Global research trends in green roofs: benefits, main developments and future needs

Tendencias globales de investigación en techos verdes: beneficios, lecciones aprendidas, retos y modelos futuros

Tendências mundiais de investigação nos tetos verdes: benefícios, principais acontecimentos e as necessidades futuras

Juan Sebastián Carvajal Muñoz*, Charlie Esperanza Carmona García**

^* Msc. in Materials Science. Texas A&M University, USA. Full time Professor, Civil and Environmental Engineering Department, Universidad del Norte, Km.5 Vía Puerto Colombia, Barranquilla, Colombia.
^** Occasional Professor, Universidad Nacional Abierta y a Distancia (UNAD). Research Group on Soil, Environment and Society (GISAS) University of Magdalena. Santa Marta, Magdalena, Colombia. Carrera 32 No 22 - 08; Postal Code 2-1-21630 E-mails: charlie.carmonagarcia@gmail.com.

Autor correspondencia: Juan Sebastián Carvajal Muñoz, email: ing.juancarvajal@yahoo.com
Artículo recibido: 23/06/2015; Artículo aprobado: 11/12/2015

Abstract

Currently, the world faces a critical time with regard to environmentally friendly technologies or green trends whose main objective is to adjust the modern social development to the requirements of environmental protection, conservation of natural resources and adaptation to sustainable development models. In this context, green roofs meet these needs and provide valuable opportunities in environmental, economic and social terms. This article aims to present current trends in research on green roofs globally so as to encourage further research at local and regional levels and facilitate its implementation in the medium and long term by recognizing its benefits, lessons learnt and challenges. The paper first presents an overview of green roofs. The following sections focus on major research topics developed in the last 10 years with regard to green roofs. In these, some relevant aspects are discussed with regard to its implementation worldwide, demonstrating its potential importance and benefits. Next, each of the sections focuses on present challenges and future research needs.

Key words: Green roofs, bioarquitecture, ecourbanism, environment, sustainable development, and green technologies.

Resumen

El mundo actual vive un momento coyuntural en torno a tendencias ambientalmente amigables o tecnologías verdes cuyo objetivo fundamental es ajustar el desarrollo social moderno a las exigencias de protección ambiental, conservación de los recursos naturales y adaptación a los nuevos modelos de desarrollo sostenible que se imponen. En este contexto, los techos verdes se ajustan a estas necesidades y brindan oportunidades valiosas en términos ambientales, económicos y sociales. El presente artículo tiene como objetivo presentar las tendencias actuales de investigación con relación a los techos verdes a nivel global para así fomentar mayor investigación a nivel local y regional y facilitar su implementación en el mediano y largo plazo mediante el reconocimiento de sus beneficios y características. El artículo presenta inicialmente las generalidades sobre los techos verdes. Las secciones siguientes se enfocan en los principales temas de investigación desarrollados en los últimos 10 años. En éstas se presentan además aspectos sobre su implementación a nivel global, lo que demuestra su potencial, importancia y beneficios. Cada sección del artículo, el artículo se concentra en presentar los desafíos y las necesidades futuras de investigación.

Palabras clave: techos verdes, bioarquitectura, ecourbanismo, ambiente, desarrollo sostenible, tecnologías verdes.

Resumo

O mundo atual vive um momento conjuntural em torno a tendências ambientalmente amigáveis ou tecnologias verdes cujo objetivo fundamental é ajustar o desenvolvimento social moderno às exigências de proteção ambiental, conservação dos recursos naturais e adaptação aos novos modelos de desenvolvimento sustentável que se impõe. Neste contexto, os tetos verdes se ajustam a estas necessidades e brindam oportunidades valiosas em termos ambientais, económicos e sociais. O presente artigo tem como objetivo apresentar as tendências atuais de investigação com relação aos tetos verdes a nível global para assim fomentar maior investigação a nível local e regional e facilitar sua implementação em médio e longo prazo mediante o reconhecimento de seus benefícios e características. O artigo apresenta inicialmente as generalidades sobre os tetos verdes. As secções seguintes se enfocam nos principais assuntos de investigação desenvolvidos nos últimos 10 anos em torno aos tetos verdes. Nestas se apresentam ademais de aspectos sobre sua implementação a nível global, o que demostra seu potencial, importância e benefícios. Seguidamente, o artigo se concentra em apresentar os desafios e as necessidades futuras de investigação.

Palavras chave: tetos verdes, bioarquitetura, ecourbanismo, ambiente, desenvolvimento sustentável, tecnologias verdes.

