Green Roof Systems Research Articles

Hydrological Performance and Runoff Water Quality of Experimental Green Roofs

Within the scope of the conducted experiment the authors analysed the efficiency of runoff reduction by the system of extensive type green roofs. The observations were based on storm events in the area of Lower Silesia at the Agro and Hydrometeorology Station Wrocław-Swojec. The authors analysed the thickness of plant substrate, and also estimated the quality of runoff waters under the conditions of periodic atmospheric deposition. Also considered were such indicators as electrolytic conductivity, N, NO3−, NO2−, NH4+, P, PO43−. The experiment included roof substrates designed in two variants, with known hydraulic and physical properties of the soil material. The analysis was performed for models with vegetation layer based on pumice and zelolite, covered with five plant species from the sedum family. The modelling of the hydraulic properties was conducted with variably saturated medium, using the Hydrus 1D software. The performance of systems with primary layer thickness of 11 cm and 9, 8, 7, 6 and 5 cm was estimated. The designed models reduced the average peak flows to 89%, and in addition they caused a delay in the initiation of the runoff which was dependent on the intensity and distribution of rainfalls in time, and on the initial moisture of the profiles. Simulations, performed for variable substrate thickness, permit the conclusion that in the case of thin-layer profiles (5 cm), the relative retention index was decidedly lower and amounted to 35.9% for the substrate with zeolite (originally 60.6%) and 41% for the substrate with pumice (originally 65.7%). In the case of total nitrogen and phosphates, statistical analysis revealed significant differences (p < 0.05) in relation to specific concentrations in the rainwater and in the control surface. The total nitrogen in the runoff from the green roof was nearly twice as high as that in the rainwater and amounted to, on average, 8.3 mg L−1.

Eco-solutions for urban environments regeneration: The economic value of green roofs

The installation of green roof systems is being used as a specific action towards a broader objective of increasing the sustainability of the built environment. Yet, their development is still limited by the absence of a full understanding of their economic value. There is an underlying assumption that these solutions can enhance the value of cities, however contrasting results of past studies do not allow to draw specific conclusions about their real economic contribution.This paper intends to improve the decision-making process by providing an adequate methodology to perform cost-benefit analyses of installing green roofs. The proposed economic evaluation balances costs and benefits at three levels of analysis: financial, economic and socio-environmental. The first level compares construction, maintenance and replacement costs of green roofs with private benefits as discount on fire insurance, energy consumption, improvement of photovoltaic performance and urban rooftop farming. The second level also includes the economic gains from increase of property value, aesthetics, recreation and sound insulation. The third level adds social benefits related to storm water management, noise reduction, air pollution removal, mitigation of the urban heat island effect, public health and ecological preservation. The all-inclusive methodology is successfully applied to Lisbon, Portugal. The study confirmed the economic feasibility of green roofs in the long term at a social level but not at a financial level. The estimated net present value of green roofs implementation in Lisbon is about 320 million euros. A sensitivity analysis is also performed to the costs/benefits included. The results show that aesthetics, recreational value and sound insulation have the highest influence on the economic value.

CO2 Payoff of Extensive Green Roofs with Different Vegetation Species

Green roofs are considered effective in the reduction of atmospheric CO2 because of their ability to reduce energy consumption of buildings and sequester carbon in plants and substrates. However, green roof system components (substrate, water proofing membrane, etc.) may cause CO2 emissions during their life cycle. Therefore, to assess the CO2-payoff for extensive green roofs, we calculated CO2 payback time it takes their CO2 sequestration and reduction to offset the CO2 emitted during its production process and maintenance practices. The amount of CO2 emitted during the production of a modular green roof system was found to be 25.2 kg-CO2·m−2. The annual CO2 emission from the maintenance of green roofs was 0.33 kg-CO2·m−2·yr−1. Annual CO2 sequestration by three grass species with irrigation treatment was about 2.5 kg-CO2·m−2·yr−1, which was higher than that of Sedum aizoon. In the hypothetical green roofs, annual CO2 reduction due to saved energy was between 1.703 and 1.889 kg-CO2·m−2·yr−1. From these results, we concluded that the CO2 payback time of the extensive green roofs was between 5.8 and 15.9 years, which indicates that extensive green roofs contribute to CO2 reduction within their lifespan.

