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Development of the Green Roof

4921 words (20 pages) Essay in Construction

23/09/19 Construction Reference this

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Development of the Green Roof

ABSTARCT

With the world economy growing, our Mother Nature is completely forgotten. With the cities growing rapidly in form of concrete structures has left us with no open grasslands.  Building structures are something which we cannot eliminate from our lives, but what we can do is make our buildings more enduring towards the nature. There are many ways and methods which can be used to do so and one of the concepts will be thrown light upon in this study. The topic of Green roof will be analyzed, concepts of green roof, advantages of green roofs, application of green roofs and its uses in design as an architectural structure of the buildings and few examples incorporating Green roofs will be explained.

TABLE OF CONTENT

Abstract………………………………………………………………………………………………………………….1

List of Figures …………………………………………………………………………………………………………..2

List of Tables……………………………………………………………………………………………………………3 

1. Introduction.………………….………………………………………………………………………………………4

 1.1 History…….………………………………………………………………………………………………………..6

 1.2 Green Roof – Types……………….……………………………………………………………………….……….7

2. Green Roof Components and Layer System….………………………………………………….……….………….8

3. Plant Selection for Green Roof…………………………………………………………………………….……….10

4. Green Roof- Advantages……………………………..……………………………………………………….…….11

5. Life of Green Roof………………………………………………………………………………………………….14

6. Green Roof- LEED Credits……………………………………………………………………..…………………..15

7. Case Study – Lawrence Tech Green Roof….………………………………………………………..………………17

  7.1 Goal/Purpose………..……………………………………………………………………………………………..17

  7.2Background…………..……………………………………………………………………………………………17

  7.3 Storm water run off……………………………………………………………………………………………….18

  7.4 Water Quality……………………………..………………………………………………………………………1

8. Conclusion……………….………………………………………………………………………………………….23

9. References……………….………………………………………………………………………………………….24

No table of figures entries found.

  1. INTRODUCTION

Green roofs are simply roofs bearing vegetation that may take many different forms. Some are mats of uniform vegetation and thickness covering a large expanse of flat or sloping roofs. [1] A green roof is a technology that can provide a vast range of benefits to the society, interested in the enhanced environment and reduction in energy consumption and that convey financial benefits to the community. (Dvorak, 2010). Green roof is often associated with various different terms like Eco roof, Living roof, Brown roof. The different terms evolved due to the featured plant materials – a combination of rich, diverse and perennial species which are not green all year round.

Green roofs is definitely more expensive when compared to the conventional roofs. But it has its own benefits and over the long run the initial cost of the installation is covered easily. The Living ( green) roof has various advantages like Aesthetics ,  Storm water management , Mitigation of the urban heat island , Thermal and Acoustical insulation , Reduction of the Energy bills , Reduction in carbon di oxide , Economical benefits and many more.

Green roof contributes to LEED (Leadership in Energy and Environmental Design). A 2008 report by a commercial real estate research company found that buildings certified by the U. S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) program or by the Department of energy’s Energy Star program fetched higher rents and enjoyed greater occupancy than comparable conventional buildings. The certified buildings, especially LEED buildings, also attracted higher sales prices per square foot. Owners of these buildings also cited the marketing value of the certifications as well as the savings on operational costs (Miller et al.2008).

1.1           GREEN ROOFS- HISTORY

As early as 500B.C green roofs have been a part of the building history. The Hanging Gardens at Babylonia is one of the best examples for this. In olden days people used to use green grass as a cover for the roofs for their buildings due to the shortage of wood. In late 1800s early American settlers started using this concept, as it would keep the house warmer during the harsh winters and warmers during the hot summers.

While roof gardens have been familiar to North Americans from a long time, the extensive green roofs concept came from Europe. Whereas in Germany this concept existed much before than in Europe. A research was done in 1960’s at Germany which helped to create a feasible market for green roofs which began in 1970s.Today the level of green roof application and use increases approximately by 145 million square feet per year (Oberdorfer et al. 2007).

In the United States such policies have always been difficult to imply on the federal level. But local incentives are increasingly popular throughout  North America.IN addition  , stronger storm water management regulations  , have come in effect under the Clean Water Act and local codes might ultimately make green roofs as common as detention basins are now. Leaving the incentives aside, the U.S federal government is providing leadership on green roofs. Many agencies now encourage or even require that the new construction conform to LEED standards, which award points for green roofs (USGBC 2009). [2]

More Government green roofs are likely to come in early 2007, under the Energy Independence and Security Act (P.L.110-140).Section 438 of that law raises the bar even more for storm water management on federal sites with a footprint of 5000 SQFT or more. The maintenance and restoration of predevelopment hydrology to the maximum extent technically feasible through site planning, design, construction, and Maintenance strategies.

