Abstract: Green roof infrastructure became an important option for the residential buildings in western countries. It has a big role in improving biodiversity, in addition to a significant number of economic, environmental and social benefits. Despite all these advantages, Doha has a lack of green roof application; maybe it is due to some people’s misconceptions, that green roofs are not suitable for this region. In this research paper, a several elements like regulation code, lack of excitement, cost and the high temperature will be studied to find the real reasons behind not accepting green roofs in Doha.
Therefore, two roofs, green roof and classical roof, will be selected and compared in term of technical, functional and economical levels. At the end of this research, appropriate technical ways will be selected to serve this region and a few suggestions will be given to solve the problems, which are related to the studied elements.
This research aims to find the real reasons behind lack of green roofs application in Doha by studying several elements such as High cost, lack of encouragement and Hot climate.
It is important to know the role of green roof in improving urban micro climate, lowering the temperature of the roof, increasing durability and retaining rain water (Manfred, Marco, Grimme and Michael, 2002). For these reasons, the research was conducted to find the encouragement that the government provide in other country to wider using green roof and a several cases will be studied to test the efficiency of green roof in different climate.
In addition to that, the article will discuss and compare the cost of both the green roof and traditional roofing. At the end of the research, several cases were found which applying green roof structure and two roofs, green roof and classical roof, will be selected and compared in term of technical level, functional level and economical level to give suggestion. There are no studied about Qatar or other country within same region but there is some research for countries with similar climate.
2 Literature Review
Green roof is a kind of structure, which enable to create buildings with minimalized maintenance energy and cost. Especially, when energy-saving structures and buildings have increasing importance by the growing costs of energy resources (Szlivka and Rajnal, n.d). For that reasons, roofing industry in Doha city should begin the process of transformation by replacing the footprint on the land with more greenery which is the only force to sustainability. Anyway, the purpose of this paper is to know the causes that obstructed the using of green roof in Doha:
2.1 Hot Climate
People in Qatar may think that the green roof is not suitable because of the hot climate. However, Semaana et al (2016) proved the opposite in their study. They compare the uses of green roofs in different countries with different climates to determine the potential influence of climate on green roofs. They compared seven studies in three different types of climate. They found that despite of different geographical locations, the green roof’s efficacy in terms of metrics evaluating key impacts in each climate remains similar. Especially in hotter climates, green roofs are mainly constructed to reduce cooling energy in building and to provide thermal comfort (Semaana et al, 2016).
2.2 High Cost
Another reason for not using green roof in Doha is the cost. Blackhurst, Hendrickson and Matthews (2010) mentioned in their research that green roofs have higher initial cost than traditional roofing. In addition to that, the lack of design standards contributes to the risk of paying increased costs for green roofs. The green roofs typically cost more and require more materials for construction, but it offers environmental benefits over a building’s lifetime (Blackhurst, Hendrickson and Matthews, 2010). Green roof has a longer service life than conventional roofs due to reduction in water ponding and stringent waterproofing standards; reduced membrane heat exposure. The service life of green roof is twice the conventional roofs service life (Blackhurst, Hendrickson and Matthews, 2010).
Green roof has potential benefits such as sequestering carbon dioxide and polluted in biomass, reducing storm-water runoff by retaining precipitation and mitigating the urban heat island at appropriate scales and density by providing a medium that uses excess heat to create water vapor (Blackhurst, Hendrickson and Matthews, 2010).
2.3 Lack of ExcitementThe government in some country specify some policies in a direct and indirect ways to encourage green roof implementation (Carter and Fowler, 2008). Some policies approach through performance or technology standards, including building code requirements, which mandate the use of green roofs over all or part of a buildings rooftop, while others utilize a market-based approach using tax incentives or government subsidies (Carter and Fowler, 2008).
2.4 Case study
-384175174033200An experiment of two small-scale metal roofs in Sydney and Rio de Janeiro to assess the thermal performance of portable small-scale modules (Figure 1,2). The experiment shows that how the portable green roof modules can be retrofitted on metal sheet roofing and how that can cool the buildings, reducing carbon emissions and contributing towards zero carbon targets (Wilkinson and Feitosa, 2015).
-847725259512Figure 1: Housing thermal experiments in Rio de Janeiro
00Figure 1: Housing thermal experiments in Rio de Janeiro
2765508221615Figure 2: Housing thermal experiments in Sydney
00Figure 2: Housing thermal experiments in Sydney
Another study in Taiwan, a single-family housing unit is used for investigating the possibility of applying extensive roof greening to achieve building sustainable development (Wen-Sheng Ou, 2018).
A literatures review was done for several journals. Those journals talked about green roof application in hot climate. Anyway, the literature review was written based on three main elements: hot Climate, high cost and lack of excitement. In addition to that, many cases were found in Taiwan and Sydney to prove that traditional roof can be converted to green roof. Beside on that, this research will do a comparison between the tradition roof and the green roof in terms of three main elements:
-The technical level: A case study of nursery school’s roof was taken to show the materials of both types of roofs and made comparison between them. A picture for the layers of the green roof and terraced roof will be provided to show the difference between them.
