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Green Roofs In Urban Environment Mert EKŞİ Research Assitant Istanbul University Faculty Of Forestry Landscape Architecture Department
Concepts • • • Green Roof Garden Terrace Garden Vegetated Roofs Eco-Roofs
Green Roofs • A vegetated roof system is simply vegetation growing on a building rooftop. This is a generalized term that has been used informally to discuss all types roof greening. The more specific terms used to describe vegetated roof systems are ecoroof, living roof, brown roof, roof garden and green roof, which are more distinctive terms, yet are often used interchangeably. (Coffman, R. R. , 2007).
Green Roofs • A green roof (or ecoroof) is a roof that contains a soil (growing media) and vegetation layer as its outermost surface. The construction between the growing media and the roof structure varies, but typically includes a drainage layer, a root barrier, and a waterproof membrane (Sailor D. J. 2008). • So, we can simply classify the roof gardens as extensive and intensive roof gardens. Roof gardens are usually classified by their constructional properties. However type of planting on the roof determines the construction properties of a roof garden. These properties have some variations according to the constructional layers or planting type.
Green Roofs • Intensive roof gardens are roofs which are planted with shrubs and trees which have similar type of systems (drainage or irrigation systems or surface pavements) like ground level gardens and they are usually established for their esthetical properties. In these types of roof gardens, growing medium is deep and other constructional layers have some complex properties. • Extensive roof gardens have shallow growing medium and they don’t require complex irrigation or drainage systems. They are mainly built for their ecological benefits for the building or the city. In extensive roof gardens, plant selection is important. Plants on the roof will be exposed to extreme climatic conditions. So in these areas, selected plants are drought resistant with high regeneration ability. Sedum species are the most preferred plant type in these gardens.
Green Roofs • “Extensive” and “intensive” are the two main terms describing greenroof design. These terms describe differences in construction, design and costs. Extensive green roofs, which have a thin growing medium, are the most typical. • Extensive green roofs use a substrate depth ranging between 5 and 15 cm (1. 97 and 5. 91 in. ) and weigh between 72. 6 and 169. 4 kg/m 2 (160. 06 and 373. 46 lb. /sq. ft. ). This shallow planting media (lowweight, soil-less) helps minimize costs and the total structural load. These low-weight synthetic planting media, combined with the challenging winds, drought and high-temperature microclimates on an elevated surface, make hardy, low-height, drought-resistant plant species necessary. Comparatively less maintenance is needed to install and maintain an extensive green roof; however, the success of any roof is measured by the survival of the plants. • Intensive green roofs can be designed for unique and esthetic amenity or recreational space including public access. Intensive green roofs feature deeper planting media, irrigation systems, complex landscaping features and a broad range of plant species. They can support large plant species such as trees, shrubs, ponds, waterfalls and other decorative features. Engineered roof surfaces that can accept heavier weights support the deeper growing media of intensive green roofs. Intensive green roof retrofits may require roof structure upgrades. They may also cost more for materials, labour, design features and heavy equipment, such as overhead cranes to get materials to the roof. (A Resource Manual for Municipal Policy Makers, Lawlor G, Anne B, Hitesh C, Ireen D, Wieditz 2006)
Green Roofs - History • History of roof gardens extends up to the old ages. First examples of roof gardens were seen in Babylon.
Green Roofs - History • Roof gardens which can be described as “modern roof gardens” were built in 1930 – 1950’s, nearly before and after the World War II (Osmundson, T. , 1999).
Green Roofs - History • Until the mid-20 th century, green roofs were viewed mainly as a vernacular building practice. However in the 1960’s, rising concerns about the degraded quality of the urban environment and the rapid decline of green space in urban areas, renewed interest in green roofs as a "green solution" was sparked in Northern Europe. New technical research was carried out, ranging from studies on rootrepelling agents, membranes, drainage, lightweight growing media, to plant suitability (Peck and Kuhn, 2001).
