Performance Of Extensive Green Roof Research Articles

How vertical drainage positions of extensive green roofs affect the runoff control performance

The capacity of extensive green roofs (EGRs) in runoff reduction and pollutants control significantly decreased with increasing rainfall intensity. This is attributed to most of EGRs are the lower-drainage method and use a thinner substrate layer because of the structural load-bearing limits of buildings. Existing solutions depend on increasing the rainwater storage by thickening the substrate layer of EGRs, or replacing the substrate materials. We propose to enhance the water retention capacity of EGRs by adjusting vertical drainage positions and moving the lower-drainage at the bottom to upper-drainage over the substrate layer. To test the runoff control performance of EGRs with the upper-drainage method, we designed three EGR models with two different (upper- and lower-) drainage methods based on the common EGR’s structure in practice and carried out total 48 experiments under different rainfall intensities with an artificial rainfall simulator. The experimental design also included adjusting structural factors of the EGR to further explore the influences of roof slope, status of vegetation growth (height and canopy cover ratio), and model size. The average runoff retention rate for the upper-drainage EGR was 61.82 %, which was much higher than the 23.94 % for the lower-drainage EGR. The concentrations of TN and TP in runoff with the upper-drainage were 2.83 and 0.18 mg/L, which were much lower than the 8.47 and 2.10 mg/L for the lower-drainage EGR. EGRs with upper-drainage overall performed better in runoff control than EGRs with lower-drainage. Vegetation height and model size did not significantly affect the rainwater control performance for different drainage methods, while the change of slope affected the rainwater interception of the EGRs with upper-drainage method.

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

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

Simulating annual runoff retention performance of extensive green roofs: A comparison of four climatic regions in China

The hydrologic performance of green roofs can be notably influenced by local climatic conditions. The majority of studies have focused on event-based retention performance of particular green roof configuration and climatic condition, making it difficult to predict green roof retention and formulate an efficient green roof configuration in a new location. To date, limited studies have assessed and compared annual or long-term runoff retention performance of green roofs in different climatic regions, and the impacts of climatic conditions on reduction effectiveness of green roofs remain unclear. In this study, a water balance model of green roofs coupling evapotranspiration rate estimation was developed to simulated the annual retention performance of green roofs. Four cities located in different climatic regions of China were selected to compare their average annual and seasonal runoff retention performances of extensive green roofs using 11 years of meteorological data, and assess the impacts of substrate storage capacity, vegetation types parameters and rainfall patterns on runoff retention performance among climatic regions. Results showed that average annual runoff retention in the dry continental climate of Lanzhou was 73.8%, which was higher than that in the humid climatic regions of Beijing (48.9%), Chongqing (45.2%) and Shenzhen (30.0%). Average runoff retention performance of extensive green roofs was the highest in spring for Beijing and Lanzhou, and in winter for Chongqing and Shenzhen. In Lanzhou and Beijing, the enhancement of increases in substrate water storage capacity on runoff retention was higher; and in Chongqing and Shenzhen, the impact for increases in crop coefficients (i.e. higher water use plants) was more efficient. Runoff retention performances of extensive green roofs were significantly decreased as rainfall depth increased. Longer antecedent dry weather period significantly lowered antecedent substrate moisture and resulted in higher runoff retention performances of extensive green roofs. These results can assist to formulate an efficient green roof configuration in local climatic condition and spatially allocate appropriate sites to optimize retention performance of green roofs.

Improvement in pollutant controlling performance by modified aggregate structure in extensive green roof substrate layer

The addition of 2% PAC to the extensive green roof substrate layer can result in the formation of an excellent aggregate structure and improve the NO3−–N, TN and TP-controlling performance of extensive green roofs during heavy rainfall events.

