Implementation Of Green Roofs Research Articles

Outdoor thermal performance of green roofs across multiple time scales: A case study in subtropical China

In recent years, roof greening technologies have been developed and implemented worldwide, as green roofs are an effective nature-based solution for alleviating outdoor heat and reducing building energy costs. While most observational green roof studies have investigated the cooling effect of model or test plots, few studies have conducted full-scale measurements; however, to guide green roof implementation, the thermal performance of full-scale roofs is crucial. This experimental study explored the ability of extensive green roofs to reduce outdoor temperatures on multiple time scales. The outdoor cooling effect of green roofs and the main factors that drive its performance were analyzed using long-term observational data collected from May 2016 to April 2019 in Nanjing, China. The results suggest that the cooling effect of green roofs exhibits significant diurnal, seasonal, annual, and vertical trends, and that the cooling performance across different time scales corresponds to weather and soil characteristics. The best cooling effect occurred at a height of 60 cm. The green roof displayed a temporary diurnal warming effect but had a good cooling effect on a seasonal time scale, with the largest amount of cooling occurring during the summer (average of 0.28 °C). The findings of this study can support the development, management, and maintenance of green roofs in subtropical areas.

Addressing the Water–Energy–Food Nexus through Enhanced Green Roof Performance

Urban densification and climate change are creating a multitude of issues for cities around the globe. Contributing factors include increased impervious surfaces that result in poor stormwater management, rising urban temperatures, poor air quality, and a lack of available green space. In the context of volatile weather, there are growing concerns regarding the effects of increased intense rainfalls and how they affect highly populated areas. Green roofs are becoming a stormwater management tool, occupying a growing area of urban roof space in many developed cities. In addition to the water-centric approach to the implementation of green roofs, these systems offer a multitude of benefits across the urban water–energy–food nexus. This paper provides insight to green roof systems available that can be utilized as tools to mitigate the effects of climate change in urbanized areas. A new array of green roof testing modules is presented along with research methods employed to address current issues related to food, energy and water performance optimization. Rainwater runoff after three rain events was observed to be reduced commensurate with the presence of a blue roof retention membrane in the testbed, the growing media depth and type, as well as the productive nature of the plants in the testbed. Preliminary observations indicate that more productive green roof systems may have increasingly positive benefits across the water–energy–food nexus in dense urban areas that are vulnerable to climate disruption.

The green roofs for reduction in the load on rainwater drainage in highly urbanised areas

Rapid weather phenomena, particularly sudden and intense rainfall, have become a problem in urban areas in recent years. During heavy rainfall, urban rainwater drainage systems are unable to discharge huge amounts of runoff into collecting reservoirs, which usually results in local flooding. This paper presents attempts to forecast a reduction in the load on the rainwater drainage system through the implementation of green roofs in a case study covering two selected districts of Opole (Poland)—the Old Town and the City Centre. Model tests of extensive and intensive roofs were carried out, in order to determine the reduction of rainwater runoff from the roof surface for the site under study. The potential of the roofs of the buildings to make a green roof was also determined using geographical information systems (GIS), for a case study of two central districts of Opole. It proposed a methodology to determine the rainwater drainage system load reduction by making green roofs. The analyses carried out lead to the conclusion that, in the districts selected for the study, the execution of green roofs on 25% of the of buildings with the potential to implement this type of roof solution could reduce the load on the rain water system by a degree that protects the city area from local flooding.

Vegetation Survival in Green Roofs without Irrigation

The implementation of green roofs as sustainable urban drainage systems provides benefits for stormwater control and the environment and is more and more encouraged. A model for the estimation of the probability of vegetation survival without irrigation is proposed. The model, developed through a probabilistic analytical derivation procedure, can also consider the effects of chained rainfall events, without the need of continuous simulation of hydrological processes. The model equations can be useful in the design of green roofs, allowing to determine the growing medium thickness in terms of an assumed risk of vegetation withering in dry periods. The proposed model is also able to identify the optimal thickness of the growing medium, over which the survival performances can be increased only with irrigation. Model performances were tested by the application to two case studies in Italy. Comparison between the probabilities and the cumulative frequencies from a continuous simulation of water content in the growing medium shows a good agreement and provide a first confirmation of reliability.

