Green Roof Systems Research Articles

Assessing the Impact of Urban Hydrological Processes on the Summertime Urban Climate in Nanjing Using the WRF Model

AbstractThe impacts of urban hydrological processes, such as anthropogenic latent heat (ALH), multilayer green roof systems (GRO), evaporation from impervious surfaces (EIMP), urban irrigation (IRR), and the urban “oasis effect” (OASIS) on regional hydrometeorology in Nanjing, are assessed by the Weather Research and Forecasting Single‐Layer Urban Canopy Models (WRF‐SLUCM). The results show that including all five urban hydrological processes, ALL best improves the prediction of near‐surface meteorology and has the largest correlation coefficients, the smallest root mean square errors, and the most accurate diurnal variations compared with observations. The improvements of ALH, GRO, and OASIS are larger than those of IRR and EIMP. The influence of ALH, GRO, and OASIS is comparable in commercial areas, whereas the influence of OASIS is significantly greater and plays essential roles in low‐intensity residential areas. Therefore, the overall effect of urban hydrological processes is especially large over low‐intensity residential areas, where the ALL case‐simulated monthly mean 2‐m air temperature (surface temperature) is reduced by approximately 1.3 (5.0) °C, the 2‐m specific humidity increases by 0.8 g kg–1, and the sensible heat (latent heat) flux is reduced (increased) at most by 90 W m–2. The changes in the vertical profiles indicate that urban hydrological processes reduce the potential temperature and wind speed, whereas they increase specific humidity over the entire urban boundary layer, leading to a more stable atmospheric conditions, reduced vertical mixing, and weaker convective rolls. These effects could mitigate the intensity of urban heat/dry islands while simultaneously exacerbating low‐level air pollution.

Estimation of modular green roof systems installation using the method of chronometry measurements

Due to the experimental studies using the method of timing measurements, the temporal values of technological operations for the installation of modular landscaping systems were calculated and technological works that have a great influence on the total device construction time were determined. A comparative analysis of the complexity of the device layers of the used coating showed that the most time-consuming is the process of laying paving slabs - 45 people-hours / 100 sq.m. (80% of the total complexity of the device layers of the used coating). Technological processes and operations associated with the installation of the pavement with the use of paving slabs under pedestrian load are more labor-intensive compared to the installation of landscaping systems. The average value of the complexity of the device operating cover for pedestrian load is 56.7 people-hours / 100 sq.m., while the average value of the complexity of the device of the coating with peeling systems is 15.6 people-hours / 100 sq.m., which is 28% lower than the complexity of the device operating cover for pedestrian loading.

Response of Near-Surface Meteorological Conditions to Advection under Impact of the Green Roof

Due to rapid urbanization, the near-surface meteorological conditions over urban areas are greatly modulated. To capture such modulations, sophisticated urban parameterizations with enhanced hydrological processes have been developed. In this study, we use the single-layer urban canopy model (SLUCM) available within the Weather Research and Forecasting (WRF) model to assess the response of near-surface temperature, wind, and moisture to advection under the impact of the green roof. An ensemble of simulations with different planetary boundary layer (PBL) schemes is conducted in the presence (green roof (GR)) and absence (control (CTL)) of green roof systems. Our results indicate that the near-surface temperature is found to be driven primarily by the surface heat flux with a minor influence from the zonal advection of temperature. The momentum budget analysis shows that both zonal and meridional momentum advection during the evening and early nighttime plays an important role in modulating winds over urban areas. The near-surface humidity remains nearly unchanged in GR compared to CTL, although the physical processes that determine the changes in humidity were different, in particular during the evening when the GR tends to have less moisture advection due to the reduced temperature gradient between the urban areas and the surroundings. Implications of our results are discussed.

