Green roofs, external and internal walls - Hulfarin Keren & Nbewany Sally

עבודה סמינריונית

: תפקיד הצמחייה במבנה בראיית קיימות

קירות חוץ ופנים ירוקים, גגות ירוקים

328938485 - קארן הולפרין 025930298 – סאלי נבואני

2009-2010ע "תש' סמסטר א | תגית כלימור | קיימות בראיה כוללת– צומח ,חי, עיר, ארץ

Abstract In the era of global warming and increasing population despite limited territories on the urban cities, the dilemma of how to create and sustain a healthy urban ecosystem becomes more prominent, and the demand of finding alternatives in construction that contribute to the improvement of the climate and life quality on the urban city is rising. Among the alternatives offered today on the green construction are green roofs and green walls, which technologies are very well established in many countries throughout Europe.

effectgreen walls and roofs how do examine the benefits and The objective of this study is to

the microclimate of the city and other aspects of the urban life. This study provide a review of these benefits of green roofs and green walls technologies.

Although costly, the installation of green roofs and walls could be justified in the long run if the environmental benefits and other savings are considered.

With this study we can contribute to clarify the main advantages and disadvantages of the green roofs and walls technologies, processes and study results that were already made. This may lead to increase the installation of green roofs and walls.

Green Roofs and Walls' initiatives around the world provide developers, communities and government with modeling of green roof performance, materials and installation services.

קירות חוץ ופנים ירוקים, גגות ירוקים : תפקיד הצמחייה במבנה בראיית קיימות

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Table of Contents

1.0 - Introduction………………………………………………………………………….……4 1.1 - Presentation of the subject………………………………….........................….4 1.2 - Purpose of the study..………………………………...………………….…..…..4 1.3 – Research question / objectives………………….................................……...5

2.0 – Brief summary of the theoretical background of the subject…..…...………….…...6

3.0 – Definitions and applications…………………………………………………….…….8

…………...……………………...………………….….8 3.1 – Green Roof definition 3.2 – Green wall definition……………………………………………………..……..9 3.3 – Benefits of the green roofs and walls..…………………………………...….10 3.4 – New Buildings and retrofits……………………………...……………………..21 3.5 – Installation and maintenance…………………………………………………..22 3.6 – Barriers to Retrofitting…….......……………………………………………..23 4.0 – Literature review……………………………………………………………………….25 4.1 - Green roof retrofitting in Europe……………………..………………………..……25 4.2 - Green roof retrofitting in Canada and North America..……………………..……25 4.3 - Green roof retrofitting in other parts of the world…..………………………..……26 4.4 - Green roof retrofitting in U.K…..……………………..………………………..……26 4.5 - Performance of green roofs and walls in different climates……………………..27

5.0 – Case Studies……………………………………………….………………………..…29 5.1 - Comparison between the examples under criteria……..…….…...…29 5.2 - Results of the examples………………....……………………………...29

6.0 – Discussion ……………………………..………………………………………………30

7.0 - Conclusions…………….……………………………………………………………....32

References……………..……..………………………………………………………………33


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Introduction–0 .1 The work is a description study of “Green Roofs and Walls” with their advantages and disadvantages, and their effects in the structures, in the microclimate of the city and in urban life. The high concentration of buildings in cities, their structure, materials and lack of vegetation have altered the climatic characteristics of urban spaces and has resulted in many environmental issues. The buildings and hardscape surfaces make cities into giant, heat absorbing sinks, creating an "Urban Heat Island Effect" which contributes to air pollution, increased energy usage and heat-related illnesses. Lack of green space in cities means rainwater runoff carries contaminants from rooftops into our waterways, often releasing untreated sewage with it. Cities increasingly struggle to cope with the urban heat island effect, stormwater runoff, altered weather patterns, air pollution, noise, and the loss of tree canopy, greenspace, and wildlife habitat. There is growing demand to develop methods that integrate environmental and economic assessment of more sustainable technologies incorporated into commercial and residential buildings. The rising ecological concerns for building design attempt to create harmony between buildings and their surroundings through mitigating their negative impact on the environment.

one of these ecological measures is essentially greening of buildingsThe Green roofs and walls, which are specially designed landscapes on the top or on the front of the buildings, can provide solutions to many of these problems, as well as enhance the quality of life for urban residents; for quality of life means mitigation of the common problems of urban environments cited above – noise, air pollution, heat (thermal comfort) . The moderation of the heat in the local environment of the urban cities is an issue that have extremely importance to all of us, and that's the reason of the choice of the work's subject, and could mean not only the sustainability of the cities, but also the potential of occupying them without the mortality risk caused by excessive heat. The objective of this study is clarify the pros and cons of this green technology and make it clear not only to the people who work or study the subject, but also for those who don't know anything about the subject and to the governments and decision-makers of the countries, to encourage them to increase the initiatives of installation of Green Roofs and Walls and know their potential. By placing vegetation in the built space of the urban fabric (in this case, urban surfaces such as building envelope), raised urban temperatures can decrease in the human habitats themselves. The coverage with vegetation could alter the microclimate of the built environment, as well as the local climate of the city. The development of contemporary approaches to green roof and wall technology began in urban areas of Germany over thirty years ago. In the United States, many green roofs are now in place. Chicago and Atlanta have municipal buildings retrofitted with green roofs. City governments, large corporations, and other entities with significant financial resources are sponsoring green roof programs and leading the way in promoting the adoption of green roof technologies.

This study contributes to architects, designers, urban planners and landscapers, whose role in this subject is to improve the life quality in urban cities, taking vegetation as a strong resource to mitigate the heat, air pollution, reduce storm water runoff and its increased pollutant-carrying potential, and as a consequence, achieve energy savings for cooling buildings.


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Theoretical background -.0 2 Definition of the fields of the knowledge

Sustainability1 Due to some adverse impacts caused by urban cities, such as energy consumption in building operations and its consequent carbon emissions, and degraded water quality with urban runoff and is consequent exacerbate flooding, a motivation to implement new designs and construction management strategies that contribute to a more sustainable built environment is increasing. The introduction of a technology such as Green roofs and walls may enable a building to be more environmentally sustainable.

Green Roofs and Walls2 Green roofs and walls are being incorporated in the urban landscapes at some places in the world, for example Toronto, Chicago, Tokyo, Berlin, Madrid, London and New York City. Some of the advantages of this ecological measure: - create better thermal conditions and mitigate the Urban Heat island effect - achieve energy saving for cooling buildings (reducing the heat flux through the roof) - improve air quality - make potential savings in urban storm water runoff reduction (reduction in storm water treatment fees) - reduce greenhouse gas emissions by the photosynthesis process There are two major types of rooftop greenery: extensive green roofs and intensive green roofs. Extensive green roofs are low cost and low height. Minimal maintenance is required and inspection is performed 1-2 times a year. Plants selected tend to be of low maintenance and self-generative type. Intensive green roofs are heavier and higher cost, with intensive planting and higher maintenance. Regular garden maintenance, such as fertilizing, watering and weeding is required. Plants selection range from bushes to trees.

Cooling Effect of Green Roofs and Walls and reduced energy use Particularly in hot climate cities, the evaporative cooling effect of the Green Roofs and Walls is effective in reducing the heat that penetrates the building, principally on the room underneath the roof. It was confirmed by field measurements that the surface temperature of the roof slab can be reduced to its half during the day, by which a 50% reduction in heat flux into the room could be expected3. The evaporative heat transfer of the green roofs act as a heat sink and the radiative energy absorbed by the green roof is smaller then that absorbed by the concrete roof, so the energy fluxes on a green surface offer lower surface and air temperatures, compared to those produced by concrete surfaces. Because of that, air masses enter the canyon much cooler from the vegetated roofs, and so the canyon air temperatures decrease. This occur because of the evapotranspirational rate from plants and the lower surface temperatures of vegetated surfaces,


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which are responsible not only for lowering the air temperature, but also for lowering surface temperatures of surfaces not covered with vegetation. Apart from creating outdoor conditions more “human-friendly”, green roofs can decrease cooling load demands inside the building very significantly due to the microclimatic modifications; in some cases, the cooling load decreases reach 100% (in places where little cooling load is needed, cooling demand is reduced to zero). Green Roofs can cool the microclimate around them, that can lead to important energy savings for cooling4 .