Prospects of green roofs in urban Thailand – A multi-criteria decision analysis

Abstract Green roof systems are considered a best practice for climate change adaptation and mitigation in urban areas affected by heat waves and stormwater flooding. Green roofs mitigate urban heat islands, improve urban air quality, buffer stormwater and improve runoff quality, absorb emissions and increase the thermal efficiency of buildings. Green roofs therefore are an interesting technology for densely populated urban areas in Thailand, but still at a rather low diffusion stage. The aim of this paper thus is to identify and quantify the main factors that influence green roof adoption using a mixed-method research design. The relevant factors were (1) identified in a qualitative content analysis, (2) structured alongside two dimensions (internal/external and positive/negative factors), and (3) quantitatively assessed in an Analytical Hierarchy Process based on expert judgments. The analysis yields three main factors influencing the diffusion potential of green roofs in Thailand: While their potential to mitigate urban heat islands is the most important facilitating factor, the lack of proper subsidy schemes as well as the lack of knowledge and skilled workforce, represent major adoption barriers. In spite of the discussed challenges and issues, a light trend towards greener buildings can already be observed among planners, architects, and also on policy levels in Thailand. If the identified issues are addressed properly, green roofs eventually could become a significant contributor to climate change mitigation and adaptation efforts in Thailand.

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.

Plant Communities Suitable for Green Roofs in Arid Regions

In extensive green roof settings, plant communities can be more robust than monocultures. In addition, native plants might be hardier and more ecologically sound choices than non-native plants in green roof systems. The objectives of this research were to (1) compare the performance of plant communities with that of monocultures and (2) compare the growth of natives to non-natives in a simulated green roof setting. We conducted a two-year experiment at an outdoor site in a desert environment using four plant morphological types (groundcover, forb, succulent and grass). Native plants selected were Chrysactinia mexicana, Melampodium leucanthum, Euphorbia antisyphilitica, and Nassella tenuissima, and non-natives were Delosperma nubigenum, Stachys byzantina, Sedum kamtschiaticum and Festuca glauca. Plants were assigned randomly to either monoculture or community and grown in 1 m × 1 m custom-built trays filled with 15 cm of a proprietary blend of 50/20/30 lightweight aggregate/sand/compost (by volume). Native forb, Melampodium, in community had greater coverage for four of the five measurements in the first year over native forb in monoculture and non-native forb regardless of setting. Native forb coverage was also greater than non-native forb for three of the four measurements in year 2, regardless of setting. Coverage of native grass was significantly greater than non-native grasses throughout the experiment. Coverage was also greater for eight of nine measurements for native succulent over non-natives succulent. However, non-native groundcover coverage was significantly greater than native groundcover for seven of nine measurements. On 1 November 2016, relative water content (RWC) for succulents (p = 0.0424) was greatest for native Euphorbia in monoculture at 88%. Native Euphorbia also had greater RWC than non-native Sedum on 4 April 2017 (78%) and 4 July 2017 (80%). However, non-native Sedum had greater root length (6548 cm), root dry weight (12.1 g), and root-to-shoot dry weight ratio (0.45) than native Euphorbia. At the end of year 2, the relative growth rate (RGR) of native Euphorbia of 0.15 g·g−1·d−1 was greater than that of Sedum. While the native succulent had a smaller root biomass, its greater RWC and RGR would indicate it had better plant water status and grew faster than the non-native. The lack of differences in plant performance regardless of assignment to monoculture or community would imply that communities and monocultures are equally suitable for arid region green roofs.

A modified FAO evapotranspiration model for refined water budget analysis for Green Roof systems

Many metropolitan cities around the world are promoting the implementation of Green Roofs (GR) as effective stormwater management systems to mitigate adverse effects of urbanization. Hourly water balance calculations are necessary for accurate prediction of the antecedent soil moisture conditions of a GR, a key parameter for rainfall-runoff modeling. However, existing evapotranspiration (ET) models have substantial errors for hourly ET predictions over a range of moisture conditions to accurately assess the hydrological performance of the GRs during storm events. Therefore, a modified Penman-Monteith equation was developed to provide improved prediction of hourly ET specifically for GR applications. ET rates predicted by the modified and established Penmen-Monteith equations were compared with ET data collected from a GR lysimeter over the summer and fall of 2016. The proposed modified Penman-Montieth equation eliminates the water availability factor (θiθfc) included in the equation’s advection term and separates the effect of plant coefficients on radiation/energy and advection terms. The modified equation was found to improve ET estimates by 8–9% (RMSE: 0.535–0.493, MAD: 0.375–0.343), under non-water limited conditions. For water-limited conditions, errors were significantly reduced. RMSE improved by 37% (0.703–0.440) and MAD was improved by 31% (0.429–0.294).

