ECO Design: Green Roofs


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ECO Design: Green Roofs

  1. 1. Nicholas Socrates 2011 TU Delft 4123875 SMART: Bioclimatic Design Green Roof Study & ResearchECO DESIGNOver the last several years, the green-building movement has really taken off.The movement has touched every aspect of commercial-building construction fromheating, ventilating and air-conditioning systems, to lighting, roofing and even carpetand paint.Green Roofs: What are they?As the name implies, green roofs areroofs made of plants. Theyrecomprised of a waterproof membranefollowed by a root barrier, a drainagelayer and finally the growing mediumand a variety of plants, grasses,sedums, cactus or shrubs -- hence, thegreen. The technology, of course, isntentirely new. For millennia, the nativesof Scandinavia and Iceland,particularly barren environments withlimited building materials, used sod ontheir roofs as insulation; in Tanzania,mud huts with grass roofs arecommon; and closer to home, manyearly settlers used sod to insulate theirwalls and prairie grass to cover their roofs.
  2. 2. IntroductionEstablishing vegetation on rooftops, commonly referred to as green roofs, is anemerging strategy for retaining storm-water runoff. In addition, green roofs offernumerous other benefits beyond storm-water mitigation. They provide insulation forbuildings, thus saving on energy consumption, increase the life span of a typical roofby protecting the roof components from damaging ultraviolet rays, extremetemperatures, and rapid temperature fluctuations, filter harmful air pollutants, providea more aesthetically pleasing environment to live and work, provide habitat for arange of organisms from microbes to birds and have the potential to reduce the UrbanHeat Island Effect.Container gardens on roofs, where plants are maintained in pots, are not generallyconsidered to be true green roofs, although this is an area of debate. Rooftop pondsare another form of green roofs, which are used to treat grey-water.Also known as “living roofs,” green roofs serve several purposes for a building, suchas absorbing rainwater, providing insulation, creating a habitat for wildlife, andhelping to lower urban air temperatures and combat the heat island effect. There aretwo types of "green" roofs: intensive roofs, which are thicker and can support a widervariety of plants but are heavier and require more maintenance, and extensive roofs,which are covered in a light layer of vegetation and are lighter than an intensive greenroof.The term green roof may also be used to indicate roofs that use some form of "green"technology, such as solar panels or a photovoltaic module; for example what mayappear as a typical, low-slope commercial roof. What distinguishes it from a typicalroof is the cap sheet material and the amount of insulation. There may be a significantamount of insulation (up to 12 inches in some locations). Building owners areinvesting in the additional insulation to lower utility costs.Green roofs are also referred to as eco-roofs, vegetated roofs and living roofs
  3. 3. Benefits of these vegetated Green Roofs consist of;1. 70-90% of rain-water retained, easing pressure on drains and prevents riverpollution2. Reduced energy and maintenance costs3. Long roof life: Protects against UV and weather damage4. Provides a habitat for fauna and flora species5. No reflected heat and prevents sealed surface heat build-up6. Cools buildings in summer and insulates in winter7. A useful, recreational space for roof gardens or terraces8. Higher property value & quality of life9. Increased efficiency of solar panels10. LEED accreditedAbsorb Storm-waterGreen roofs are a best practice for onsite water management. They slow the velocity ofrunoff volume to sewer systems by 60 to 90%.During heavy rainfalls excess water and the water contaminants associated can lead tocombined sewer overflows into our watersheds. Green roofs present an opportunity tomitigate this all-too-common problem by absorbing much of the water in the root systemsand releasing the rest back into the atmosphere through evapotranspiration. If there isrunoff, green roofs slow it down so that the sewer system isnt overburdened during peak
  4. 4. usage in times of extreme rainfall.Most commercial spaces are required to retain storm-water on site. A green roof eliminatesor greatly decreases the space needed and costs associated with dealing with the storm-water.Reduce Energy CostsGreen roofs greatly reduce the temperature of the roof in the summer time. It works best inbuffering against daily temperature extremes. Roofs can reach temperatures of 70º C. Witha green roof the temperatures stay closer to 26º C. This means in the summer when energydemands and their associated utilities costs are the highest, you are reducing the amount ofenergy the building requires. The same is true in the winter, that the green roof acts asextra insulation keeping the heat in the building, but to a lesser degree.In todays world of rising energy costs, green roofs provide a tremendous benefit.Extend Service Life of the RoofThe application of a green roof protects the waterproofing membrane from UVradiation, therefore the life of the waterproofing membrane is extended three to fourtimes its average life, meaning that, in the long run, money is saved and fewermaterials go into the landfill because it does not need to be replaced as frequently.Green roofs also protect the roof surface from human traffic, dust and other debris.Create Wildlife HabitatsGreen roofs create new wildlife habitats for pollinators and insects.Improve Air QualityLike all plants, green roof plants sequester carbon dioxide from the air and release oxygen.Additionally, they remove smaller amounts of other contaminants in the air.Reduce Heat Island EffectA natural function of plants is to cool the air through evapotranspiration (or release ofwater through plants into the atmosphere). With an increase of green roofs in theurban fabric we will start to see a reduction of the overall heat trapped in our cities.