Fig 1: Many buildings owned or managed by the US federal government, including the Department of Transportation in Washington, D.C, have green roofs

Fig 2: Green roofs in Germany

1.2           GREEN ROOFS- TYPES

Green roof is of two types. The division is done based on the depth of the substrate layer. The types of green roofs are Intensive, Semi-Intensive, and Extensive. The depth of soil , the variety of plants , weight of plantation , irrigation , maintenance requirement and the most important the cost of the system all these are the classifications based on which the division is made.

  1. Intensive roof: A roof type that consists of different types of vegetation starting from grasses, shrubs to small trees. It may also include walkways, benches, tables, and fountain on the roof. The intensive green roof has a depth greater than 150mm. This roof has heavy weight and high maintenance. Intensive green roof can weigh from 171 – 391kg/m2 (Breuning, 2015).

An intensive roof required more soil depth and variety in the plant community than the extensive roof (Kristin and D. 2006). The growing medium is 8 to 12 inch (British Columbia Institute of technology). This type of roof garden provides a  space where people come and interact with nature (Amanda, Jim, McRae, Kathy, Michael 2014), children can play in the same way they do in a normal public garden hence , this roof is also known as a Garden roof.

Fig 3: An image showing Intensive roof

  1. Extensive roof: A simpler roof when compared to Intensive. It is lightweight, requires low maintenance and drought resistant plants usually sedum, herbs, mosses and desert grass, the reason behind them is they are shallow- rooted.  Thickness is of less150 mm. Extensive green roof can weigh from 73kg/m2 to 122 kg/m2 (Breuning, 2015). Considering the sustainability aspect, this roof can be used more widely and more often in various places because of its low weight. 10-20% of organic matter is required in the soil. The cost of this roof is very low when compared to Intensive and semi intensive roofs.

Fig 4: An image showing Extensive roof

  1. Semi-Intensive Roof: A combination of elements from both Intensive and extensive roof types gives rise to a Semi- Intensive roof type. The growing medium ranges from 6 – 8 inches. According to the International Green roof association this roof type helps in reducing the loss of storm water better when compared to Extensive roof and has more design options. Grass, herbs, herbaceous plants, small shrubs that require moderate maintenance and periodical irrigation. This roof provides uses for a mixed habitat. The roof weighs between 170.9 to 244.1 kg/m^2.

Fig 5: An image showing Semi- Intensive roof

Tab 1: Characteristics of different types of green roofs

2       GREEN ROOFS- COMPONENTS AND LAYERS

In roofing terminology, the whole green roof assembly above the waterproofing membrane is known as the overburden. The most basic green parts of a green roof are the growing medium and plants. Green roofs has several layers in it. Vegetation layer, growing medium or soil layer, filter fabric layer, drainage layer, root barrier, insulation waterproofing membrane layer and then the roof deck all these are the components or the layer system of a Green roof.

Fig 6: Built up system of Green roof (www.greenroofs.org)

There are two methods of placing the layers of Green roof. The built-up system are arranged in layers and they are been put together layer by layer as shown in fig 6 above. The Modular system is quite different from the built-up system where as in the modular system, the growing media or soil, filter cloth, drainage layer are transportable or arranged around the roof like a floor-covering or grid pattern shown in fig 7 below.

Fig 7: Modular method of arranging Green roof (www.greenroof.org)

  • Vegetation Layer: This is layer is top most layer of a green roof. It comprises of the grass, plants, trees and many other things that helps in keeping the building cooler and warmer as when required. Also the vegetation provides biodiversity. It is also known as Green Layer.

 

  • Growing Medium: This is the foundation base for the vegetation or green layer. The main purpose of this layer is to provide the right depth, mixture and type for the plants chosen to be on the green roof. These being the basis for the vegetation to grow and also to hold them and protect them from the harsh winds.

 

  • Filter Layer: This layer as the name says does the job of filtration. It is placed between the growing medium and vegetation layer. It prevents any clogging and also saves from the draining of the excess organic material.

 

  • Drainage layer: The main purpose of this layer is to prevent waterlogging .It also helps saving the excess water from draining it, which can be used during dry weather conditions. It is a protective cover to the underlying waterproofing systems.