-The economical level: the economical level will be studied for both types of roofs by using the case study of nursery school. That will be in two terms:
1. Thermal insulation: A sensor will be located at the top of both roofs to test the performance and diagrams will be provided to show the overview results in both winter and summer.
2. Cost: the cost analysis was taken from the nursery school and it is based on the utilizing life cycle cost analysis (LCCA)
-The functional levels: it contains pictures of some Friedenreich Hundertwasser’s building with green roof. Also, it has pictures for flat roof, which was taken beside on the observation.
4 Comparison between green roof and traditional roof
4.1 Technical level
-880745300072500Szlivka and Rajnal (n.d.) did an experiment for the nursery school roof in Hungary to measure the thermal energy for both types of roofs and made comparison between them. Nursery school roof building has the green roof installed only on the half of the roof, while the rest is covered with concrete pavement (Figure2). The main layer of the two roofs in this experiment are similar and the only different is in the upper layers. The basic layers from inside: scooped reinforced concrete slab panel, concrete slope layer, vapor proof layer, thermal insulation, waterproof layer. While, Green roof layers: plastic drainage layer with geotextile, vegetation layer Terraced roof layers: gravel ballast, concrete pavement (Figure1) (Szlivka and Rajnal, n.d).
-614680115307Figure 3: Layers of the green roof and terraced roof with the green roof temperature distribution in stationary state
00Figure 3: Layers of the green roof and terraced roof with the green roof temperature distribution in stationary state
-789940-18678Figure 4: Green roof and terraced roof with the measuring unit
00Figure 4: Green roof and terraced roof with the measuring unit
4.2 Economical level
4.2.1 Thermal insulation
According to Szlivka and Rajnal (n.d.) results in summer, the evaporation of the vegetation in the green roof made the top layer much higher temperature in daytime than air, while at night the same value is about 10°C lower than air temperature (Figure3). However, in the terrace roof condition it has higher temperature values than air in both day and night. Which means that, green roof layers have much better thermal insulating properties with average 10°C difference. It could be because of the heat capacity of soil, which is changing depending on the water content or it could be the ability of evaporation to cool down the structure (Szlivka and Rajnal, n.d).
-899160359327Figure 5: Overview diagram with all sensors (green roof and terraced roof), summer conditions
00Figure 5: Overview diagram with all sensors (green roof and terraced roof), summer conditions
Besides the summer condition results, in winter conditions the green roof’s upper layer has a 1-1.5°C lower temperature value than the outside air and has an approximately 1-hour delay (Szlivka and Rajnal, n.d). While, the same layer of the terraced roof has 1-1.5°C higher temperature than outside air (Figure4). Szlivka and Rajnal (n.d.) mentioned that, it might be because of the heat flux from inside the building, which is higher in case of the terraced roof as it has a lower heat insulation value. Anyway, the result shows that the green roof has higher heat attenuation with almost the double thickness of the gravel and pavement of the other roof (Szlivka and Rajnal, n.d).
-7353301818513Figure 6: Overview diagram with all sensors (green roof and terraced roof), winter conditions
00Figure 6: Overview diagram with all sensors (green roof and terraced roof), winter conditions
Green roofs have higher initial cost than the traditional roofing. Moreover, the lack of design standards contributes to the risk of paying increased costs for the green roofs. The green roofs typically cost more and require more materials for construction, but it offers environmental benefits over a building’s lifetime (Blackhurst, Hendrickson and Matthews, 2010). Blackhurst, Hendrickson and Matthews, (2010) mentioned that green roof service life is twice the traditional roof life. McRae (2016) Estimated that green roof lasts 40 years due to the protection from ultraviolet light, while traditional roof typically lasts only 17 years. However, in order to address the cost savings, disparity in life cycle, and repeatability factor the most applicable approach is utilizing life cycle cost analysis (LCCA) (McRae, 2016). The LCCA will help the decision maker to know which roofing option will cost less in the long run. It allows the analyst to compare cash flows over an equal analysis period despite unequal project life spans. After doing the analysis, roof’s types selection become up to the stakeholder. It is recommended that the selection be based on estimated financial benefits, which should be relatively conservative and omit obscure and indirect cost savings (McRae, 2016).
4.3 Functional level
Friedenreich Hundertwasser is one of the architects which he beliefs that vegetation should grow on all horizontal surfaces by designing and constructing green roofs, covering buildings in plants and Integrating nature into dwelling (Po?rov? and Vranayov?, 2014). Green roof will add aesthetic appearance in modern city and will make the building a place that giving people wildness, freedom, security, place to feel free and relaxed (Figure 7) (Po?rov? and Vranayov?, 2014). In addition to that, green roofs can increase privacy by not exposing people on the top to the neighbors. On the other hand, we have the traditional roof, which is inactive space. Anyway, in many Doha’s buildings, the traditional roof is used as storage area, which carry the air condition’s compressors machines and carry the water tank (Figure 8).
