each public benefit (and energy efficiency) were examined within the Waterloo context. Estimates were made regarding the magnitude of the benefits that could be realized in Uptown Waterloo if 25% of the available flat roof space was greened. Findings were as follows. For stormwater management, green roofs can improve Uptown Waterloo by reducing the rate and volume of runoff, delaying runoff and improving water quality. With 25% of the available flat roof space greened, an annual reduction in volume of runoff of about 11,000m 3 or 11 million litres could be expected. A reduction in the urban heat island effect is also expected in Uptown Waterloo if about 26,000m 2 of roofs contain vegetation. The reduction expected is perhaps 1-2 C in the Uptown Waterloo area. Green roofs in Uptown are not expected to alter temperatures outside of the study area. Some improvement in air quality is also expected as well as a reduction in the incidence of smog. This is due to the lower urban heat island effect, and the tendency for deposition of particulate and some pollutants on vegetation. Increasing the amount of vegetation through the addition of 26,000m 2 of green roofs could remove 5200kg of particulate annually. Energy efficiency gains are also expected, but are specific to individual buildings. Green roofs can provide amenity or community space in Uptown Waterloo and provide space for urban agriculture. For example, if an area the size of Waterloo Town Square was devoted to public space, that would be 17,000m 2 of new public space in the Uptown core. Also, if 10% of the area considered in this study was used for urban agriculture, that would be 2600m 2, about half a football field available for food production. Barriers and Challenges to Implementation of Green Roofs Key challenges facing implementation of green roofs include the high capital cost, predominantly old buildings with unknown structural capacity for green roofs, and limited incentives for builders and developers. The key benefits are public benefits but the costs are borne by the builder. Without public incentives or regulatory requirements, it is difficult to encourage green roof development effectively. Another challenge that is not exclusive to Waterloo is the varying and often unknown structural capacity of older buildings. Some may have the structural capacity to vi

8 add a green roof, but verification can be time-consuming and costly, especially if there are no architectural drawings available. Developers, roofers, homeowners, building owners, and policy makers need to be educated about the value of green roofs and their applicability. One of the most effective ways to prove the usefulness of green roofs is to lead by example showcase the benefits and prove that the concept works. Conclusions and Recommendations Key recommendations for the City of Waterloo to promote green roof implementation in the Uptown area are as follows: Partner with the Region of Waterloo and other local municipalities to undertake studies, carry out educational campaigns, and develop incentive programs in the future. Examine potential policy initiatives at both levels of government to determine what would be effective in encouraging green roofs. Develop an educational campaign in Waterloo to educate developers, builders, the public, City staff and councillors about green roofs. Prepare an inventory of the buildings in Uptown Waterloo. The City should perform an initial assessment of publicly and privately owned buildings within Uptown Waterloo to determine which buildings may be suitable for further investigation and green roofs. Prioritize issues related to the benefits of green roofs. These priorities can be used to develop a green roof development strategy for Uptown Waterloo. For example, is the City more concerned with stormwater or greenspace, and how should implementation proceed given the priorities. Involve the community in green roof development plans and decision making. Involvement of community groups, organizations and individuals is important for the success of green roofs. Promote research within the community. Partner with the local universities and colleges to encourage research. Green roofs are an exciting new technology that can be applied in areas such as Uptown Waterloo where there is little available space for other environmental initiatives. Waterloo has an opportunity to be a leader in this field in Canada by partnering with other municipalities, both locally and elsewhere, to demonstrate the viability of green roofs as a tool for improving urban environments. This in turn should attract the support of other levels of government. vii