Fig 8: Layer and Components of Green roof (www.greenroof.org)

 

 

  • Root barrier: As the name suggests it is a barrier which protects the roots from entering the roof deck. It sometimes may cause leakage and hence it is placed above the drainage layer. Usually the placement of this layer is between the insulation layer and protection fabric.

  • Insulation layer: One of the most important layers. It is very strong and can hold the weight from the saturated soil, drainage and vegetation layer. Its main purpose is that it avoids the heat from entering during summers and avoids loss of heat during winters. This helps in reducing the energy bills to a great extent.
  • Waterproof Membrane: It is the last layer of the roof membrane and it is very important .It protects and prevents from any water leakage into the roof deck.

The other layers may be included in roofs like membrane protection board, additional insulation, moisture retention layer, and irrigation and erosion blanket. The design of this component and layer systems depends upon the purpose of the green projects (Kristin and D. 2006).

3       GREEN ROOFS- PLANT SELECTION

A successful green roof requires the selection of growing medium and plants that will work with the site, fulfill the project’s design intent and thrive over the long term with the project resources available for maintenance. Attention to the standard roofing issues, including structural loading, waterproofing, and drainage, is also an integral part of the roof design. [2, p. 51].

Plants are the main aspect of a green roof not just because they add to the aesthetic beauty but also because they are the key to the storm water management. It is important to remember that green roof though bears a visual resemblance to the normal garden but it does not actually resemble a public garden when compared to the components and plant selection. Factors like wind , sunlight , heat are at the peak on a roof and the qualities for a good soil grade( heavy organic material ) is not good for the green roof because it leads to the weed pressure and degradation of the quality of plants and the project.

A green roof plant has to bind the medium together with a roof system that persists all year round to prevent wind scour and provide horizontal continuity to the system, improving its function and efficiency [2, p. 64].It should be able to pump water from the atmosphere through evapotranspiration, and also be able to live during the dry conditions.

Characteristics of successful green roof plants include ease of establishment, a shallow lateral root system, low nutrient and maintenance requirements, resistance to damage from insects and disease, lack of windborne seeds and light weight at maturity.

  • Extensive roof: Plants with shallow roots, high drought capacity should be used. The plants used here are of the similar types at the different regions like mountains, desert, coasts and many other such regions. The sedum is the famous choice for the extensive roof (Dunnett and Kingsbury 2004), and Grasses are also used in the roof, that deliver native attention to green roof along with that; they support biodiversity.

    Fig 9: Extensive roof showing grass, mosses, herbs, drought

  • Intensive and Semi intensive roofs: This allows a variety of plant selection due to its deeper layers, higher irrigation and high maintenance. But before choosing this type verification of that building roof is essential that whether it can take up that much load of deeper and heavier layers.

Fig 10: Intensive roof plants (myroof.com)

4       GREEN ROOFS- ADVANTAGES

Green roof is known to be used widely in our world today because of its numerous advatages to our environment and some of them can be illustrated in the picture below.

Fig 11: Benefits of Green roof (Stater, 2008)

  • Storm water Management: The growing medium of the green roof absorbs the water with the help of plant and vegetation above it. The green roof can reduce storm water runoff by 50 to 60% and in the case of, lower storm event, a green roof can totally stop storm water runoff (Vanvert et al. 2005). The extensive roofs reduce the storm water by 90%.

Most of this absorbed water is returned to the water cycle through evaporation and transpiration (evapotranspiration) (Kristin and D 2006). The excess water is filtered and drains-off with the delay along with the reduced volume. This delay runoff leads to lower the burden on the storm water structure and sewers during the peak flow period (Kristin and D 2006). The water runoff from the conventional roof is usually full of pollutants, but the water runoff which is coming from green roof is less polluted when compared to the traditional roof. The owners of the facility could create a water tank to store this delay runoff water.

  • Reduction of Heat Island Effects: The temperature differences between urban area and the rural area is known as heat island effect. The solar rays, warms up the concrete, asphalt and other construction material faster and hotter than the green area. Hence the cities get warmer in winters and hotter in summers.

The Growing medium due to the transpiration concept reduced the solar gain by 90%. The vegetation layers absorbs the sunrays and hence lesser heat is transferred to the roof deck. The multiple layers of green roof keeps the temperature controlled and helps in cutting down on the energy bills. It also helps in reducing the energy demand for that building.