Introduction

Green Roofs are sloped or flat rooftop mainly designed to support vegetation (Goddard, Dougill, & Benton, 2009; Henry & Frascaria-Lacoste, 2011). These have several ecological, technological, architectural and environmental characteristics that allowfor applications such as aesthetic and decoration, reduction of heat, minimization of AC systems usage, optimization of energy usage and other uses currently being investigated worldwide as presented in this paper. In terms of design, green roofs are typically composed by several layers of membranes that include waterproofing, barriers to prevent roots to grow excessively and damage underlying layers, drainage and filtration barriers, and vegetative layers that support a wide variety of plant species. Their incorporation into architectural design can have several alternatives as those presented in Figure 1. Green roofs are also called eco-roofs, living-roofs or roof gardens. The importance of this technology is mainly provided by several environmental benefits that can potentially be used in today’s society to face global warming and develop smarter-environmentally friendly cities. In this regard, additional additional and detailed environmental aspects of green roofs are presented in a recent publication by Berardi, Ghaffarian Hoseini, & Ghaffarian Hoseini (2014).

Multiple research studies have been conducted in the last two decades with regard to green roofs involving a wide number of topics that involve not only design and technical aspects, but also environmental, aesthetic, biological and modelling considerations. Nevertheless, there’s a lack of a comprehensive study showing the different lines of research mainly studied worldwide along with their main outcomes, as well as the summary of some successful study cases.

Therefore, based on the importance of green roofs in the context of environmental sustainability and climate adaptation, the main objective of this paper is to introduce the main lines of research currently developed with regard to green roofs by introducingthe trending research topics, potential uses and prospective research. Consequently, the second objective of this paper is to promote a deeper understanding of green roofs to facilitate further progress in research as well as implementation of these technologies, mainly in developing countries. Nine sections that will cover the most important topics researched in the last ten years around the globe compose the paper. These sections introduce some of the most relevant lines of research and provide important highlights on the benefits, limitations, challenges, and prospective research. The topics include: (i) effects on water management, (ii) biological assessments, (iii) climatic adaptation and urban planning considerations, (iv) performance evaluations and thermal efficiency, (v) economic assessments, (vi) life cycle assessments, (vii) modelling applications and technological developments, (viii) aesthetic evaluations, and (xi) case studies in the globe.

Effects on Water Management

According to recent research, green roofs influence water management strategies at the local and global levels (Lamera, Becciu, Rulli, & Rosso (2014); Beecham & Razzaghmanesh 2015; Metselaar, 2012; Gregoire & Clausen, 2011; Lee, Moon, Kim, Kim, H. & Han, 2013; Malcolm, Reese, Schaus, Ozmon, & Tran, 2014). For instance, Beecham et al. 2015 studied different types of green roofs (i.e., sixteen intensive and extensive green roof beds without maintenance and fertilizers) in terms of the water quantity and quality. The quantity of water was assessed by collecting it via storm waterdrainage points during five events of rainfall, whereas the quality was evaluated considering water quality parameters (NO2, NO3, NH4, PO4, pH, EC, TDS, Turbidity, Na, Ca, Mg and K). Based on the experimental design, the authors concluded on the significant differences found for vegetated versus non-vegetated green roofs in terms of the water quantity and quality, which suggests on the influence of this variable on water management systems when integrated into building strategies for reducing water consumption and increase its recycling rate (e.g., for nonpotable use such as toilet flushing and landscape irrigation). In addition, the ability of green roofs’ vegetation to reduce pollutants in runoff and its advantages as water retainers were highlighted by the authors. Similarly, modelling approaches have been used for studying the capacity of green roofs for favoring water management. Lamera et al. developed a bucket model to simulate the existing relationship between rainfall and runoff in green roof in order to determine the hydrological influence on a watershed which led to concluding on the importance of this technology for water harvesting. Also, the authors highlighted green roof as valuable systems in today’s world to promote Sustainable Urban Drainage Systems. Likewise, Metselaar (2012) used modelling for evaluating the connection between vegetation types in green roofs and the hydrological water retention potential. Some additional recent approaches involved with water management include those developed by Versini, Ramier, Berthier, & De Gouvello (2015), Lee, J., Lee, M., & Han (2015) and Poë, Stovin, & Berretta (2015). The research conducted by these focused on hydrological assessments of green roofs at different levels and scales of analysis, starting from pilot study to building and basin scales. In addition, the authors also included several hydrological, hydraulic and biological considerations, since designing green roofs not only comprise individual components of engineering but also, integrate several criteria simultaneously.

In terms of future research to be conducted in water management, some of the topics suggested by the authors include the information presented in Table 1.

Biological Assessments

This section focuses on some research studies recently conducted about biological assessments of green roofs intended to characterize vegetation types, diversity, growth and effect of substrate type.