Simulation of humidity and temperature distribution in green roof with pozzolana as drainage layer: Influence of outdoor seasonal weather conditions and internal ceiling temperature

The outdoor seasonal weather conditions can influence the insulation performance of extensive green roof. In addition, the thermal behavior of extensive green roof can be affected by the thickness of its layers including substrate and drainage layer. On the other hand, the replacement of polyethylene modular panel with porous aggregates as drainage layer can affect the water retention capacity of green roof. Therefore, in this study, the green roofs with pozzolana (porous volcanic gravel) as drainage layer under constant and variable inside temperatures were modeled and subjected to the weather conditions of winter and summer to assess the humidity and temperature variations in the depth of the systems. The results showed that there was a decrease in temperature through the depth of the green roof system for the winter period, while the reverse occurred for the relative humidity. During the winter period, the green roof model with the 10-cm substrate and 8-cm pozzolana was recommended to be used. However, the model with the 8-cm substrate and 6-cm drainage layer had the best insulation performance, particularly for the summer period. Moreover, the internal ceiling temperature fluctuation of system under variable inside temperature was higher than that under constant inside temperature.

Factors affecting the ability of extensive green roofs to reduce nutrient pollutants in rainfall runoff

Green roofs can retain urban rainfall runoff, but there are doubts about whether they can reduce urban nonpoint source pollution. To explore the factors affecting the ability of green roofs to reduce nutrients in rainfall runoff, nine types of extensive green roofs (EGRs) were analysed during 38 natural rainfall events and two early spring irrigation runoff events from 1 March to 30 November 2019 in Beijing. Differences among the module scale, growing medium material, growing medium depth, drainage layer material, planting time, rainfall characteristics and seasonal variation were examined to study their correlation with pollutant event mean concentration (EMC) and the load reduction performance of EGRs. The results showed that EGRs had higher total nitrogen (TN), ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) concentrations than traditional concrete roofs, but total phosphorus (TP) concentrations were similar, and EGRs could reduce some of the nutrient loads. One-way analysis of variance showed that the module scale, growing medium material, growing medium depth, drainage layer material, and planting time had no significant effect on TN and NO3−-N concentrations (p > 0.05). The growing medium material had a significant effect on the TP concentration (p < 0.05). From the perspective of nutrient load reduction, module scale had a significant effect on TN and NH4+-N loads (p < 0.05). The growing medium depth had a significant effect on NH4+-N loads (p < 0.05). In addition, the growing medium material had a significant effect on TP loads (p < 0.05). When porous wool fibre and a bumpy plastic drainage board were selected as drainage layer materials, the effect on the NO3−-N load differed significantly. In other situations, there were no factors with significant differences. In addition, the rainfall characteristics and seasonal variation influenced the pollutant concentration and EGR runoff load.

Thermal and hydrological performance of extensive green roofs in Amazon climate, Brazil

Improper urban planning has been proven to produce excessive environmental impacts in urban areas, such as urban flooding and urban heat islands. A new approach to protecting the urban environment brought forward the idea of low-impact urban development, which uses rainwater-control devices such as cisterns, permeable pavements and green roofs. This study aimed to evaluate the potential of green roofs in two important environmental dimensions: thermal and hydrological. An experimental study was conducted at the Federal University of Pará Guamá Campus, Belém, Brazil. Hydrological and thermal data from a green roof and a fibre-cement roof were collected and compared to analyse the performance of the roofs. The results showed extensive green roofs to be an effective tool for reducing rainfall run-off at the roof scale, particularly for small-storm events, as well as an efficient thermal roof insulation.

