Green Roof Installation Research Articles

Increasing Evapotranspiration on Extensive Green Roofs by Changing Substrate Depths, Construction, and Additional Irrigation

Urban environments are characterized by dense development and paved ground with reduced evapotranspiration rates. These areas store sensible and latent heat, providing the base for typical urban heat island effects. Green roof installations are one possible strategy to reintroduce evaporative surfaces into cities. If green roofs are irrigated, they can contribute to urban water management and evapotranspiration can be enhanced. As part of two research projects, lysimeter measurements were used to determine the real evapotranspiration rates on the research roof of the University of Applied Sciences in Neubrandenburg, Germany. In this paper, we address the results from 2017, a humid and cool summer, and 2018, a century summer with the highest temperatures and dryness over a long period of time, measured in Northeast Germany. The lysimeter measurements varied between the normal green roof layer (variation of extensive green roof constructions) and a special construction with an extra retention layer and damming. The results show that the average daily evapotranspiration rates can be enhanced from 3 to 5 L/m2/day under optimized conditions. A second test on a real green roof with irrigation was used to explain the cooling effects of the surface above a café building in Berlin.

Carbon footprint of green roof installation on school buildings in Greek Mediterranean climatic region

ABSTRACTGreen roof installation in contemporary urban centres is increasing due to their numerous benefits, including microclimate improvement. However, the magnitudes of influence of the green roof design to energy savings is not fully clear, as well as the environmental benefit, in terms of reducing greenhouse gases emissions. The aim of this study was to estimate the effect of green roofs design on energy savings and their carbon footprint when installed on school buildings. The cooling and thermal insulation features of green roofs have been studied by using the TRNSYS simulation software. Different types of green roof systems (extensive and semi-intensive) and construction options are studied in four types of school buildings. Results showed that the estimated reduction in annual CO2 emissions due to energy savings and CO2 capture by plants was many times greater than the CO2 emissions that caused from roof construction.

Assessing Practice and Criteria for Green Roof Maintenance on High-rise Residential Building in Malaysia

Urbanisation inevitably shows a positive sign in increasing the economic reputation of a country. Nevertheless, it has led to several problems including the deficit in green spaces and destruction of the natural environment, therefore green building is introduced as an alternative to overcome crucial environmental issues. Numerous approaches were also adopted to reduce other environmental issues such as urban heat island, air pollution and lack of green spaces. One of the sustainable approaches that help to minimise the environmental problems is by using the means of vegetation or plant material on rooftops or also known as the green roof. The implementation of the green roof on top of buildings is becoming a trend in the urban cities as it provides numerous benefits to the green development. The green roof is also part of criteria in green building and among the benefits, implementing green roofs will reduce heat flux, optimise energy efficiency and improve stormwater management. However, despite the benefits, enhancement on the green roof installation and maintenance consideration are two factors which are still largely unexplored as the main significant factor in the viability of the green roof installation. Hence, this paper is aimed to determine the vital criteria of maintenance and its ranking towards the establishment of best practice maintenance for the green roof, by focusing on high-rise residential. Questionnaires were distributed by email and through an online survey to 30 maintenance managers of green roof of high-rise residential in Kuala Lumpur and the samples are drawn by using purposive sampling technique. The results showed that the most significant maintenance criteria of the green roof are drainage, followed by waterproofing, irrigation, water retention, and roof slab. The outcome of this study has provided a significant contribution to the current maintenance practice of green roof by prioritising the criteria of maintenance and key address of green roof, where it may help to standardise the maintenance practice of the green roof in the tropical climate of Malaysia.