Decision support system for green roofs investments in residential buildings

When designing green roofs, decision-makers continually face the difficult task of balancing benefits against costs. The use of decision analysis methods is essential in complex decision-making processes including different perspectives, multiple objectives, and uncertainty. This is the case when choosing between green roof systems, since different stakeholders show diverse concerns, and each solution has a different cost and performance. One of the most used methods in decision analysis is multicriteria analysis. The present study aims to adapt existing multicriteria decision models for the context of green roofs installation. The proposed methodology is based on the MACBETH method (Measuring Attractiveness by a Categorical Based Evaluation Technique) and determines the green roof option with the best trade-off between costs and benefits in agreement with the preferences of the users/investors. The paper presents the application to a real case study in Lisbon, Portugal, comparing the installation of 6 different green roofs over a parking lot. The methodology application identifies the intensive green roof as best solution classifying with a score of 69.43 out of 100. The conclusions on the best option remained robust in the sensitivity and robustness analysis. This approach supports the decision-making process of green roofs and enables robust and informed decisions on urban planning, while optimizing buildings retrofitting.

A comparative study on effects of various insulating layers of roof system on energy usage of building envelope

The purpose of paper is to analyse the effectiveness of various roof systems based on insulations layers in hot climatic condition of Hyderabad, India. In this paper, Energy analysis using Autodesk’s Green Building Studio cloud computing software has been done. The Energy analysis results gives indication about the Energy usage of building as well as overall life cycle costing. The roof system has been studied with their carbon emission and Embodied Energy to understand the sustainability aspect of the insulating layers in combination to provide a green roof system. The materials used for studying the insulating effects of roof system which were analysed in combinations were cork, gypsum board, expanded polystyrene, rock wool, fibre glass, PVC mesh, Polyurethane, etc. Due to the insulating layers the heat transfer is reduced through the roof system, which affects the cooling load of building envelope which reduces the energy consumption. The study is significant to understand the occupant’s indoor comfort, environmental and long-term economic benefits of insulation for a building envelope.

Prospects and restraints of green roofs for high-rise buildings in Sri Lanka

PurposeGreen roofs are acknowledged as a method to substitute greenery washed out by the urbanization. They provide many ecological and sustainable benefits of greenery; reduce the adverse effects of high-rise building constructions. Though this concept is more popular across many countries over the past few decades, still, implementation of this technology in Sri Lanka is new and scant. Hence, the purpose of this paper is to identify and analyze the potential of green roofs in high-rise buildings in Sri Lanka.Design/methodology/approachThe data collection was conducted through expert interviews and questionnaire survey. Expert interviews were carried out to validate the prospects and restraints identified through literature review to the Sri Lankan context and analyzed using content analysis. Questionnaire survey identified the most significant prospects and restraints using descriptive statistics and paired sample t-test. Purposive sampling was used to select participants.FindingsReduction of air pollution, aesthetical appearance, thermal benefits and energy savings, reduction of an urban heat island effect, the addition of points in the green rating system are the top most significant prospects that need to be highlighted in promoting green roof systems in Sri Lankan high rises. Less space allocation on rooftops, lack of technical competence and lack of awareness and research are restraints that need most effective elimination strategies to encourage green roof systems.Originality/valueThe first identified and quantified prospects and restraints for green roof system in Sri Lankan high-rise buildings can be utilized by the government, donors, multi-lateral agencies to promote the sustainable development in Sri Lanka and this knowledge could be used in different scale awareness programs. The value of this paper is such that the paper discusses the links of green roofs with the other facets of sustainability. The new legal reforms and amendments in Sri Lanka could potentially be pending with findings of this study.

Heat Transfer Behavior of Green Roof Systems under Fire Condition: A Numerical Study

Currently, green roof fire risks are not clearly defined. This is because the problem is still not well understood, which raises concerns. The possibility of plants catching fire, especially during drought periods, is one of the reasons for necessary protection measures. The potential fire hazard for roof decks covered with vegetation has not yet been fully explored. The present study analyzes the performance of green roofs in extreme heat conditions by simulating a heat transfer process through the assembly. The main objective of this study was to determine the conditions and time required for the roof deck to reach a critical temperature. The effects of growing medium layer thickness (between 3 and 10 cm), porosity (0.5 to 0.7), and heating intensity (50, 100, 150, and 200 kW/m2) were examined. It was found that a green roof can protect a wooden roof deck from igniting with only 3 cm of soil coverage when exposed to severe heat fluxes for at least 25 minutes. The dependency of failure time on substrate thickness decreases with increasing heating load. It was also found that substrate porosity has a low impact on time to failure, and only at high heating loads.