Air Pollution Removal5 Vegetation can reduce air pollutants through a dry deposition process (its foliage is an effective sink for air pollutants) and has an indirect effect on pollution reduction by modifying microclimates (it reduces the use of electricity for air conditioning, so the emission of pollutants from power plants decreases due to reduced energy use). But, in a densely populated city, the percentage of impervious areas is big, sometimes it reaches more than 90%; green roof is a solution to this dilemma, since rooftops are usually 40-50% of the impermeable area in a city. However, green roofs cannot be used as the only measure in air pollution controls because of its high cost. Storm Water Runoff reduction6 Green roofs have been implemented as a low impact technology for controlling storm water. It reduces storm water runoff and its increased pollutant-carrying potential. A study from the U.S. Department of Energy (2007) found that green roofs absorb, filter, and retain about 75% of the precipitation that falls on the roof. This could be described as a reduction of non-permeable surfaces, that leads to a decreased rain water runoff, which would lead to a combined sewer overflow event. This reduction of non-permeable surface area, while increasing the permeable surface area, would ensure delayed release of stored rainwater. This would effectively “hold” the runoff and release it over time, which would allow the sewers time to transport the excess water away from the building. As a result, the municipality and the taxpayers would save money by not having to enlarge the storm and sanitary sewer systems to handle large water events. This savings would also include the reduction of construction and operations of river filtration systems to clean the runoff as it washes toxins and other harmful solutions into the local rivers and lakes. Green roofs in an urban setting can effectively be used to reduce peak runoff rates during small storm events by up to 26%. However, green roofs themselves cannot solely provide stormwater management in an entire watershed. Other rain-gathering technologies (such as rain-barrels, porous-pavements, and retention tanks) should be used to minimize the runoff caused by rain events. Green roofs reduce the CSO (the combination of storm sewers and sanitary sewers) of the entire surface area of the building footprint by 40%. With this reduction, one can assume that if all structures in the representative neighborhood have this technology, a 40% reduction in total flow could be implied. CSO reduction also translates into a reduction in water pollution costs.


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Definitions and applications–.0 3

3.1 – Green Roof definition Green Roofs are roofs with a vegetated surface and substrate, an engineered roofing system that enables the growth of vegetation on conventional rooftops. This green roof technology includes: -Insulation above the roof structure -a waterproofing membrane, often with root repellent inserted -a drainage layer, sometimes with built-in water reservoirs -a landscape or filter cloth to contain the roots and the soil -a specialized growing medium -the plants

Most green roof systems fall into two categories, extensive and intensive. This categorization is based on soil depth, but determines a variety of factors including weight, cost, maintenance, plant selection, and function.

Table 1: Comparison between Extensive and Intensive Green Roof Systems

Intensive Green RoofExtensive Green Roof- deep soil, irrigation system, more favorable conditions for plants

-thin soil, little or no irrigation, stressful conditions for plants

Brief Description

- greater diversity of plants and habitats- good insulation properties- can simulate a wildlife garden on the ground- can be made very attractive- often visually accessible- diverse utilization of roof (recreation, growing food, as open space)

- 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 of planning approvals

Advantages

- greater weight loading on roof- need for irrigation and drainage systems; hence, greater need for energy, water, materials,…- higher cost- more complex systems and expertise required

- more limited choice of plants- usually no access for recreation or other uses- unattractive to the some people, especially in winter

Disadvantages

Source: adapted from Johnston, 1996, p.54


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Table 1 provides generic information only. Each individual green roof system will be a combination of intensive and extensive, depending on factors such as: location, structural capacity of the building, budget, material availability and client needs. There are other sub-classifications of green roofs, which include: semi-intensive green roofs, earth sheltered buildings (where the earth covers all or part of the building) and hydroponic systems. Green Roofs can be classified as being "accessible" or "inaccessible". An accessible green roof is an open space for people use as a garden or terrace. These types of green roof often involve surface planting, pathways, seating, play areas and shade structures, and can provide an important social benefit to their users and increase the market value of the building. An inaccessible green roof is only accessible for periodic maintenance. The green space can be viewed but not used, and the roofs can be flat, curved or sloped up to 30°.

3.2 – Green wall definition

Green walls, also called "vertical gardens", define the growing of plants on, up, or against the façade of a building or on an interior wall of the building. Strategies for vertical garden development include: planting in planter boxes (at grade, attached to walls, on window ledges and as part of horizontal and vertical sun screens over windows, doors or glazed areas) and planting in a vertical hydroponic system. Suitable plants include a wide variety of perennial and annual vines as espaliered trees. A vertical garden is a system with many of the benefits of a green roof, and often without the added weight or cost implications. It has more potential to impact the area per building, because the greening of a building's façade encompasses four times the area of the roof, and this can be increased to 20 times the area of the roof if the building is high. Wind can be a limiting factor in the effectiveness of vertical gardens, especially for plants and planter boxes located above eight floors.

Green Façades - are made up of climbing plants growing directly on a wall or of designed supporting structures - The plant shoot system grows up on the side of the building while being rooted to the ground

ACTIVE LIVING WALL

plastic containers, geotextiles, are often made of polypropylenemodular panelsthe -irrigation systems, a growing medium and vegetation

integrated into a building's air circulation systemwall is : a new concept–‘ 'Active living walls - beneficial microbes degrade the pollutants in the air : draw air through the root system of the wall -

returning the new, fresh air back to the buildings interior before air filtration that increase the capacity of biofiltersHave -

by absorbing ) such as greywater(e plants may purify a little the polluted water th: water reuseDo -the dissolved nutrients - bacteria mineralize the organic components to make them available to the plants


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less likely to evaporate than in the circulating water on a vertical wall is: suitable in arid areas -horizontal gardens

urban agriculture or urban gardeningcould also function for - for its beauty work of artmay be built as a -

cure sick building syndromeSometimes is built indoors to help - Passive living walls (INACTIVE WALL) - do not have any means of moving the air into the root system where most of the degradation of pollutants occur - have no mechanized air circulation their impact on air quality are scientifically questionable -

- promote as much free air circulation as possible 3.3 – Benefits of the green roofs and walls Urban landscapes create imbalances in the natural ecosystem. These imbalances result, in large measure, from factors such as: concentrated human populations - the introduction of areas of hard and impermeable surfaces, which are devoid of flora and fauna - the importation of energy and other resources from outside of the city - the creation of waste products which cannot be reintegrated into the ecosystem as a resource, resulting in water, soil and air pollution Through the reintroduction of plants on the walls and roofs of buildings, some of the lost equilibrium in the urban ecosystem can begin to be rebuild. The "greening" of the urban regions can also help to better manage many of the wastes that are generated in the air and water and so contribute to improved human and ecosystem health. There are some environment, social and economic benefits caused by green roofs and walls technologies in an urban ecosystem.

3.3.a – Improvement of Air Quality Urban areas tend to perpetuate their own air pollution. During the summer months, when the concrete, glass, stone and asphalt surfaces of roads and buildings are heated, vertical thermal air movements are created and the dust and dirt particles found on the ground and in the air are carried and spread. A green wall will block the movement of dust and dirt particles along the sides of a building and filter them. A green roof will reduce the amount of energy available for heating, which decreases the tendency towards thermal air movement and will also filter the air moving across it. Air particulates tend to get trapped in the leaves and branches surface areas of plants and when it rains, they get washed into the soil/substrate below. Plants are also known to absorb gaseous pollutants through photosynthesis and sequester them in the leaves (which fall to the ground in autumn to create humus)7.

7 Minke, 1982, p.11


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Studies have shown that treed urban streets have only 10-15% of the total dust particles found on similar streets without trees8. This air cleansing quality of green roofs and walls directly decreases summer smog and other forms of air pollution. The widespread use of these technologies would also extend the life of all urban infrastructures that are susceptible to damage from air pollution.