9 Chapter 1 Introduction Urban environments concentrate people, goods, and resources and as a result have numerous significant environmental impacts. The built urban system consists of the buildings and physical infrastructure that have been constructed to house and service human activities. The built system affects the natural system through removal of species and habitat, excavation and movement of soil, alteration of hydrological systems and temperature regimes, and so on. While these effects are experienced both in the broader environment and within the urban environment, they are concentrated in the urban environment and can damage human health through poor water quality, poor air quality, urban heat islands, noise, the amount of available green space, and other less direct avenues. One particular problem area is that urban environments have an abundance of impervious surfaces, such as parking lots, roads, sidewalks, and rooftops. These intensify problems relating to stormwater management, the urban heat island effect and poor air quality in most urban centres including the City of Waterloo. Reducing the impervious surface area in a densely developed area can help to mitigate these negative effects. This research will study the urban use of green roofs to determine how they can improve the urban environment in order to understand how valuable they may be as a tool for environmental problems in Uptown Waterloo. It will also provide some discussion about other benefits of green roofs and how they can be realized in Uptown Waterloo. 1.1 Study Objectives To determine how green roofs can help deal with the challenges created by an abundance of impervious surfaces in Uptown Waterloo, and to identify lessons applicable beyond the study boundaries, the project will Provide a general overview of benefits associated with green rooftops. Identify the problems green roofs can mitigate, and confirm their existence. For example, identify the air quality problems in Uptown Waterloo, identify current stormwater practices and problems and confirm the existence of the urban heat island effect. Nada Sutic 1

10 Determine the role that green roofs can play in mitigating the identified urban environmental problems in Uptown Waterloo, by: o assessing the benefits to provide estimates of: improvements in stormwater management, reduction in summer temperatures and the urban heat island, particulate removal, any reduction in SO 2, NO x, and smog reduction if 25% of the available flat roof space in Uptown Waterloo was greened. o Identifying the role of green roofs in providing other less widely quantified benefits, such as energy efficiency *, urban agriculture, community gardening, amenity space, community space and aesthetics. Discuss the value of each of the benefits of green roofs in the context of Uptown Waterloo. That is, how valuable these benefits are when the green roof tool is applied in Waterloo. Identify some of the barriers to implementation in Waterloo and identify future research needs. 1.2 Rationale It is important to find out how green roofs can mitigate urban environmental problems to develop an understanding of how valuable they may be in Uptown Waterloo for dealing with those issues. Green roofs offer a range of benefits including stormwater runoff management, air quality improvement, urban heat island reduction, urban agriculture, greenspace, and energy efficiency. The diversity of benefits that green roofs offer increases their potential importance. Determining the value of green roofs is important to provide some direction regarding whether or not green rooftops are an initiative that should be pursued further in Waterloo. The City of Waterloo is currently interested in gaining support for green roofs, and it has funding to perform a feasibility study with the possibility of a pilot project in the future (Moyer, 2002, 7). Before encouraging widespread implementation of green roofs, it is important to have some understanding of the potential value of this tool in its proposed application, and the feasibility study, a pilot project as well as this research can each play a role in determining that value. This study will provide a first look at the * Energy efficiency can be quantified, but because it is very specific to a building, it is difficult to quantify across a wider area, such as Uptown Waterloo. Nada Sutic 2

11 suitability of some green roof benefits in Uptown Waterloo by examining the current problems or challenges, the current responses and then the opportunity for green roofs to be an effective response. Furthermore, in determining the ability of green roofs to mitigate problems in Uptown Waterloo, it requires that these issues be defined first. The City of Waterloo s Environment First policy, requiring all operations are completed with consideration of the natural environment and using sustainable development principles (City of Waterloo, 2002, 1). During the Imagine! Waterloo * visioning process, regard for the environment was ranked at the top of community values, and air quality, water quality and access to natural areas (greenspace) were key quality of life indicators (City of Waterloo, 2002, 1). Hence, examining the effectiveness of green roofs in improving the urban environment is important in understanding how this tool can improve the quality of life in Uptown Waterloo. 1.3 Methodology A combination of research methods has been used to determine the application of green roofs in Uptown Waterloo. First, a literature review provided an overview of green roof benefits in general. The value of these benefits were then examined in the context of Uptown Waterloo by identifying and examining existing problems that green roofs may be able to address, identifying current responses to those problems and then determining the role that green roofs can play and how effective they can be. Literature review and secondary research determined baselines and current responses to the issues that green roofs can address. Based on the literature, some estimates were made to determine the magnitude of the benefits that could be expected in Uptown Waterloo if 25% of the available flat roof space was greened. Essentially, the purpose is to determine the effectiveness of green roofs in mitigating some Uptown issues. One of the most important issues in evaluating the effectiveness of any tool is to determine a baseline for comparison. For each major benefit of green roofs, a comparison was done between the current situation and the potential situation with widespread implementation of green roofs. Baseline information was gathered from a * In the spring of 2000, the City of Waterloo initiated a visioning process, called Imagine! Waterloo. It was a large public consultation that involved individuals, community groups, businesses and considered over 12,000 comments when forming the City s vision for Nada Sutic 3