Effect of substrate type

The substrate in green roofs plays a key role in several aspects as described by recent research (Bates, Sadler, Greswell, & Mackay, 2015; Zhao, Tabares-Velasco, Srebric, Komarneni, & Berghage, 2014; and Farrell, Mitchell, Szota, Rayner, & Williams, 2012). For instance, use of virgin substrates versus recycled aggregates can have effects on the quality of the vegetation, the aesthetic aspects and the overall performance of the green roofs systems. In fact, Bates et al. assessed the influence of using recycled aggregates substrates (i.e., crushed brick, crushed demolition aggregate, solid municipal waste incinerator bottom ash aggregate, and a mix of the previous in two combinations) during a 6-year period. The authors emphasized on the importance of developing multi-year studies to reach relevant conclusions in terms of vegetative development in green roofs. Similarly, Zhao et al. evaluated the effect of substrate and plant type on the thermal performance during the summer season. Conversely, Farrell et al. focused not only on summer climate conditions, but also assessed other seasons’ influences on water use and substrates in green roofs. Moreover, Kanechi, Fujiwara, Shintani, Suzuki, & Uno (2014) studied vegetation in relation to irrigation and substrate type that allowed for conclusions on the importance of appropriate selection of plant species and substrates to promote irrigation and facilitate the thermal and water efficiency of green roofs systems.

Vegetation type, diversity and development

Several layers compose green roofs systems, whose main function is supporting vegetation and providing adequate conditions for their development. In this respect, the study of vegetation in green roofs systems has become a major topic for research in the last years globally. Several assessments have been considered that include, but are not limited to: types, diversity, growth, development and other biological and environmental characteristics of interest. For instance, germination and colonizing has been studied by Miller, Heim, & Lundholm (2014). Similarly, green roofs are considered as important systems for promoting biodiversity, which supports the development of research on this area (Heim & Lundholm, 2014; Madre, Vergnes, Machon, & Clergeau, 2014; Bates, Sadler, & Mackay, 2013; Song et al. 2013). Information on detailed benefits from vegetation diversity can be found elsewhere (Cook-Patton & Bauerle, 2012; Nagase & Dunnett, 2012; Nagase & Dunnett, 2013). Also, considering the relevance of climate change in ecological adaptations and biological development, some additional studies have selected climate change scenarios and climatological conditions as reference points to determine beneficial conditions for vegetation in green roof systems (Vanuytrecht et al. 2014; Getter, Rowe, & Cregg, 2009) as well as highlighted the positive effects of vegetation on thermal efficiency and other global warming related-aspects (Susca, Gaffin, & Dell’Osso, 2011).

Climatic Adaptation and Urban Planning Considerations

Taking into consideration the fact that climate change imposes challenges for ecosystems to adapt to extreme conditions, the evaluation of climatic adaptation processes acquires special relevance in the context of green roof research. For instance, Jim (2015) focused on global warming and urban heat island (UHI) in Hong Kong due to the significance of these in climate adaptation. In particular, by monitoring thermal performance of Sedum and Perennial Peanut and climatic conditions in summer, the author concluded on some design and management strategies to counteract global warming in compact cities. Additionally, Virk et al. (2015) focused on microclimatic effects from the general and specific outlooks in order to better understand green and cool roofs in London. According to the authors, green roof usage in buildings can have a positive effect on the reduction of energy consumption on an annual basis, especially when summer conditions are prevalent because winter performance tends to lead to energy penalties and lower reduction in energy consumption. By developing a modelling approach set to 2050, it was determined that both cool and green roof produce savings in annual energy use, meaning that these have significant advantages from the economical perspective as well. Nevertheless, the authors concluded on the better performance that can be obtained by using conventional isolation to minimize energy consumption, implying that its combination with neither cool roofs nor green roof is convenient in terms of the effectiveness for these systems.

Some other studies have been undertaken to determine if green roof have the potential for carbon sequestration (Luo et al. 2015; Whittinghill, Rowe, Schutzki, & Cregg, 2014). For instance, Luo et al. investigated two substrate types that included mixed-sewage-sludge (MSSS) and local natural soil (LNS), from which the former exhibited lower carbon sequestration potential (i.e., 3.89 kg C m^-2 yr^-1 vs 3.81 kg C m^-2 yr^-1) whereas the carbon storage followed a reversal trend (13.15 kg C m^-2 for MSSS and 8.58 kg C m^-2 for LNS). Similarly, Whittinghill et al. (2014) studied nine in ground and three green roof landscape systems in order to better understand their carbon sequestration potential and the main outcomes relate to the higher carbon content found for woody plants. Future research suggest on the need for developing more comprehensive studies focused on evaluating scaled-up systems with several configurations of substrates and vegetation (Luo et al. 2015). Also, management practices are to be thoroughly assessed, along with landscaping tools to determine the potential carbon sequestration and allow for improved permanence of it on the systems when considering an equilibrium point.

