Green Roof Installation Research Articles

Capacity Assessment of a Combined Sewer Network under Different Weather Conditions: Using Nature-Based Solutions to Increase Resilience

Severe weather conditions and urban intensification are key factors affecting the response of combined sewer systems, especially during storm events. In this regard, the capacity assessment of combined sewer networks under the impact of rainfall storm events of different return periods was the focus of this work. The selected case study area was a mixed-use catchment in the city centre of Thessaloniki, Greece. The hydraulic performance of the examined sewer network was assessed using an InfoWorks ICM model. The results indicated that mitigation strategies, such as the application of nature-based solutions (NBSs) or low-impact developments (LIDs) are considered essential for controlling combined sewer overflows. A multicriteria analysis was conducted to select the most appropriate NBSs/LIDs to be located in the study area to enhance the system’s capacity. The results of this multicriteria analysis were used to propose a combined sewer overflow mitigation scenario, based on the installation of green roofs, as the most highly ranked solution in the analysis performed. Incorporating the proposed NBS/LID in the hydrologic-hydraulic model significantly increased the performance of the studied combined sewer network.

Is LCZ Enough? Physical Properties, Thermal Environments and Cooling Effects of Green Roofs in High-Density Urban Industrial Blocks

With rapid worldwide urbanization, the urban heat island (UHI) effect is becoming more and more serious. The UHI effect is more intense in industrial areas. Green roofs are an effective way to mitigate UHIs in high-density cities, which calls for thorough examination. This study explored the associations between the block characteristics and block thermal environment in high-density industrial areas based on the widely accepted Local Climate Zone (LCZ) scheme. The pedestrian air temperature comparisons before and after virtual green roof installations presented the cooling effects of green roofs. Thirty-six typical industrial blocks were involved in the study and the simulations were conducted utilizing ENVI-met. The results showed that (1) the air temperature in LCZ4 is significantly lower than those in LCZ2 and LCZ6, but no significant differences were identified between other pairs of LCZ types; (2) the cooling effect of green roofs significantly differs among LCZs, and is associated with sky view factor (SVF), average building area (ABA) and average building shape index (ABSI); (3) in high-density urban areas, additional functional parameters and building-volume indices should be included to better address the physical characteristics, thermal environment, and green roof cooling effect of industrial blocks. This study could improve the validity of LCZ classification for high-density industrial blocks and may provide direct implications for green roof planning.

Development of predictive indices for evaluating the UHI adaptation potential of green roof- and wall-based scenarios in the Mediterranean climate

Urban heat islands can jeopardize urban inhabitants, but the installation of green roofs (GRs) and walls (GWs) can contribute to mitigating urban overheating. The present study provides novel indices to easily predict the spatial median variation in air temperature at pedestrian heights related to the application of GR- and GW-based scenarios during the hottest hours of a typical summer day by varying the building height (BH), coverage percentage, and leaf area index. The indices are meant to be applied to built areas with 0.3–0.4 urban density in the Mediterranean climate and are derived from regression models fed with the outputs of 281 simulations of three urban areas developed and run in ENVI-met software. The developed models are all highly significant. The GR model shows that mitigation is influenced by all three parameters, and it can estimate mitigation with a root mean square error of 0.05 °C. Compared with the other parameters, the GW models revealed that the BH did not influence the decrease in air temperature. The green façade and living wall (LW) indices predict mitigation with errors of 0.04 °C and 0.05 °C, respectively. However, for the LW model, further parameters should be considered to improve its reliability.

Assessing Ecosystem Services through a multimethodological approach based on multicriteria analysis and cost-benefits analysis: A case study in Turin (Italy)

Ecosystem Services (ESs) are benefits that humans derive from nature, including climate regulation, air and water purification, soil formation, and recreation. Currently, ESs are at the center of green city policies tackling sustainability challenges. Traditionally, ESs have been assessed using monetary estimations, Environmental Impact Assessments (EIAs), and Cost-Benefit Analysis (CBA). These methods are useful for integrating environmental aspects in land use planning but have practical limitations since they focus on analyzing biophysical values and economic benefits. Due to the value pluralism of the ESs concept, intangible/extra-economic elements and the plurality of perspectives of the different stakeholders involved need to be included. Within this context, Multicriteria Decision Analysis (MCDA) allows the consideration of multiple problem dimensions and accommodates value pluralism. Based on these premises and limitations, the present paper proposes the integration of CBA and MCDA to evaluate alternative project solutions for green roof installation. The multidimensional outputs from CBA and MCDA are combined in a common aggregation procedure called COSIMA. Starting from a real case in Turin (Northern Italy), this article illustrates the application of COSIMA from the point of view of the best trade-off on the preferences of users and investors. The study results show the suitability of COSIMA for integrating all ESs values (i.e., biophysical, sociocultural, and economic) in urban governance processes.