3.3.b – Climate change – mitigation and adaptation Urban areas are a significant source of greenhouse gas (GHG) emissions, with space/air conditioning playing a significant role in urban energy demand9. If widely implemented, green roof and walls can provide an effective and proven methods for governments, companies and building owners to reduce these GHG emissions through direct shading of individual buildings, improving insulation values and reducing the Urban Heat Island Effect (section 3.3.f). Energy cost savings are very difficult to standardize accurately since every building and installation is different. GHG emission reductions and associated cost savings depends on a number of factors, such as: -specific siting on the building -climate -choices of roofing materials and design -insulation -mechanical system -thickness of growing medium -primary sources of energy used to meet heating and cooling needs -types of plants used -extent of alternative functions of green roofs and walls, such as displacing the need for cooling towers and local food production

Even though estimates of climate change mitigation specifically due to green roofs and walls installations are not readily available, the following examples provide some illustrative data: -Approximately one-third of a home's basic thermal unit demand for heating in winter is created by the wind, which makes the outside walls colder and reduces the effectiveness of insulation. Protecting a house from wind can reduce the wind chill factor by 75% and cut the heating demand by 25%. In the summer, every degree (F) of summer heat requires an additional 5-7% of cooling energy. Hence, a 10° F reduction in the outside air temperature achieved through the judicious arrangement of shade trees (green roofs and walls), can reduce energy consumption for air-conditioning by 50-70%10.

8 Johnston, 1996, p.10

9 Mercier, 1998 10 Gaudet, 1995, p.24


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-Canadian studies have shown that vines lower the inside temperatures as effectively as shade trees if allowed to grow on south or west walls11. Studies from Britain have also shown that over a one year period, energy costs for a conventional house can be reduced by as much as 25%. This is achieved through the reduction of wind penetration by, for example, careful perimeter planting of deciduous species of trees. These trees also provide summer shading and winter solar gain12. Similar results could be expected with a green wall.

3.3.c – Temperature regulation Climate can be understood at four basic levels: 1. Climatic Zones – broad, geographic bands, affected primarily by large water bodies land mass and distance from the equator. Significant changes to climatic zones, such as global warming, can occur only on a global scale.

2. Regional Climate – refers to the regional variations within climatic zones, with accompanying differences in annual temperatures, sunniness, snowfall, rainfall, wind, etc. 3. Local Climate – occupies a smaller footprint. The Urban Heat Island Effect (section 3.3.f) is an example of an anthropogenically produced local climate.

4. Microclimate – are site-specific, for example: rooftop will often have a different microclimate from the grade surrounding the building. Microclimate is directly influenced by a variety of elements on and around the site (land contour, vegetation, water, soil conditions and buildings) which affect the site's sunniness, warmth or coldness, humidity, wind, snowdrift and runoff patterns and degree of wind chill. By manipulating these site elements, the microclimate of a site can be substantially changed.

Much of the sun's energy falling upon a typical concrete, asphalt or hard surface is reradiated as heat. Using a layer of vegetation to intercept the sunlight can reduce this heat. Of the sun's light energy that falls on a tree leaf, 2% is used in photosynthesis, 48% is passed through the leaf and stored in the plant's water system, 30% is transformed into heat (used in transpiration) and only 20% is reflected. Since a large amount of incident radiation on a plant canopy is used for evapo-transpiration, plants on vertical and horizontal surfaces are able to regulate wild temperature swings. On a warm summer day their absorption of energy lowers the temperature of the shaded surface and regulates humidity while at night and in the winter, they give off energy/heat. This can reduce the amount of sun-energy falling on a hot summer day by up to 90%13

11 Gaudet, 1985, p.29

Johnston, 1996, p.14 12 13 Minke, 1982, p.11-12


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In a city, the impact of evapo-transpiration and shading can significantly reduce the amount of heat that would otherwise be re-radiated by building and street surfaces.

3.3.d – Creation of Microclimates Changing a site's microclimate through rooftop and vertical greening can have a complex and layered effect on urban climate. Green roofs and walls create their own specific microclimate, different from surrounding conditions, both around the building and at grade. Depending on height, orientation and the location of surrounding buildings, the roof is subject to extreme temperature swings (hot during the day and cool at night), with constants exposure to sunlight and wind – a desert-like climate suitable only to specific types of plants. Although this can be tempered by additional irrigation and greater soil depth, a green roof is closer to an arid or alpine environment than it is to the surrounding environment grade. This means that designers and installers must have a specialized knowledge of the flora and fauna best suited to these conditions. Once established, the green roof will have a noticeable impact on the heat gain and loss of the building beneath it, as well as the humidity, air quality and reflected heat in the surrounding neighborhood. In conjunct with other green installations, the green roof will also play an important role in altering the climate of the city as a whole. The same can be said for green walls. One German source remarked that a "healthy" urban climate could be achieved by greening only 5% of all roofs and walls within the city18. 3.3.e – Plants and Building Insulation The role of insulation is to slow down the rate of heat transfer between the inside and outside of a building, which is a function of the difference between the inside and outside temperatures. Insulation mitigates the impact of this temperature differential. In the winter, insulation slows down the rate of heat transfer to the inside. The greening of vertical and horizontal surfaces has long been used as a technique for insulating buildings through exterior temperature regulation. The insulation value of a building's "skin" (roof and wall) can be increased in several ways: -by trapping an air layer or "pillow" within the plant mass, the building surface is cooled in summer and warmed in winter -by covering the building with vegetation, the summer heat is prevented from reaching the building's skin, and in the winter, the internal heat is either prevented from escaping, reflected or absorbed -since wind decreases the energy efficiency of a building in winter by 50%19, a plant layer will act as a buffer that keeps wind from moving along a building surface With a green façade, it is created an exterior insulation, and the added cost of interior or traditional exterior insulation is avoided. The need to re-apply finish surface materials or cladding and the loss of space resulting from thicker walls can be avoided too through the use of green facades. Besides that, the insulation applied to the exterior of buildings is much more effective than interior insulation, especially during the summer months.

187 Minke, 1982, p.

19 Minke, 1982, p.14

Ideally, if winter heat-loss is a concern, one should choose evergreen plants that do not lose their leaves during the winter months. However, a protected southern or western exposure, this seasonal loss of foliage could serve as a passive solar technique. This would be advantageous since the lack of foliage would allow the sun to heat up the wall during the day. During the summer it is important to place green facades on the southern and particularly western exposures, since they receive the largest amount of incoming solar energy. Installation of south and west-facing "green" window shades can add significant insulation to buildings with large window exposure, since much of the summer heat gain is from the absorption of incoming solar energy by walls and other objects in a room. With plants shading the windows, the heat will not reach the interior. With a green roof, the insulation value is in both the plants and the growing medium. It is unclear which of the two has the most benefit since much depends on the depth of the growing medium and type of plants chosen. An extensive application is much more effective as an insulator than an intensive one. A layer of mixed grass performs better than a layer of limited-species grass, which in turn is better than a layer of low-growing sedum. Under a green roof, indoor temperatures (without cooling) were found to be at least 3-4°C lower than hot outdoor temperatures between 25-30°C. Green roofs can also play a role in pre-cooling the make-up air that is required by most mechanical systems. As the outdoor air temperature in the summer is often warmer than the exhausted, internal air it is replacing, the air needs to be pre-cooled before it is allowed into the building. A green roof and the strategic planting of specific vegetation to shade the intake valves will lower the air temperature at roof level, thereby reducing the air temperature, the demands on air-conditioning equipment and result in net energy savings. 3.3.f – Moderation of the Urban heat island Effect The "Urban Heat Island Effect" is a macroclimate caused by the difference in temperatures between a city and the surrounding countryside. This difference is mainly due to the expanse of hard and reflective surfaces in urban areas, which absorb incoming solar radiation and re-radiate it as a sensible heat20. In the surrounding areas, there is a higher proportion of "greened" surface area, which is able to absorb and transform this radiation into biomass and latent heat. Re-radiated heat, waste heat generated by industry, vehicles and mechanical equipment and increased levels of air pollution, have combined to raise urban temperature levels up to 8°C warmer than their surroundings on warm summer evenings. And if estimates are correct, global warming will exacerbate the Urban Heat Island Effect by raising summer temperatures an additional 5°C. Higher urban temperatures increase the instability of the atmosphere, which in turn can increase the chance of rainfall and severe thunderstorms. In cities already plagued by overextended stormwater systems and combined sewage overflows, the problems caused by severe rainfall are likely to worsen with global climate change. Higher temperatures also have a direct effect on air quality, since heated air stirs up dust and airbourne particulates as it rises. On a hot summer day, a typical gravel-covered roof in middle Europe tends to heat up by 25°C, to between 60°-80°C. This temperature increase means that