Mosses inhibit germination of vascular plants on an extensive green roof

Mosses are capable of tolerating harsh conditions, and are commonly found on both conventional bare roofs and engineered green roofs. Intentional planting of mosses on green roofs has shown that mosses can improve ecosystem services such as stormwater retention and microclimate cooling. Past studies of moss interactions with vascular plants on green roofs and in other habitats demonstrate both positive and negative effects on juvenile and adult tracheophytes. Moss can aid vascular plants by buffering environmental extremes, facilitating seed establishment, and improving nutrient and water availability. Conversely, moss can also hinder young seedling germination by blocking access to the soil column and/or light. In the green roof context, few studies have examined the relationship between moss and vascular plant germination. Since mosses commonly colonize green roofs it is important to understand the effects of established moss colonies on incoming plant propagules. The purpose of this study was to examine how four moss species, Atrichum undulatum (Hedw.) P. Beauv., Polytrichum commune Hedw., Polytrichum piliferum Hedw., and Racomitrium lanuginosum (Hedw.) Brid. affected the germination of weedy and native vascular plant seeds in a green roof system. Seeds were added to six pre-established moss treatments: monocultures of each moss species, a mixture which included all four moss species, and a substrate only control in pots on a rooftop. Overall, the control (moss-free) treatment resulted the highest germination rates for the majority of seeded species examined, an indication that for these vascular plants, mosses tend to inhibit germination of incoming seeds.

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.

Putting rooftops to use – A Cost-Benefit Analysis of food production vs. energy generation under Mediterranean climates

In today's growing cities, where land is an expensive commodity and direct exposure to sunlight is a valuable asset, rooftops constitute vast underexploited areas. Particularly with growing urban environmental concerns, the potential of transforming these areas into productive spaces – either for food cultivation or energy generation – has emerged as a viable option in recent years. Both food production and energy generation have benefits in the urban environment. Rooftop farming is an environmentally and economically sustainable way of exploiting urban rooftops, reducing “food miles” and providing local jobs, while roof-integrated solar photovoltaic (PV) modules provide clean energy, are increasingly cost-effective, and offer job opportunities. In both cases, a rooftop network of production could directly supply a portion of a necessary resource – either food or electricity – to the local community while concurrently reducing the burden on the environment. To provide a basis for comparing the implementation of these productive uses of rooftops in Mediterranean cities, this article applies a Cost-Benefit Analysis (CBA) to a mixed-use neighborhood located in Lisbon to assess the following uses: (1) open-air rooftop farming on intensive green roofs; (2) food production in low-tech unconditioned Rooftop Greenhouse (RG) farms; (3) Controlled-Environment Agriculture (CEA) in high-tech RG farms; and (4) solar PV energy generation. Relative costs, cost-saving benefits and added value of these four alternative productive uses of rooftops were modeled over 50 years and deducted from present value, considering two levels of analysis: (a) effects directly incurred by the operator of the systems; and (b) societal effects on the local community. To the authors' knowledge, this is the first comprehensive comparison of rooftop PV versus rooftop farming technologies. The results have shown food production to be more beneficial than energy generation, for both the owner of the system and the local community, under the modeled conditions and given the selected items of comparison. In particular, the results show that rooftop greenhouse farming can provide significant benefits over rooftop green roof and solar PV systems when assessed from a holistic perspective that accounts for impacts on both the operator and the local community.

Life Cycle Assessment (LCA) for Water re use System of a Green Roof

In urban contexts climate change and urbanization alter the correct management of outflows. The need to reduce CO2 emissions and increase the green areas presence is linked to forecast targets to facilitate the correct management of urban risks. To achieve these objectives the new technologies are available, such as green roofs, which are useful for reducing the impacts of climate change in urban areas and for the proper management of outflows, indeed, the green roofs can be connected to rainwater reuse systems. The collection and reuse water system can be studied using the Life Cycle Assessment (LCA) methodology. In this paper a sustainability estimate of the green roof and reuse water system is proposed in the Urban Hydrological Experimental Park at the University of Calabria (Italy).