Optimization of green roof processes

This research is devoted to the optimization processes of installation of the green roof systems in combination with the Building Information Model (BIM) technologies used in the engineering design of such systems. There is a decision of such models which contained the most optimal parameters for the cost and time of the construction processes. The aim of our study is to explore the potential of a patented green roof technology for the residential and office buildings. The modular green roof system is the upper roof structure, technically advanced design solution of roofing, with innovative technological multifunctional advantages and the ability to integrate devices that convert solar and wind energy - solar panels and wind turbines. This technique has proved to be highly effective in reducing the nutrient load in a runoff, controlling watering over a period of time.

Growth of prairie plants and sedums in different substrates on an experimental green roof in Mid-Continental USA

Many prairie plant habitats have similarities to the harsh and stressful growing environments of green roofs. In the Mid-Continent Region of the USA under a hot summer climate, little research has been done to study prairie plant communities and their performance with different substrates on green roofs. To explore more sustainable, diverse green roof ecosystems, this research assessed the first-year growth (June to October 2018) on an experimental green roof in the Flint Hills Ecoregion, which has some of the most extensive coverage of intact tallgrass prairie in North America. A mixture of plants (four native prairie grasses and two sedums) were grown on two substrates—a commercial substrate (rooflite® extensive 800) and a regionally mixed substrate (Kansas BuildEx)—placed at two depths: 6.0–13.0 cm (called the “shallow depth”) and 16.5–25.5 cm (called the “deep depth”). Plant height, coverage, survival, visual appearance, leaf stomatal resistance, and volumetric substrate water content were measured. Supplemental irrigation was provided equally to each experimental plot during the growing season. It was shown that the regionally mixed substrate had greater effect on plant height at the shallow depth and on coverage at the deep depth. However, volumetric water content was usually higher in the commercial substrate. Substrate type did not affect visual appearance and leaf stomatal resistance. Substrate moisture was inversely related to leaf stomatal resistance at low soil moisture levels. All prairie species survived, while Sedum reflexum had poor survival and coverage. Bouteloua curtipendula, Bouteloua gracilis, Schizachyrium scoparium, and Sedum rupestre performed well in a green roof community. Bouteloua dactyloides grew very well, but may be too aggressive when planted with sedums. The findings of this study will be of practical value for the design of mixed-species green roof systems in similar mid-continental regions with hot summers.

Environmental factors affecting greenhouse gas fluxes of green roofs in temperate zone

This paper investigates the full seasonal greenhouse gas (GHG) dynamics of fluxes from three green roof systems (lightweight clay aggregate-based green roof – LR; grass roof – GR; sod roof – SR) and natural control site on shallow Leptosol (NC), using closed static chambers in the period April 2014 to December 2015. CO2, CH4 and N2O fluxes are measured and their relationships to meteorological parameters and substrate physicochemical characteristics are quantified. Median CO2 flux values were 21 (LR), 38 (GR), 62 (SR), and 82 (NC) mg CO2-C m−2 h−1. The results show ecosystem respiration (Reco) clearly increased until July and then decreased until November. Net ecosystem CO2 exchange (NEE) was more variable than Reco, depending on plant growth phase and weather conditions. Median NEE values for study period (from April to November 2015) were −7 (LR), −17 (GR), −136 (SR), and −82 (NC) mg CO2-C m−2 h−1. The percentage of autotrophic respiration (Ra) in Reco showed clear rise from LR (35%) to NC (62%). CH4 consumption dominated resulting in median fluxes as follows: −2 (LR), −1 (GR), −15 (SR), and −23 (NC) μg CH4-C m−2 h−1. N2O flux was low and highly variable in time, with median values varying from −0.07 (GR) to 2.18 (NC) μg N2O-N m−2 h−1. During the maximum vegetation growth, NEE exceeded Reco value. Green roofs are effective CH4 sinks, but they do not significantly affect N2O flux. The main environmental factors determining GHG fluxes in linear models were parameters describing moisture regime, meteorological parameters and soil physical characteristics. These models can be used to predict GHG fluxes from similar green roof systems in analogous climatic conditions. We conclude that green roof technology may be used to mitigate excessive ambient GHG levels in urban areas.