  • Reduction in Carbon Dioxide: As we know the fact that plants, trees, shrubs etc. absorb all the carbon dioxide as part of photosynthesis process which they undergo. Hence the more number of green areas we have will help in the amount of carbon dioxide in air .Green roofs exactly help us in this manner, the vegetation layer absorbs the carbon dioxide in atmosphere reducing the pollution to a great extent.
  • Insulation: The green roof layers not only help in reducing the heat gain and loss, but also helps in reduction of the noise from entering the building. It acts as a sound barrier. The study indicates that green roof reduces sound refection up to 3 decibels and improve sound insulation up to 8 decibels as well as reduce indoor sound as much as 40 decibels (IGRA). So, it creates a much livable environment considering both indoor and outdoor.
  • Aesthetics: The green layer not only helps in reducing the air pollution, the heat gain/loss in the buildings, reduce storm water runoff but also gives an additional beauty to the building. In this concrete world where greenbelt is rare, the rooftop gardens deliver quiet green spaces for pleasure relaxation and recreation. The greenery brings in more productivity, makes us healthier, happy and brings about the creativeness in us.
  • Biodiversity: The concept of green roof and the green layer at the top of the roofs becomes the home for so many isolated animals and insects. The sedums, herbs, grasses and soil of green roof help to recreate habitat for insects, butterfly and many others. This rooftop habitat serves as stepping stone, to create corridors to connecting other isolated refuges within the city .it called habitant corridor (green corridor) (Amanda, Jim, Mcrae, Kathy, Michel 2014). The extensive green roof at ford motor company, assembly plant, Dearborn, Michigan has 29 insect species, seven spider species and two bird species (Coffman and Davis, 2005).

5       GREEN ROOFS- LIFE SPAN

The conventional roof undergoes the harsh climatic changes every day and even the water proofing membrane gets damaged due to heavy storms. The green roof, the green layer helps in reducing the heat gain/loss in the building, also reduces the damage by the storms and hence increases the life span of the roof deck to a greater extent. A green roof deck has a longer life than the normal conventional roofs.

According to the study of Michigan state university, 21,000 SQ. Ft. Conventional roof installation cost is $335,000 ($401,827 in 2016) and same size green roof installation cost was $464,000($556,561 in 2016) in 2006. But, over the life, the green roof would save about $200,000 ($239,897 in 2016) in energy costs. The absorption of heat and cutting down on the heat gain/loss of the building, ultimately helps in reducing the energy demand which directly reduces the energy bills.

6       GREEN ROOFS- LEED CERIFICATION

Leadership in Energy and Environmental Design known as LEED is an environmental rating system originally developed by the U S Green building Council to help identify and rate sustainable designs.

There are basically 6 parts to achieve a LEED certification.

Part 1 – Sustainable sites: There are two sub categories of application for green roofs:

  • Reduced site disturbance , protect or restore open space
  • Landscape design that reduces the urban heat island effect.

A project could be awarded points by demonstrating that existing site areas are protected and damaged areas of the site are restored to provide habitat and promote biodiversity. This helps achieve nearly 3 points. Also a green roof which features the habitat, could also demonstrate that these roofs reduce the heat island effect. A substantial green roof that covers at least 50% of the roof surface can earn credits under LEED.

Part 2- Water Efficiency: Credits are awarded for storm water management, water efficient landscaping, water use reduction, and innovative waste water techniques. If potable water is eliminated as a source for green roof irrigation then two more LEED points can be earned. Further credits can be earned by reducing the potable water usage. For ex: storm water can be captured and stored in tanks and can be used for flushing toilets. Also the green roof could be designed in such a way that it helps treat and filter grey water, which is domestic wastewater from dish washing, hand washing and bathing.

Part 3- Energy Efficiency: Energy performance, renewable energy and reduction of ozone depleting surfaces are the main aspects of this part. Green roofs provide thermal insulation and reduce the energy consumption demonstrating energy efficiency .Further the use of photovoltaic cells on a green roof either to generate electricity or to power the irrigation unit for the green roofs helps in contributing towards getting the credits for LEED. Green roofs also reduce the use of refrigerants such as chlorofluorocarbons which is harmful for the ozone layer. This is because of the cooling effect created by Green roofs. Hence this also helps in achieving LEED credits.

Part 4- Materials and Resources: Green roofs are helpful here because of the storage and collection of the recyclables. For Ex: A green roof could function as a depository for compost, which diverts waste from the local landfill and enriches the growing medium of the green roof.

Part 5 – Indoor environmental quality: Due to the thermal insulation provided by the green roof the indoor environment remains much cooler/ warmer depending upon the climatic conditions. Hence this can achieve the LEED credits here to maintain a good thermal insulated indoor environment.