Performance Evaluations and Thermal Efficiency

In big cities, green roofs are valuable systems for counteracting the effects of global warming, minimize energy consumption and mitigate thermal stress and urban heat (Krüger & Emmanuel, 2013), while contributing with positive aesthetic improvements and environmental benefits (Berardi, Ghaffarian Hoseini, & Ghaffarian Hoseini, 2014). As a result, green roofs performance represents an important source of information for better understanding of the advantages, disadvantages and challenges faced nowadays to achieve higher thermal efficiency, energy savings and biological value while promoting appraisable landscapes for greener cities. Some approaches recently carried out for assessing performance of green roofs and the corresponding recommendations for future research include those presented in Table 2. A comprehensive review on energy aspects of green roofs with relevant findings and topics of future research is available in a recent publication by Saadatian et al. (2013). Future research suggested in terms of performance include the evaluations of energy efficiency and indoors thermal comfort in green roofs when combined with other systems such as nocturnal ventilation (Gagliano et al. 2014).

Economic Analysis

Economic analysis constitutes an important topic of recent research on green roofs worldwide. In effect, recent publications have studied aspects such as energy savings (La Roche & Berardi, 2014; Castleton, Stovin, Beck, & Davison, 2010), comparison of green roofs types (Sproul, Wan, Mandel, & Rosenfeld, 2014), economic performance (Chan & Chow, 2013), cost benefits assessments for the public and private sectors (Claus & Rousseau, 2012) and effectiveness of green roofs for lower energy consumption (Refahi & Talkhabi, 2015).

Life Cycle Assessments

As a supplement to economic analysis of green roofs, life cycle assessments (LCA) is to be conceived as an essential approach to better understand the environmental, economic, social and technical aspects related to these systems in various conditions that depend upon a wide range of variables such as materials, geographic location, initial costs, period of design, vegetation types, among others. In this context, several current studies are available with respect to LCA (Chenani, Lehvävirta, & Häkkinen, 2015; Rincon et al. 2014; Bianchini & Hewage 2012a, 2012b; Kosareo & Ries, 2007).

Modeling Applications and Technological Developments

Research not only has been conducted on real scenarios, but also future or ideal scenarios have been studied in modeling green roofs projects worldwide. This is mainly due to the technological developments currently available and the possibilities of pairing these with real scenarios through experiments and field evaluations. In this line of thinking, Feng, Zheng, Wang, Yu, & Su (2015) developed a non-traditional photovoltaic/thermal/day lighting (PV/T/D) system coupled to optical simulation software to be utilized in green roofs as alternative for greener building design and improved thermal efficiency. This system allowed for improved thermal efficiency and provided excellent light control at noon and other technical advantages as compared to other green roofs systems. Gagliano, Detommaso, Nocera, Patania, & Aneli (2014), carried out a study in south Sicily, Italy, which involved simulation through Design Builder^® software to assess building energy performance and dynamic thermal behavior in an extensive green roof. Their results indicated that significant reductions in energy consumption were found for cooling and heating load (i.e., 80% and 34%, respectively), which essentially indicates the benefits of green roofs in greener buildings to allow for thermal efficiency in buildings, while allowing for energy savings and maintain comfort conditions throughout the day. Modeling also has applications in: hydrologic performance, as presented in recent publications by Hakimdavar, Culligan, Finazzi, Barontini, & Ranzi (2014). and Stovin, Poë, & Berretta (2013); economic and energy performance (Chan & Chow, 2013), green roof forecasting and demand (Tsang & Jim, 2013).

Aesthetic Assessments

Contrary to what might be expected, design of green roofs not only involves technical and economic aspects but also biological, environmental and aesthetic deliberations as previously presented, which are mainly intended for providing these structures with the ability to suit both functionality and efficiency, while providing buildings with greener attractiveness. As a result, some recent research around the globe has evaluated green roofs design from a more holistic approach, involving, for instance, studies regarding novel ecosystem design of green roofs (Van Mechelen, Van Meerbeek, Dutoit, & Hermy 2015) and assessments of user’s preferences, attitudes, expectations and reactions with regard to green roofs use in big and small cities (Jungels Rakow, Allred, & Skelly 2013; Fernandez-Cañero, Emilsson, Fernandez-Barba, & Machuca 2013; White & Gatersleben 2011; and Yuen & Hien 2005). In particular, the authors have concluded on the positive influence of green roofs on user’s perception when comparing conventional nogreen roofs buildings with those having green roofs at any level (i.e., industrial, academic, and domestic, extensive, intensive). Lines for future research are mainly focused on improving functional diversity and other biological-related components as those reported by Van Mechelen et al. (2015).

Case Studies in the Globe

The previous sections introduced recent research conducted on several aspects of green roofs around the globe, indicating the current relevance of this topic and the valuable lessons learnt from its implementation. To further supplement this information, this section focuses on some case studies of green roofs in different geographic locations, covering several topics from preceding sections and indicating their main findings and lines for further research.

In a recent study undertaken in Jordan, Goussous, Siam & Alzoubi (2015) assessed the energy and thermal efficiency of green roofs for applications in buildings. Computer simulations developed with Autodesk Ecotect Software were employed to determine the efficiency of heating, ventilating and air conditioning in a four-story residential building located in Amman. Clay and grass were recommended as suitable materials for green roofs. As suggested, future research should include development of new materials and detailed characterization of these for use in green roofs systems in order to facilitate improved efficiency.