ANALISA TAMAN ATAP DALAM UPAYA MENGURANGI LIMPASAN AIR HUJAN PADA BANGUNAN PERKOTAAN

With the increasing public awareness of the human relations system with the surrounding environment, communities are beginning to shift towards better sources and methods to help improve the environment. One of the methods that began to be utilized is the application of green roof construction. There are many benefits for installing a green roof whether it is in a home or office building. The study was conducted on applicable green roof construction, the benefits of installing a green roof and a process run for a green roof installation with a construction approach applicable to urban housing buildings in Jakarta and on cost analysis on material requirements and installation. And in its efforts to reduce rainwater runoff. Green roof as one in the management of rainwater in urban areas. From the result of the research resulted the calculation on survey location percentage of runoff decrease 26%. While in the test object / mock-up there is a reduction of 95% runoff volume. It can be concluded that the use of a green roof / roof garden can reduce the runoff volume produced by rainwater, resulting in reduced surface runoff automatically reduced. This will also reduce the drainage-drainage burden of the city in accommodating water. The Roof Garden plays a role in the management of rainwater management to cope with puddles up to the danger of flooding

Mediterranean Green Roof Simulation in Caldes de Montbui (Barcelona): Thermal and Hydrological Performance Test of Frankenia laevis L., Dymondia margaretae Compton and Iris lutescens Lam

Green roofs provide a number of environmental advantages like increasing urban biodiversity, reducing pollution, easing burdens on drainage systems, and lowering energy costs thanks to thermal insulation. Frankenia laevis, Dymondia margaretae and Iris lutescens were tested in a green roof installation. For all three species, we assessed two minimal irrigation treatments and one rain-fed treatment to resemble Mediterranean climate conditions analyzing the thermal and hydrological performance of all three species and their substrates through an evaluation of green cover, mortality, and biomass. The most influential factors registered for all three species are the relationship between air and water in the substrate and the interaction between green cover and substrate, respectively, for summer and winter seasons. In particular, D. margaretae preserved more water in its substrate than the other species both in summer and winter and after each rainfall event. F. laevis registered the highest level of variation in terms of substrate water content and of rainwater retention. I. lutescens achieved low hydrological performance, a limited amount of green cover, and slow growth. Our results suggest the absolute need of additional irrigation, managed in accordance with specific functional objectives, for all three species analyzed under Mediterranean conditions and different water regime.

Optimal planning of the joint placement of photovoltaic panels and green roofs under climate change uncertainty

Photovoltaic (PV) panels directly convert sunlight into electricity; but, sunlight also heats the panels, negatively impacting their efficiency. Green roofs are vegetative layers grown on rooftops, mainly to provide added insulation on the roof to save energy. Green roofs also cool near-surface air temperature. Hence, the joint installation of PV panels and green roofs may potentially lead to higher efficiency of PV panels in certain climates. We develop a two-stage stochastic programming model to optimally place PV panels and green roofs under climate change uncertainty to maximize the overall profit from energy generated and saved. We calibrate the model using the literature, industry reports, and the data from different, at times conflicting, climate projections. We then conduct a case study for a mid-size city in the U.S., perform extensive sensitivity and robustness analyses and provide insights.

Assessing the Hydrologic Performance of a Green Roof Retrofitting Scenario for a Small Urban Catchment

In an existing urban environment, retrofitting low impact development (LID) solutions can provide an opportunity to address flooding and water quality problems. Taking into account the need to effectively estimate the impact of vegetated LIDs, particular attention has recently been given on the evapotranspiration (ET) process that is responsible for the restoring of green roof water-holding capacity. The present study aims to develop a methodological approach to estimate the actual ET as climate input data in the United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) continuous simulation. The proposed approach is calibrated on a single green roof installation based on one-minute continuous simulations over 26 years of climate records. Then the calibrated methodological approach has been implemented to perform continuous simulation of a small urban catchment retrofitted with green roofs. Based on simulation results, the peak and volume reduction rate evaluated for the 1433 rainfall events are equal to 0.3 on average (with maximum values of 0.96 for peak and 0.86 for volume). In general, the adopted methodology indicates that the actual ET estimate is needed to suitably assess the hydrologic performance of vegetated LIDs mainly concerning the volume reduction index; furthermore, the methodology can be easily replicated for other vegetated LID applications.