Part 6- Innovation in Design: The various unique ways in which the roof is designed and then green roof concept is used brings about an innovation in design, helping earn LEED credits.

7       GREEN ROOFS- CASE STUDIES

Case study 1(Empire State Building 30th Floor West)

  • West Green Roof is located on 30th floor in Empire state building, New York City, USA. It’s an extensive green roof of 112 square meter
  • It has a slope of 1o. It is light in weight. The plants grown are sedum species of succulent leaves together with ferns and moss species. The plants were grown on a mat off site and were brought to the site for installation.

Fig 12: Green roof showing sedum species (www.greenroofs.com)

  • It was designed by Xero Floor America, LLC and it was built in 2013. This green roof is only accessible for maintenance. There are other green roofs on the 21st floor and 25th floor with sizes of 321 square meter and 93 square meter respectively.
  • The use of green roofs has helped in reducing energy consumption and as a result that the building is acknowledged with Energy Star rating of 80 by Energy Star Program and it is considered as one of the top 20% energy efficient buildings in the Program and it has been credited with LEED-ED Gold recognition by USA Green Building Council.

Case Study 2 (Hewlett Packard Building 4A Green Roof)

  • The Hewlett Packard Building 4A green Roof is located at Palo alto California, USA, designed by Royston Hanamoto, Alley and Abey.
  • It was built in 2011, and it has a size of 1747 square meter and a slope of 1o. The roof consist of green area and paved walkways. The green area consist of sedum plant species mixed with some perennial plants and three combinations were used.

Fig 13: Green roof plants and paving (www.greenroofs.com)

  • Sun & Shade combined with Fragaria chiloensis and Stipa tenuissima, Color Max combined with Escholzia californica Maritima and Achillea millefolium Paprika, All seasons combined with Thymus Serphyllum Coccineum. This green roof is private and accessible.

    Tab 2: Comparison between the two case studies.

Empire State Building 30th Floor West Green Roof

Hewlett Packard Building 4A Green Roof

Location

Manhattans New York, USA

California USA

Plants

Sedum species

Sedum species and perennials

Green roof type

Extensive

Extensive

Size

112 square meter

1747 square meter

Climatic Region

Humid Continental

Mediterranean Like

Slope

1%

1%

In Case Study 1 (Empire State Building 30th Floor West Green Roof) the green roof is simpler which was characterized by the use of suitable Sedum species mainly succulents there by defining the green roof as an extensive type. This green roof is only accessible when it comes maintenance therefore its main purpose is to provide environmental benefits and that’s also a reason why Extensive green roof was chosen.

In Case study 2 (Hewlett Packard Building 4A Green Roof) the green roof is an extensive green roof but it can also be refer to semi-extensive because it contains both features of extensive and intensive green roof. The use of high maintenance plants in this case study makes the green roof to serve as roof garden.

8       CONCLUSION

Earlier days due to the less pollution, population and mainly the less advancing infrastructure in cities there was no need for green roofs. But now due to the fast growing cities and less of green areas the need for sustainable concepts have arose. Green roof is one of the categories in sustainable constructions and hence now it’s booming up.

When economic development of green roof is seen, it is ahead than the traditional roof. The green roof reduces heat island effects to achieve energy savings in cooling and heating systems. Together with this the life expectancy of a green roof is high than the asphalt roof due to the presence of vegetation and growing medium above the roofing membrane.

The advantage of wasted spaces in the normal flats roofs of the buildings can be taken by the urban cities, by making it into a green roof in order to make environment more sustainable. After a through observation it is seen that the installation of green roofs involves lot of technicalities and hence it is ideal to get green roof installed by calling the professionals to do it.

9       REFERENCES

  1. The Green Roof Manual by Edmund C. Snodgrass and Linda Mclyntyre.
  2. Green Roofs in Sustainable Landscape Design by Steven L. Cantor
  3. Rufai and Halil (2016) “an evaluation of green roofing in buildings “, ISSN 2250-3153, www.ijsrp.org.
  4. Amanda, Jim, Mcrae, Kathy, Michel (2014) “green plants for green building “ , presented by green plants for green buildings www.greenplantsforgreenbuilding.org
  5. EHS journal, practical solution for the environment, health and safety professions, http://ehsjournal.org.
  6. Green roof technology, http://www.greenrooftechnology.com
  7. My plant connection, green roof, http://www.myplantconnection.com.
  8. Soil science society of America, https://www.soils.org.
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