12 variety of sources, and sources varied depending on the particular issue being examined. For example, information on stormwater management challenges in Uptown Waterloo was from the City of Waterloo, while data on air quality was from the Ontario Ministry of the Environment. Where possible and relevant, quantitative data was gathered, so that green roof potential can be assessed with quantitative estimates. In addition to determining the current situation, current responses in Waterloo are discussed. Responses focus on municipal policies or programs at both levels of government, the Region of Waterloo and the City of Waterloo. It is important to be aware of current and existing initiatives in order to make realistic and relevant conclusions regarding the potential for green roofs to improve upon those situations in Uptown Waterloo. Also, some alternatives to green roofs for addressing the same issues are identified. This document is organized according to the benefits, and the specific methodology and criteria for assessing the green roof potential for each particular benefit will be discussed in that particular section. Any particular limitations will also be discussed there, but general limitations to the study are discussed below. One of the key limitations to being heavily dependent on literature is that sources may be biased. Some sources are definitely biased towards the benefits of green roofs, and are likely to downplay any negative points. Furthermore, in determining current municipal actions about problems affecting Uptown Waterloo, there may be bias in determining which information gets published or put on a website. As such, critical analysis of all literature is important. Another limitation is regarding any quantitative analysis. There are always assumptions associated with quantitative data, and it is important to be aware of their existence when using the data. Also, in using various sets of data to quantify a benefit, it is important to understand that the numbers arrived at will only be an estimate, and will not be absolute. Moreover, an underlying assumption of this study is that research done elsewhere regarding green roof benefits is applicable to Waterloo, because there is no prior research about green roofs in Waterloo. Being critical and using a diversity of sources are important factors in providing a reliable analysis of the potential for green roofs to be a useful tool in Uptown Waterloo. Nada Sutic 4

13 Also, being aware of the limitations and disadvantages of green roofs is an important factor in determining the role that green roofs can play in improving Uptown Waterloo. The approach of this study is that it examines a particular tool, considers the benefits and uses of the tool, and then considers the problem that those benefits or uses address. Although some might argue that this approach is problematic and even backward, it is simply that the focus of the research is the tool, rather than the specific problems it can address. Instead of being problem-focused research, it focuses on exploring the benefits and issues associated with a tool that is fairly new in the Canadian context, and especially the local Waterloo context. 1.4 Organization of Study The following chapters discuss green roofs in general, provide background about City of Waterloo and then discuss the benefits of green roofs as they apply to the Uptown Waterloo. Chapter 2 explains what green roofs are, how they are constructed and how they differ from conventional roofs. They are described primarily in the context of flat roofs although green roofs can be built on sloping roofs. In Chapter 2, there is also an overview of the state of the green roof industry both in Canada and elsewhere. The core of the chapter is about the benefits of green roofs. There is also discussion of some of the barriers to their implementation in Canada. Background about the City of Waterloo is in Chapter 3, and includes a description of its urban structure and growth potential. The Uptown Waterloo study area and the available flat roof space in it are defined. The core of the study is in Chapter 4. For each major green roof benefit, the problem in Waterloo is defined and described and current responses to those problems are identified. After these two key factors are identified, the potential for green roofs to fit in as part of the overall solution is examined. Conclusions are drawn in each section identifying the potential value of green roofs as a response to the relevant problem. Also, any relevant alternatives or initiatives for dealing with the problem are also discussed briefly. Chapter 4 includes a summary of the benefits of green roofs in Uptown Waterloo. Nada Sutic 5

14 An overall analysis is provided in Chapter 5. Conclusions from each subsection of Chapter 4 will be drawn together to determine the overall potential value of green roofs in Uptown Waterloo. There is also some discussion of spin-off benefits, any negative effects, and opportunities and challenges in Waterloo. In Chapter 6, conclusions are made regarding the effectiveness of green roofs in solving urban environmental problems in Uptown Waterloo. Recommendations are also made regarding future directions for Waterloo and future research needs. Nada Sutic 6