Combined strategies for green roof incentive policies in Lisbon: Evaluating the potentiality of concession grants and identifying priority intervention areas

Incentive policies to promote new technologies is a strategy often employed by policymakers and governments. In some cities worldwide, mechanisms to encourage the adoption of Green Roofs (GR) have been implemented over the years. Although GR is not a new technology, the use of incentives, such as subsidies and tax abatements and/or exemptions, is still a recent strategy in many countries. The study covered in this paper proposes to explore the potential of combined incentive mechanisms for green roofs, using direct incentives (financial subsidies) and indirect incentives (tax/fee rebates). The granting incentives were verified by the feasibility assessment from both private (saved money) and public perspectives (reduction in municipal revenue) using scenarios of abatement percentages for fees and taxes and combining direct and indirect incentives. In addition, priority intervention areas for the installation of green roofs were defined based on three parameters: (i) the proportion of existing green spaces, (ii) urban heat islands and (iii) the potential of the building stock for green roof retrofit. The results show that granting a combined solution can be an effective option for facilitating the implementation of green roof projects. Moreover, the study serves as a decision support guide for politicians, urban planners, and public managers to formulate incentive proposals and make well-informed decisions regarding the incentive policies for GR.

Assessing multifunctional retrofit potential of urban roof areas and evaluating the power and carbon benefits under efficient retrofit scenarios

Green roof installations and photovoltaic (PV) systems are widely employed roof retrofits that aid cities in mitigating climate change impacts, while avoiding the need for increased land utilization. By integrating PV systems with vegetation on urban roofs, a photovoltaic-green (PV-Green) system can be achieved for multifunctional use of the roof space, thereby simultaneously achieving PV and greening benefits. However, current research solely based on one retrofit type cannot meet the requirement for assessing the multifunctional retrofit potential of urban roofs. In this study, an assessment method is proposed to identify and quantify the multiple retrofit potential of urban roofs by integrating roof attributes (slope, orientation, and area), roof type (gable or flat), solar attributes (radiation and irradiation duration), and biogeochemical simulation. Moreover, three roof retrofit scenarios, Scenario 1 (S1): maximization of PV-Green roofs, Scenario 2 (S2): maximization of PV economic benefits, and Scenario 3 (S3): maximization of public subjective well-being through roof greening, were designed to allocate the use of urban roof spaces and evaluate their respective potential power and carbon benefits at the city scale. Using Shanghai's downtown as an example, the results showed that 85,722 roofs (or 7310.86 ha) were available for multifunctional use. S1 revealed that applying PV-Green roofs can increase the additional green biomass by 0.74 × 107 kg C/yr compared to only installing PV roofs. Moreover, S1 produced the highest power output of 2.31 × 1010 kWh/yr to meet 15.4% of Shanghai's electricity demand. S2 identified 609 flat roofs and 70,527 gable roofs that were uneconomical for PV system installation. This indicated that the solar radiation received by most gable roofs was insufficient to cover the installation cost. S3 offered a biomass production of 1.48 × 107 kg C/yr and increased carbon stocks in Shanghai by 0.87%. This assessment method provides urban planners and policymakers with an analytical tool to optimize the use of urban roof spaces, thereby enhancing urban livability and sustainability.