Green Roofs - History A Norvegian House (Osmundson, 1999) First example of a green roof - Vydimri Church – Iceland
Green Roofs have 4 main layers. These are; • • Drainage Layer Filter layer Growing Medium Mulch
PLANTING TYPES IN GREEN ROOFS In extensive green roofs, there are three planting methods except traditional planting method. 1. Sedum mats ; polyester based mats which contains 2 cm deep growing media. 2. Biodiversity planting ; planting of the green roof is being left to the nature. Seeds and plant parts start to grow in the roof without any intervention. 3. Hydroseeding / hydroplanting ; Plant parts or seeds are put in a special mixture and they are sprayed onto growing medium
Benefits of Green Roofs Economic Benefits • Protection of roof membrane resulting in a longer material lifespan (it is estimated that green roofs will last up to twice as long as conventional roofs), resulting in decreased maintenance and savings in replacement costs; • Savings on energy heating and cooling costs, depending on the size of the building, climate and type of green roof. (www. greenroofs. org)
Benefits of Green Roofs Sound Insulation • Soil, plants and the trapped layer of air can be used to insulate for sound. Sound waves that are produced by machinery, traffic or airplanes can be absorbed, reflected or deflected. The substrate tends to block lower sound frequencies and the plants block higher frequencies. • A green roof with a 12 cm (4. 7 inches) substrate layer can reduce sound by 40 decibels; a 20 cm (7. 9 inches) substrate layer can reduce sound by 46 -50 decibels(www. greenroofs. org).
Benefits of Green Roofs Improved Air Quality Filtration of Airborne Particulates: • A green roof will not only absorb heat, decreasing the tendency towards thermal air movement, but will also filter the air moving across it. • 1 m 2 (10. 76 ft 2) of grass roof can remove up to 2 kg (4. 4 lbs) of airborne particulates from the air every year, depending on foliage type. Carbon Dioxide/Oxygen Exchange: • Through the process of photosynthesis, plants convert carbon dioxide, water and sunlight/energy into oxygen and glucose. This cyclical process supplies animals and humans with oxygen and food. • 1. 5 m 2 (16. 15 ft 2 ) of uncut grass, produces enough oxygen per year to supply 1 human with their yearly oxygen intake requirement.
Benefits of Green Roofs Temperature Regulation Moderation of the Urban Heat Island Effect • Through the daily dew and evaporation cycle, plants on vertical and horizontal surfaces are able to cool cities during hot summer months. In the process of evapotranspiration, plants use heat energy from their surroundings (approximately 592 kcal per L of water) when evaporating water. One m 2 (10. 76 ft 2) of foliage can evaporate over 0. 5 litres of water on a hot day and on an annual basis the same area can evaporate up to 700 litres of water. • This process reduces the 'Urban Heat Island Effect' in the summer. The 'Urban Heat Island Effect' is the difference in temperature between a city and the surrounding countryside. It is mainly due to the expanse of hard and reflective surfaces, such as roofs, which absorb solar radiation and re-radiate it as heat. Reduction of the 'Urban Heat Island Effect' will also reduce the distribution of dust and particulate matter throughout the city and the production of smog. This can play a role in reducing greenhouse gas emissions and adapting urban areas to a future climate with warmer summers.
Benefits of Green Roofs Building Insulation: • Historically, green roofs have been used to insulate buildings. Shading the external surface of the building envelope has been shown to be more effective than internal insulation. • Green roofs insulate buildings by preventing heat from moving through the roof. Their insulation properties can be maximized by using a growing medium with a low soil density and a high moisture content and by choosing plants with a high leaf area index (i. e. the bigger the leaves, the better). This could play a role in reducing greenhouse gas emissions and adapting urban areas to a future climate with greater incidences of drought and extreme heat. Industrial Cooling: • The Possman Cider Cooling and Storage Facility in Frankfurt, Germany yielded a 2 -3 year payoff of their green roof system through savings in heating and cooling costs, as well as in equipment costs, since additional cooling towers had become unnecessary.