A framework for optimizing hydrologic performance of green roof media

One of the primary functions of green roofs in urban areas is to moderate rainwater runoff, and one of the major impediments to the survival of plants on an extensive green roof (EGR) is a lack of available water during dry periods. Runoff moderation and water storage are both influenced by the composition of the growing media. Here we present a framework for evaluating the hydrologic performance of EGR growing media and also provide hydrologic attribute data for several commonly used EGR media constituents. In this three-phase study, we: 1) measured hydrologic attributes of individual EGR media constituents, 2) predicted attributes of media mixtures using individual constituent data, and 3) tested the seven top-ranking mixtures to evaluate hydrologic performance. Hydrologic attributes included wet weight and water held at maximum retentive capacity, long-term water retention, and hydraulic conductivity. Because perlite was light in weight yet held the greatest amount of water both at its maximum retentive capacity and in the long term, media mixtures dominated by perlite were predicted to have the best overall hydrologic performance. Mixtures dominated by pumice were also predicted to perform relatively well but were heavier. Despite the slightly greater weight and slightly lower performance, pumice may be a preferred alternative to perlite because perlite is a processed constituent with greater estimated embodied energy. Results indicate that performance of mixtures can be adequately predicted using performance of individual constituents for wet weight, water held, and long-term water retention. Hydraulic conductivity was less predictable because the pore volume in mixtures can be unrelated to the pore volume of the individual constituents. The framework presented here can be used to evaluate the performance of other EGR media, and the media attribute data can be used in formulating EGR media mixtures for specific applications. In addition, the attribute data can serve as a benchmark for evaluating other EGR media. Our results underscore the need for standardization of methods for more effective comparisons of EGR substrates, and also reinforce the need to evaluate EGR components using real-world scenarios.

Performance assessment of extensive green roof runoff flow and quality control capacity based on pilot experiments

Green roof is an important measure in “Sponge Cities” to reduce the runoff and improve the runoff quality. The runoff quantity and quality control capacity of five types of extensive green roofs (EGRs) were analyzed in Beijing for 51 nature rainfall events and 6 simulated events from July 2017 to October 2018. Different module scales (sizes) and substrate depths were examined to study their correlation to runoff retention, peak flow reduction, pollutant event mean concentration (EMC) and load reduction performance of EGRs. In general, both the single-field rainfall events and the long-term monitoring showed that as the module scale and substrate thickness increased, the retention capacity of the EGRs increased. As the module scale increased, the peak flow reduction rate (Pfrr) of the EGR modules increased, while the thickness of the substrate appeared to have less of an effect on Pfrr. When water quality effect was considered, compared with module scale, the substrate thickness had a more obvious effect on the average EMC of different pollutants. As the substrate thickness increased, the EMC of pollutants decreased. Under six simulated design rainfalls, EMC reduction rate of suspended solid (SS) of all types of EGRs ranged from 64.3%–73.1% while no reduction was found in the EMC of chemical oxygen demand (COD). The EMC trends of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total nitrogen (TN) and total phosphorus (TP) were almost the same, and their EMCs decreased with increasing total rainfall depth. When the pollutant load was considered, the EGRs in this study were a sink of NH4+-N, NO3−-N, TN, and TP but a source of COD.

Long term experimental analysis of thermal performance of extensive green roofs with different substrates in Mediterranean climate

Green roofs are passive construction systems that can contribute to reduce the energy demand of buildings and achieve the European goal of nearly zero energy buildings. The main objective of this work was to determine experimentally the thermal performance of extensive green roofs with different substrates, compared to a traditional gravel ballasted roof. Hence, a study on the annual reduction of energy demand throughout two years warmer than average years, 2016 and 2017, and a dynamic analysis based on decrement factor, DF, time lag, TL, cooling potential, CP, for these three green roofs were carried out.The results showed that significant reductions of DF and increases of TL and CP were achieved, especially in the green roof with 100% of commercial growing medium substrate. Annual reductions of energy gains and losses were obtained in the three green roofs, with annual average reductions of 66% and 63%, respectively, compared to the traditional roof. These results were mainly related to the composition of the substrates, their capacity to retain water and the quantity of vegetation in each plot. This study indicates that the use of green roofs contributes significatively to reduce the energy demand of existing buildings under warm climatic conditions.

Hydrological performance of extensive green roofs in response to different rain events in a subtropical monsoon climate