Assessing city-scale green roof development potential using Unmanned Aerial Vehicle (UAV) imagery

While green roofs have been deemed promising in mitigating environmental issues caused by rapid urban development, city-scale green roof studies have faced various obstacles, especially difficulties in obtaining accurate data for analysis. This study developed a new, cost-effective approach to assessing green roof development potential by using ultra-high-resolution (UHR) (0.09 m) Unmanned Aerial Vehicle (UAV) imagery in a case study site (Central Luohe with an area of 158 km2) in China. Specifically, the data was processed, interpreted, and classified to create highly accurate land-use and building roof spatial resources databases. A decision-making flowchart was developed for preliminary determination of a building stock’s suitability for green roof implementation and the preferred type based on the five influencing factors and building roof classification. Subsequently, a two-stage strategy for large-scale green roof development was proposed. The approach demonstrated in this research greatly improves the accuracy of city-scale studies on roof spatial resources and enables better planning and development of urban green spaces at the local level.

Development of a Management Framework for Applying Green Roof Policy in Urban China: A Preliminary Study

Increased consumption of energy and resources by urbanization has caused increasing concerns regarding the sustainability of building practices around the world. Green roofs (GRs) are attracting increasing attention as an important means to overcome environmental challenges related to urbanization. Although GRs have been widely applied in some areas throughout the world, their development is lagging in China. This paper reviews international GR policies with the aim to develop a framework for applying GR policies in suitable areas of China. After summarizing the typical environmental characteristics and GR policies in China, policies that can expedite GR implementation were recommended. By analyzing the national conditions (climate conditions, economic development, urban construction and policy circumstances), 23 GR policies were identified and divided into three categories (i.e., mandatory policies, incentive policies and assistance policies). Based on the attributes, the policies were developed into a framework that combined the three development stages of GRs (i.e., the pilot exploration stage, the progressive promotion stage and the overall application stage). These findings will help to formulate a GR strategy in China and provide important insights for other countries.

Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States

Green roofs are among the most popular type of green infrastructure implemented in highly urbanized watersheds due to their low cost and efficient utilization of unused or under-used space. In this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area in the Pacific Northwest, United States. We utilized a spatially explicit ecohydrological watershed model called Visualizing Ecosystem Land Management Assessments (VELMA) to simulate the resulting stormwater hydrology of implementing green roofs over 25%, 50%, 75%, and 100% of existing buildings within four urban watersheds in Seattle, Washington, United States. We simulated the effects of two types of green roofs: extensive green roofs, which are characterized by shallow soil profiles and short vegetative cover, and intensive green roofs, which are characterized by deeper soil profiles and can support larger vegetation. While buildings only comprise approximately 10% of the total area within each of the four watersheds, our simulations showed that 100% implementation of green roofs on these buildings can achieve approximately 10–15% and 20–25% mean annual runoff reductions for extensive and intensive green roofs, respectively, over a 28-year simulation. These results provide an upper limit for volume reductions achievable by green roofs in these urban watersheds. We also showed that stormwater runoff reductions are proportionately smaller during higher flow regimes caused by increased precipitation, likely due to the limited storage capacity of saturated green roofs. In general, green roofs can be effective at reducing stormwater runoff, and their effectiveness is limited by both their areal extent and storage capacity. Our results showed that green roof implementation can be an effective stormwater management tool in highly urban areas, and we demonstrated that our modeling approach can be used to assess the watershed-scale hydrologic impacts of the widespread adoption of green roofs across large metropolitan areas.