Johnston, 1996, p.1120


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a vertical column of moving air is created over each roof. Studies have shown that there is no vertical thermal air movement over grass surfaces. These surfaces will not heat up more than 25°C. Air movement along vertical heated surfaces is even greater than over horizontal surfaces. With strategic placement of green walls, plants can create enough turbulence to break vertical air flow which cools the air at the same time it slows it down21. 3.3.g – Carbon Dioxide and Oxygen Exchange Plants play a crucial role in the survival of life on our planet. Through the photosynthesis process, which takes place within green leaves and stems, plants convert carbon dioxide, water and sunlight/energy (solar energy) into oxygen and glucose. Plants supply humans and other animals with oxygen and food, and animals, in turn, produce the carbon dioxide and manure required by the plants. Although the production of oxygen is an important contribution of urban greening, in evaluating this benefit we should take into consideration some facts: -plants only produce oxygen during the daytime; at night, the process reverses so that they take in oxygen and give off carbon dioxide (but there is still a net increase in oxygen) -the decomposition of organic matter on top of, and within, the growing medium also requires oxygen -in extensive green roof systems, where the plants and grass layer is allowed to dry up during the summer, with no additional irrigation, the plants are unable to participate in photosynthesis. By increasing the amount of biomass in an urban area, green roofs and walls can contribute to reducing the carbon dioxide levels produced by vehicles, industry and mechanical systems, leading to improved air quality and reduced respiratory problems.

3.3.h – Stormwater Management The stormwater is diverted from the cities through constructed stormwater systems, since much of the surface area in a city is paved or covered with buildings, and most of precipitation can't be infiltrated into the ground or be intercepted by vegetation. This has created a number of problems, such as: -contamination of stormwater, which, as it runs off impermeable surfaces, it picks up particulates, pesticides, oil, grease, heavy metals, and garbage from roads, roofs and pavements before it reaches the drain. In some cities, stormwater is the number one cause of water pollution in local rivers. -Combined Sewage Overflows (CSO). Many stormwater systems run parallel to a city's sewage system, overflowing into the sewage system if they cannot handle the volume of water during heavy rainfall. During a storm event, diluted raw sewage is discharged into the local streams and rivers, resulting in beach closures and other negative impacts. -increase in water temperatures, that negatively impacts aquatic plants and animals and encourage algae blooms -severe flooding, often resulting in loss of human life due to the high volume of run off

21 Minke, 1982, p.12


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One solution to this problem involves the enlargement or expansion of stormwater infrastructure, which can be a costly process. Some of other alternatives include the disconnecting of downspouts, increased use of swales adjacent to parking lots, constructed wetlands, rain barrels, cisterns, retention ponds and requiring the use of porous pavement. These solutions require associated inspection and maintenance, and the cost of additional surface area at grade. Green roofs and walls can provide viable alternatives where, in older urban areas, there is a lack of suitable land at grade to address alternative stormwater management approaches. If sufficiently implemented in an urban area, green roof systems can help to improve stormwater management. Green roofs absorb 75% of precipitation that falls on them, meaning a discharge reduction to 25% of normal levels. Runoff that occurs is also stretched out over several hours, helping to reduce the risk of flash flooding22 and the frequency of combined sewage overflow events. Most of the stormwater is stored by substrate and then taken up by plants, through which it is returned to the atmosphere through evapotranspiration. Green walls interrupt rainfall and delay runoff, especially during heavy rainstorms with strong winds, where the rain is falling more horizontally than vertically. If widely implemented, green roofs and walls provide new opportunities to address urban stormwater management in a manner that also results in other environmental and social benefits.

3.3.i – Water Filtration and Quality Improvement Greened surfaces not only retain much of the precipitation that falls on them, they also moderate the temperature of the water and act as natural filters for any of the water that happens to runoff. Heavy metals and nutrients carried by the rain end up being bound in the substrate instead of being discharged. Studies show that as much as 95% of cadmium, copper and lead, and 16% of zinc have been taken out of rainwater by green roof systems23.

3.3.j – Other water-based Benefits In addition to the generic benefits from green roof systems, they can also be design to perform particular functions, which help to increase the return on investment for the building owner. For example, the use and reuse of water can be integrated into the design of a green roof system in a number of different ways: -A factory of biodegradable laundry products in Belgium has 2 acres of native grasses and wildflowers on its roof. Effluent produced by the factory is treated in an on-site sewage pond at grade and then filtered through the green roof while at the same time acting as irrigation and nutrient source for the plants. -In the new inner-city development of Block 103 in Berlin, nearly 40% of the roofs have been greened and many of the facades have been planted with climbers and vertical gardens, including a unique "vertical swamp", which cleans the building's grey water

22 Johnston, 1996, p.17 23 Johnston, 1996, p.12


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through a system of planters filled with swamp grasses and aquatic plants. Water is released in measured amounts form the roof into the top planter and then through a system of pipes and drains, is filtered through successive layers of grasses. Upon reaching ground level the cleansed water can be reused24. -The Possman Cider Cooling and Storage Facility in Frankfurt, Germany, uses a water-based heat exchange system to cool the building. The green roof was designed as a marsh with a rain and roof water collected in an underground cistern pumped through the building to collect heat, run through the vegetation layer on the roof for cooling and filtration and then recycled back into cistern. -Roofs can also be used as water collectors and storage "cisterns" by using a floating layer of plants to decrease evaporation and act as a filter. By recycling the stored rainwater, whether in the building or on the site, companies like Possman eliminate the need to purchase water from other sources and consequently, are able to realize cost savings25.

3.3.l – Sound Insulation Soil, plants and the trapped layer of air between the plants and the building surface can be used to insulate for sound. Sound waves produced by machinery, traffic and airplanes can be absorbed, reflected and deflected. The substrate tends to block lower frequencies while the plants block higher frequencies. Tests have shown that a 12 cm. layer of substrate can reduce sound by 40dB; 20 cm. can reduce sound by 46dB26 (with some reductions as high as 50dB)27.

3.3.m – Building Envelope Protection and Life Extension Green roofs have been proven to protect the roofing membrane against ultra-violet (UV) radiation, extreme temperature fluctuations and physical damage from recreation or maintenance. On a roof, temperatures can swing over the course of a day. A 10cm. thick green roof layer can reduce this range of temperatures, thus ensuring less expansion and contraction stress on the roof membrane, which in turn reduces cracking and aging. The longer life-span decreases the need for re-roofing and the amount of waste material bound for landfill, both of which are direct cost savings for the building owner. Reducing building waste also helps to conserve municipal landfill capacity. It is not true that green walls will damage the wall they are covering; as long as the original cladding is in good repair, even vines that cling with their roots will not threaten the integrity of the wall. If the wall is not in good conditions or if periodic maintenance of the cladding is required, vines can be grown up on another structure that is kept separate from the wall itself or on a bottom-hinged system, which can be pivoted towards the ground while keeping the plants intact. Green facades protect the exterior finishes and masonry from UV radiation, avoiding the wear and tear caused by moisture and temperature differentials.

24 Johnston, 1996, p.75-76

25 Johnston, 1996, p.12 Minke, 1982, p.1526

27 Hooker, 1994, p.3


17

In cold climates, a facade can heat up to 60°C and then cool to minus 10°C; with a layer of plants, temperatures will only fluctuate between 30° to 5°C28. Plants will also increase the air tightness of windows and cladding by decreasing the effect of wind pressure29.

3.3.n – Aesthetic Improvements Urban greening has long been promoted as an easy and effective strategy for beautifying the built environment. Studies have shown that from earliest recorded times, Western cultures have conditioned their citizens to appreciate nature and to have negative associations with cities and their aesthetic. A layer of plants can enhance good design or disguise bad design30. Plants can add visual interest to plain walls and roofs, soften industrial and commercial properties and allow a new building to blend in better with rural or suburban surroundings.