Effects of substrate depth and precipitation characteristics on stormwater retention by two green roofs in Portland OR

Study RegionThis study took place in Portland Oregon, a city of over 600,000 residents located in the Willamette Valley in the state of Oregon in the Pacific Northwest region of the United States. Portland experiences a temperate climate with Mediterranean features. Study FocusRunoff patterns from two extensive green roofs with substrate depths of 75 and 125 mm, situated on a 5000 square meter retail store, were compared over a one year period. Precipitation, irrigation, and storm water discharge were continuously monitored and the performance of the green roofs for storm water control was investigated in detail. New Hydrological Insights for the RegionOver the study period, the 125 mm and 75 mm green roofs retained 32.9% and 23.2% of all precipitation by volume, respectively. The hydrologic response of the green roofs during individual storm events was found to depend strongly on the total depth of the storm event as well as the length of the antecedent dry weather period. Differences in performance between the two substrate depths were most pronounced for small storms with long antecedent dry weather periods. Both green roofs showed strong seasonal dependence in storm water retention, with higher percent retention in the relatively dry summer months compared to lower retention in the wetter winter months. These findings have important implications for the effective installation of green roofs for stormwater management in our region. Because of the increased frequency of storm events during the Pacific Northwest winters, it is imperative that efforts to increase storage capacity through increased substrate depth be paired with efforts to ensure rapid removal. If deeper substrates are to be utilized effectively; more research is needed to identify ways to increase evapotranspiration, for example via more informed plant selection, during wet winter months.

Retention performances of green roofs worldwide at different time scales

AbstractUrbanization process is rapidly converting forested areas and grasslands to residential, commercial, or industrial spaces, triggering soil degradation and significantly increasing impervious surfaces. Consequently, man‐made environments experience significant decrease of infiltration and groundwater recharge, enhancing the problems related to the management and protection from increased stormwater runoff. Green roofs are structural measures able to mitigate these negative drawbacks due to anthropic transformation, retaining and detaining stormwater runoff, with the main advantage of reducing hydraulic loads on combined storm sewer systems. Hydrological performance of green roofs have been studied in different parts of the world under different climatic conditions, but a comprehensive study that provides global responses, even in an approximate way, is still missing. The aim of this work is to assess the convenience and the feasibility of installing green roofs in any target area of the world, providing a rough indication of geographic regions where green roof installation is possible with good hydrological performance, and feasible in rainfed conditions with low vegetation water stress. To do that, we explored in silico green roofs' hydrological performance worldwide, using climatological forcings from ERA‐Interim database as input for a simple conceptual hydrological model to estimate green roof outputs, in terms of evapotranspiration and runoff.

Viability of Green Roofs as a Flood Mitigation Element in the Central Region of Chile

Population increase and urban development over the last 20 years in Chile have outgrown most rainwater drainage and evacuation systems. Many cities located in the central region suffer from frequent floods in some of their sectors during winter rainfall events. In addition, the lack of green spaces in these cities leads to biodiversity loss, increasing temperatures, greater energy demands, etc. Green roofs offer a solution that can mitigate climate change by reducing the runoff in cities with extensive, highly impermeable areas. This work analyses the installation of green roofs as a potential solution to the sectorial floods suffered by many cities in central Chile. The methodology includes the identification of conflictive sectors in the city of Curicó, hydrological modelling with the Storm Water Management Model (SWMM) software, the consideration of different distributions and types of green roof surfaces, and computational simulations to determine the feasibility of green roofs for preventing floods. The results show that, for moderate rainfall events, all studied sectors could avoid flooding if at least 50% of the surrounding area had green roofs (irrespective of the type of green roof). In contrast, in the presence of strong rainfall events, only some semi-extensive and extensive green roofs covering 60% to 95% of the surrounding area, respectively, could prevent flooding.