15 Chapter 2 Green Roofs Overview 2.1 What are Green Roofs? Green roofs, also known as eco-roofs, nature roofs, roof greening systems and including roof top gardens, are living, vegetative roofing alternatives (Velazquez, 2002). Green roofs are a way to make use of roof space, which tends to be considered wasted or unusable space. There are several layers of material in a green roof. These other layers on top of a traditional roof actually extend the life of the roof green roofs can last up to twice as long as conventional roofs (Cardinal Group, 2002a). The layers of a typical green roof include: the plants, often specially selected for particular applications, an engineered growing medium, which may not include soil, a landscape or filter cloth to contain the roots and the growing medium, while allowing for water penetration, a specialized drainage layer, sometimes with built-in water reservoirs, the waterproofing / roofing membrane, with an integral root repellent, and the roof structure, with traditional insulation either above or below. (Peck and Kuhn, 2001, 4). Green roofs can be intensive or extensive. An intensive green roof consists of a diversity of plants, including flowering shrubs and trees, and is usually intended for human interaction. As such, it must conform to applicable loading requirements. Intensive roofs are on flat roof surfaces or on a mild slope of up to 3%, and require a soil depth from cm (8-24") (Peck and Kuhn, 2001, 5). Intensive green roofs generally require traditional landscaping maintenance and infrastructure such as water collection cisterns, reservoir boards, irrigation and fertilization (Velazquez, 2002). Essentially, an intensive green roof is an actual rooftop garden, much like a typical garden, except that it happens to be on a roof, and it requires similar regular maintenance and upkeep. Intensive green roofs are more expensive than extensive gardens in both their creation and their maintenance. The growing medium is heavier because of its depth and composition (largely organic and soil based), and this means that the roof must be able to take on the load or be upgraded to bear the load. The saturated weight increase can be between kg/m 2 ( pounds per square foot [lbs/ft 2 ]) (Peck and Kuhn, 2001, 5). The plants are larger and usually more diverse, which makes them more Nada Sutic 7

16 expensive to purchase. Furthermore, intensive green roofs have expensive upkeep because of the regular maintenance requirements. In comparison, extensive green roofs are lightweight, low maintenance and often inaccessible. Velazquez (2002) defines them as lightweight veneer systems of thin layers of drought tolerant self-seeding vegetated roof covers using colorful sedums, grasses, mosses and meadow flowers requiring little or no irrigation, fertilization or maintenance. Drought-resistant and alpine plants are favoured, because of low maintenance requirements. These types of plants are capable of handling a variety of arduous conditions including hot, dry and windy conditions, and they are good at storing water. Native plants seem to perform better than cultivars (Pearce, 2003). Extensive green roofs can be put onto roofs with slopes of up to 33%, and with little or no additional structural support (Velazquez, 2002). The growing medium of most extensive green roofs is a mineral-based mixture of sand, gravel, crushed brick, leca, peat organic matter and some soil, and varies in depth between five and 15 cm (2-6 ) (Peck and Kuhn, 2001, 4). The added wet weight (i.e. fully saturated) to a roof from an extensive roof usually ranges between 72.6 and kg/m 2 (16-35 lbs/ft 2 ) (Peck and Kuhn, 2001, 4). Maintenance for an extensive roof is limited to watering in the first year, so that plants can become established, and occasional weeding of any invasive species in the following years. Extensive roofs are generally not intended as recreational space or to support people, trees or shrubs. There are also green roofs that are semi-intensive, which usually means that they are accessible, have a slightly heavier growing medium than an extensive roof and use typical extensive vegetation as well as perennials and shrubs. Table 2.1 summarizes the differences between extensive and intensive green roofs by listing their respective advantages and disadvantages. Nada Sutic 8