Modeling the Effect of Green Roofs for Building Energy Savings and Air Pollution Reduction in Shanghai

Building energy consumption is an essential source of greenhouse gas (GHG) and air pollution. Green roofs can directly absorb ambient CO2 and remove air pollutants through their vegetation layers, but a limited number of studies have examined their effects on GHG and air pollutant reduction associated with building energy savings, especially in the context of climate change. This research examined the performance of green roofs on CO2 and air pollutant reduction, including SO2, PM2.5, and NOx, through building energy demand savings in Shanghai, China. Climate change mitigation effects were assessed based on the energy consumption of five types of buildings before and after the installation of green roofs under 2020 and 2050 climate conditions, respectively. EnergyPlus software 9.5.0 was applied to simulate hourly energy consumption for different building prototypes with and without green roofs. Green roofs on all building types exhibited positive energy savings on annual, monthly, and diurnal scales, and they can save more energy for most of the building types under the projected 2050 climate condition. Moreover, most of the building energy saved by green roofs came from the Heating, Ventilation, and Cooling (HVAC) systems. In addition, this study discovered that the energy-saving benefits of green roofs vary based on the type of building they were installed on. Green roofs were found to have the largest energy saving on the shopping mall, especially on extremely hot summer days. Finally, a Geographic Information System (GIS)-based approach was developed with the ability to quantify the amount of GHG and air pollutant reduction associated with building energy savings for existing buildings in the Huangpu District of Shanghai. This approach was also utilized to present the spatial distribution of buildings with different levels of suitability to install green roofs by considering their location attributes and air pollutant reduction potential together, which is the major innovation of this research. The purpose of this study is to provide valuable guidance to policy makers regarding the performance of green roofs in building energy-saving and air quality improvement in the urban environment when facing the challenge of climate change, which is essential for urban sustainability.

More than sedum: Colonizing weedy species can provide equivalent green roof ecosystem services

Green roofs are typically constructed for their provision of both environmental and associated economic benefits including increased habitat, thermal regulation, mitigation of air and noise pollution, and stormwater retention. The provision of these various ecosystem services is sharply influenced by plant species composition, with particular species and traits known to excel at specific services. For this reason, increased biodiversity can improve the overall provision of ecosystem services. However, one key contributor to green roof biodiversity, colonizing species, is understudied. In this study we examine the contribution of common colonizing species (lawn weeds) and one green roof species, to three important ecosystem services: stormwater retention, temperature reduction, and nitrogen retention. This experiment used replicated green roof modules to examine 13 different treatments: eight colonizing species in monoculture, one green roof species monoculture, two treatments with a mix of colonizing species, one treatment where vegetation was allowed to spontaneously colonize, and one substrate only control. Results from this study show that mixtures of colonizing species performed well for all three monitored ecosystem services, with a few of the monocultures, especially those with high biomass or canopy density, performing similarly. While it is unlikely that green roof installations would proceed equally well without adding vegetation, our results indicate that colonizing species can support a viable green roof ecosystem. This study shows that spontaneous growth and/or allowing new species to colonize may be a viable design alternative for green roofs, decreasing cost while maintaining the desired ecosystem services.

Environmental and Social Benefits of Extensive Green Roofs Applied on Bus Shelters in Edinburgh

The presence of green roofs in urban areas provides various ecosystem services that help mitigate climate change. They play an essential role in sustainable drainage systems, contribute to air quality and carbon sequestration, mitigate urban heat island, support biodiversity, and create green spaces supporting public well-being. Bus stops provide good opportunities for installing green roofs. Various cities worldwide have started installing green roofs on bus shelters, but often without thoroughly comparing expenses and the resulting benefits. This study quantifies the social and environmental benefits of installing green roofs on bus shelters in the City of Edinburgh. An assessment of the benefits and their monetary values was conducted using the B£ST analysis tool combined with manual calculations, which is easily transferable to other cities worldwide. It was compared to the current situation with no green roofs installed at bus stops. Installation of green roofs on all bus shelters in the City of Edinburgh may result in £12.9 million–£87.2 million in total benefit present value. The total cost was projected to be £15,994,000. By green roof installation, the City of Edinburgh can be closer to being carbon-neutral by 2030, a sustainable city as part of the City Plan 2030 and City Vision 2050.