  5. 5. Higher Property Value & Quality of LifeAlthough difficult to quantify, green roofs provide many auxiliary benefits; • Introduce an attractive and a dramatic amenity and transform rooftop eyesores into assets. • Reclaim space for relaxation and passive recreation for employees and residents. • Increase productivity for employees and recovery time for patients in health care facilities. • Reduce noise heard by occupants, particularly near highways and airports. • Create green space in neighborhoods that have little ground level space, increasing livability and helping to meet municipal mandates for green space. • Create marketing value for your building and organization, resulting in higher rents and increased resale value.Increase the Efficiency of Solar PanelsSolar panels operate most efficiently at 80° F. In general, a standard roof surface canreach temperatures of 70°C-80°C during the summer season. A green roof will lowerthe ambient temperature to 26°C even on the hottest days, therefore making the solarpanels work more efficiently. This is why green roof systems and solar energy panelsmake for a great energy saving solution when used in combination.
  6. 6. LEED CreditsGreen roofs can earn LEED credits in the following categories of the USGBCs greenbuilding rating system:PART 1: SUSTAINABLE SITES• Reduced Site Disturbance, Protect or Restore Open Space• Reduced Site Disturbance, Development Footprint Credit• Landscape Design That Reduces Urban Heat IslandsPART 2: WATER EFFICIENCY• Storm Water Management• Water Efficient Landscaping• Water Use Reduction• Innovative Wastewater TechnologiesPART 3: ENERGY & ATMOSPHERE• Optimize Energy Performance• Renewable Energy• CFC and Ozone Depleting Substance ReductionPART 4: MATERIALS & RESOURCES• Storage and Collection of Recyclables• Recycled content materialsPART 5: INDOOR ENVIRONMENTAL QUALITYPART 6: INNOVATION IN DESIGN
  7. 7. Green Roof Summary Green roofs are used to: • Grow fruits, vegetables, and flowers • Reduce heating (by adding mass and thermal resistance value) and cooling (by evaporative cooling) loads on a building — especially if it is glassed in so as to act as a terrarium and passive solar heat reservoir — a concentration of green roofs in an urban area can even reduce the citys average temperatures during the summer • Increase roof life span • Reduce storm-water run off • Filter pollutants and carbon dioxide out of the air • The soil and plants on green roofs help to insulate a building for sound; the soil helps to block lower frequencies and the plants block higher frequencies. • Filter pollutants and heavy metals out of rainwater • Increase wildlife habitat in built-up areas    Types of Green Roofs Green roofs can be categorized as "semi-intensive", intensive, or extensive, depending on the depth of planting medium and the amount of maintenance they need. Traditional roof gardens, which require a reasonable depth of soil to grow large plants or conventional lawns, are considered "intensive" because they are labour-intensive, requiring irrigation, feeding and other maintenance. Intensive roofs are more park-like with easy access and may include anything from kitchen herbs to shrubs and small trees. "Extensive" green roofs, by contrast, are designed to be virtually self-sustaining
  8. 8. and should require only a minimum of maintenance, perhaps a once-yearly weedingor an application of slow-release fertilizer to boost growth. Extensive roofs areusually only accessed for maintenance. They can be established on a very thin layer of"soil" (most use specially formulated composts): even a thin layer of Rockwool laiddirectly onto a watertight roof can support a planting of Sedum species and mosses.Extensive or Intensive Green Roofs?There are two general types of green roofs: extensive and intensive. Intensive greenroofs, commonly thought of as “garden roofs,” are the more complex of the two,exhibiting much greater plant diversity, and a greater need for design expertise, saysPeck. Planting media for intensive green roofs are a 30cm deep at minimum, and areheavy.They are almost always used for new construction, intensive green roofs can beanything from a public garden to an entire park — as is the case with the world’slargest green roof, Millennium Park in Chicago, which is 24.5 acres of landscaping ontop of two subterranean parking garages.Extensive green roofs, with a much lighter saturated weight are most common. Withplanting media (soil) of 1 to 5 inches thick, most extensive