17 Table 2.1: Comparison of Extensive and Intensive Green Roof Systems Brief Description Extensive Green Roof -thin soil, little or no irrigation, stressful condition for plants Advantages lightweight suitable for large areas suitable for roofs with 0-30 slope low maintenance often no need for irrigation and drainage systems relatively little technical expertise needed often suitable for retrofit projects can leave vegetation to develop spontaneously relatively inexpensive looks more natural easier for planning authority to demand green roofs be a condition for planning approvals Disadvantages more limited choice of plants usually no access for recreation or other uses unattractive to some, especially in winter little or no opportunity for food gain Adapted from Peck et al., 1999, 14. Intensive Green Roof -deep soil, irrigation system, better condition for plants greater diversity of plants and soil good insulation properties can simulate a wildlife garden on the ground can be made very attractive often accessible diverse utilization of roof (ie for recreation, growing food, as open space) food gain urban agriculture greater weight loading on roof need for irrigation and drainage systems, hence, greater need for energy water, materials, etc. higher cost more complex systems and expertise required 2.2 Conventional Flat Roofs All roofs have a waterproof membrane to keep precipitation out of the building. A conventional roof puts the waterproofing membrane at the top of the roof where it is subject to environmental forces such as wind, temperature and ultra-violet radiation (Baskaran and Frégeau, 1996). There are also protected membrane roof systems, or inverted roofs, where the membrane is covered by insulation, protecting it from the elements. When a green roof is installed, it acts as a protective barrier for the waterproof membrane, extending its life. A regular flat roof usually needs to be replaced every years (Peck et al., 1999, 30; Baskaran and Frégeau, 1996). A green roof can at least doube the life of a roof (Peck and Kuhn, 2001, 6). One of the factors affecting the life of a roof is the temperature Nada Sutic 9

18 extremes it is subject to. A conventional roof often has pavers or gravel and tar on top of the membrane to provide some protection. Daytime temperatures on a conventional rooftop can range between -20 in winter and 80 C in summer (Peck et al., 1999, 31). A green roof layer 10cm thick can reduce this range to between 10 and 30 C, resulting in less expansion and contraction stress on the membrane, reducing cracking and aging (Peck et al., 1999, 31). A conventional flat roof with gravel weighs about 12 pounds per square foot and costs about $7-8 USD per square foot ($ CAD/m 2 ) to install, while a green roof costs about $15-20 USD per square foot ($ CAD/m 2 ) because of more materials and labour required (Scholz-Barth, 2001, 96). Note that a gravel roof is heavier than some other types of roofs, such as one with a bituminous membrane, but a gravel roof does provide some shading and protection to the membrane underneath (Köhler et al., 2002, 386). Drainage is an important part of any roofing system. Flat or low-slope roofs usually have drains on the roof surface connected to internal downpipes or leaders, which connect to a storm sewer or drainage ditch (Baker, 1972). The number and size of drains is determined by rainfall information for the geographic area and on drainage information for drains and leaders (Baker, 1972). A flat roof is never actually perfectly flat due to structural deflection, and should slope towards the drains. To minimize damage to the waterproofing membrane, water should not be allowed to pool on the roof. Green roofs help to prevent pooling by reducing the amount of water that reaches the roofing membrane. Conventional roofs, particularly the waterproofing membrane are subject to a variety of environmental factors that reduce their lifespan. A green roofing system can extend the life of the membrane significantly and help to reduce the impact of some environmental factors. 2.3 Green Roof Systems As noted above, a green roofing system includes a vapour control layer, thermal insulation, support panel, waterproof and root repellent membrane, drainage layer, filter membrane, growing medium and vegetation. Three illustrative commercial options are Soprema s Sopranature system, Garland s GreenShield system and GreenTech s ITM system. Note that there are several other companies that produce green roof systems, Nada Sutic 10

19 such as American Hydrotech Inc., American Wick Drain Corporation, the Barrett Company, and Roofscapes Inc. Sopranature is a green roof system manufactured by Soprema, a company that the manufactures SBS modified bitumen waterproofing membranes. The Sopranature system, as shown below, has many layers. From the top down, there is vegetation, growing medium, filter medium, drainage layer, root repellant and waterproof membrane, a base sheet, support and insulation. The key elements are described below. Figure 2.1: Sopranature System (Source: Soprema Canada, 2002.) Sopralene Flam Jardin Cap Sheet: 2-ply system that waterproofs the deck and contains root repelling agents. Drainage Layer: facilitates water flow to roof drains. Depending on roof slope it is made of Sopradrain PSE (expanded polystyrene for slopes of less than 5%), or Sopradrain GEO (drainage geotextile for slopes greater than 5%). Filter: non-woven synthetic geotextile is used to prevent fine particles from clogging drainage. Growing Medium: designed and manufactured to achieve optimum water retention, permeability, density and resistance to erosion. It varies with each project. Nada Sutic 11