3.3.o – General Health Benefits and Horticultural Therapy Visual contact with vegetation has been proven to result in direct health benefits, cause psychological well-being and reduces the stress of urban living. Psychological studies have confirmed these beliefs by clearly demonstrating that the restorative effect of natural scenery holds the viewers' attention, diverts their awareness away from worrisome thoughts and elicits a meditation-like state. Windowless rooms or rooms with little or no visual access to the outdoors are disliked and cause stress, especially in the workplace and in healthcare facilities. People living in high-density developments are known to be less susceptible to illness if they have a balcony or terrace garden31. This is partly due to the additional oxygen, air filtration and humidity control supplied by plants. Trees in a park setting can filter out up to 85% of airbourne particulates, with the leaves of climbing plants providing an equally large surface area capable of filtering out dust and pollutants. There are therapeutic benefits from the act of caring for plants. The variety of sounds, smells, colors and movement provided by plants, although not quantifiable, can add significantly to human health and well being.

3.3.p – Improved Safety A garden or amenity space on a roof is often considered safer than one located at grade for the following reasons: -there is less vandalism because access to the roof is usually restricted to building tenants or employees. -the public services and utilities that may hamper garden installation or digging on the ground do not exist on the roof -pollution levels on the roof are lower than at street level -soil quality, including contamination through heavy metals, hydrocarbons and the use of pesticides and herbicides, can be controlled since everything has to be sourced and then

28 Minke, 1982, p.18

Minke, 1982, p .25 29 30 Johnston, 1996, p.32

Johnston, 1996, p.2731


18

brought up to the roof (this is of particular relevance if the green roof is being used for food production).

3.3.q – Recreation/amenity Space Studies have shown that leisure activities in natural settings such as gardens and parks are important for helping people cope with stress and in meeting non-stress-related needs32. Green roofs and walls can help to address the lack of green space in many urban areas. Many urban residents consider the roofs and walls of buildings as a city's greatest unexplored resource. Finding new ways to utilize roof and wall space can generate added economic impetus and make cities more livable by providing significant amounts of accessible outdoor recreation or amenity space close to work and home. Greening is often the only legal and also one of the least expensive ways that an individual tenant can personalize or change the exterior of their building, apartment unit or exterior living space.

3.3.r – Community Building Apartment buildings, although densely populated, rarely become "communities" unless the residents are able to rally around a common goal or against a common problem. The creation of shared gardens allow residents to feel ownership of their building and meet neighbours in a relaxed setting. The propensity of apartment dwellers to grow plants on their balconies attests to the potential for vertical gardens to help build communitites.

3.3.s – Job Creation and production of food Green roofs and walls installations can create and enhance a lot of job markets, like suppliers and manufacturers of roof membranes, root repellent layers, drainage layers, landscaping cloth, irrigation systems, light-weight soils, professionals as designers, landscapers, engineers and contractors, besides maintenance companies. There is great potential for producing high quality food in urban areas. Many places have realized this potential and grow significant amounts of food for local consumption. There are a lot of benefits associated with increasing local food production, like: - increased access to food by everyone, including lower income, inner-city communities -fresher produce -local economic opportunity in growing food, processing them and their distribution -decreased travel and environmental costs, such as greenhouse gases generated by long range transportation and cooling requirements -improved control of soil, fertilizers and pesticides The use of green roofs and walls to produce high quality food and other alternative uses of wasted building space hold a big promise through the application of rooftop and vertical garden technologies.

32 98Ulrich, 1992, p.


19

3.3.t – Preservation of Habitat and Biodiversity With the growing of the cities around the world, buildings are replacing natural habitats. This cause plants, animals and insects to adapt, find other locations to live or become extinct. Green roofs and walls can be designed as acceptable alternative habitats although they should never be considered as substitutes for natural habitat or as a justification to destroy natural habitat at grade33. Green roofs are also specifically designed to mimic endangered ecosystems/habitats. In Germany, 20% of all endangered plants are arid/semi-arid grassland plants, conditions specific to an extensive green roof installation. Dryness, heat, frost and lack of oxygen are rooftop conditions that are very similar to the dry grassland ecosystem which have been seriously degraded by fertilizing, irrigation and other forms of human interference. Extensive green roofs, because of their lack of human intervention, are more protected and can become home to sensitive plants that easily damage by walking and to bird species that only nest on the ground. The soil on an inaccessible green roof is also less likely to be disturbed, so it becomes a safer habitat for insects as well. The deeper the soil the more insect diversity the green roof will support. The animals and invertebrates found on a green roof tend to be highly mobile, not only because they have to be able to reach the roof in the first place, but because the varying and intense temperature and moisture levels force them to move from one location to the next34. Green walls can also create important habitat for birds and insects. Birds eat insects as well as the berries and fruits produced by certain vertical garden plants.

3.3.u – ECONOMIC BENEFITS The typical economic benefits and opportunities for building owners that implement green roofs and walls include: -increase of insulation of the walls and roof of the building, resulting in energy cost savings for heating and cooling and leading to reductions in greenhouse gas emissions -protection of the roof membrane and the wall cladding, resulting in a longer material life span, decreased maintenance and associated savings in replacement costs -increase in stormwater management may offset these costs elsewhere in a development by, for example, reducing the need for stormwater management ponds or reducing fees. In Germany, residents with green roofs receive discounted rates. -increase in property values. Green roofs and walls offer vary similar visual and environmental benefits; aesthetic appeal can directly increase the value and marketability of a property. Urban beautification will also have as impact on tourism and the way visitors view the city -The cleansing of wastewater and the growing of herbs and other urban agricultural products can add economic value to underutilized roofs and walls. Other example, the implementation of gardens by hospitals can improve patient recovery rates, which translates into cost savings in health care. Noise reduction benefits can also help offset additional costs for buildings where noise control is an issue.

33 Johnston, 1996, p.49 34 Johnston, 1996, p.69


20

Standard cost savings through the greening of roofs and walls are often related to reduced heating and cooling costs, but pay back periods are medium to long-term. The installation of a green roof or a green wall requires an up-front capital investment, especially in a retrofit situation, that will be returned through cost savings35. If the concept is included at the beginning of the design phase for a new building, a green roof or wall can be installed at little or no extra capital cost36. The life cycle costs would be increased by the maintenance of the garden, but would be decreased by the extended durability and minimized maintenance of the building envelope37and by the savings in energy costs. A green roof or wall becomes even more viable where the price of land, or the lack of available adjacent land, prevents the creation of garden or green space at grade. By providing green space, developers, building owners and companies are often more effective at attracting and retaining buyers and tenants38. There are some economic benefits for the community, like: -job creation in design, manufacturing, installation and maintenance -increased livability of cities, including worker productivity and creativity -air quality improvements that have an impact on human health and well being -ability to retain and treat stormwater runoff, that can help decrease operational expenditures on related urban infrastructure -the benefits of experiences with nature and vegetation decrease the need for health care services39

Green roofs and walls can be located in courtyards, terraces, balconies and rooftops and will increase property values.

3.4 – New Buildings and retrofits There are several application issues in green roofs that must be pointed. The requirement for additional loading capacity is one of the main factors in determining both the viability and cost of a green roof. If a green roof is part of the initial design of the building, the additional loads can be accommodated easily and at relatively minor costs. If a green roof is installed on an existing building, then the design is limited to the current carrying capacity of the roof, unless the owner is prepared to upgrade the structure which can be a significant investment. If the green roof is to be accessible to the public, certain safety requirements must be added, including guardrails, adequate access and exiting, depending on roof size and number of occupants, lighting, fire safety equipment and structural integrity. These elements are much easier and less expensive to include in the initial design of the building than after the building is constructed.