“PET tool” – a software tool for lightweight extensive green roofs performance analyses

Due to energy, environmental, and social benefits, green roofs are recognized as a bioclimatic technology and sustainable construction systems and are becoming a predominant solution in connection with urban planning and building envelope retrofitting. To support design and marketing of Urbanscape® lightweight extensive green roofs a special software tool was developed, which is presented in the paper. Performance evaluation tool (PET tool) is validated based on extensive and continuous 5-years in-situ monitoring of thermal and hydrological response of different Urbanscape green roofs. The key performance indicators of Urbanscape green roofs are evaluated based on calculated thermal and hydrological response. To emphasize the advantages of green roofs thermal response and performance indicators are determined also for non-vegetated roof for the same boundary conditions. PET tool enables i) evaluation of Urbanscape green roofs’ whole year thermal and hydrological response, ii) to search for the optimal design of the Urbanscape green roof system in terms of energy and water performance, iii) evaluation of comparative advantages compared to non-vegetated roof, iv) energy savings and CO2 emission reduction analyses for heating and cooling season. Analyses can be made for arbitrary worldwide climate conditions since meteorological parameters are gathered from Meteonorm database.

Simulation and optimization of energy consumption systems in buildings in varying climatic conditions

Green roof research has grown rapidly over the past decade. The green roof has been proposed as a lasting move to reduce urban-related complications. The installation of green roof systems has been made as a specific measure to achieve a wider objective to enhance environmental sustainability. As one of the effective parameters on energy consumption, buildings have always been considered the attention of engineers to reduce the amount of energy consumption. In this study, the effect of different factors including effect of different facades on energy consumption has been investigated, for this purpose, the Energy Plus software has been used to model and perform sample building calculations at three parts of Tehran, Tabriz and Bandar-e-Abbas. The results of this study show that the city of Tehran will have the best performance in reducing energy consumption and it will be suitable for Tabriz city of color concrete, as well as in Bandar-e-Abbas, a warm climate representative, the use of travertine 1 is suitable.

Soil Microbial Assemblages Are Linked to Plant Community Composition and Contribute to Ecosystem Services on Urban Green Roofs

Green roofs are a way for cities to mitigate environmental stressors, such as heatwaves and droughts. However, these environmental stressors can adversely affect green roof vegetation, causing challenges for plant growth and survival and subsequently reducing the ability of green roof systems to deliver critical ecosystem services such as heat mitigation and nutrient cycling. Plant-associated microbes may facilitate the resilience and tolerance of green roof vegetation to climate-associated stress. However, despite their crucial role in plant growth and survival in natural ecosystems, there has been little research on plant-associated microbes in green roof systems. Plant choice on green roofs may also determine which microbes established in green roof growing media, and particular plant-microbial combinations may be more resilient to environmental stress. This project sought to characterize soil microbial community composition on green roofs across New York City with different plant palettes and assess how different combinations of green roof plant species and root-associated microbial assemblages responded to isolated and simultaneous heat and drought treatments. We surveyed green roofs planted with either Sedum species or with a mixed-vegetation palette (i.e. wildflowers, grasses, and succulents). We found that mixed-vegetation and Sedum green roofs had distinct soil bacterial and fungal communities (p<0.0001) with a higher relative abundance of mycorrhizal fungi on mixed-vegetation roofs, and higher pathogen loads on Sedum roofs. Concurrently, we conducted a greenhouse experiment in which plants were grown from seed with live inocula collected from the two different types of vegetation on the green roofs we surveyed. We observed that plant species, soil inoculum, and abiotic stress treatment was correlated with shifts in soil fungal communities. This study demonstrated that soil microbial assemblages on green roofs are linked to the roof vegetation, and that they may facilitate green roof plants’ tolerance and resilience to environmental stressors.