20 Vegetation: varies with each project, but is selected because of its ability to adapt to extreme weather conditions. In extensive systems, primarily ground covers are used, and in semi-intensive systems, perennials, shrubs and grass are grown in an irrigated garden. (Soprema Canada, 2002) In addition to the layers, a border is used to protect edge and roof structures. Soprema uses a prefabricated border of concrete, metal or wood to contain the vegetated areas, and uses a 500mm band of gravel or pavers to protect the edge and other roof structures (Soprema Canada, 2002). The Garland GreenShield system consists of the same type of layers as the Sopranature system. GreenShield uses a modified multi-ply bitumen system, StressPly EUV, for waterproofing (Garland Company, 2002). According to Garland, it is the strongest and most durable membrane available, and uses post consumer and post industrial recycled materials (2002). Another option for greening a roof is the GreenTech Integrated Turf Management System (ITM). The ITM system is modular, containing its own drainage, and not needing a filter cloth, root repellant membrane or waterproofing layer, because it is entirely encased in plastic containers. Air pruning substitutes the root repellant membrane (as roots are exposed to air, they become ineffective), and water can be channeled from the modules directly to the roof drains (GreenTech, 2002). Figure 2.2: GreenTech ITM System (Source: GreenTech, 2002.) Nada Sutic 12

21 Equally important as the type of roofing system, is the growing medium used. The growing medium affects the weight of the roofing system, and must be suitable for the type of vegetation grown. The growing medium can be specially selected and mixed for any project. It usually involves a mixture of native soil mixed with organic or mineral additives, such as peat, humus, wood chips, sand, lava, or expanded clay (Velazquez, 2002). This helps to achieve optimum water retention, permeability, density and erosion control necessary to support the green roof vegetation (Velzquez, 2002). The growing medium must provide anchorage for the plants, and provide essential nutrients (nitrogen, phosphorous, magnesium, calcium, oxygen). It is also important that the growing medium retain its volume, and does not become compacted or muddy, because this could lead to acidification of the soil. The composition and depth of the growing medium will vary with every green roof to meet different needs. The types of plants used for green roofs can vary. Generally, plants on an extensive green roof are low and hardy, often being from alpine or prairie environments. Indigenous plants are ideal if they are able to withstand a dry climate and high winds, as would be expected on a rooftop. Sedums, sedges and grasses are commonly used. Because intensive roofing systems have more maintenance associated with them, the variety of plants that can be used is greater and includes growing foods. 2.4 Building Green Roofs In addition to the type of green roof, roofing system and growing medium, plants and irrigation needs, green roof builders must consider the structural capacity of a building. The structural capacity needed ranges between 72.6 and kg/m 2 (16-35 lbs/ft 2 ) for an extensive roof, and between 290 and kg/m2 ( lbs/ft 2 ) for an intensive green roof (Peck and Kuhn, 2001). Roofs can be constructed to be even lighter than 16 lbs/ft 2 have been built, such as the Rouge River Ford Manufacturing Plant in Dearborn Michigan, which is about 12lbs/ ft 2. Capacity calculations consider what the weight would be if the growing medium is completely saturated. A roof in Waterloo also needs to be able to handle a particular snow load, plus any infrastructure related load, such as heating, ventilating, and air conditioning (HVAC) units, and meet the Ontario Building Code. According to the Ontario Building Code, the ground snow load for Nada Sutic 13