35 Johnston, 1996, p.12 36 71Johnston, 1996, p.

37 Hooker, 1994, p.3 38 Johnston, 1996, p.12

39 Ulrich, 1992, p.101


21

The real limit to retrofitting is the structural capacity of the existing roof and the building structure. If the roof and building can take extra load due to spare capacity and the budget for the project can afford the construction, a retrofit is a feasible option. There are difficulties associated with safely determining the spare capacity of the roof can arise, depending on the materials and type of construction. Retrofitting green roofs, as opposed to using on new buildings, has the greatest potential for the maximum impact on environmental issues, considering the relatively small roof areas of new build projects compared with existing buildings. In addition, retrofitting can be combined with a renovation already taken place, allowing the additional cost to be relatively low.

3.5 – Installation and maintenance

In green roof installations, the most crucial element is the roof membrane. Organic materials are not roof-proof, but this problem can be solved by placing a metal foil between the layers. Parapets, edges, skylight, mechanical systems, vents and chimneys should be protected with a gravel drainage layer and sometimes a weeping drain pipe. Without greening, flat roofs are 50% more susceptible to damage after 5 years than slightly sloped roofs (5% slope), because water tends to pool instead of running off. If the drainage layer isn't sufficient or if drainage routes become blocked, green roofs can cause some flat roofs to leak due to continuous contact with water or wet soil. With insufficient drainage, the plants will also be susceptible to the impact of wide degrees of variability in the moisture content of the soil (for example, with too much water, the soil can go sour and the plants can drown or rot)40. If the slope on the roof is greater than 20°, the roofer needs to ensure that the plant layer does not slip through its own weight, especially when is wet. This can be prevented through the installation of horizontal strapping, placed either under the membrane or laid on top of the membrane. In vertical garden applications, vines require very little maintenance once established, and crop plants, such as beans and lettuce, require the same level of maintenance as they would in a garden at the ground. Since vertical gardens can be designed to keep plants from direct contact with a building's wall, no additional maintenance on the wall is required. Vines, which are often grown directly on the wall, will not damage a surface that is already in good condition. Rather, vertical gardens will actually reduce the damage caused by rapid temperature variations such as freeze-thaw cycle, acid rain, ice accretion and pollution. In retrofitting situations, there are many variables when designing a green roof, such as type and depth of substrate, type of planting, pitch, selection of drainage layer, etc. All these influence the many impacts green roofs can have, sometimes in conflicting ways. For example, the greater the pitch, the less water is retained, which is positive if considering retrofitting on a roof with little spare structural capacity but not if the primary need is to prevent runoff. Another example is that of a green roof designed to be a Sustainable Urban Drainage

40 Minke, 1982


22

System and retain the maximum water, which if not carefully considered could result in the substrate rotting plants or reducing the effectiveness of insulation.

3.6 – Barriers to retrofitting

Structural capacity Although this is the primary issue if considering retrofitting, people's perception are far more negative in this respect than they need to be. A survey of various professionals carried out in London showed that while 92% of developers agreed that "the physical structure of many buildings prevents the establishments of green roofs", only 27% of the engineers questioned held the same opinion41.

Cost While many building and renovation projects are carried out with an approach that recognizes long-term gains and the advantages of investing in initially more expensive options, there is still a reluctance to invest in fitting green roofs. One reason for this is that the benefits green roofs and walls have to offer, financial and environmental, are not widely known as they could be. Another reason is that some building owners may simply not care about increased life of the roof and long-term gains if it reaches beyond their probable ownership. In terms of cost, the argument for retrofitting is strong if the existing roof needs repairing or updating anyway. This is a trend in Germany, where architects are more likely to recommend a green roof when the old one needs replacing, rather than include one in a new project with a tight budget42

Maintenance Most people believe green roofs require more attention and maintenance than other roofs. Although intensive roofs require as much maintenance as any garden, extensive green roofs need little extra maintaining than other flat roofs covered with paving slabs. It is recommended maintenance twice a year, as with all roofs. The main issues of retrofitting initially seem to be technical, but in fact the major factors preventing more retrofitting are the perceptual barriers that effect planning, policies and general attitudes of potential clients and the public. There are many successful examples of retrofitted roofs around the world, so there is a very strong argument that green roofs can be feasibly retrofitted43.

41Living Roofs, 2005 Herman, 2003 42

Living Roofs, 2005 43


23

4.Literature review – retrofitting around the world

4.1 – Green roof retrofitting in Europe Germany is at the center of green roof technology around the world and home to the major manufacturers of green roof systems. In the 1980s, official government support was offered to building projects incorporating green roofs and now 43% of cities have incentives for green roof building. Part of the reason of this development was the Federal Nature Protection Act, which affected the building codes, obliging all new developments to replace and enhance any landscape which might be changed as a result44. Another reason was the publication in 1982 of the first green roof standards by the Landscape Development and Landscape Construction Research Society. These standards have been updated over time, reflecting lessons learned from many projects. Emphasis on the importance of green roofs has changed over the years as more has been learned, and the initial ecological drive evolved into the prominence of energy saving and effectiveness. The concentration is on stormwater retention; most of the 2.5 million square maters of green roofs fitted between 2000 and 2001 (60-65% of which were retrofitted) were done for this reason45. There are government grants, state grants and city grants, as well as a large number of organizations offering support and guidance for those wishong to incorporate green roofs into new and existing buildings. Retrofitting in Germany is common. The ideas and technologies involved are familiar in the building world, and architects and engineers have no inhibitions to retrofit. Similar legislations exist in other countries such as Switzerland, Sweden, Norway and Austria. In Switzerland, 25% of all new community developments must incorporate green roofs. Retrofitting is also common and there are many examples of hospitals which have had green roofs retrofitted. In Sweden, a non-governmental organization (IGRI) coordinates research on his issue and has close links with the International Green Roof Journal.

4.2 – Green roof retrofitting in Canada and North America The green roof industry in Canada and in North America has been growing interest and awareness in recent years. The first financial incentive in Canada has been initiated by Quebec's Energy Board: the green Roof Financial Incentive program46. Some retrofit projects have objectives such as one planned for a head injury recovery centre in Toronto, where horticultural therapy will be used to speed patients' recovery and also reduce drug use. In Portland, stormwater runoff is an important issue as polluted water entering the rivers damage local salmon stock47. Recent changes to design codes in Ontario, Canada, have also increased the capacity of many existing buildings48.

44 Dunnet, 2004 45 Herman, 2003

46 Liu & Baskaran, 2003. Dunnet, 200447

48 Peck & Kuhn, 2000


24

4.3 – Green roof retrofitting in other parts of the world In Singapore and Japan, interest of green roofs on the urban heat island effect has encouraged research and changes. All new buildings taking up an area greater than 1000m² must replenish at least 20% of the developed site with vegetated areas, which encourage the use of green roofs49 . However, examples of retrofitted buildings are not so prevalent. Areas in southeast Asia and South America with tropical climates could potentially benefit from the application of green roofs to problems such as flooding, water erosion and drainage. However, there are problems with green roofs that arise in climates of prolonged and heavy rainfall, such as saturated soil, heavy erosion causing damage and the possibility of an increased risk of malaria if the roofs attract mosquitoes50 and no retrofitted projects in these areas are known of. 4.4 – Green roof retrofitting in the U.K. Projects incorporating green roofs in the U.K. are not as frequent as in the Northern Europe, which has a similar temperate climate. Green roofs appear on high profile buildings such as environmental centers or on purpose built sustainable housing (such as BedZed project in Beddington), and increasingly green roofs appear on buildings such as schools – either on new buildings or extensions made. In terms of retrofitting green roofs, a number of building owners who have opted to retrofit as part of a necessary roof renovation. There are no financial incentives (local or national) that encourage the use of green roofs in new-build or retrofit projects. However, in 2005 a report¹ was made by the London mayor to promote "living roofs", in which it is stressed the importance of outdoor access and the potential for converting roofs into gardens. Retrofitting green roofs is encouraged in this report, as well as new-build projects. Although this does not solve all of the problems associated with taking retrofitting forward, the report is part of a larger move to guide planners and architects. This green roof movement in London is partly due to the "Urban Renaissance" programme initiated in 1999 by the government, aiming to "revitalize town and cities"51. It builds on a recognition of the current and future pressure in Britain on urban spaces (with an estimated 3.8 million new households to be incorporated by 2021). Although these movements and task forces do not specifically target green roofs as the only solution, they provide a promising climate in which green roofs could become more widely recognized.