Following the approach presented in the aesthetics section, Loder (2014) developed an interesting study case in the United States and Canada territories, covering the cities of Chicago and Toronto, respectively. The experiment involved two vegetation types (i.e. Prairie and Sedum). As indicated by the author, the perceptions of people with regard to green roofs are mainly based upon aesthetics, past experiences with nature, considerations about progress, modernity and native habitat. Furthermore, cultural components also had an influence on the responses from Chicago and Toronto participants. In general, public acceptation of green roofs depend of several aspects that need to be further studied and considered in other regions to determine which of these have more potential for successful implementation from the aesthetics standpoint. Also, perceptions of comfort, dwelling and place can have an influence when comparing workers of cities where scarce nature is available nearby. Access, scale and distance are also considered as important factors to be considered for further research by considered the importance of nature in human life. Finally, psychological and ecological aspects of green roofs were reinforced by the author, who encouraged more ecological aesthetics assessments.

Comprehensive reviews for specific regional aspects of green roofs are important informational sources for encouraging research that focuses on the gaps found by the authors. In this context, Chen (2013), and Xiao, Lin, Han & Zhang (2014) published state-of-the-art papers covering performance evaluations in Taiwan and research tendencies and development of green roofs in China. Widely available researches carried out in the United States territory can be found in journals with regard to green roofs, such as the study cases by Dvorak & Volder (2013), Dvorak & Volder (2010) and Yang, Yu & Gong (2008). Other studies in additional geographical locations provide additional insights on green roofs research activities in some of the areas covered in this paper, as supported by Italian researchers D’Orazio, Di Perna & Giuseppe (2012), Parizotto & Lamberts (2011) from Brazil, Nagase & Dunnett (2013) from the United Kingdom and Al Ali & Emziane (2013) from Abu Dhabi.

Conclusive Remarks

Based on the literature review presented in this article, it is clear that significant research efforts have been made in the last ten years for deeper understanding of the benefits, implementation, efficiency, challenges and other topics concerning green roofs around the globe. More specifically, the topics covered in the article included water management; biological assessments; climatic adaptation and urban planning; performance evaluations and thermal efficiency; economic analysis; life cycle assessments; modeling applications and technological developments; aesthetics and; some case studies from around the globe. From these, guidelines for topics to be undertaken in the near future were provided in order to contribute to advances in these areas. In fact, additional research outcomes in the coming years are expected as a response to the need of enabling a more massive use of this environmentally friendly technology with enormous potential for facing the global challenges with respect to global warming, climatic adaptation, energy efficiency, water management, biological conservation and other interesting fields of study. Nevertheless, research is not the only path to contribute in this area; implementation projects at various levels as well as a cooperative synergy between academy, industry and government can facilitate a more massive use of green roofs, especially in developing countries such as Colombia and other Latin-American counterparts, by using the great human potential and capabilities that these can offer in terms of pertinent technological and innovative developments.

References

Al Ali, M., & Emziane, M. (2013). Performance Analysis of Rooftop PV Systems in Abu Dhabi. Energy Procedia, 42, 689-697.         [ Links ]

Bates, A. J., Sadler, J. P., Greswell, R. B., & Mackay, R. (2015). Effects of recycled aggregate growth substrate on green roof vegetation development: A six year experiment. Landscape and Urban Planning, 135, 22-31.         [ Links ]

Bates,A. J., Sadler, J. P., & Mackay, R. (2013). Vegetation development over four years on two green roofs in the UK. Urban Forestry & Urban Greening,12(1), 98-108.         [ Links ]

Beecham, S., & Razzaghmanesh, M. (2015). Water quality and quantity investigation of green roofs in a dry climate. Water research, 70, 370-384.         [ Links ]

Berardi, U., Ghaffarian Hoseini, A., & Ghaffarian Hoseini, A. (2014). State-of-the-art analysis of the environmental benefits of green roofs. Applied Energy, 115, 411-428.         [ Links ]

Bianchini, F., & Hewage, K. (2012a). How "green" are the green roofs? Lifecycle analysis of green roof materials. Building and Environment, 48, 57-65.         [ Links ]

Bianchini, F., & Hewage, K. (2012b). Probabilistic social cost-benefit analysis for green roofs: a lifecycle approach. Building and Environment, 58, 152-162.         [ Links ]

Castleton, H. F., Stovin,V., Beck, S. B. M., & Davison, J. B. (2010). Green roofs; building energy savings and the potential for retrofit. Energy and buildings, 42(10), 1582-1591.         [ Links ]

Chan, A. L. S., & Chow, T. T. (2013). Energy and economic performance of green roof system under future climatic conditions in Hong Kong. Energy and Buildings, 64, 182-198.         [ Links ]

Chen, C. F. (2013). Performance evaluation and development strategies for green roofs in Taiwan: A review. Ecological Engineering, 52, 51-58.         [ Links ]