Rapid urbanization transforms permeable land into developed areas with predominantly impervious surfaces, significantly increasing stormwater runoff and exacerbating the risk of pluvial flooding. Green roofs provide an attractive strategy for increasing surface permeability by mimicking pre-development hydrologic functions and mitigating flood risks in compact cities. However, the potential of this strategy has not been rigorously assessed, despite advances in global stormwater management. This is mainly due to insufficient scientific knowledge of hydrologic performance and a lack of experimental studies of rainwater-harvesting capacity under specific climatic conditions. This study evaluated the hydrologic performance of a real-scale extensive green roof (EGR) constructed in a subtropical monsoon climate in Nanjing, China. Overall, the EGR showed considerable ability to retain rainfall (mean retention ~ 60%, accumulated retention ~ 30%), although retention performance varied from 11% to 100% depending on the rainfall event considered, and decreased with increasing rainfall. Event-based rainfall–runoff comparisons demonstrated that the EGR retained rainwater efficiently during the early stages of a rainfall event and significantly attenuated peak runoff flows compared to bare roofs. Statistical analysis showed that total rainfall depth, rainfall duration, and substrate layer moisture influenced the overall retention most strongly, but also the percentage retention and runoff depth, highlighting the impact of substrate properties in addition to rainfall characteristics on EGR hydrologic performance. These findings provide new knowledge of and important insights into the hydrological performance of green roofs in subtropical monsoon climates, which could be used to guide EGR construction to increase landscape permeability, mitigate the risk of pluvial flooding, and enhance the climatic resilience of urban regions.

Using Edible Plant and Lightweight Expanded Clay Aggregate (LECA) to Strengthen the Thermal Performance of Extensive Green Roofs in Subtropical Urban Areas

Gazing at natural landscapes and participating in agricultural activities can elicit psychophysiological restoration. However, most buildings are constructed merely to meet the minimum legal requirements for structure weight load. Extensive green roofs consisting of vegetables and a lightweight growth medium can be designed to provide not only passive-cooling effects on bare rooftops, but also to convert idle rooftops into temporary retreats for stressed individuals. The purpose of this study is to both measure the surface temperature reduction and heat amplitude reduction of a bare rooftop using the extensive green roofs containing a lightweight expanded clay aggregate (LECA) and Ipomoea batata as well as conduct a weight-reduction-and-cost analysis to measure the weight loss of the extensive green roofs incurred through LECA replacement. A four-stage field experiment was performed on the flat rooftop of a dormitory in a subtropical climate during summer. The results indicated that roofs with Ipomoea batata had a significantly higher passive-cooling effect than did roofs without Ipomoea batata. The roofs with 10%–40% LECA exhibited a slightly higher passive-cooling effect than did roofs with conventional garden soil. At a slightly different average air temperature (0.56 °C; i.e., 32.04 °C minus 31.48 °C), the combined effects of LECA and Ipomoea batata helped to significantly reduce the average temperature of the bare rooftop by an additional 10.19 °C, namely, temperature reduction of the bare rooftop increased from 9.54 °C under a roof with 0% LECA and without plants in the second stage to 19.73 °C under a roof with 10% LECA and with plants in the fourth stage.

The influence of structural factors on stormwater runoff retention of extensive green roofs: new evidence from scale-based models and real experiments

Green roofs, in contrast to conventional roofs, retain significant stormwater, and are considerably appealing for urban regions to help mitigate flooding events and addressing serious environmental impacts of excessive or uncontrolled runoff. In designing a green roof, a careful selection of substrate material/depths, vegetation or slopes, or its optimal combination, is imperative but this issue remains underexplored by practicing hydrologists. Scale-based models of extensive green roofs were purposely designed and simulated rainfall experiments were conducted to comprehensively quantify runoff retention performance of extensive green roofs, to precisely determine the contribution of structural factors to stormwater retention. The results indicated that green roofs can effectively retain stormwater and delay the start of the runoff. To aver with this finding, influential contribution of four structural factors are ordered as follows: substrate material > substrate depth > slope > vegetation. This finding denotes that substrate material and its depth are major contributors to a green roof’s stormwater retention capability. Statistical tests conducted on runoff retention showed the substrate materials and vegetation types had statistically significant effects, no statistically significant difference in runoff retention abilities among the three substrate depth treatments and the slope gradients considered. Given the same conditions, the study ascertains that runoff retention of low intensity events is likely to be relatively higher, while that of the heavy events is lower than its counterparts. The antecedent moisture contents of the substrate have a significant negative influence on the runoff retention and the time to the runoff.