URBAN HEAT ISLAND MITIGATION USING GREEN ROOF APPROACH

In urban environments, vegetation has largely been replaced by impervious and often dark surfaces. These conditions contribute to an Urban Heat Island (UHI) effect. This phenomenon is demonstrated in many cities and produced effects such as higher atmospheric temperatures, intensive precipitation, excessive solar radiation and increasing air pollution. Therefore, reducing the surface temperature of roofs in a building may play an important role in improving the conventional roof surfaces with green roofs that offer much lower temperatures throughout a day to reach their thermal performance and reduce the absorption of solar radiation. Thus, this study is focused on determining the effectiveness of the existing green roof in reducing the ambient temperature and humidity of the air above it by comparison with conventional open roof top without vegetation. This study also aims to evaluate the potential of green roof to reduce the air pollutants in improving air quality in urban cities. As a result, by adopting green roof system, it has reduced temperature during the hottest hour in a day at 1230 hour (hr) by 4.3°C when compared to open roof. Green roof has also recorded higher percentage of humidity compared to open roof. Most importantly, it was proven through this study that green roof has the potential of absorbing pollutants in the air by reducing the concentrations of Sulphur dioxide (SO2), Ammonia (NH3), Nitrogen dioxide (NO2), Ozone (O3) and Carbon monoxide (CO) compared to open roof. Thus, green roofs can be considered to be one of the effective methods to mitigate UHI effects in urban cities.

Indoor Air Quality and Thermal Conditions in a Primary School with a Green Roof System

This paper presents experimental results from a typical school building in Athens, equipped partly with a green roof system (GRS). Environmental monitoring took place in six classrooms located both under the concrete roof and the GRS sectors as well as in the immediate external environment during the warm and cold periods of a school year. Daily measurements of pollutants CO2, TVOCs (Total Volatile Organic Compound), PM1, PM2.5, and PM10 were performed in selected classes. Moreover, indoor ambient temperature (T) and relative humidity (RH) measurements were implemented in order to estimate the absolute humidity (AH) and assess the indoor environmental conditions. The results highlight that during summer, the GRS reduces temperature in a classroom on the top floor by about 2.8 °C, in comparison with the respective classroom under the concrete roof and that AH remained relatively stable for both classrooms. Amid winter, a reverse behavior occurs only for temperature. Moreover, air exchange rates (AER) were calculated by using the CO2 decay method for all of the classrooms. The results demonstrated insufficient ventilation for all experimental sights. Finally, concentrations of PM1, PM2.5 and PM10, were found to be relatively decreased, with average values of 0.79, 3.39, and 27.80 μg m−3. Levels of CO2 and TVOCs were elevated during class hours ranging from 469 to 779 ppm and from 6.63 ppm to 13.33 ppm, respectively, but generally within the respective limits of exposure. The examination of the indoor/outdoor (I/O) ratio of air pollutants, demonstrated that the outdoor meteorology affects only PM1 and PM2.5, as PM10 and TVOCs are strongly affected by internal sources and the activities of pupils.

Energy Savings and Economic Impact of Green Roofs: A Pilot Study

ABSTRACTThis study focuses on the energy savings and economic impact of green roof systems applied to Central Bodrum, a district in southwestern Turkey. Energy savings of the buildings were evaluated based on the added thermal resistance on the roofs and corresponding heat transmission through the roofs. Four different scenarios, two without green financing and two with green consumer loans for retrofitting financed by the central government via the state-owned banks, were studied. The economic impact of this activity on the economy is estimated based on sectoral employment multipliers for a period of 10 years. Based on the scenario analysis and the priorities of the Turkish economy, given the employment benefits and energy savings which would reduce the energy demand in the area in the peak season, we propose that the government implements green consumer loans for retrofitting through the state-owned banks.