Investigation of single-storey residential green roof contribution to buildings energy demand reduction in different climate zones of Iran

ABSTRACT The share of the building sector accounts for one-third of the total energy consumption in the final energy demand in the world, and they are, indeed, paramount factors for CO2 emissions. Energy consumption in developing countries piles up to 40%, while this is higher in Iran, and for this reason, energy saving in this sector plays a prominent role. This paper aims to study the effects of using green roofs (GR) on energy consumption and CO2 emission rate of a sample building in various climate, calls, dry hot, cold, and humid hot, which can correctly represent different climates of Iran. Simulations are done for the entire year using DesignBuilder, which is a popular tool in this regard. Besides, the building construction materials considered in the simulation are the most utilized in Iran, and 15 cm height grass is selected to be used in the roof. Results indicate 6.19%, 2.07%, and 9.45% energy consumption reduction and 238, 100, and 370 kg of emission reduction for Tehran, Tabriz, and Bandar Abbas, respectively. In addition, an economic analysis is conducted to explore the economic viability of green roof implementation. It has been concluded that, according to the tariffs for water and electricity in Iran, the application of green roofs is not economically viable in current economic conditions.

Water and thermal regime of extensive green roof test beds planted with sedum cuttings and sedum carpets

Implementation of green roofs could help to reduce rapid runoff and help cities to mitigate heat islands. The aim of the study is to assess the water and temperature regimes of four experimental green roof test beds having different growing media and plant coverage during the vegetation season 2018. Experiments were conducted in four test beds (1 × 1 m) established on a flat roof. Two types of growing media were used. The first (A) was a substrate composed of crushed spongolite, crushed expanded clay, and peat. The second (B) was a coarser substrate, composed of crushed expanded clay, crushed bricks, peat, and compost. Two test beds, hereafter designated ACu and BCu, were filled with substrates A and B respectively and planted with a mixture of Sedum spp. cuttings with approximately 10% coverage. The substrate thickness was 6 cm. Two other test beds, designated ACa and BCa, were filled to a depth of 4 cm with A and B growing media, respectively, and planted with a carpet of Sedum spp. with approximate coverage of 100%. The experiment was conducted over one growing season. Continuous monitoring of substrate temperature, water content, and outflow was conducted on each test bed. The lowest runoff coefficient was observed in test bed ACu, while the highest runoff occurred in test bed BCu, with twice the amount of outflow as ACu. The total runoff coefficient of ACa was more than one-third higher than that of ACu. The lowest maximum substrate temperature on the hottest day of the season was observed in bed ACa with a temperature of 40.6 °C, while the highest temperature was seen in bed BCu, 7.9 °C higher. The analysis of the rainfall-runoff relationship calculated for individual rainfall events demonstrated that runoff coefficients depended on initial water content, rainfall intensity, rainfall depth, substrate type, and vegetation cover. Beds planted with sedum carpets and having more extensive vegetation coverage were superior at moderating extremes of temperature.

POTENTIAL FOR URBAN GREENING WITH GREEN ROOFS: A WAY TOWARDS SMART CITIES

Abstract. Cities are experiencing increased pressure on social, economic, and environmental sectors due to the rapid urbanisation and increasing risk owing to climate change affecting the urban environment. Solutions such as green roofs are often discussed in the context of smart and sustainable cities as they present a multi-functional and solution-oriented approach to address these challenges. Green roofs become extremely relevant in the context of highly urbanised and compact cities where impervious surfaces are abundant. Therefore, in this paper, we analyse the potential of green roofs at a city scale with the help of parameters such as area and slope of the roof and structure of the building. We also identify the priority zones based on environmental and socio-economic parameters. The study is carried out in the city of Liege, Belgium. The results suggest that around 20% (350 hectares) of the total buildings in the city have the potential for developing green roofs. Moreover, the potential of green roofs is quite significant in terms of roof area in the priority zone. Due to significant socio-economic deprivation in high priority zones, implementation of green roofs might not be affordable. Buildings with larger roof sizes are mostly owned by companies or commercial establishments, thus, making larger roofs more relevant for retrofitting green roof. Thus, our approach can act as a preliminary decision-making tool for urban planners to analyse the potential of green roofs and prioritize them in deprived areas.