Landscape and Horticultural Fertigation Using Roof-Derived Storm Water: The Potential Multiple Benefits of Blue Green Roof Installations

A contribution to the sustainable management of storm water is the use of sustainable drainage (SuDS)-derived water as an unconventional source for irrigation. If storm-water runoff contains dissolved nutrients in excess of those found in conventional irrigation, reusing this water can contribute to the nutrient demands of horticulture or landscaping, which is known as “fertigation”. Green roofs are SuDS devices, and those with below-substrate water storage, blue green roofs, can be additional water sources. The nutrients released from a roof-substrate-growing medium could contribute to the growth of crop and landscape plants, but materials from blue green roofs must not release residues harmful to fertigated plants or receiving soils. This plant growth experiment examined the effects of water from a blue green roof on plant growth and health and the effects on soil and roof-harvested water when functioning as a nutrient-rich irrigation source. Tomatoes and ryegrass were used as examples of horticultural and landscaping plants, respectively. Blue green roof water was compared with potable water irrigation. The blue-green-roof-derived water provided a distinct growth advantage for tomatoes and lower sodium in fruits than tap water, at 285 mg/kg and 636 mg/kg, respectively. For ryegrass, the differences were minimal, but there was no disadvantage to using roof water for fertigation. Following three years of a blue green roof’s operational life, export of inorganic nutrients from the roof, local storage, and then application to plants were effective in contributing additional fertiliser.

Determining social-psychological drivers of Texas Gulf Coast homeowners’ intention to implement private green infrastructure practices

Green infrastructure (GI) has been demonstrated to be an efficient flood mitigation measure and an effective approach for building community resilience, especially in the context of climate change. Drawing on Protection Motivation Theory, this study offers insight into the factors influencing residents' intention to implement individual GI practices by homeowners along the Texas Gulf Coast. The GI practices examined included the potential installation of (1) green roofs, (2) rain barrels, (3) rain gardens, (4) permeable pavement, and (5) tree protection and planting. Our findings revealed that homeowners expressed little interest in adopting GI practices owing to the lack of information, absence of incentives, and guidance on how to implement GI practices. Moreover, the findings from our modeling confirmed that perceptions of the effectiveness and cost of GI had the strongest influence on respondents’ intention to implement GI. Other significant indicators such as threat appraisal, reliance on public flood protection, perceived co-benefits, age, and the number of children varied with specific GI practices. These findings provide valuable information for city policymakers and planners in coastal regions concerning the promotion and development of GI that can meet the needs of their residents, provide the impetus for implementation, and in turn, contribute to community resilience.

Awareness and willingness to pay for green roofs in Mediterranean areas

Green roofs have been extensively investigated in recent years, showing that their implementation in urban areas provides multiple benefits (e.g., pluvial flood mitigation, urban heat island reduction, energy saving, increase of biodiversity, CO2 sequestration) and supports sustainable urban development. Although green roof benefits have been widely recognized, the perception that the community has of these nature-based solutions and the willingness to pay for their installation in urban areas is still not clear nor quantified. Societal perception and willingness to pay for green roofs are fundamental for urban planners and decision makers, since they represent the community participation in the sustainable development of urban areas. In this work, we aim to analyze how citizens perceive green roofs and how willing they are to pay for the installation and maintenance of these nature-based solutions. We used an online survey to investigate the perception and the knowledge of green roofs as a potential solution to common environmental issues (i.e., urban flood, increase of temperature, energy consumption, air pollution and lack of green spaces), and the interest and willingness to pay for green roof installation on both public and private roofs. Based on the answers of 389 respondents living in Sardinia (Italy), our analysis revealed that most citizens are aware of what green roofs are, and they are aware that, although these nature-based solutions can not completely solve environmental issues, they can greatly contribute to the mitigation of these phenomena. Results also show a higher interest in the installation of green roofs on public buildings than on private ones, due to the high installation costs. Moreover, for private roofs, the possibility to install photovoltaic panels instead of GRs is generally preferred. Most of the respondents are willing to spend less than 100 € per year for the maintenance of green roofs on public buildings and to invest less than 5000 € for the installation on their own house.