Temporal variations in the potential hydrological performance of extensive green roof systems

Existing literature provides contradictory information about variation in potential green roof hydrological performance over time. This study has evaluated a long-term hydrological monitoring record from a series of extensive green roof test beds to identify long-term evolutions and sub-annual (seasonal) variations in potential hydrological performance. Monitoring of nine differently-configured extensive green roof test beds took place over a period of 6 years in Sheffield, UK.Long-term evolutions and sub-annual trends in maximum potential retention performance were identified through physical monitoring of substrate field capacity over time. An independent evaluation of temporal variations in detention performance was undertaken through the fitting of reservoir-routing model parameters. Aggregation of the resulting retention and detention variations permitted the prediction of extensive green roof hydrological performance in response to a 1-in-30-year 1-h summer design storm for Sheffield, UK, which facilitated the comparison of multi and sub-annual hydrological performance variations.Sub-annual (seasonal) variation was found to be significantly greater than long-term evolution. Potential retention performance increased by up to 12% after 5-years, whilst the maximum sub-annual variation in potential retention was 27%. For vegetated roof configurations, a 4% long-term improvement was observed for detention performance, compared to a maximum 63% sub-annual variation. Consistent long-term reductions in detention performance were observed in unvegetated roof configurations, with a non-standard expanded-clay substrate experiencing a 45% reduction in peak attenuation over 5-years. Conventional roof configurations exhibit stable long-term hydrological performance, but are nonetheless subject to sub-annual variation.

Thermal regulation capacity of a green roof system in the mediterranean region: The effects of vegetation and irrigation level

The increasing interest in green roof implementation and research is based on the environmental benefits of this technique. The thermal regulation capacity of a green roof system is considered a very relevant benefit due to its environmental and economic interest.In this study, an experimental modular evaluation was performed to quantify the contribution of vegetation cover by evaluating two Mediterranean native species and the effect of irrigation water volume on the thermal capacity of a green roof system in a Mediterranean area.A positive effect of the vegetation presence was evidenced, with important substrate temperature reductions during spring and summer. Daily heat gain and loss were reduced as a consequence of vegetation presence. Sedum sediforme performed as a better insulator than Brachypodium phoenicoides during the experimental period in spring and summer, with few differences in autumn and winter. The modules with the 25% of potential evapotranspiration applied as limited irrigation reported lower heat flux values than well irrigated module (considered as 50% of potential evapotranspiration) in all seasons. The plant response to irrigation treatment is here evaluated to explain the thermal regulation effect during the whole year. The main conclusion is that there is a positive influence of species selection and irrigation management in the thermal regulation properties of green roofs under Mediterranean conditions.

Studies on Sedum taxa found in Sicily (Italy) for Mediterranean extensive green roofs

One type of green roof whose function is ecological and environmental rather than aesthetic is the extensive green roof. Many studies have shown that Sedum performs very well compared to other hardy species in substrates of less than 10 cm. It seems that Sedum species are able to survive in very thin substrates; they tolerate extreme temperatures and sudden variations in temperatures, high levels of solar radiation, strong winds, poor substrate fertility and extreme drought. In particular, this paper looks at the potential of a number of species from the Sicilian taxa of the genus Sedum (Crassulaceae), which are considered to be those xerophytes most suited for use in extensive green roof systems for Mediterranean areas. Each taxon was subject to in situ and ex situ observations to gain phenological and ecological data, information on its vegetative propagation capacity and its plant ground cover capacity. The results of this study have led to greater understanding of Sicilian pluriennal Sedum genus entities of potential use in green roof systems in the Mediterranean. The taxa respond particularly well to agamic propagation, showing characteristics suited to nursery production of green roof systems, with the exception of S. amplexicaule subsp. tenuifolium. Growth indices and plant development (ground cover) demonstrated the capacity of a number of Sedum taxa to form a uniform green mantle over time. S. sediforme and S. album subsp. album. showed interesting results, for because of their ability to colonize the substrate, and they could be fundamental in determining the plant structure of the green systems. However, there are also other plants, such as S. amplexicaule var. tenuifolium, and, to a lesser extent, S. dasyphyllum var. dasyphyllum and S. ochroleucum, which are able to contribute to floral diversification and lead to greater biodiversity in the system. These taxa could be used when creating associations of Sedum at lower percentages compared to the structuring species (≤20%).