EFFECT OF GREEN ROOF DESIGN ON ENERGY SAVING IN EXISTING RESIDENTIAL BUILDINGS UNDER SEMI-ARID MEDITERRANEAN CLIMATE (AMMAN AS A CASE STUDY (

In Jordan, residential buildings consume up to 48% of electrical energy, a significant amount of almost the half of energy goes for heating. Green roof is one of the passive techniques that improves energy performance. This paper examines the energy performance and Carbon Dioxide (CO₂) reduction of the green roof technology in the semi-arid Mediterranean climate of Amman by considering a typical apartment in Jordanian residential building as a case study. The effect of soil thickness, air gab and irrigation were determined for the performance of extensive green roof regarding to their plant. Malva Parviflora has been chosen for study. The base case model annual energy consumption has been determined by DesignBuilder software without a green roof installed. The result shows that installing extensive green roof saves annual energy consumption up to 14.25%.

Factors Affecting Runoff Retention Performance of Extensive Green Roofs

The runoff retention effectiveness of 10 extensive green roof (EGR) modules (100 mm substrate planted Sedum lineare Thunb.) were analyzed in Beijing for 22 rainfall events (2.4–46.4 mm) from 1 July to 30 September 2017. Differences between minimum inter-event dry periods, module scales, substrate hydraulic conductivity and depths, drainage layer types and rainfall characteristics were examined to study their correlation to the retention performance of EGRs. In general, EGRs with lower substrate hydraulic conductivity, deeper substrate and lower rainfall depth had higher runoff retention performance. By comparsion, no siginificant correlation was found between rainfall duration, prior dry period, average rainfall intensity, drainage layer type and EGR runoff retention rate. Analyses of variance (ANOVA) and Tukey tests supported these results. Low or moderate rainfall (&lt;15 mm) may or may not have an effect, but heavy rainfall (&gt;25 mm) definitely affects the EGR retention performance of the next rainfall event.

Investigating the Plant Species and Rainfall Factors on Stormwater Retention Performance of Extensive Green Roofs in Malaysia

Information on the influences of native plant species and rainfall characteristics on the stormwater retention performance of extensive green roofs in Malaysia is still scarce. More local data is still required because rainfall and runoff generation processes in tropical environment are very different from the temperate regions. This study is aimed to investigate the stormwater retention performance of native plant species in extensive green roofs with respect to different rainfall characteristics in Malaysia. Two test beds consist of pro-mixing potting soil were vegetated each with different native plant species (Axonopus Compressus (cow grass), Portulaca Grandiflora (sedum) and one test bed with no vegetation (bare ground) was prepared as a control. A total of 22 significant storm events were collected over a 3-month period from March 2016 to May 2016. The rainfall depths for monitored storm events were ranged from 4.5 mm to 63.2 mm and rainfall intensities ranged from 0.5mm/hr to 58.5 mm/hr. The results showed that sedum exhibited higher mean runoff retention percentage than grass which is 75.8% and 70.9%, respectively. Bare soil was the least effective for reducing water runoff with retention percentage of 62.6%. Overall, sedum and grass species provided 90.6% and 88.2% of cumulative rainfall retention in this study. The rainfall depth and intensity are correlated negatively with stormwater retention performance of green roofs. Meanwhile, longer dry weather period are likely to increase the water retention capacity of green roof.

A Review on the Controlling Factors that Affecting the Stormwater Retention Performance of Green Roof

Green roofs have become a popular strategy in urban stormwater management in the recent years. However, the hydrological performance of green roofs can vary substantially due to design characteristics and environmental conditions. This study is aimed to review all the controlling factors that affecting the stormwater retention performance of green roofs. Current hydrological research on green roofs involving different plant species, substrate types and environmental conditions are reviewed and evaluated in detail. Better understandings on the controlling factors that affecting the hydrological performance of extensive green roofs will be benefiting to the successful implementation of green roof system in the future.