Increasing the ability of a green roof to provide ecosystem services by adding organic matter and earthworms

The aim of this study was to increase the ecosystem services provided by a green roof by ameliorating the biological and chemical properties of a commercial green roof substrate through the addition of earthworms and compost. We conducted a mesocosm (120 × 80 × 33 cm) experiment with a plant community comprising Hylotelephium maximum,Centaurea jacea, Lotus corniculatus, Koeleria glauca, and Dianthus carthusianorum. Two substrates were compared (i) a low complexity commercial green roof substrate with no alterations and (ii) a high complexity substrate with a layer of locally produced vermicompost and earthworms (Lumbricus terrestris) placed on top of the commercial substrate. The mesocosms were placed on the roof of a 20 m high building and at ground level.Results show that the percent of vegetative cover on both substrates was lower in the roof mesocoms than on those placed at ground level. This is explained by climatic conditions, such as higher light intensity at roof level. The substrate with earthworms and vermicompost had significantly higher enzyme activity, microbial biomass, and metabolic activity. This resulted in more available nitrogen and phosphorus for plants, increased the plant biomass, floral nectar volume and sugar concentration which resulted in the flowers receiving more diverse and abundant insect pollinators. This is the first time that adding earthworms and compost to a green roof substrate has been shown to have a significant effect on plant growth and plant-pollinator interactions. These findings will help in designing green roof systems that are more efficient at preserving ecosystem services in urban areas.

Thermal behaviour of a green roof containing insulation cork board. An experimental characterization using a bioclimatic chamber

Green roof technology is increasingly being used to improve the energy and environmental performance of buildings. However, the description of the thermal behaviour of green roofs is very complex since it depends on several variables and relies on intricate phenomena.In this work the authors characterize a green roof system that replaces the conventional drainage and water storage polyethylene membranes with insulation cork boards (ICB). To enable the experimental characterization of this system, a double walk-in bioclimatic chamber was designed and built to recreate indoor and outdoor environmental conditions. Winter and summer environments with steady and unsteady conditions in both dry and wet states were simulated. Thermocouples and heat flux sensors were used to collect data over time from the different layers of the green roof prototypes.Measurements were first performed on a concrete slab insulated with ICB to assess the contribution of the latter to the thermal performance of the system. The effect on the heat transfer was further evaluated for systems of increasing complexity, containing first a substrate layer and then vegetation. It was noted that the substrate and vegetation layers improved the thermal insulation, and reduced heat fluxes and the thermal amplitude within the system. The vegetation layer was found to be of key importance to the overall performance of the green roof. It was also found that ICB and the substrate layers lose part of their insulation capacity when the system was wetted, although it was fully restored in the ICB layer within a few hours.

Selection of (Green) Roof Systems: A Sustainability-Based Multi-Criteria Analysis

A wide diffusion of green envelopes in cities can be an opportunity to improve urban environment conditions and reduce negative effects of climate change. The green roof system is a widespread solution adopted all over the world due to the relative simplicity of installation and the large private and social benefits provided. Despite this, some factors hinder the diffusion of the green roof system, not only economic factors (due to the higher installation costs compare to a traditional roof solution), but also technical factors connected to lack of knowledge. The present paper investigates the factors influencing designers in the choice of a building roof systems, comparing a traditional solution and a greening system. The involvement of architects, engineers, and researchers allows the selection of the most important factors. Results of the study identifies their priority, and through a sustainability-based multicriteria analysis, the role played by each one in the decision process. This approach provides interesting hints to identify effective strategies to support a wider diffusion of greening systems for urban resilience.