green roofs are notdesigned for public access or to be walked on any more than a typical membrane roofwould. Several modular extensive green roof products have emerged in the last fewyears that allow plants to be grown at the factory prior to actually being installed on aroof, so it is possible to get an instant green roof.Flat & Pitched Green RoofsAnother important distinction is between pitched green roofs and flat green roofs.Pitched sod roofs, a traditional feature of many Scandinavian buildings, tend to be ofa simpler design than flat green roofs. This is because the pitch of the roof reduces therisk of water penetrating through the roof structure, allowing the use of fewerwaterproofing and drainage layers.UsageMany green roofs are installed to comply with local regulations and government fees,often regarding storm-water runoff management. In areas with combined sewer-storm-water systems, heavy storms can overload the wastewater system and cause itto flood, dumping raw sewage into the local waterways. Green roofs decrease the totalamount of runoff and slow the rate of runoff from the roof. It has been found that theycan retain up to 75% of rainwater gradually releasing it back into the atmosphere viacondensation and transpiration, while retaining pollutants in their soil.Rainwater Harvesting SystemsThe new code for sustainable homes requires a vast reduction in water consumption.Rainwater harvesting can provide this, very cost effectively.
  9. 9. Recently, water demand has started to exceed supply, and localized flooding hasbecome an issue. Industry experts are now recognizing the important role thatrainwater harvesting has to play in alleviating both these problems.Rain-water is part of a never ending cycle. It is the perfect sustainable solution.Watermetric Rain Water System. (Domestic Rainwater Harvesting System).What are the Benefits in Rainwater Harvesting?As well as being environmentally friendly, collecting and using your own water cansignificantly reduce your water bills. 
Delivering precious clean tap water requires more and more effort, energy andexpense, and for irrigation we simply dont need to use purified drinking mains water.Harvesting rain-water is another free resource to use and is perfect for automatedwatering irrigation systems, landscape irrigation, lawn irrigation domestic andcommercial irrigation.Domestic rainwater harvesting systems are designed to collect roof and/or ground rain
  10. 10. water via pipes filtering out leaves and particles, and store collected water above orbelow ground tanks.  Green Roofs HistoryGermany spearheaded the modern movement back to grassy rooftops, but this timewith an urban twist. During the 1970s, the densely populated country began installinggreen roofs to prevent storm water from surging into its ageing sewer systems, and theindustry has since boomed, experiencing rapid and sustained growth. Today, roughly14 percent of the countrys total roofs are greened, the industry continues to grow 10percent per year and some German cities actually levy a "rain tax" on non-greenedasphalt rooftops.Germanys pioneering work has encouraged other countries such as Australia, Japan,Mexico, the Netherlands, the United Kingdom and Switzerland to actively embracethe concept. But theres more to the mounting buzz than sheer novelty. In an era whenglobal warming, catastrophic weather patterns, flooding, sustainability issues, andmans very tangible impact on the planets health grab daily headlines, green roofingoffers positive solutions.Energy Budgets of Individual BuildingsGreen roofs have been investigated for their effects on building energy costs. Theinsulating effects of added materials seem likely to reduce the penetration of summerheat and the escape of interior heat in winter and there is some scientific evidence tosupport these notions. There is possibly an even greater benefit in the summer due tothe cooling created by the evapotranspiration effect from plants and the evaporationof retained moisture from the soil.Green roofs prevent temperature extremes and the insulation value of the soil on thestructure lowered the cooling energy costs.Green Amenity SpaceSome researchers believe that the need for meaningful contact with nature may be asimportant as people’s need for interpersonal relationships (Kaplan, 1993). Moreover,impediments to meaningful contact with nature can be seen “as a contributing factorto rising levels of stress and general dissatisfaction within our modern society”(Zubevich, 2004).Many urban buildings are positioned along busy streets and transportation routeswhere access to green space is negligible. Green roofs provide a measurablepsychological benefit to urbanites by adding tangible, accessible natural viewingspace for social interaction, recreation, and relaxation. A green roof offers buildingoccupants proximity to common spaces where they can relax, dine, meditate, do yoga,interact with friends or business colleagues, and enjoy proximity to green plants.Research on human behavior suggests that a view of gardens and green plants servesto restore calm and reduce stress in humans - particularly those that drive a vehicle