Thermal performance of extensive green roofs in a subtropical metropolitan area

Extreme weather events caused by climate change intensify the heat island effect, and a lack of greenery in urban areas increases the psychological stress and anxiety of city dwellers. This study compared the temperature reductions and heat amplitude reductions provided by four types of green roofing that can cover bare rooftops. The four types of plants grown on extensive green roofs in this study were: shrubs, perennial herbs, vines, and groundcover; these are potentially healing plants. Furthermore, this study investigated the effects of air temperature, relative humidity, and solar radiation on temperature reduction of the rooftop. Four-stage field experiments under various ambient temperatures were conducted on the roof of a typical residential townhouse in the Taichung metropolitan area, in central Taiwan, which has a warm oceanic climate/humid subtropical climate (Cfa). The results indicated that the bottom temperature of the perennial herb, shrub, vine, and groundcover green roofs were lower than the bare rooftop temperature by 17.75°C, 12.57°C, 11.55°C, and 9.31°C, respectively. The heat amplitude reductions of the bare rooftop were defined as 1 minus the result of dividing the experimental temperature fluctuation by the rooftop temperature fluctuation; the heat amplitude reductions attributed to the shrub and perennial herb green roofs were similar (83.32% and 82.58%, respectively); smaller reductions were produced by the vine (79.78%) and groundcover (74.88%) roofs. Moreover, air temperature and solar radiation were positively related to temperature reduction of the bare rooftop, and relative humidity was negatively related to temperature reduction. Finally, plants in extensive green roofs can further reduce the surface temperature of a bare rooftop when compared with that of bare soil roofs.

Soil-roots Strength Performance of Extensive Green Roof by Using Axonopus Compressus

Green roof technology has been proven to provide potential environmental benefits including improved building thermal performance, removal of air pollution and reduced storm water runoff. Installation of green roof also involved soil element usage as a plant growth medium which creates several interactions between both strands. This study was carried out to investigate the soil-roots strength performance of green roof at different construction period up to 4 months. Axonopus compressus (pearl grass) was planted in a ExE test plot with a designated suitable soil medium. Direct shear test was conducted for each plot to determine the soil shear strength according to different construction period. In addition, some basic geotechnical testing also been carried out. The results showed that the shear strength of soil sample increased over different construction period of 1st, 2nd, 3rd and 4th month with average result 3.81 kPa, 5.55 kPa, 6.05 kPa and 6.48 kPa respectively. Shear strength of rooted soil samples was higher than the soil samples without roots (control sample). In conclusion, increment of soil-roots shear strength was due to root growth over the time. The soil-roots shear strength development of Axonopus compressus can be expressed in a linear equation as: y = 0.851x + 3.345, where y = shear stress and x = time.

Green roof seasonal variation: comparison of the hydrologic behavior of a thick and a thin extensive system in New York City

Green roofs have been utilized for urban stormwater management due to their ability to capture rainwater locally. Studies of the most common type, extensive green roofs, have demonstrated that green roofs can retain significant amounts of stormwater, but have also shown variation in seasonal performance. The purpose of this study is to determine how time of year impacts the hydrologic performance of extensive green roofs considering the covariates of antecedent dry weather period (ADWP), potential evapotranspiration (ET0) and storm event size. To do this, nearly four years of monitoring data from two full-scale extensive green roofs (with differing substrate depths of 100 mm and 31 mm) are analyzed. The annual performance is then modeled using a common empirical relationship between rainfall and green roof runoff, with the addition of Julian day in one approach, ET0 in another, and both ADWP and ET0 in a third approach. Together the monitoring and modeling results confirm that stormwater retention is highest in warmer months, the green roofs retain more rainfall with longer ADWPs, and the seasonal variations in behavior are more pronounced for the roof with the thinner media than the roof with the deeper media. Overall, the ability of seasonal accounting to improve stormwater retention modeling is demonstrated; modification of the empirical model to include ADWP, and ET0 improves the model R2 from 0.944 to 0.975 for the thinner roof, and from 0.866 to 0.870 for the deeper roof. Furthermore, estimating the runoff with the empirical approach was shown to be more accurate then using a water balance model, with model R2 of 0.944 and 0.866 compared to 0.975 and 0.866 for the thinner and deeper roof, respectively. This finding is attributed to the difficulty of accurately parameterizing the water balance model.