22 Waterloo is 1.8 kpa (37.5 lbs/ft 2 ) and the ground rain load is 0.4 kpa (8.3 lbs/ft 2 ) (MMAH, 1998, 2-21). The composite load, which considers 60% of the snow load plus the rain load is 1.48 kpa or approximately 31 lbs/ft 2 (MMAH, 1998, 2-21). However, the specified loading due to snow is calculated with attention to several other factors, including a wind exposure factor, a slope factor and an accumulation factor (MMAH, 1998,4-11). Green roofs can be designed to meet a variety of goals and needs. For example, roofs can be specifically designed to achieve stormwater management goals, energy efficiency goals, food production objectives and greenspace initiatives, among other uses. Determining the type of green roof and the planned use of the roof will help to determine the best roofing system, the type of growing medium, the type of plants, and any irrigation needs. 2.5 Green Roof Industry The green roof industry in North America is at an infancy stage. There are only a handful of manufacturers or importers of roofing systems and growing media. Some American companies have partnered with European companies to bring the technology and experience of the Europeans to the USA (Scholz-Barth, 2001, 84). In Canada, the National Research Council and Environment Canada have units involved in green roof research. There is also a group of private and public actors involved in the green roof industry called Green Roofs for Healthy Cities. The group s mandate is to develop a multi-million dollar market for green roof infrastructure products and services in cities across North America in order to take full advantage of the multiple benefits of these proven technologies (Cardinal Group, 2002c). Germany and Japan have fairly well developed markets for green roof industry, and will be discussed briefly here. Britain, Switzerland, Austria and Scandinavia have also moved forward with green roofs, but Germany remains the leader. The following will provide a brief overview of what green roof developments have taken place in Germany, Japan and North America, and why they have occurred. In 1989, Germany enacted legislation that required all new buildings to have a green roof (Peck et. al., 1999). Federal environmental laws require mitigation or compensation for the destruction of natural open space caused by development Nada Sutic 14

23 (Velazquez, 2002). As a result, Germany s green roof industry is well established, supported and documented. According to Peck et. al. (1999), over 10 million square metres of roofs were greened by Municipalities provide subsidies to developers and building owners to encourage green roofs and offset the costs. Some municipalities reduce property taxes for buildings with green roofs by 50-80% to reflect their savings in construction, maintenance and replacement of stormwater management facilities (Velazquez, 2002). Other indirect subsidies include development ordinances to compensate for lost open space at a green roof to open space ratio of 0.50 or 0.70 (Velazquez, 2002). Some cities also provide direct subsidies to offset capital costs, and these range from $0.51 to $6.20 USD ($ CAD) per square foot (Velazquez, 2002). Government subsidies and initiatives have played a significant role in increasing green roof development in Germany, making it a world leader in the industry. In Japan, the Tokyo Plan 2000, implemented April 1, 2001required that all new buildings in Tokyo greater than 1000 square metres or one-quarter acre must green at least 20% of the roof. Other Japanese cities are planning to develop and implement similar initiatives by Because Tokyo has seen a dramatic increase in urban temperatures over the last four decades, implementation of green roofs has become increasingly important as a way to curb the urban heat island effect (Velazquez, 2002). In North America, there are green roofs in existence, and some policies and incentives are starting to come into place. However, there are currently no such policies or incentives in Canadian cities. In the United States, the American Society for the Testing of Materials established a Green Roof Standards Task Group in 2001 to establish national standards for green roof technologies (Velazquez, 2002). Also, in the USA, under the US Green Building Council, the Leadership in Energy and Environmental Design (LEED ) program now includes green roofs in the rating system used to certify buildings to LEED (Velazquez, 2002). LEED is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings (USGBC, 2002). The LEED program is applied to commercial, institutional, high-rise residential new construction and major renovation projects (Velazquez, 2002). In Portland, Oregon, there are some incentives to build green roofs. All building projects must incorporate some stormwater pollution reduction measures, and green roofs are an acceptable Nada Sutic 15

24 measure (Velazquez, 2002). Also, Portland builders can increase their floor area ratio by building a green roof, and they can enjoy reduced stormwater utility fees (Velazquez, 2002). The Cityof Chicago enacted an Energy Conservation Ordinance in June 2002, which requires all new and refurbished roofs to install green roofs or reflective roofing (Velazquez, 2002). Canadian cities are beginning to look into incentive programs, but find it difficult to provide financial incentives at a municipal level. Nonetheless, there are green roofs in several Canadian cities. These include the Toronto City Hall, the Vancouver Public Library, the Eastview Neighbourhood Community Centre in Toronto, Mountain Equipment Co-op in Toronto, the Fairmont Waterfront Hotel in Vancouver, the Royal York Hotel in Toronto, the Environmental Sciences Building at Trent University, the Boyne School for outdoor education near Shelbourne Ontario, the Computer Science Building at York University, the YMCA's Environmental Learning Centre at Paradise Lake in St. Clements, northwest of Waterloo, and Mary s Place (YWCA) in Kitchener. In addition to the actual existence of green roofs and demonstration projects in Canada, there are a variety of research projects exploring urban heat island mitigation ability of green roofs, barriers to green roof implementation, stormwater management implications and the energy efficiency potential of green roofs. These include the works of the Adaptation and Impacts Research Group of Environment Canada, the National Research Council s Institute for Construction, Green Roofs for Healthy Cities, the Toronto and Region Conservation Authority, the Toronto Atmospheric Fund, and a variety of consultants. Although the green roof industry in Canada is relatively small, it is growing. Canadian cities have the opportunity to learn from the works of others and to move forward with that knowledge and apply it locally. 2.6 Green Roof Benefits That Improve the Urban Environment There are numerous benefits associated with the implementation of green roofs. The building owner reaps some benefits, while some are community wide. Communitywide benefits include improved stormwater management, reduction of the urban heat island, Nada Sutic 16