Benefits of Green Roofs Creation of Microclimates: • A green roof will have a noticeable impact on the heat gain and loss of a building, as well as the humidity, air quality and reflected heat in the surrounding neighbourhood. In conjunction with other green installations, green roofs can play a role in altering the climate of the city as a whole. • On a summer day, the temperature of a gravel roof can increase by as much as 25 °C (77 °F), to between 60 -80 °C (140 - 176 F). Covered with grass, the temperature of that roof would not rise above 25 °C (77 °F), thus resulting in energy cost savings. • 20 cm (7. 9 inches) of substrate with a 20 -40 cm (7. 9 - 15. 7 inches) layer of thick grass has the combined insulation value of° 15 cm (5. 9 inches) of mineral wool. • Rooms under a green roof are at least 3 - 4 °C (5. 4 - 7. 2°F) cooler than the air outside, when outdoor temperatures range between 2530 °C (77 - 86 °F).
Benefits of Green Roofs Water Stormwater Retention: • Water is stored by the substrate and then taken up by the plants from where it is returned to the atmosphere through transpiration and evaporation. • In summer, depending on the plants and depth of growing medium, green roofs retain 70 -90% of the precipitation that falls on them; in winter they retain between 25 -40%. For example, a grass roof with a 4 -20 cm (1. 6 - 7. 9 inches) layer of growing medium can hold 10 -15 cm (3. 9 - 5. 9 inches) of water. Water Filtration: • Green roofs not only retain the rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that happens to run off.
Benefits of Green Roofs Temporal Delay of Stormwater Runoff and Reduced Runoff Volume • Green roofs reduce the amount of stormwater runoff and also delay the time at which runoff occurs, resulting in decreased stress on sewer systems at peak flow periods.
Benefits of Green Roofs Habitat • Rooftop habitats can play one of two roles: a 'stepping stone' habitat connecting natural isolated habitat pockets with each other, or an 'island' habitat remaining isolated from other habitats at grade. • Green roofs can be specifically designed to mimic endangered ecosystems/habitats, including the prairie grasslands of the midwest US, the rocky alvars of Manitoulin Island the Great Lakes Region in Canada. • The Toronto City Hall Demonstration Project features a black oak prairie ecosystem and native plant butterfly plot.
Benefits of Green Roofs Flora & Fauna • Green roofs designed for minimal maintenance are very protected and can become home to plants easily damaged by walking and to birds that nest on the ground. Since the soil on these green roofs is also less likely to be disturbed, it becomes a safer habitat for insects, and the deeper the soil the more diversity the roof can support. • In Germany, for instance, research has shown that green roofs can support anywhere from 10 to 40 different insect species and have even been found to harbour nesting bird species. • The Toronto City Hall Demonstration Project features two urban agriculture plots that are growing a variety of annuals and perennials. • Also green roofs are aesthethical structures for the urban environment.
Rainfall and Stormwater Runoff Controlling the stormwater runoff in urban environment is very important. Green roofs are supplementary structures to control the stormwater runoff. In some cities, green roofs are used as wide scale drainage structures. For details : http: //www. ciria. org. uk/suds/icop. htm
Rainfall and Stormwater Runoff In this chart, REF : Refence Roof GR-1 : Green Roof with 75 mm growing medium GR-2 : Green Roof with 150 mm growing Medium Rainfall and runoff values can be seen on figure. Source: BCIT Green Roof Research Summary 2005
Conclusion • Modern extensive systems can be used instead of roof tiling because they are almost in same weight. But the roof plate under the roof garden or roof tiling must be strong. There are no restrictions for roof slope. Modern extensive systems can be applied up to 36 degrees. • Certainly, green roofs can not replace natural ecosystems. But green roofs can be thought as regulating structures in urban environment. • There must be a policy which supports the improvement of urban environment. If there are many green roofs in the city - like in some German cities – they can be thought as an integrated drainage system or regulating structures for urban environment.