  11. 11. (Cackowski & Nasar, 2003).Other studies suggest that humans generally prefer a view of natural settings ratherthan congested or cluttered built environments and that accessibility to nature,specifically by way of a window or a walk, which improves worker concentration andjob satisfaction, and buffers negative job stress (Hertzog, Maguire & Nebel, 2003,Laumann, Garling & Morten Stormark (2003) and Leather, Pygras, Beale, &Lawrence (1998).A study by Tayor et al. (2001) determined that children with Attention DeficitDisorder (ADD) were noticeably more relaxed and better behaved after playtime ingreen settings compared with children who did not have access to green space.There is significant evidence springing from multiple research projects to support thetheory that people’s exposure to natural elements increases their ability to focus, copewith stress, generate creative ideas, reduce volatility and promote the perception ofself as part of a meaningful greater whole.Exposure to natural elements enhances an individual’s mental well-being.Habitat PreservationMany authors report that adding green space in the form of green roofs to denselypopulated urban environments provides eco-restorative habitats for displacedcreatures. Green roofs provide food, habitat, shelter, nesting opportunities and a saferesting place for spiders, beetles, butterflies, birds and other invertebrates(Brenneisen, 2003; Gedge, 2003).Green roofs are being studied for their unique ability to provide undisturbed, viablesanctuaries for rare and nearly extinct species. Studies report that this elevated urbanecosystem affords unique protection from grade level predators, traffic noise andhuman intervention.Studies reveal that butterflies can access green space on the 20th floor of a building(Johnston & Newton, 1992).Air Quality ImpactsDeclining air quality is an ongoing problem in cities globally, and solutions are beingproposed. Some have been acted upon, ranging from local initiatives to globalaccords. Among these are both restriction of point-source emissions and restoration ofbiological systems that reduce airborne contaminants.In cities there is strong interest in measuring and dealing with air pollution levelssince air contaminants are intensified due to the density of human activity, includingthe increased use of fossil fuels, the presence of the urban heat island and the absenceof natural biological controls.Inter-regional transport and global warming concerns serve only to heighten the issue,
  12. 12. as the magnitude and frequency of smog alerts and summer heat waves increase.Smog forms when nitrogen oxides (NOx) reacts with volatile organic compounds, aprocess that is accelerated by higher ambient temperatures.Evidence suggests that green roofs provide one opportunity to reduce local airpollution levels by lowering extreme summer temperatures, trapping particulates andcapturing gases.Johnson and Newton (1996) estimate in urban forestry studies that 2,000 m2 of un-mowed grass on a roof could remove as much as 4,000 kg of particulates from thesurrounding air by trapping it on its foliage.Several researchers report that vegetation benefits air quality by trapping particulatesand dissolving or sequestering gaseous pollutants, particularly carbon dioxide,through the stomata of their leaves.Urban Heat IslandThe air in urban areas is typically warmer than that in surrounding undeveloped areas.This concept has been recognized in publications since early in the IndustrialRevolution. Over the years, concern for the catastrophic effects on human health hasprompted the development of strategies for reducing the urban heat island effect.These strategies have included reducing heat radiation and other emissions, expandingvegetated spaces, and most recently the implementation of cool roofs and green roofs.The most frequently