Analysis of potential benefits on flood mitigation of a CAM green roof in Mediterranean urban areas

In the last decades, green roofs have been proposed among several nature-based solutions, as promising and sustainable tools to mitigate urban flood risk and adapt to climate changes. Several vegetation types have been suggested as green roof top layers, depending on the region and the purpose of the roof. In a Mediterranean climate, the Crassulacean Acid Metabolism (CAM) vegetation represents a particularly advantageous choice for green roofs since it does not require artificial irrigation and maintenance. However, the flood mitigation performance of CAM green roofs has not been investigated as adequately as other vegetation types. In this framework, we aim to define the potential retention capacity of a no maintenance-cost spontaneous CAM green roof, located at the entrance of the University of Cagliari (Italy) and to compare it to C3 vegetation type. The structure has been equipped with gauges to measure the water fluxes in and out of the roof. Local observations are used to calibrate a conceptual ecohydrological model. A 51-year rainfall time series and corresponding potential evapotranspiration are then used to simulate and compare the relative performance of green roofs vegetated with spontaneous CAM and more common C3 plants. Results show the good performances of the CAM green roof in mitigating rainfall extremes, with an average retention capacity of 0.52 over the whole investigated period, while C3 presents an index of retention equal to 0.71, but it requires frequent irrigation. Moreover, this work highlights some potential economic and environmental benefits of CAM green roof implementation in Mediterranean areas.

Simulation of green roofs and their potential mitigating effects on the urban heat island using an artificial neural network: A case study in Austin, Texas

The growing number of densely populated cities has resulted in a decrease in vegetation coverage, which in turn, has resulted in a temperature increase in urban areas. This phenomenon is known as urban heat island (UHI). Several strategies have been proposed to mitigate the effect of urban heat islands in recent years, including usage of green roof coverage. However, there is a need for a rigorous analysis of the relationship between UHI and different urban characteristics using advanced models for urban planners to make policy-decisions to mitigate the UHI effect. In this study, the cooling effect of the green roof strategy in the city of Austin, considering 2D/3D urban characteristic parameters was investigated. To begin with, land surface temperature (LST) was estimated from Landsat 8 TIRS data in July 2016. Also, 3D urban morphology parameters derived from light detection and ranging (LiDAR) data. To simulate the green roof strategy, Sentinel 2A satellite images were used to calculate the normalized difference vegetation index and the normalized difference built-up index because of higher spatial resolution than Landsat 8 OLI. Then a multilayer feed-forward neural network was applied as a nonlinear model to find a relationship between LST and various urban characteristic parameters simultaneously. Furthermore, the importance of the variables in LST modeling was evaluated using sensitivity analysis. After that, some downtown residential and office buildings, which had the potential to become a green roof, were selected to implement the green roof strategy. Finally, by analyzing the relationship between LST reduction due to green roof simulation and urban indicators, the best buildings for green roof implementation were determined. Results showed that the accuracy of the LST modeling was reached to R2 = 0.786 and RMSE = 0.956 °C. In addition, by greening 3.2% of total building roofs, the average of LST decreased by 1.96 °C. Moreover, the results indicated that the building green roofs with (i) heights of 15–25 m, (ii) the highest values of sky view factor and solar radiation, and (iii) the lowest distance to the water body, had the greatest cooling effects on LST. Consequently, these findings indicated that the green roof has a significant effect on temperature reduction, especially by selecting the buildings with the above mentioned characteristics.

Green roof effects on daytime heat in a prefabricated residential neighbourhood in Berlin, Germany

Berlin currently experiences increasing environmental challenges especially through the combined effect of urbanization and climate change. The intensification of summer temperature extremes has become increasingly evident in recent years, urging the city to promote mitigation and adaptation measures for local heat load reduction. Green roofs have been widely recognized as an effective urban greening strategy to reduce heat stress in cities. This study thus analyses the effect of rooftop greening on outdoor thermal conditions in an inner-city prefabricated residential area in Berlin. The studied neighbourhood is one of the inner-city hot-spot areas of environmental loads, highlighting the need for green solutions. We quantified thermal effects of intensive green roof implementation using the ENVI-met model which, for the first time, has been applied at the city’s official planning scale. The study thereby aims at overcoming the mismatch between research scales and planning scales, facilitating the knowledge transfer between the science community and urban practitioners, particularly in land use planning. Results indicate that on a hot summer day, green roofs can significantly improve daytime thermal comfort at the roof level with an estimated decrease in physiological equivalent temperature (PET) by 9 K. Green roofs can thus provide spaces of qualitatively increased thermal comfort compared to street-level areas. Overall, our results highlight the effectiveness of rooftop greening in terms of heat adaptation at the neighbourhood level. Therefore, this study suggests that these greening systems should be emphasized in future effect-oriented and sustainable urban planning assessments, especially of inner-city prefabricated housing estates.