Implementation of green roof technology in residential buildings and neighborhoods of Cyprus

Green roofs are considered as an appropriate nature-based measure to increase the environmental resilience of cities. This paper examines this technological solution applied to typical urban residential buildings in the Mediterranean island of Cyprus, with respect to energy, environmental, and economic aspects. The analysis shows a clearly positive energy and environmental contribution of green roofs. Although such an investment does not seem to be cost-effective in residential buildings, sensitivity analysis demonstrates that green roofs become financially favorable compared to flat roof constructions with only modest reductions in their current installation cost. Moreover, green roofs offer environmental benefits that are currently difficult to monetize, which can clearly improve urban resilience to climate change. In order to quantify the impact of green roof installations on the surrounding environment, the analysis was expanded from the individual building perspective to neighborhood scale implementation, using appropriate simulation software to evaluate the contribution of green roofs to urban heat island mitigation. Focusing on the ambient air temperature at the pedestrian level, a noticeable decrease was estimated.

Evaluating Plant Species Suitability for a Substrate-Free Tropical Green Roof

Greenroofs reduce building exterior-interior thermal flux and mitigate high internal air temperatures, especially in tropical climates. Tropical greenroofs are given little attention and their use remains restricted to a very low percentage of roofs due to high costs compared to traditional roofs, weight overload (mainly due to the chosen substrate) and potential waterproofing problems. We here present an alternative greenroof technique based on a reduction of the current Modern Extensive Greenroof (MEG) technique to half of its original layers. The feasibility of superficially rooting plant species from extreme habitats was tested in full scale on a single family house over three consecutive years. The innovative horticultural system is based on a substrate-free method, which has several advantages over traditional systems, including easier maintenance and minimal total weight. The reduced layout also lowers material and labor costs, facilitating widespread retrofitting of installations, mainly on low income houses in urban areas of developing countries. From a sparse initial planting, total coverage was attained in two years and 218 taxa, belonging to 20 families and various growth types, were successfully grown on the new greenroof system. Species were able to survive and grow even though signs of dynamic photoinhibition were detected. The viability of the plant assemblage together with the ability to store water due to a high degree of succulence among species indicates a broad potential for research into the use of cultivated epiphytic, lithophytic and psammophilous flora for the installation of tropical greenroofs.

Identifying and assessing the critical criteria affecting decision-making for green roof type selection

Green roofs are categorized into different types based on their characteristics, and each type of green roofs offers different benefits and costs for both private and social sectors. Although there are studies conducted in many aspects of green roof installation, there is lack of study focusing on decision making (DM) for green roof type selection. The aim of this paper is to identify and assess the criteria affecting DM for green roof type selection from the standpoint of multi-criteria decision making in Kuala Lumpur, capital of Malaysia. Enhanced fuzzy Delphi method (EFDM) was developed for criteria identification. EFDM consists of two rounds; firstly, knowledge acquisition through a semi-structured interview, and secondly, criteria prioritization using a Likert scale questionnaire. As the results of EFDM, 19 criteria for green roof type selection were ranked, and categorized in four groups. Then, Decision Making Trial and Evaluation Laboratory was employed for the assessment of the causal relationships among the identified groups and criteria. It was concluded that the application of green roof is the most effective group for DM, while the cost of green roof is highly affected by other groups. Moreover, four highest influential criteria in DM for green roof type selection were discussed.

EFFECT OF GREEN ROOF AGE ON RUNOFF WATER QUALITY IN PORTLAND, OREGON

Green roofs have become a common method to increase water retention on-site in urban areas. However, the long-term water quality of runoff from green roofs is poorly understood. This study evaluated the water quality of stormwater runoff from a regular (non-vegetated) roof, a green roof installed 6 months previously, and a green roof installed 6 years ago in Portland, Oregon. Samples of runoff were taken during every rain event for 10 months, and analyzed for total phosphorus (TP), phosphate (PO3-4), total nitrogen (TN), nitrate (NO-3), ammonia (NH3), copper (Cu), and zinc (Zn). Runoff from the green roofs had higher concentrations of TP and PO3-4 and lower concentrations of Zn compared to the regular roof. Average TP concentrations from the 6-year old roof and 6-month old roof were 6.3 and 14.6 times higher, respectively, than concentrations from the regular roof, and average PO3-4 concentrations from the 6-year old roof and 6-month old roof were 13.5 and 26.6 times higher, respectively, compared to the regular roof. Runoff from the 6-month old green roof had higher concentrations of TP and PO3-4 than the 6-year old green roof during the wet season, but lower concentrations during the dry season. The 6-month old green roof installations where receiving waters are sensitive or impaired may need additional treatment methods to reduce phosphorus levels. As green roofs age, water retention decreases and phosphorus leaching increases during the dry season.