observed and documented climatic effect of urbanization is theincrease in surface and air temperatures over the urban area, as compared to the ruralsurroundings. Oke (1995) simply defines an urban heat island (UHI) as the‘characteristic warmth’ of a town or city. This warmth is a consequence of humanmodification of the surface and atmospheric properties that accompany urbandevelopment. This phenomenon is given its ‘island’ designation due to the isothermpatterns of near-surface air temperature which resemble the contours of an islandrising above the cooler conditions that surround it.The maximum difference in the urban peak temperature and the background ruraltemperature defines the urban heat island intensity. Over large metropolitan areas,there may be several plateaus and peaks in the surface temperature. Cooler patchescoincide with open areas where vegetation or water are found.The intensity of an urban heat island depends on many factors, such as the size of cityand its energy consumption, geographical location, absence of green space, month orseason, time of day, and synoptic weather conditions.Oke (1987) recognized that the urban heat island is especially related to the highurban densities and configurations of buildings in downtown areas. He demonstratedthat buildings can create ‘canyons,’ which substantially reduce the amount of skyview available for long wave radiation heat loss at night.Other factors contributing to the intensity of the heat island effect include:containment of heat by pollutants in the urban atmosphere, daytime heat storage due
  13. 13. to the thermal properties of urban surface materials, emission of heat (from buildings,transportation, and industrial operations), decreased evaporation due to the removal ofvegetation and the hard surface cover in the city which prevent rainwater percolationinto the soil.The absence of vegetation and the nature of this hard surface cover can be addressedby green roof treatments. It is impermeable urban surfaces (buildings, roadways,sidewalks, patios, parking lots etc.), and an absence of soil and vegetation that resultsin rapid shedding of water from rainfall and snowmelt.In the presence of stored moisture, energy is naturally used to evaporate water (as inrural and open areas). This sensible heat used to evaporate water creates a coolingeffect, thereby reducing the temperature of the surroundings. In cities, the absence ofsuch stored moisture, due to the increase of impervious surfaces, results in anelevation of surface temperature, which in turn increases the air temperature due toradiative heat transfer.Through better understanding of the general causes and associated problems of theurban heat island, specific strategies for reversing the effect have been gainingacceptance by municipalities. These include designs to exploit natural sources ofcooler air from the surrounding countryside and adjacent water bodies, parks withinthe city, air circulation created by urban structures themselves, and evaporativecooling from vegetation or other sources of water in the city.Designs to reduce the heating of surfaces are also seen as especially useful inovercoming the urban heat island effect. The benefits of tree planting programs inmetropolitan areas have been significant in cooling the air, as well as adding to theaesthetics, and reducing greenhouse gas (CO2) contributions.However, the demand for space in cities inhibits expansion of forested areas.Green roofs present the opportunity to expand the presence of vegetated surfaces byreplacing impermeable surfaces in urban areas, providing for a reduction in peaksummer urban heat island temperatures.The urban environment, the lack of vegetation, which controls evapotranspiration, isthe most significant factor contributing to the urban heat island. Therefore green rooftechnology offers the possibility of a great impact on the urban heat island effect.It should be noted that UHI is of major concern in summer months. It is not deemedto be of much concern in the winter months in northern climates.Storm-water Management ImplicationsMany consider storm-water runoff mitigation to be the primary benefit of green roofsdue to the prevalence of impervious surfaces in urban and commercial areas and afailing storm-water management infrastructure. Rapid runoff from roofs and otherimpervious surfaces can exacerbate flooding, increase erosion, and result in combinedsewer overflows that could potentially discharge raw sewage directly into ourwaterways.