A preliminary study on new cooling techniques for stingless bees hive

Stingless bees are a type of insect which are very sensitive to the changes of their surroundings, especially to severe heat wave. A report stated that at temperature as high as 38 ºC can cause death of the bees especially to the pupae. Therefore, the objective of this research is to evaluate new methods in regulating the temperature in the hive. To achieve this goal, two cooling methods were studied. One method is using greenroof, a type of roof which contains green vegetation and soil. It is used to cool down the space under the roof. Another method is using a photovoltaic (PV) powered thermoelectric cooler (TEC). Three units of MUSTAFA-hives were exposed under sunlight, one is without any temperature regulation and the other two hives used cooling techniques stated above. The temperatures inside each hive was measured at two points, and was compared with the hive without temperature regulation. It was found that, for the hive integrated with greenroof, the average hive temperature was about 3 ºC and 6 ºC lower in the honey cassette and brood-cells compartment, respectively. On the other hand, the hive with PV powered TEC recorded average temperatures of about 0.5 °C and 3 °C lower in honey cassette and brood-cells compartment, respectively. Therefore, it can be concluded that the implementation of greenroof or TEC could solve the problem of stingless bees’ hive overheating. However, the greenroof has a better thermal performance, besides being economic and simpler solution.

Pollinator emerging from extensive green roofs: wild bees (Hymenoptera, Antophila) and hoverflies (Diptera, Syrphidae) in Geneva (Switzerland)

By the end of 2020, 75% of the Swiss population will live in cities. The urban densification will result in habitat and biodiversity loss. One solution to mitigate this loss in urban environments is the implementation of green roofs that are now recognised as a tool for the maintenance of epigeal and aerial arthropods. Green roofs can provide various services such as pollination and food supply for insects and various arthropods (e.g. arachnids) and animals (e.g. birds). The objective of this study was to evaluate the diversity of pollinating insects emerging from urban green roofs. Wild bees (Hymenoptera) and hoverflies (Diptera) were sampled using emergence traps on six extensive green roofs in the urban area of Geneva (Switzerland), from March to August 2017. Five species of wild bees and two species of hoverflies were identified: Lasioglossum morio (Halictidae) and Sphaerophoria scripta (Syrphidae) are the only two species considered as emerging from green roofs in our study. Ecological traits of these two species indicated generalists, well adapted to xero-thermophilic conditions.

Fractal analysis of green roof spatial implementation in European cities

To face the consequences of climate change and unsustainable urbanization, green roofs are currently widely implemented in urban environments. Despite their benefits to restore ecosystem services are quite well established at the roof scale, green roofs need to be widely and appropriately distributed to perform efficiently at larger scales. However for now, this scale-factor is not considered to guide and conduct green roof implementation policies.Here we show that a multi-scale analysis based on fractal theory is helpful in providing information for green roof implementation and in assessing the relevance of these policies.Computed for 9 European cities, green roofs fractal dimensions are sparse, ranging 0.49 to 1.35, and illustrate some different degrees of progress in urban greening. These results demonstrate some significant inconsistencies between political ambition and their in situ realization, and the necessity to better take into account the spatial distribution of green roof implementations in order to optimize their performances.

State-of-the-Art Green Roofs: Technical Performance and Certifications for Sustainable Construction