Chenani, S. B., Lehvävirta, S., & Häkkinen, T. (2015). Life cycle assessment of layers of green roofs. Journal of Cleaner Production, (90), 153-162.         [ Links ]

Claus, K., & Rousseau, S. (2012). Public versus private incentives to invest in green roofs: A cost benefit analysis for Flanders. Urban Forestry & Urban Greening, 11(4), 417-425.         [ Links ]

Cook-Patton, S. C., & Bauerle, T. L. (2012). Potential benefits of plant diversity on vegetated roofs: a literature review. Journal of environmental management,106, 85-92.         [ Links ]

Coutts, A. M., Daly, E., Beringer, J., & Tapper, N. J. (2013). Assessing practical measures to reduce urban heat: Green and cool roofs. Building and Environment, 70, 266-276.         [ Links ]

D'Orazio, M., Di Perna, C., & Di Giuseppe, E. (2012). Green roof yearly performance: a case study in a highly insulated building under temperate climate. Energy and Buildings, 55, 439-451.         [ Links ]

Dominique, M., Tiana, R. H., Fanomezana, R. T., & Ludovic, A. A. (2014). Thermal behavior of green roof in Reunion Island: Contribution towards a net zero building. Energy Procedia, 57, 1908-1921.         [ Links ]

Dvorak, B., & Volder, A. (2010). Green roof vegetation for North American ecoregions: a literature review. Landscape and urban planning, 96(4), 197-213.         [ Links ]

Dvorak, B., & Volder, A. (2013). Rooftop temperature reduction from unirrigated modular green roofs in south-central Texas. Urban Forestry & Urban Greening,12(1), 28-35.         [ Links ]

Farrell, C., Mitchell, R. E., Szota, C., Rayner, J. P., & Williams, N. S. G. (2012). Green roofs for hot and dry climates: interacting effects of plant water use, succulence and substrate. Ecological Engineering, 49, 270-276.         [ Links ]

Feng, C., Zheng, H., Wang, R., Yu, X., & Su, Y. (2015). A novel solar multifunctional PV/T/D system for green building roofs. Energy Conversion and Management, 93, 63-71.         [ Links ]

Fernandez-Cañero, R., Emilsson, T., Fernandez-Barba, C., & Machuca, M. Á. H. (2013). Green roof systems: A study of public attitudes and preferences in southern Spain. Journal of environmental management, 128, 106-115.         [ Links ]

Gagliano, A., Detommaso, M., Nocera, F., Patania, F., & Aneli, S. (2014). The retrofit of existing buildings through the exploitation of the green roofs-a simulation study. Energy Procedia, 62, 52-61.         [ Links ]

Getter, K. L., Rowe, D. B., & Cregg, B. M. (2009). Solar radiation intensity influences extensive green roof plant communities. Urban Forestry & Urban Greening, 8(4), 269-281.         [ Links ]

Goddard, M. A., Dougill, A. J., & Benton, T. G. (2010). Scaling up from gardens: biodiversity conservation in urban environments. Trends in Ecology & Evolution, 25(2), 90-98.         [ Links ]

Goussous, J., Siam, H., & Alzoubi, H. (2015). Prospects of green roof technology for energy and thermal benefits in buildings: Case of Jordan. Sustainable Cities and Society, 14, 425-440.         [ Links ]

greenroofs.org,. (2015). 2014 Award Winners. Retrieved 4 April 2015, from http://www.greenroofs.org/index.php/events/awards-of-excellence/2014-award-winners         [ Links ]

Gregoire, B. G., & Clausen, J. C. (2011). Effect of a modular extensive green roof on stormwater runoff and water quality. Ecological Engineering, 37(6), 963-969.         [ Links ]

Hakimdavar, R., Culligan, P. J., Finazzi, M., Barontini, S., & Ranzi, R. (2014). Scale dynamics of extensive green roofs: Quantifying the effect of drainage area and rainfall characteristics on observed and modeled green roof hydrologic performance. Ecological Engineering, 73, 494-508.         [ Links ]

Heim, A., & Lundholm, J. (2014). Species interactions in green roof vegetation suggest complementary planting mixtures. Landscape and Urban Planning,130, 125-133.         [ Links ]

Henry, A., & Frascaria-Lacoste, N. (2012). The green roof dilemma-Discussion of Francis and Lorimer (2011). Journal of environmental management, 104, 91-92.         [ Links ]

Jaffal, I., Ouldboukhitine, S. E., & Belarbi, R. (2012). A comprehensive study of the impact of green roofs on building energy performance. Renewable Energy, 43, 157-164.         [ Links ]

Jim, C. Y. (2015). Assessing climate-adaptation effect of extensive tropical green roofs in cities. Landscape and Urban Planning, 138, 54-70.         [ Links ]