THE INFLUENCE OF «GREEN» ROOFS ON THE REDUCTION OF STORM DRAINS

The study examines a way to reduce stormwater runoff in urban conditions using the device of «green» roofs in the design and construction, reconstruction and overhaul of buildings and structures. The sewer system of modern increasingly growing cities often cannot cope with the load exerted on it. Therefore, an environmentally friendly and effective reduction of storm runoff is one of the main challenges in the field of urban planning today. Despite the fact that foreign works devoted to this topic, as well as the experience of practical application of roof greening technolo-gies abroad have proved a significant reduction in runoff, the question of the expediency of this method in Russian realities remains open. It is important to take into account not only the water-holding capacity of «green» roofs as such, but also the meteorological peculiarities of the territory where construction is planned, the methods of produc-tion technology and the construction materials used. Until now, the study of this aspect in the Russian Federation has not been given sufficient importance, which, in turn, delayed the introduction of modern technologies for the installa-tion of green roofs in our country, and also slowed down the development and approval of the necessary regulatory framework. The article provides a theoretical proof of the effectiveness of «green» roofs in reducing rain and snow-melt runoff in the climatic conditions of Central Russia, based on statistical and empirical data. The results obtained may be valuable for the further development of «green» technologies in construction and for ensuring environmental safety in our country.

Green roof installation as a living lab for outdoor learning in higher education

Technology and construction knowledge are harder to understand among higher education students if the teaching and learning process is only conducted inside the classroom. Learning should be versatile, and the subject will be more interested in experiencing the students with materials and processes outside the classroom. It also boosts site awareness, especially when the students must collaborate on the design and construction technology for the site. Thus, a living lab approach was introduced to prepare students with sound designer and construction technical knowledge. The research aims to expose students and the community to extensive green roof installation as part of teaching and learning activities. The green roof subject was selected as it was an example of engaging design students with current technology. The participation from various student backgrounds are from Master of Science in Green Architecture, Bachelor of Science in Architecture, Bachelor of Science in Building Surveying, Diploma in Landscape Architecture and other communities from the nearby campus. The results show the materials and process of building an extensive green roof on campus and significant to the design and build consultant/contractor, academicians, students, and nearby community to understand the process involved in site. The discussion part elaborated on the issues of green roofs, such as managing green roofs and biodiversity.

Evaluation of a Green Roof for Heat Mitigation in a Building Located in a City with a Hot and Humid Climate

The expansion of the urban population has contributed to the formation of urban agglomerates; whose spatial morphology favors the formation of heat islands. The installation of Green Roofs (GR) is a strategy that can be applied to mitigate the effects of this phenomenon, especially in regions lacking vegetation cover. The objective of this paper is to evaluate, through Computational Fluid Dynamics (CFD), the potential to reduce the internal temperature of a building located in the city of Rio de Janeiro, Brazil. The temperatures of the inner surface of the roof were measured in two buildings, one with GR and one without GR. This information was used as input data into Solidworks software to simulate the heat distribution inside the building. Results indicated that the temperature was reduced by about 2°C in the building with GR, proving the technology's effectiveness, notably in the hottest months of the year.

Efficiency enhancement in energy production of photovoltaic modules through green roof installation under tropical climates

This study is aimed to assess the performance of green roof-PV system; and determine the optimum installation height of green roof. In this study, two units PV panels of 1 kW each were setup at building rooftop level. Modular green roofs were established at three different heights of 0.3 m, 0.6 m and 0.9 m from rooftop floor level, respectively. The effects of each green roof height on the PV module temperature, ambient temperature and daily power yield were monitored for 6 months’ period. The results showed that green roof-PV system exhibited lower ambient and PV module temperatures of 3.36% and 17% compared to bare roof-PV system. Other than that, green roof enhanced the power generation efficiency averagely by 1.6%. It is found that green roof installed at 0.3 m has increased the power generation performance by 3% and 11% compared to that of 0.6 m and 0.9 m, respectively.

Green Roofs- A Review

As the green area continues to get replaced because of the increase in population and urbanization, the requirement to recover this area has become crucial for improving environmental quality. Installation of green roofs is one way that can curb the negative affect of growth and establishment while providing various environmental and economical benefits. Various names are given to green roofs such as “eco-roofs”, “roof-gardens”, etc. And these are roofs with vegetation at the top surface. The most specific reason for installing green roofs in the building is because of its energy efficiency. Along with this, other benefits do exist like their vegetation aids photosynthesis and their soil layer absorbs rainfall, typically leading to development in water runoff quality. This review paper focuses on green roofs along with research efforts created by researchers. The discussion concentrates on each part of the green roof elements, i.e., vegetation, growth substrate, filter layer, drainage layer, waterproofing layer, and root barrier. This paper also includes experimental studies on the assortment of efficient green roof elements to satisfy public expectations. Moreover, the advantages provided by green roofs are highlighted.