25 air quality improvements, community greenspace and aesthetic value, and food production. Private benefits include: energy efficiency gains, improved roof durability and life span, amenity or recreational space and aesthetic value, horticultural therapy, sound insulation, and food production. There is some overlap between public and private benefits, because some benefits are realized throughout the community and by the building owner. The benefits that improve the urban environment will be discussed in this section, with a section following to describe other benefits. Those that improve the urban environment are the public benefits Stormwater Management Densely developed urban areas generally involve extensive areas of concrete and paved surfaces that do not allow water penetrate to the soil and recharge aquifers. Numerous water quality and quantity problems are caused by the abundance of impervious surfaces in urban areas. During rain events, all the water runs off of these hard, flat surfaces relatively quickly, often overloading a local watercourse. Many urban watercourses end up with a low base flow and high peak flow. Many older downtown areas also have combined sewers, meaning that the storm and sanitary sewers run parallel, and the stormwater overflows into the sanitary if the volume becomes too great. When it rains heavily, the combined flow can overload the local wastewater treatment facility, resulting in diluted raw sewage entering a local water body. Because stormwater systems are engineered to provide quick removal of water from buildings and streets, there is also an increased risk of flooding. A high volume of runoff can also cause erosion at the discharge area of the stormwater. Another stormwater problem is the quality of the water, which is particularly important in areas where the stormwater moves directly to a local Nada Sutic 17

26 watercourse. The runoff from streets and parking lots usually contains some pollutants, such as hydrocarbons, sediment, road salt and litter. This ties to the water quantity problem caused by impervious surfaces, because if the quantity and speed of flow is reduced, it can help to reduce the sediment and litter in the water. Another water quality issue relates to compounds that are already in the rain as it falls, such as nitrogen and phosphorous. In addition, stormwater runs over hot pavement, concrete and roofs, gaining heat, which is ultimately transferred to the water body or water course that it discharges to. Improving stormwater management in urban areas can mitigate some of these impacts. Green roofs can have a big impact on stormwater quantity, because they retain a portion of the precipitation. In fact, they may be the single most effective solution to combat urban runoff from impervious surfaces, (Scholz-Barth, 2001, 84). Information regarding how much rain green roofs can retain varies. Some sources say that the growing medium can retain up to 75% of the stormwater (Scholz-Barth, 2001, 86), while others suggest that between 70 and 100% of water can be retained in summer months and 40 to 50% in winter (Peck et al., 1999, 28). Factors that affect these estimates include substrate and vegetation depth, temperature, wind, sun and the duration of the rain. Green roofs are most useful for smaller rainstorms. For longer rain events, green roofs can still retain a portion of the water, but eventually become saturated, resulting in runoff. A major two-inch rainstorm drops about 1.25 gallons per square foot (59L/m 2 ) and a green roof retains about 0.5 gallons per square foot (24L/m 2 ) (Scholz-Barth, 2001, 86). Figure 2.3 below shows how green roofs affect rain runoff. The light blue dashed line for the case with no green roof, shows that almost 75% of rainfall runs off in a region with about 700mm of annual rainfall. The green lines indicate various depths of green roofs, and show that in the same region, only 20 to 35% of the rainfall would run off from the same area. The data shows runoff from the entire lot or property, not just the rooftop. Nada Sutic 18