Jim, C. Y., & Peng, L. L. (2012). Weather effect on thermal and energy performance of an extensive tropical green roof. Urban Forestry & Urban Greening, 11(1), 73-85.         [ Links ]

Jungels, J., Rakow, D.A., Allred, S. B., & Skelly, S. M. (2013). Attitudes and aesthetic reactions toward green roofs in the Northeastern United States. Landscape and Urban Planning, 117, 13-21.         [ Links ]

Kanechi, M., Fujiwara, S., Shintani, N., Suzuki, T., & Uno, Y. (2014). Performance of herbaceous Evolvulus pilosus on urban green roof in relation to substrate and irrigation. Urban Forestry & Urban Greening, 13(1), 184-191.         [ Links ]

Klein, P. M., & Coffman, R. (2015). Establishment and performance of an experimental green roof under extreme climatic conditions. Science of the Total Environment, 512, 82-93.         [ Links ]

Kosareo, L., & Ries, R. (2007). Comparative environmental life cycle assessment of green roofs. Building and environment, 42(7), 2606-2613.         [ Links ]

Krüger, E., & Emmanuel, R. (2013). Accounting for atmospheric stability conditions in urban heat island studies: The case of Glasgow, UK. Landscape and Urban Planning, 117, 112-121.         [ Links ]

La Roche, P., & Berardi, U. (2014). Comfort and energy savings with active green roofs. Energy and Buildings, 82, 492-504.         [ Links ]

Lamera, C., Becciu, G., Rulli, M. C., & Rosso, R. (2014). Green roofs effects on the urban water cycle components. Procedia Engineering, 70, 988-997.         [ Links ]

Lamnatou, C., & Chemisana, D. (2015). A critical analysis of factors affecting photovoltaic-green roof performance. Renewable and Sustainable Energy Reviews, 43, 264-280.         [ Links ]

Lee, J.Y., Moon, H.J., Kim, T.I., Kim, H.W., & Han,M. Y. (2013). Quantitative analysis on the urban flood mitigation effect by the extensive green roof system. Environmental Pollution, 181, 257-261.         [ Links ]

Lee, J. Y., Lee, M. J., & Han, M. (2015). A pilot study to evaluate runoff quantity from green roofs. Journal of environmental management,152, 171-176.         [ Links ]

Lin, B. S.,Yu, C. C., Su,A.T., & Lin,Y. J. (2013). Impact of climatic conditions on the thermal effectiveness of an extensive green roof. Building and Environment, 67, 26-33.         [ Links ]

Loder, A. (2014). 'There's a meadow outside my workplace': A phenomenological exploration of aesthetics and green roofs in Chicago and Toronto. Landscape and Urban Planning, 126, 94-106.         [ Links ]

Luo, H., Liu, X., Anderson, B.C., Zhang, K., Li, X., Huang, B. & Jiang, M. (2015). Carbon sequestration potential of green roofs using mixed-sewage sludge substrate in Chengdu World Modern Garden City. Ecological Indicators,49, 247-259.         [ Links ]

Madre, F., Vergnes, A., Machon, N., & Clergeau, P. (2014). Green roofs as habitats for wild plant species in urban landscapes: First insights from a large-scale sampling. Landscape and urban Planning, 122, 100-107.         [ Links ]

Malcolm, E. G., Reese, M. L., Schaus, M. H., Ozmon, I. M., & Tran, L. M. (2014). Measurements of nutrients and mercury in green roof and gravel roof runoff. Ecological Engineering, 73, 705-712.         [ Links ]

Metselaar, K. (2012). Water retention and evapotranspiration of green roofs and possible natural vegetation types. Resources, conservation and recycling, 64, 49-55.         [ Links ]

Miller, L. E., Heim, A. E., & Lundholm, J. (2014). Green roof vegetation type affects germination and initial survival of colonizing woody species. Urban Forestry & Urban Greening, 13(4), 892-899.         [ Links ]

Moody, S. S., & Sailor, D. J. (2013). Development and application of a building energy performance metric for green roof systems. Energy and Buildings, 60, 262-269.         [ Links ]

Nagase, A., & Dunnett, N. (2012). Amount of water runoff from different vegetation types on extensive green roofs: effects of plant species, diversity and plant structure. Landscape and Urban Planning, 104(3), 356-363.         [ Links ]

Nagase, A., & Dunnett, N. (2013). Performance of geophytes on extensive green roofs in the United Kingdom. Urban Forestry & Urban Greening, 12(4), 509-521.         [ Links ]

Parizotto, S., & Lamberts, R. (2011). Investigation of green roof thermal performance in temperate climate: A case study of an experimental building in Florianópolis city, Southern Brazil. Energy and Buildings, 43(7), 1712-1722.         [ Links ]

Poë, S., Stovin, V., & Berretta, C. (2015). Parameters influencing the regeneration of a green roof's retention capacity via evapotranspiration. Journal of Hydrology, 523, 356-367.         [ Links ]