Adaptation of Salvia fruticosa, S. officinalis, S. ringens and interspecific hybrids in an extensive green roof under two irrigation frequencies

With the ultimate goal of introducing new species of sage to the green roof industry, the adaptation of the Mediterranean sage species Salvia fruticosa, S. officinalis, S. ringens and the interspecific hybrids S. fruticosa × S. ringens and S. officinalis × S. ringens was investigated, under normal and sparse irrigation in an extensive green roof in Athens, Greece. Rooted cuttings were planted (April 2021) on shallow (10 cm) substrate (grape-marc compost: perlite: pumice, 3:3:4, v/v) and irrigated when substrate moisture was 16-22% (normal irrigation) or 7-11% (sparse irrigation). All sage types established satisfactorily on the green roof, even under sparse irrigation, except S. fruticosa, which had the highest vegetative growth and at the end of the experiment (September 2021) showed the highest mortality rate regardless of irrigation frequency. Similar to the S. fruticosa response showed the S. fruticosa × S. ringens hybrid under normal irrigation. Both hybrids, S. fruticosa × S. ringens and S. officinalis × S. ringens had a lower mortality rate under sparse irrigation compared to the parental species. S. officinalis × S. ringens formed more lateral shoots than its parental species and had an almost spherical compact canopy, which is a nice feature for an ornamental plant. S. officinalis and S. ringens developed bigger horizontal diameter, which is valued for rapid substrate coverage in a green roof installation. All sage types flowered except S. fruticosa. All sage types showed higher values of stomatal resistance under sparse irrigation, while ΦPSIIo values under both irrigation frequencies indicated normal operation of the photosynthetic apparatus. S. officinalis, S. ringens and S. officinalis × S. ringens hybrid are highly recommended for sustainable extensive green roofs in arid/semi-arid regions.

Performance of green roof installed on highly insulated roof deck and the plants’ effect: An experimental study

Extensive green roof system is widely used due to its lightweight, thin growing media, limited or no maintenance, low cost, and high potential application for use over the new or existing lightweight structures. This study is focused on the energy performance and rainwater retention performance of extensive green roofs when coupled with highly insulated roof deck. In this experimental study, three roof systems: conventional roof (CR) and two extensive green roofs with plants (GR) and with no plants (GM) are constructed, instrumented and their responses to real environmental conditions are monitored for over a year and analyzed. The experimental results suggest that during wet period, the rainwater retention potential of green roof is only about 21%, while in the summer the rainwater retention capacity increases as high as 100%. Plants play an important role in rainwater interception, growing media wetness, rain runoff and the green roof's thermal performance by modifying short- and long-wave radiation and as well as convective heat exchanges. Installation of green roofs on highly insulated roof decks yields a mixed performance in a mild and wet climate. The heat loss through the green roof during the heating months is about 2% higher than a similar roof without green roof. Whereas during the cooling months the green roof is able to reduce the heat gain by 66%. This substantial heat gain reduction can help to reduce overheating problems in highly insulated buildings.

Investigating the Performance of Green Roof for Effective Runoff Reduction Corresponding to Different Weather Patterns: A Case Study in Dublin, Ireland

This article aims to analyse the performance of green roof in runoff reduction. A case study has been conducted through a deployed green roof at the custom house quay building in Dublin, Ireland. Modular green roofs have been deployed which have IoT scales associated to it for measuring the effective reduction in runoff. Hydro-meteorological variables such as rainfall, temperature, relative humidity and wind speed values were corresponded to the amount of runoff reduction by means of a regression-based relationship. Comparison of the observed runoff reduction from a modular green roof and that estimated based on the developed regression relationship yielded a R2 value of 0.874. Through this research, a pattern was identified which established that longer records and better weather variables data have the potential to improve the performance of the regression model in predicting the amount of runoff reduction corresponding to different rainfall and weather patterns. In general, performance of green roof was found to be highly positively correlated to the amount of rainfall received; however, low correlation between rainfall and the percentage of runoff reduction indicate that saturated soil in green roofs considerably deteriorates the performance in runoff reduction. Overall, this study can help in identification of locations where installation of green roofs can help mitigate floods at a city scale.