Effects of recycled glass and different substrate materials on the leachate quality and plant growth of green roofs

Green roofs are a key component to building sustainable cities because of their multiple environmental benefits, but without the proper level of care, the leachate from green roofs might contain pollutants and become a new nonpoint pollution source in urban areas. Because its leachate quality is affected by the substrates and plants used, the objective of this study is to evaluate the effects of the substrates and plants with the aim of improving green roof applications. This study tested 3 materials – normal cultivated (C) substrate, commercial green roof (L) substrate, and mixed C and recycled glass (R) substrate – with a focus on using recycled glass materials in the green roof system. Recycled glass is a lightweight and porous material that improves pollutant absorption and water quality purification. Three different types of plants were tested: a sedum, a fern, and a shrub. Therefore, this study evaluated 9 combinations, each with 3 replicates. The differences in the substrates exerted significant effects on the chemical oxygen demand (COD) and phosphorous (P) concentrations. The nitrogen (N) concentrations were affected by differences in both the substrates and the plants. The changes in the observed water quality with time implied that compact substrates and mature plants reduced pollutant concentrations, except for N concentrations, in the outflow. The L substrate contained high levels of nutrients, and the plants grew better in this substrate than in the other two substrates; however, the L substrate also produced higher pollution concentrations. The R substrate, with recycled glass, performed well in the neutralization of acid rain but did not significantly reduce the levels of other pollutants. To enhance the purification ability of the recycled glass, the mixing ratio between the recycled glass and organic substances and the placement in the substrate are important factors.

Hydrological performance of modular-tray green roof systems for increasing the resilience of mega-cities to climate change

This paper investigates the performance of modular-tray green roof systems on rainwater retention and total runoff delay under heavy rain conditions, typical of countries with a tropical climate. It involved the building of a rain-spray system simulator and worktops to support the experimental units. Three green roof modular-tray systems were studied, M-4L, M-17L and F-17L, with a mix of succulent plant species. The volume and delay of total runoff were sampled for both dry and wet soil-moisture stages for a simulated rainstorm of 155 mm/h and duration of 7 min, which approaches the value of the design rainfall of 10-year return-period and an observed rainfall event that caused flooding in 2011 in the area where the experiments took place. These results were compared to three bare-soil similar experimental units and with a control unit consisting of a corrugated fibre-cement roof sheet. In addition, classic rainfall-runoff parameterization, also important for catchment analysis, such as the rational coefficient method (C) and Curve Number (CN) were also applied. The results showed to be consistent. Overall, module F-17L presented the best performance with regard to both water retention and delay of total runoff. The average percentage of retention, considering all module types, was 58% of the total induced water volume, and the average delay for total runoff was approximately 12 min. In some tests, for the wet soil stage, the bare soil units performed better than the vegetated units. Soil moisture analysis revealed that considering the same period of time, the bare soil units lost more water through evaporation than the vegetated units through evapotranspiration. The average values of C for vegetated units for the wet and dry soil stages were equal to 0.66 and 0.27, respectively. The CN values were high, ranging from 88 to 97. Although fairly new on the market in Rio de Janeiro, modular-tray green roof systems are easy to build and hydrologically effective, mainly in the dry soil stages, performing as well as other extensive green roof systems. The values obtained for C and CN may be useful for the modelling of catchment rainfall and runoff especially for scenarios involving green roofs, as well as for establishing regulatory benchmarks towards more resilient and sustainable cities.

Energy consumption and CO2 emission reductions trough refurbishment of residential buildings’ roofs by applying the green roof system: Case study

Climate changes which we are experiencing at the moment are affecting the entire globe. Serbia, as a developing country, is in the process of defining its own energy strategy and priorities when it comes to the problem of increased energy consumption in its building stock. Research shows that residential sector consumes the largest quantity of energy. CO2 emissions present another big problem which is in a direct correlation with energy consumption. Green roofs have multiple positive effects on buildings and their surroundings which make them a desirable option for retrofitting roofs. The aim of this paper is to investigate thermal properties of chosen green roof system and its potential to positively influence energy consumption for heating buildings and therefore CO2 emissions trough refurbishing existing old flat roofs. New Belgrade was chosen for this research for its unique urban characteristics - existence of large number of similar or identical buildings, which have same structural characteristics and similar surroundings. For the purpose of this paper, blocks 45 and 70 were chosen. Results of this research are applicable on all of the 132 buildings found at this location, which have total roof area of 90990m2. By calculating energy quantity needed for heating the building with the existing roof and two hypothetical models, which have green roof, it was possible to quantify energy savings, which are in a direct correlation with CO2 emissions. A control roof was introduced in order to examine if the proposed green roof possesses better characteristics than a traditional solution, most commonly used in Serbia. Apart from energy savings, overall impact of the green roof on the CO2 reduction per building was calculated. By multiplying these results, we drew the conclusion that a project such as greening roofs of existing residential buildings in blocks 45 and 70 would have a noticeable effect on both the energy savings and CO2 emissions.