There are many examples of retrofitting around the world, which show us that it is feasible. Countries such as Germany have integrated green roof technology into wider aims of social and environmental improvement. For many years these benefits have been accepted and encouraged financially by the government as well as state and local authorities. Any practical issues have become part of common knowledge among architects, engineers and roof installers and there is greater public awareness, understanding and acceptance.

49 Liu & Baskaran, 2003

50 Dunnet, 2004 51 Frith, 2003


25

4.5 - Performance of green roofs and walls on different climates52 A study of thermal benefits of green roofs and walls was made in 9 cities with different climates, and a before and after measurement and an experiment (a model) were carried out, to explore the thermal effects of the greening of building. The measurements were carried out on a hot day on the hottest month of the year for each place. The thermal effects of green roofs and walls have different results for different climates. To study the thermal effects, we have to take into consideration not only the climates themselves, but also other parameters like the urban canyon geometries, wind directions, canyon orientations.

Some conclusions in relation to the climates: -The measurements have proved that the hottest and most arid of all the climates

The hotter .om green walls and roofsbenefit the most fr , like a desert climate, examinedand drier a climate is, the more important the effect of green walls and green roofs on mitigating urban temperatures is.

and ter climate hotthe for : with green roofs and wallsdecreasestemperature The greatest -high solar radiation with

-Places more humid, like a rain forest climate, reach smaller decreases than places more arid when roofs and walls are covered with vegetation (Fig. 1 and 2).

lower colder and within much : The lowest surface asphalt temperature decreases-)Cº.90maximum decrease of (insolation Moscow

-The colder climates, like temperate, subartic and continental climates, benefit the least with the green walls and roofs.

Some conclusions in relation to the decreases in temperature and other parameters:

when walls and roofs are ) in all climates examined (Air temperatures lower significantly-covered with vegetation

are covered with both walls and roofsCanyon air temperatures lowers the most when -vegetation, because air masses enter the canyon much cooler from the vegetated roofs

are covered with vegetation, air masses enter the canyon heated by the only wallsWhen -plain roofs, which absorb great amounts of summer insulation

t roof level both inside the canyon and a,significantly decrease is Surface temperature- lower even more due to the greatest amount of solar radiation Roof surface temperature-

horizontal surfaces receive in summer when vegetation t affect temperature decreases so significantly’orientation doesnThe -

covers its vertical surfaces and roofs (despite the fact that it plays an important role in temperature distributions in the canyon) -The magnitude of the effect strongly depends on the geographic latitude (examples of Hong Kong-22.16N and Athens-37.59N) -The amount and geometry of vegetation is more important than the canyon’s orientation

differs Only when the amounts of solar radiation received by the vertical planes -, the orientation have an important role in temperature decreases due to significantly

vegetation

52 Alexandri, 2008


26

- The largest cooling load decreases occur for the combination of green roofs and wall -For the green roofs and walls cases, cooling load decreases are very significantly, while for the case of only green walls it is less dramatic -This difference between the cooling loads of these two cases are smaller for humid climates and greater for arid climates, due to the different humidity concentrations in the 2 climatic groups -The cooling of the microclimate by the vegetated surfaces can lead to energy savings for cooling, depending on the climatic type and the amount of vegetation on the building - In places when little cooling load is needed, its demand can be reduced to zero when building surfaces are covered with vegetation; in other cases, energy savings vary from 35% to 90% -For Savanna climate and the humid subtropical climate, cooling load decreases for the case of green roofs and walls reach 100% - after the surfaces covered, no cooling load is needed -The temperate and continental cool summer climates are not affected, because no cooling load is needed for the examined day, even before vegetation was placed

:caseseen roofs and walls For gr -Riyadh (desert climate) has a high cooling load decrease (90% - lowering from 12 to 5 hours its cooling demand) and Montreal (subartic climate) too (85% - lowering from 8 to 4 hours its cooling demand) -Mumbai (rain forest climate) reaches a 72% decrease (lowering from 11 to 6 hours its cooling demand) -Athens (mediterranean climate) and Beijing (steppe climate) reaches a 66% and 64% decrease (lowering by 4 and 3 hours its cooling demand)

FIGURE 1 FIGURE 2


27

5.Case studies Criteria

Study recommendation

Qualitative/Quantitative Changes due to green roof Monitoring Location Study

The complex composition of green roofs represents a decisive additional buffer zone; the lowering roof temp. And added insulation effect are undeniably positive for indoor climate; the durability of flat roof is increased significantly

Green roof reduced surface temp. But also more importantly reduced the max- temp amplitude by half.

As early as 1984 surface temperatures of a green roof were monitored. The surface temp; shadowed surface temp of gravel; shadowed surface temp of green roof; temp of substrate; ambient air temp. were all measured

Berlin, Germany

Kohler et al. (2002)

The substrates could be light in colour (with the tendency to absorb less heat during the day time). Coverage of greenery in most systems is not extensive. It is believed that better thermal performance of rooftop greenery could be achieved when extensive vegetation is planted.

The green roof tends to experience lower surface temperature than the original exposed roof surface, especially in areas well covered by vegetation. A maximum temperature difference of 18° C was observed.

A "before and after" measurement was carried out. Six weather parameters, ambient air temperature, relative humidity, solar radiation, wind speed, wind direction and rainfall, were monitored with the use of the Hobo weather station, which was placed in the centre of the rooftop. Two sets of Yokogawa data loggers were employed to record the surface temperatures.

Singapore Wong NH et al. (2007)

Reducing temp.-Saving energy

usage

The substrates could be light in colour (with the tendency to absorb less heat during the day time). It is believed that better thermal performance of rooftop greenery could be achieved when extensive vegetation is planted.

Lowering urban temperatures when, the hotter and drier a climate is, the greater the effect of vegetation on urban temperatures. Also humid climates can benefit from green surfaces, especially when both walls and roofs are covered with vegetation. Temperature decrease due to vegetation is primarily affected by the vegetation itself (amount and geometry), more than the canyon orientation in hot periods. In general, the larger amounts of solar radiation a surface receives, the larger its temperature decreases are when it is covered with vegetation. For the low air velocities inside the canyon, the wind direction does not have any significant effect on temperature decreases due to vegetation

A two-dimensional, prognostic, micro scale model has been used, developed for the purposes of this study. The climatic characteristics of nine cities, three urban canyon geometries, two canyon orientations and two wind directions are examined. The thermal effect of green roofs and green walls on the built environment is examined in both inside the canyon and at roof level.

Around the world

Alexandri & Jones (2008)

Retrofit to counteract climate change and land use densification, to restore watershed

Green roofs protect stream health and reducing flood risk to urban areas. green roof redevelopment on existing buildings could help to restore watershed health over time. Green roofs able to filter contaminants out of rainwater that has flowed across the roof Surface, they can also degrade contaminants, either by direct plant uptake, or by binding them within the growing medium itself

Evaluating the stormwater management benefits; water balance Modmel

Vancouver Graham and Kim (2003)

Stormwater saving and

filtering On average green roofs can retain 61% of total rainfall. During light rain events (<2mm daily), their green roof retained up to approximately 98% of rainfall, whereas the same green roof was capable of retaining only 50% of the heavy rain events (when rainfall >6mm).

Slope and substrate depth influence on runoff quantity; Model TE525WS tipping bucket rain gauges; 2 months

Michigan Rowe et al. (2003)


28

CriteriaStudy recommendation Qualitative/Quantitative Changes due to green roof MonitoringLocationStudy

Application of green roofs in urban areas for reasons such as: reduced ambient air temperature, improved air quality and reduced glare from buildings

Reduction of surface temperatures by 15- 20 degrees C; visible light (glare) from green roofs lowered by 12-56%; air quality improvements noted in sulphur dioxide by

37%; nitrous acid by 21%; but nitric acid

increased by 48%; PM 2.5 and PM 10

increased (possibly from re-suspended

chips related to gravel ballast and bare

spots on green roof) and particle number

concentration decreased by 6% on green

roofs.

substrate, air; HOBO data loggers, infrared radiometer (Thermo tracer TH7102WX, NEC Japan); HOBO Weather Station for humidity, solar radiation, wind speed and rainfall; air quality measured with annular denuder

system (URG, Chapel Hill,

NC, USA), particle counter

(TSI, St. Paul, MN, USA) and

air quality with an aerosol

sampler (Airmetrics, Eugene,

OR) and to measure black

cargon mass Aethalometer

(Magee Scientific

Singapor

e

Yok and Sia,

(2005)

Air quality

Recommends the application of urban vegetation at grade and/or elevated surfaces to mitigate air pollution with resulting population health benefits.