Creating a low-carbon campus in Chaoyang University of Technology (CYUT)

Founded in 1994, the campus of Chaoyang University of Technology (CYUT) is located in the suburban area of Taichung, Taiwan. In 2009, the president of CYUT signed the Talloires Declaration to show his commitment for promoting environmental sustainability on campus. In 2012, CYUT and many other universities in Taiwan cofounded the Green University Union of Taiwan (GUUT) to collaboratively promote the concept of environmental sustainability. Following the announcement of the Sustainable Development Goals (SDGs) set by the United Nations in 2015, CYUT has been putting a lot of effort into converting itself into a green university. Four different fields of management, which are energy and resources management, accident prevention and rescue management, occupational safety and health management, and environmental management, have been promoted in the campus of CYUT for this cause. Furthermore, four management practices including implementing management systems, organizing green courses, promoting green activities and creating green environment, have been applied to improve the effectiveness of the campus management. In the case of energy and resources management in particular, not only ISO 50001 and 14001 management systems were implemented but also an intelligent energy network (iEN) was established for maintaining effective usage of the campus energy. For years of striving in creating a green university, CYUT had several remarkable accomplishments. The green open space ratio in campus is 94.43%. Water-saving equipment was installed in the whole campus and reclaimed water is collected for urban reuse. Garbage reduction and classification have been enforced to make ease for later treatments. For issues related to energy and climate change, strategies, such as renewal of high energy consuming facilities, installation of green roofs, utilization of recycle energy and education of staffs were enacted and the consumed energy in campus gradually decreased in recent years. For example, the electricity and oil (including gasoline and diesel) consumption in campus of 2017 were 7.59% and 14% lower than those of 2016, respectively. In order to overcome the challenges from climate change, CYUT will continue on its process of creating a low-carbon campus focusing on energy sustainability.

ANALYTICAL REVIEW OF MAINTENANCE CRITERIA FOR GREEN ROOF IN MALAYSIA

The implementation of green roof on top of buildings is becoming a trend in the urban cities and provides numerous benefits to the green development growth. Despite the benefit and enhancement on green roof installation, maintenance consideration is still largely unexplored as the main significant factor in the viability of green roof installation. This paper is aimed to identify the significant criteria of green roof maintenance practice in Malaysia. The literature findings revealed that there are generally twenty (20) criteria pointed as maintenance criteria. Out of 20, six maintenance criteria were identified as the most significant factors towards the best practice of green roof maintenance.

Substrate Composition and Depth Affect Soil Moisture Behavior and Plant-Soil Relationship on Mediterranean Extensive Green Roofs

The Mediterranean basin is extremely vulnerable to climate change, and one of the areas most impacted by human water demand. Yet the green roofs increasingly created both for aesthetic reasons and to limit pollution and urban runoff are themselves very water-demanding. Successful green roof installation depends on the establishment of the vegetation, and the substrate is the key element: it conserves water, and provides the nutrients and physical support indispensable for plant growth. Since typical Mediterranean plant communities require no maintenance, this study seeks to develop techniques for creating maintenance- and watering-free horizontal green roofs for public or private buildings in a Mediterranean context. The innovative aspect of this study lies in creating two soil mixes, fine elements (clay and silt) and coarse elements (pebbles of all sizes), in two different thicknesses, to assess vegetation development. Monitoring of substrate moisture was carried out and coupled with local rainfall measurements during summer and autumn. As expected, substrate moisture is mainly influenced by substrate depth (the deeper, the moister) and composition (the finer the particles (clays and silts), the higher the moisture content). Vegetation cover impacts moisture to a lesser extent but is itself affected by the composition and depth of the substrates. These results are subsequently discussed with relation to the issue of sustainable green roofs in Mediterranean climates. Considering applications of our results, for an optimal colonization of a Mediterranean vegetation, a substrate thickness of 15 cm composed mainly of fine elements (75% clay-silt and 25% pebble-sand) would be recommended in green roofs.