-741266187960Figure 7: Hundertwasserhaus’s green roof
00Figure 7: Hundertwasserhaus’s green roof
-710979267970Figure 8: Traditional roof in one of Doha’s house
00Figure 8: Traditional roof in one of Doha’s house
In my opinion, the lack of using green roof in Doha related to many reasons: First one is the climate. People in Doha may think that green roof will not functioning well because of the hot climate, so it would not worth the money that they will spend on it. Which is the opposite thought of what Semaana et al (2016) found in his study. The second reason of not using green roof in Doha is the cost. People in Doha will not be taking the risk of applying green roof, while there is lack of design standards contributes to the risk of paying increased costs for green roofs as Blackhurst, Hendrickson and Matthews (2010) mentioned. In addition to that, the green roof’s construction required expert and specialize people, which is difficult to find. However, green roof might be accepted, if the government encourage people to use it and specify some policies including building code requirements, which mandate the use of green roofs over all or part of a buildings rooftop (Carter and Fowler, 2008). Anyway, some of the residential building in Doha have no place for planting in the ground floor level because the land size is small, and they have a big family. Therefore, they extend the building and remove the green area. So as a solution, greening the roof is the perfect way to solve the problem and to increase the privacy. In addition to that it will make people feel free and relaxed as Po?rov? and Vranayov?, (2014) mentioned.
5 Significance of the study
This study is important because it helps to remove one of many obstacles that hinder our moving toward a sustainable and modern city. Today, there is ability of compensate the lost natural surfaces in cities by greening the top of the buildings. Although that Doha’s buildings have expanded horizontally very fast and without much green areas, it is never too late. The green roof can be installed not only on newly built roofs, but even on existing buildings. It just requires a structural calculation considering the additional weight.
In conclusion, there are lists of Drivers and barriers to wider use of green roofs. Although the green roof is less maintenance required during roof life cycle, high aesthetic values provide wider bene?t to society, increasing worker health, productivity and creativity and additional recreational opportunities for people and building occupants, it has obstructions of Perceived as high cost, lack of awareness, poor appreciation by government and general public and reluctance to adopt new technologies and techniques. Despite the barriers, economic, social and environmental arguments supporting widespread adoption of green roof technology are clear and convincing (Wilkinson and Reed, 2009).
I would like to express my deepest appreciation to all those who provided me the possibility to complete this report. A special thank I give to the doctor, Dr Ouhrani, whose contribution in stimulating suggestions and encouragement, helped me to coordinate my project especially in writing this report. Furthermore, I would also like to acknowledge with much appreciation the crucial role of Qatar university, which gave the permission to access the E-Resources to get all required information to complete the report.
Semaan, M., & Pearce, A. (2016). Assessment of the Gains and Benefits of Green Roofs in Different Climates. Procedia Engineering, 145, 333. Retrieved from of Architectural Engineering. Dec2010, Vol. 16 Issue 4, p136-143. 8p. 9 Charts, 1 Graph
Carter, T., & Fowler, L. (n.d.). Establishing green roof infrastructure through environmental policy instruments. ENVIRONMENTAL MANAGEMENT, 42(1), 151164. Multidisciplinary Scientific Conference on Social Sciences 2014, p707-712, 6p
Sara J. Wilkinson, & Richard Reed. (2009). Green roof retrofit potential in the central business district. Property Management, 27(5), 284. Retrieved from search.ebscohost.com.mylibrary.qu.edu.qa/login.aspx?direct=true&db=edb&AN=45205414&site=eds-live&scope =site
Kohler, M., Schmidt, M., Grimme, F. W., Laar, M., de Assuncao Paiva, V. L., & Tavares, S. (2002). Green roofs in temperate climates and in the hot-humid tropics–far beyond the aesthetics. Environmental Management & Health, 13(4), 382. Retrieved from =site
Wilkinson, S., Feitosa, R. C., Kaga, I. T., & Franceschi, I. H. de. (2017). Evaluating the Thermal Performance of Retrofitted Lightweight Green Roofs and Walls in Sydney and Rio de Janeiro. Procedia Engineering, 180,231240. 16/j.proeng.2017.04.182Ou, W.-S. (2018). Sustainable development of building of extensive roof greening in Taiwan. International Journal of Green Energy, 15(6), 371375. mylibrary.qu.edu.qa/10.1080/15435075.2016.1242072Standard Guide for Selection, Installation, and Maintenance of Plants for Vegetative (Green) Roof Systems
SZLIVKA, D. F., & RAJNAI, Z. (2016). Examination of Temperature Change of Green Roof and Flat Roof in Frequency Range. Annals of the Faculty of Engineering Hunedoara – International Journal of Engineering, 14(4), 221226. Retrieved from com.mylibrary.qu.edu.qa/login.aspx?direct=true&db=asn&AN=119375007&site=ehost-live&scope=siteMcRae, A. M. (2016). Case study: A conservative approach to green roof benefit quantification and valuation for public buildings. Engineering Economist, 61(3), 190206. 3791X.2016.1186255