Green roof systems, a technology which was used in major ancient buildings, are currently becoming an interesting strategy to reduce the negative impact of traditional urban development caused by ground impermeabilization. Only regarding the environmental impact, the application of these biological coatings on buildings has the potential of acting as a thermal, moisture, noise, and electromagnetic barrier. At the urban scale, they might reduce the heat island effect and sewage system load, improve runoff water and air quality, and reconstruct natural landscapes including wildlife. In spite of these significant benefits, the current design and construction methods are not completely regulated by law because there is a lack of knowledge of their technical performance. Hence, this review of the current state of the art presents a proper green roof classification based on their components and vegetation layer. Similarly, a detailed description from the key factors that control the hydraulic and thermal performance of green roofs is given. Based on these factors, an estimation of the impact of green roof systems on sustainable construction certifications is included (i.e., LEED—Leadership in Energy and Environment Design, BREEAM—Building Research Establishment Environmental Assessment Method, CASBEE—Comprehensive Assessment System for Built Environment Efficiency, BEAM—Building Environmental Assessment Method, ESGB—Evaluation Standard for Green Building). Finally, conclusions and future research challenges for the correct implementation of green roofs are addressed.

A review of green roof incentives as motivators for the expansion of green infrastructure in European cities

Nowadays green roofs play a key role in alleviating the negative effects of urbanization. Despite investors awareness of the advantages of green roofs, there are still some barriers that hinder investments on a large scale. As a result a financial and non-financial incentives are implemented. The review presented in this paper allowed to identify the most popular initiatives and to formulate recommendations for creating incentive supporting implementation of green roofs in urban areas.

Re-Naturing Cities: Evaluating the effects on future air quality in the city of Porto

The effect of different “green” measures, such as the increase of urban green areas, the application of green roofs and the increase of surfaces albedo on urban air quality were evaluated with the WRF-CHIMERE modelling system. In order to account for the heterogeneity of urban areas, a single layer urban canopy model was coupled to the WRF model. The case study consists of a heat wave occurring in the Porto (Portugal) urban area in a future climate scenario, considering the Representative Concentration Pathway RCP8.5. The influence of the selected measures on PM10, NO2 and O3 concentrations was quantified and compared with a control run (without measures) simulation scenario. The results revealed that all the measures are able to mitigate the effects of heat waves by reducing the air temperature between −0.5 °C and −1 °C (maximum differences for the mean of the episode). Positive and negative effects were found in terms of air quality. The implementation of green roofs and the increase of surfaces albedo promoted an overall increase of PM10 (between +0.6% and +1.5%) and NO2 (between +0.8% and 3.5%) concentrations, which are closely related to a decrease of vertical mixing in the urban boundary layer. The increase of green urban areas promoted an overall decrease (on average) of both PM10 and NO2, by around −1% and −3%, respectively. The O3 levels increased with the increase of urban green areas, mostly located over the Porto urban area. Slight differences were promoted by the implementation of green roofs. For the increase of surfaces albedo, both increases and decreases of O3 concentrations were observed. The obtained results contribute to the knowledge of the chemical composition of the urban atmosphere and can be of great importance for stakeholders and decision-makers to deal with climate change impacts.

Kajian Persepsi Arkitek terhadap Pelaksanaan Bumbung Hijau di Malaysia: Faedah, Halangan dan Cadangan

The implementation of a green roof as a sustainable method to reduce the urban heat island effect is still new in Malaysia. Although it has not been tested on a city scale, many studies have found that green roofs can balance the impact of urbanization by improving environmental quality. Its low usage in Malaysia is due to various factors, such as cost and the lack of awareness among the construction industry players. This study aims to identify the perceptions of local architects towards the implementation of green roof and its benefits, obstacles and recommendations to overcome the challenges in implementation. Questionnaire survey were used to determine the views of local architects, on ten benefits, nine obstacles of green roof implementation and eight recommendations to overcome the green roofs obstacles. The results indicated that the most important green roof benefit was minimizing the urban heat island effect (N = 8.14). Meanwhile, the weakest green roof benefit was increasing the roofing thermal insulation (N = 3.73). The most significant obstacle of green roof application was the constraint of implementation by the client (N = 4.22), with the weakest obstacle was inadequacy in the confidence of the architect towards the benefits of the green roof (N = 2.62). In addition, the most significant recommendation to overcome its implementation obstacles was enhancing the incentive to green roof operators (N = 4.37), while the weakest recommendation is by bringing in foreign expertise and technology transfer (N = 3.65). The findings of the study will facilitate in promoting the implementation of green roofs in Malaysia and enhancing the contribution of the green roof to the interior and exterior environment of buildings.