Refahi, A. H., & Talkhabi, H. (2015). Investigating the effective factors on the reduction of energy consumption in residential buildings with green roofs. Renewable Energy, 80, 595-603.         [ Links ]

Rincón, L., Coma, J., Pérez, G., Castell, A., Boer, D., & Cabeza, L. F. (2014). Environmental performance of recycled rubber as drainage layer in extensive green roofs. A comparative Life Cycle Assessment. Building and Environment,74, 22-30.         [ Links ]

Saadatian, O., Sopian, K., Salleh, E., Lim, C. H., Riffat, S., Saadatian, E. & Sulaiman, M.Y. (2013).A review of energy aspects of green roofs. Renewable and Sustainable Energy Reviews, 23, 155-168.         [ Links ]

Song, U., Kim, E., Bang, J. H., Son, D. J., Waldman, B., & Lee, E. J. (2013). Wetlands are an effective green roof system. Building and Environment, 66, 141-147.         [ Links ]

Speak, A. F., Rothwell, J. J., Lindley, S. J., & Smith, C. L. (2013). Rainwater runoff retention on an aged intensive green roof. Science of The Total Environment, 461, 28-38.         [ Links ]

Sproul, J., Wan, M.P., Mandel, B.H., & Rosenfeld, A.H. (2014). Economic comparison of white, green, and black flat roofs in the United States. Energy and Buildings, 71, 20-27.         [ Links ]

Stovin, V., Poë, S., & Berretta, C. (2013). A modelling study of long term green roof retention performance. Journal of environmental management, 131, 206-215.         [ Links ]

Sun,T., Bou-Zeid, E., & Ni, G.H. (2014). To irrigate or not to irrigate: analysis of green roof performance via a vertically-resolved hygrothermal model. Building and Environment, 73, 127-137.         [ Links ]

Susca, T., Gaffin, S.R., & Dell'Osso, G.R. (2011). Positive effects of vegetation: Urban heat island and green roofs. Environmental Pollution, 159(8), 2119-2126.         [ Links ]

Tsang, S. W., & Jim, C. Y. (2013). A stochastic model to optimize forecast and fulfillment of green roof demand. Urban Forestry & Urban Greening, 12(1), 53-60.         [ Links ]

Van Mechelen, C., Van Meerbeek, K., Dutoit, T., & Hermy, M. (2015). Functional diversity as a framework for novel ecosystem design: The example of extensive green roofs. Landscape and Urban Planning, 136, 165-173.         [ Links ]

Vanuytrecht, E., Van Mechelen, C., Van Meerbeek, K., Willems, P., Hermy, M., & Raes, D. (2014). Runoff and vegetation stress of green roofs under different climate change scenarios. Landscape and Urban Planning, 122, 68-77.         [ Links ]

Versini, P. A., Ramier, D., Berthier, E., & De Gouvello, B. (2015). Assessment of the hydrological impacts of green roof: From building scale to basin scale. Journal of Hydrology, 524, 562-575.         [ Links ]

Vijayaraghavan, K., & Raja, F. D. (2015). Pilot-scale evaluation of green roofs with Sargassum biomass as an additive to improve runoff quality. Ecological Engineering, 75, 70-78.         [ Links ]

Virk, G., Jansz, A., Mavrogianni, A., Mylona, A., Stocker, J., & Davies, M. (2015). Microclimatic effects of green and cool roofs in London and their impacts on energy use for a typical office building. Energy and Buildings, 88, 214-228.         [ Links ]

White, E. V., & Gatersleben, B. (2011). Greenery on residential buildings:Does it affect preferences and perceptions of beauty?. Journal of environmental psychology, 31(1), 89-98.         [ Links ]

Whittinghill, L. J., Rowe, D. B., Schutzki, R., & Cregg, B. M. (2014). Quantifying carbon sequestration of various green roof and ornamental landscape systems. Landscape and Urban Planning, 123, 41-48.         [ Links ]

Xiao, M., Lin, Y., Han, J., & Zhang, G. (2014). A review of green roof research and development in China. Renewable and Sustainable Energy Reviews, 40, 633-648.         [ Links ]

Yang, J., Yu, Q., & Gong, P. (2008). Quantifying air pollution removal by green roofs in Chicago. Atmospheric environment, 42(31), 7266-7273.         [ Links ]

Yang, W.Y., Li, D., Sun, T., & Ni, G. H. (2015). Saturationexcess and infiltration-excess runoff on green roofs. Ecological Engineering, 74, 327-336.         [ Links ]

Yuen, B., & Hien, W. N. (2005). Resident perceptions and expectations of rooftop gardens in Singapore. Landscape and Urban Planning, 73(4), 263-276.         [ Links ]

Zhao, M., Tabares-Velasco, P. C., Srebric, J., Komarneni, S., & Berghage, R. (2014). Effects of plant and substrate selection on thermal performance of green roofs during the summer. Building and Environment, 78, 1.         [ Links ]