Air contaminant reductions between varying levels of vegetation in one neighborhood in Toronto over a one year period

UFORE – Urban Forest Effects Model from Northeaster Forest Service, Research Station, Syracuse, New York–quantified vegetation effects on air contaminants based on one year of data from Environment Canada’s 3 local weather stations in Toronto

TorontoCurrie, (2005)

The residents enjoy the use of the green roof. Provide new access to a rooftop that was not used before. It was designed to create an accessible terrace for people living in the co-op (which is located on a main commercial street with no green spaces in the surrounding area).

The rooftop is landscaped with a garden of succulents, ground covers, bulbs and herbs. The green roof utilizes Soprema SOPRADRAIN PSE for drainage, a Soprema SOPRAFILTRE filter, and the growing medium is Soprema SOPRAFLOR-X.

Quebec City, Quebec

Peck et al (1999)

Environmental, Social

Lower costs by not using western red cedar and do some surface planting (i.e. put a lawn on the roof).

Each year more tenants use the green roof (tenants have formed gardening group) and more perennials get planted. Birds and insects are now found on the roof. The success has not been quantified, except that the roof terrace is used and vandalism has decreased after the first year.

The green roof was built using cedar planters lined with insulation and filter cloth and contains triple mix soil, vegetables, fruit trees, berry bushes and vines, ornamental annuals and perennials.

Toronto, Ontario

Peck et al (1999)

Environmental,

ecological

Any opportunities for erecting interpretation panels and display boards should be vigorously taken up; they will further educate the local residents, commuting office workers and the passing public

in general, of the ecological

value of the green roofs and

brown fields in our cities.

Green roofs in urban London are providing useful and interesting habitats for invertebrates and other wildlife. Many of these invertebrates are species adapted to harsh dry or well-drained conditions and which are obviously benefiting from the peculiar habitat afforded by the roofs. Several very unusual and uncommon species have been found that have not otherwise been recorded in the London area and which, it would seem, have taken advantage of a new type of niche not available elsewhere in the capital.

Seven roof sites were initially selected as suitable for study. Each was visited once in spring and once in late summer. An additional site was visited only once, in late summer.

LondonJones (2002)


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6. Discussion – Disadvantages

Green roofs not only add aesthetic appeal to the unused roof space that is available in most urban areas; they also provide many benefits. Green roofs can protect the roofing membrane from exposure to ultra violet radiation and hail damage. They can reduce energy demand on space conditioning, and hence greenhouse gas emissions, through direct shading of the roof, evapotranspiration and improved insulation values. If widely adopted, green roofs could reduce the urban heat island which would further lower energy consumption in the urban area. They can also be used as part of the stormwater management strategy in the urban area. Part of the rain is stored in the growing medium temporarily, and to be taken up by the plants and returned to the atmosphere through evapotranspiration. Green roofs delay runoff into the sewage system, thus help to reduce the frequency of combined sewage overflow (CSO) events, which is a significant environmental problem for many major cities in North America. The plants and the growing medium can also remove airborne pollutants picked up by the rain, thus improving the quality of the runoff. In addition, green roofs can improve air quality, provide additional green space in urban areas, and increase property values53. As was in this work, and many researches, there are many advantages for green roofs. On the other hand, there are few of such roofs. Some of them are: Costs: Green roofs are more expensive to install than white roofs54. Moreover, the performance of the green roof will increase, with respect to the environmental benefits, if each of the of green roof technology characteristics increases in quantity. However the cost of green roof increases with the increase in the depth and area coverage. Also, for existing buildings structural load limitations impose a restriction on the nature of the green roof that can be implemented.

Costs: Green roofs are more expensive to install than white roofs55. Moreover, the performance of the green roof will increase, with respect to the environmental benefits, if each of the of green roof technology characteristics increases in quantity. However the cost of green roof increases with the increase in the depth and area coverage. Also, for existing buildings structural load limitations impose a restriction on the nature of the green roof that can be implemented. Structural load: existing buildings structural load limitations are an important criterion and therefore it prevents green roofs with deep growing medium. In order to allow deep growing, the roof structure should pass strengthening.

Benefit quantified: Not all benefits of green roofs can be quantified at this time, and in many cases, it is hard to isolate variable in order to enumerate and investigate the social and environmental benefits of green roofs56. Hence, Many questions remain to be answered

Liu & Baskaran, 200353 54Gaffin et al, 2003, p9

55 Gaffin et al, 2003, p9 56 Banting et al, 2005, p62.


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regarding the uncertainty of the benefits, impact of less than 100% green roof coverage, impact of building specific constraints, the quantification of costs leading to a complete cost benefit analysis, quantification of other social benefits and consideration of the effect of alternative technologies that may be able to perform one or more of the functions of a green roof. These questions are important and will need to be considered in further studies. Policy decisions regarding green roofs will need to consider the impact of these questions. Exceeding temperature: When the substrate is very dry, the substrate temperature can exceed the surface temperature of the original exposed roof57 New architecture: The green roofs create new advantages in building architecture that still need to be investigated. Adding a green roof to a building needs new architectural consideration that still not defined well. Substrates58: The colour of substrates is mostly dark and this will absorb more solar heat and easily incur higher surface temperatures. A prolonged drought period can make the substrate very dry and evaporative cooling effect is marginal. Thermal capacities of substrates of the extensive roof garden systems are rather small compared with the intensive system. With thin layer and lightweight substrate, the heat can easily build up during the day time and dissipate at night. This is the reason why the fluctuation of surface temperatures of the substrate surface is so large.

57Wong et al, 2007, p53 Wong et al, 2007, p3058


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7.Conclusion The necessity to recover green space is becoming increasingly critical to maintain environmental quality. Vegetated or green roofs and walls are one potential remedy for this problem. Establishing plant material on rooftops and on interior and exterior walls of the buildings provides numerous ecological, economic, social and environmental benefits, as described in this work. The construction and maintenance of green roofs provide business opportunities for landscape contractors, irrigation specialists, and other green industry members while addressing the issues of environmental stewardship59 For architects, this provides a way for new structures to have stormwater management built in to their designs60. These typically unused spaces can become a way to reclaim habitat that was lost as a result of construction while also aiding in the protection of our environment through more sustainable practices. Although these numerous benefits, some conclusions from studies should be taken in to account: 1. The temperature distribution through the thickness of the lawn is influenced not only by the heat flow but also by moisture content, and the water (vapor and liquid) diffuses through the lawn. The solar radiation is absorbed through the lawn layer and affects the results of the roof significantly61. 2. The impacts of different types of vegetation may vary. Those with relatively extensive greenery coverage led to better thermal performance62.

Despite the many social, economic and environmental benefits of these technologies and their widespread use throughout many countries in the world, Israel have been slow to implement them. This work provides a review of the benefits of green roofs and walls technologies. With this in mind, here is a question for further studies: With the proposal of a National Action Plan, will Israel be capable, in a medium or long-term period, to generate a new industry of these technologies that will improve too the health and liveability of our urban environments?

Green roofs and walls provide a lot of advantages – and some disadvantages that have to be taken into consideration – in areas such as air quality, reduction of greenhouse gases, water quality and quantity improvements and economic benefits for building owners and for the community. Will these benefits present a strong case for federal and municipal government policy and program support to create a strong and viable market for these technologies throughout Israel?

59 Getter, 2006; Peck et al, 1999

60 Carter, 2005 61 Onmura, 2001

62 Wong, 2007


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Green roofs, external and internal walls - Hulfarin Keren & Nbewany Sally

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