  14. 14. Green roofs help mitigate the impact of high-density commercial and residentialdevelopment by restoring displaced vegetation.Studies have shown that green roofs can absorb water and release it slowly over aperiod of time as opposed to a conventional roof where storm-water is immediatelydischarged. Research has indicated that an extensive green roof, depending onsubstrate depth, can retain 60 to 100% of incoming rainfall.This reduction in quantity of runoff from a green roof leads to improved storm-waterrunoff and surface water quality. Results from a Vancouver, BC, modeling studysuggest that if all of Vancouvers existing buildings were retrofitted with green roofsover the next 50 years, the health of the area watershed could be restored to naturalhydrologic conditions in terms of flood risk, aquatic habitat, and water quality(Graham and Kim, 2003).This would occur because green roofs have the ability to filter numerouscontaminants from rainwater that has flowed across the roof surface.Other studies showed roof runoff contained higher amounts of numerous heavymetals and nutrients when compared with rainfall, probably due to the runoff pickingup particulate pollutants when flowing across the roof. For green roofs, thesepollutants can be taken up and degraded by the plants or bound in the growingsubstrate of green roofs.Rainfall and snowmelt in urban areas are typically more problematic than in ruralenvironments. Under natural conditions, precipitation is impeded from runoff byvegetation, ground-surface retention and subsurface storage. The retained rainwaterwill contribute to the soil moisture and ground water replenishment. Urban landscapesare dominated by impervious surfaces, such as concrete sidewalks, building walls androofs, and paved parking lots and roads. These collect the flow and direct it into stormgutters, sewers and engineered channels (collectively called the urban drainagesystem). Urban runoff eventually reaches receiving waters as sudden uncontrolledsurges. Many surface contaminants are picked up in the passage of this runoff and arecarried with this surge of storm-water. Common contaminants include suspendedsolids, heavy metals, chlorides, oils and grease, and other pollutants that arise fromthe use of roadways and from other surfaces the water has passed over.There are two basic categories of interrelated problems concerning urban runoff andwastewater from areas served by drainage systems: quantity management and qualitymanagement. Quantity management problems arise from upstream and downstreamflooding, associated with overloaded sewer systems, and from erosion of conveyancechannels downstream in the drainage basin.Untreated overflows to receiving waters from combined storm and sanitary sewersystems result in water quality management problems. Sanitary overflows usuallycontain high concentrations of organic compounds, bacteria and nutrients, whichcause short and long-term quality problems to receiving waters. On the other hand,storm overflows often contain a considerable amount of trace metals and a highconcentration of suspended solids, which may have long-term impacts on receivingwaters as pollutants slowly release from deposited sediments. The following sectionsdescribe quantity and quality problems associated with each type of drainage system.
  15. 15. ConclusionModern architecture is essentially closed blocks of concrete and glass. Heating andcooling these structures is done with high-energy output and considering limited oilreserves and rising energy costs, this is a highly negative effect.Because city surfaces absorb, rather than reflect the suns heat, surface temperaturesquickly rise. Green roofs, however, make a noticeable impact on a buildings heat andgain loss. During the summer, for example, the temperature of a gravel roof canincrease by as much as 25 degrees Celsius, fluctuating between 60 and 80 degreesCelsius. But covered with grass, the roof temperature doesnt rise above 25 degreesCelsius. Not only do they absorb less heat, green roofs also help cool theirsurroundings, suck up airborne toxins and put oxygen back into the air.As cities continue to expand, theres increasing concern whether their additionalwarmth will further impact global temperatures. The disastrous 2003 summer heatwave that lead to 35,000 deaths in Europe showed how global climate changeadversely impacts health. While scientists debate what exact influence cities have onclimate change, one thing is for certain, urban heat islands effects city dwellers --nearly half of the words population.In addition to mitigating water runoff and heat, green roofs boast a variety of gains,the first being economic. Because they are protected from ultraviolet radiation and theextreme fluctuations in temperature that cause roof membranes to deteriorate, greenroofs offer longer roof life -- they can last up to 40 years -- and lower roofmaintenance. They beautify bare concrete stretches, are able to grow food, attractwildlife and provide habitat in areas with fewer resources; they provide businessopportunities for nurseries, landscape contractors and irrigation specialists, and alsooffer substantial noise insulation, which is why Amsterdam and Zurich use it at theirairports.Green roofs offer so many benefits -- they reduce energy consumption, create greaterbiodiversity and help mitigate the effect of urban land use. For a few additional costs,they bring greater long-term economic benefits, as well as a hugely betterenvironment in the city center.
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