SIMULATION OF SURFACE RUNOFF REDUCTION IN URBAN BUFFER AREA USING GREEN ROOF SYSTEM

Steady developmental increase in urban and its buffer areas causes a decrease in rainwater catchment areas. Green roof system is emerging as a new form of technology that can improve the built environmental conditions. The purpose of this study was to simulate the application of green roof systems with cocopeat as planting media in reducing surface runoff water in urban buffer zones. Sub-watershed boundary analysis was carried out to determine the boundary of study area followed by land cover analysis using web-based software “i-Tree Canopy” to obtain the area of roof cover within the study area. Rainfall analysis (2005-2014) was carried out to obtain the design flood discharge value at the study location. The simulation results show that the green roof system with 10 cm depth of cocopeat as planting medium is able to delay peak discharge in the study area to exceed the concentration time for all flood return periods. Green roof application simulation of 5% and 10% of the total roof cover area resulted in a reduction in peak discharge up to 3.12% and 6.24% respectively. This green roof system needs to be combined with rainwater harvesting systems to further reduce peak discharge in the study area.

DESIGNING A GUIDELINE FOR GREEN ROOF SYSTEM IN MALAYSIA

Green roof system is widely implemented because of its environmental and economic benefits and aesthetic value to a building. There are numerous successful green roof projects, both extensive and intensive in Malaysia. However, there is no specific technical guideline for the planning, design and construction of green roof system catered to the climate and background of Malaysia. The aim of the research is to propose and develop a technical guideline of extensive green roof system in Malaysia on the planning, design and construction aspects of vegetation, substrate, filter, drainage and root penetration barrier. Comparative literature review of guidelines from Hong Kong, Singapore and Sydney were leveraged upon to propose an appropriate guideline for Malaysia’s market. In-depth interviews were carried out with green roof experts to collect feedbacks on the proposed guideline in the validation stage. The output from this research will conceptualise a framework for a technical guideline for future implementation of green roof systems in Malaysia.

GREEN ROOFS TO IMPROVE THE ENERGY RENOVATION RESILIENCE OF HISTORIC BUILDINGS

The introduction of vegetation in urban areas, through both green roofs and green walls, is a sustainable strategy for improving the environment and the quality of life, as well as crucial for urban biodiversity since the moment it is able to create new habitats for plant and animal species. The design and realization of green roof systems abroad is promoted and stimulated while in Italy, this subject, is still an innovation not supported by many real implementations. The application of this technological green system has a great importance for the redevelopment of existing building heritage, especially for historic buildings, to improve their energy-performance qualities, with respect for their architectural value. The aim of this study is to identify the technical issues for the realization of green roofs in urbanized contexts by focusing on the implementation of a green roof on a building of Leghorn following intervention guidelines developed. This research shows that not only does this system allow higher energy saving, but it also brings a decrease of load bearing on the structure.

Urban Heat Islands in Bahrain: An Urban Perspective

Cities across the Arab Gulf region, especially those in Bahrain, have undergone a notable transformation by virtue of the rapid urbanization of the region. Thus, the characteristics of these cities have encountered massive transformation. Accordingly, both governmental and non-governmental projects are authorized for collaborative work to meet the accelerating demands resulting from the increase in population in the Kingdom of Bahrain. However, such projects have been neglected due to other crucial environmental issues. For instance, these projects have resulted in excessive carbon dioxide gaseous emissions. Consequently, these cities are left to suffer from disregarded public spaces and a limited percentage of designed urban open spaces. The case in Bahrain can be summarized as suffering from an absence of the three pillars of sustainability. This has been a fertile ground for the emergence of various urban devastations, among which the “Urban Heat Island” phenomenon adversely affects the urban context of the city. This research investigates these problems, offering propositions to control Urban Heat Islands (UHIs) in Bahrain. Moreover, it aims to recognize the effect of Green Roof Systems in terms of sustainability in order to mitigate UHIs and reduce the threat of Global Warming.