Comparing reduction of building cooling load through green roofs and green walls by EnergyPlus simulations

Green roofs (GRs) and green walls (GWs) are good strategies for urban greenery. This study explores the cooling load benefits of GRs and GWs simultaneously for comparison. EnergyPlus simulation programme is used for estimating annual cooling load reduction for different buildings and scenarios in Hong Kong. In simulating GR, a built-in thermal model is used. For GWs, a self-developed thermal model is used, which has been developed and validated in our previous study. The simulation covers a single-storey building and two multi-storey buildings, each with four different coverage areas for GR and GWs. The GWs are assumed to be on building facade facing the west, east, north, and south. Results reveal that both GRs and GWs are capable of protecting building envelop from reaching higher temperatures and of reducing cooling load. In a single-storey building with an equal area of GR and GW, GR is more effective in energy saving. However, in a multi-storey building GR can provide energy benefits only to the topmost floor. An equal area of GW can provide benefits to multiple floors, which may result in higher benefit. Furthermore, the available area for GWs is larger. When considering the effect of orientation of GW, the west-facing GW contributes to the highest annual energy saving. It should be noted that the effect of orientation may differ with location and climatic conditions, and also with the shading effect of surrounding buildings. Therefore, installation of GRs or GWs should be considered case by case, taking into consideration the scale and surroundings of the building, the climatic condition, and area of greenery coverage.

Un enfoque metodológico para áreas verdes urbanas: un caso de estudio en Madrid

Introduction: Urban residents are aware of the positive effects of being surrounded by nature. Objective: A method was tested for identifying urban green areas and determining the attitude of the actors involved in the process of ground and roof greening. Materials and methods: Roofs available for the establishment of green areas were quantified. Residents were interviewed to ascertain their willingness to install and maintain a green roof. The study was carried out through a techno-socioeconomic evaluation. The Willingness-To-Green Index (WTG) was used to analyze the presence or absence of plants on roofs. Results and discussion: A new index, named the Green Evaluation Weighted Index (GEWI), was proposed to measure the presence of green in an urban environment. The index establishes the relationship between the number of roofs and the WTG of the inhabitants. The districts of Salamanca (Madrid), San Marti (Barcelona) and Nervion (Seville) had greater GEWI; that is, greater presence of urban agriculture. Conclusions: The proposed methodology and index show the different possibilities that the study areas have to increase their green areas. Some factors such as reducing paperwork or facilitating the installation of green roofs could help achieve this goal.

Temperature and cooling demand reduction by green-roof types in different climates and urban densities: A co-simulation parametric study

This paper presents a parametric study on the effect of four green-roof types on outdoor/indoor temperature and cooling demand under four different climates and three urban densities using co-simulation approach with ENVI-met and EnergyPlus. Results reveal an outdoor nighttime warming effect of not more than 0.2°C which is most obvious with the semi-extensive while the outdoor and indoor cooling effect ranges between 0.05–0.6°C and 0.4–1.4°C, respectively depending on the green-roof type, urban density and time of the day. These daytime temperature reductions also vary per prevailing climates and follow this order: hot-dry, hot (or warm)-humid, and temperate which can be explained by the interplay between solar intensity/air temperature and relative humidity between the regions. In a hot-humid region, the evaporative cooling potential of greenery is dampened when compared to hot-dry region. This is also true for region with low solar intensity and humidity like the temperate region. In terms of cooling demand reduction, 5.2% was observed in hot-dry climate on the hottest day of the year with full-intensive green-roof while the least saving of 0.1% was found with semi-extensive green-roof in temperate climate. In general, for both outdoor temperature and cooling demand reduction, semi-intensive green-roof was found more effective than its full-extensive counterpart while the higher spatial green-roof is most important for indoor temperature reduction irrespective of the leaf density of the greenery. Therefore, the intent of green-roof installation should be a determining factor for the type and spatial extent to be implemented.