Carbon Footprint of Green Roofing: A Case Study from Sri Lankan Construction Industry

Global warming potential comparison between green and conventional roofs in cold climate using life cycle assessment

Highlights There were no significant differences (a = 0.05) in rainfall retention between blue and green roofs. Blue roofs appear to be a viable option to green roofs when the priority is stormwater management. Blue and green roofs need to be studied on larger scales to gain more confidence in the treatment provided. Abstract. Impervious surfaces caused by urbanization alter hydrologic conditions. In ultra-urban areas (75% or more impervious), rooftop stormwater control measures (SCMs), such as green roofs, exploit underutilized rooftop space. Green roofs reliably attenuate rainwater, but associated water quality treatment results are not as consistent. This study explored the viability of blue roofs, an emerging technology, as an alternative to green roofs. Nine adjacent plots consisting of three each of conventional (control), green, and blue roofs were constructed in Raleigh, NC. As a part of hydrology monitoring, on-site rainfall was measured using a tipping bucket and verified using a manual gauge. Water quantity data were collected using water level loggers in storage bins placed under the roof plots to record outflow. Measured rainfall retention was similar for blue and green roofs, and both systems were significantly (a = 0.05) and substantially (50%) more retentive than control roofs. A comparison of evaporation rates suggested blue roofs may be more effective at regenerating storage capacity than green roofs. Thirteen water quality events were sampled, and the mean total nitrogen (TN) concentration from the green and blue roofs was 5.83 and 2.18 mg/L, respectively. Similarly, the mean total phosphorus (TP) concentration from the green and blue roofs was 2.75 and 0.25 mg/L, respectively. Total suspended solids (TSS) data were collected, but seven of 13 samples were below the practical quantitation limit (2.5 mg/L), and the data were not statistically analyzed. Total kjeldahl nitrogen (TKN), TP, and orthophosphate (O-PO4 3-) concentrations from green roof treatments were significantly (a = 0.05) larger than concentrations from blue roofs. Except for nitrate/nitrite nitrogen (NO2,3-N), there were no significant differences between blue and control roof pollutant concentrations. However, green roofs often discharged substantially higher pollutant loads than control roofs for every pollutant other than NO2,3-N and total ammonical nitrogen (NH3-N). While blue roofs may lack the aesthetic appeal of green roofs, this study suggests blue roofs are a relatively cost-effective option, likely preferable, when solely focused on the benefits of stormwater management from rooftops. Keywords: Blue roofs, Conventional roofs, Green roofs, Hydrology, Monitoring, Stormwater control measures, Water quality.

Life cycle assessment of green roofs: A literature review of layers materials and purposes

Integrating conventional and green roofs for mitigating thermal discomfort and water scarcity in urban areas

Green roofs (GRs) have been one of the most popular solutions for water harvesting in urban areas. Apart from their water retention role and increasing biodiversity, they constitute the missing link between the built and the natural environment, which is required for sustainable human living in cities. This paper aims to calculate the ecological (EE) and economic effect (EcE) of water harvesting via GRs, by contrasting with a traditional roof, and to perform an economic analysis of the social cost benefits that GRs generate during their life cycle, using the Net Present Value (NPV) method. All the calculations and analyses were conducted for both intensive and extensive GRs in 11 of the largest municipalities in Poland, with a population of >250,000 inhabitants. According to the results of this study, water retention and the economic and ecological effects of GRs are highest in the municipalities with the highest assumed number of GRs (Warsaw, Krakow, Wroclaw, and Szczecin). The average EE and EcE equals 507,000 m3/yr and 621,000 USD/yr. The NPV results show that the effectiveness of investments in intensive GRs is, to a certain extent, more significant than in extensive GRs and the average equals 60.77 and 4.47 USD/yr for intensive and extensive GRs, respectively. The results could serve as a reference for the evaluation and optimization of the energy efficiency of rainwater harvesting schemes, in European cities.

PDF HTML阅读 XML下载 导出引用 引用提醒 亚热带季风区城市典型绿化屋顶的径流削减效应 DOI: 10.5846/stxb201808281837 作者: 作者单位: 南京工业大学,南京工业大学,南京工业大学,南京工业大学,南京工业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41871189，51408303）；江苏省自然科学基金（BK20140941，BK20161547） Assessing the rainwater runoff reduction effects of typical green roofs in a humid subtropical city Author: Affiliation: Nanjing Tech University,Nanjing Tech University,Nanjing Tech University,Nanjing Tech University,Nanjing Tech University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:屋顶绿化能够削减暴雨径流，降低城市内涝发生频率，促进可持续雨洪管理。针对亚热带季风气候区典型绿化屋顶的全年径流削减效应，以南京为研究区，以简易型、花园型两类绿化屋顶为研究对象，基于1年现场观测数据及水量平衡方程，分析屋顶雨水的滞蓄、蒸发与径流量随季节变化规律及其关键影响因子，采用SCS-CN模型计算绿化屋面的径流曲线数（CN），并估算城市尺度大面积屋顶绿化的暴雨径流削减效果。结果显示，简易型、花园型绿化屋顶全年径流削减率分别为42%和60.7%；径流削减效应的四季排序为春季 > 冬季 > 秋季 > 夏季，平均径流削减率依次为78.6%、47.5%、33.2%、32.9%（简易型）及98%、84.3%、49.5%、48.1%（花园型）；土壤基质层对雨水截留起主导作用，分别占径流削减总量的52%和62%；雨量和雨强是影响径流削减效应的关键因子，与径流削减率均呈显著负相关关系（P < 0.01），初始土壤湿度与简易型绿化屋顶的径流削减率呈显著负相关（0.01 < P < 0.05），但与花园型的径流削减率无显著相关性；基于全年77次降雨事件的降雨量-径流量数据测算得到简易型和花园型绿化屋顶的CN值分别为92和88；若南京主城区所有建筑屋顶面积的60%实施两类绿化，则其全年径流量可分别削减2.8×107 m3和4.2×107 m3。以上研究结果可为城市雨洪管理和海绵城市建设提供科学依据。 Abstract:Roof greening provides a promising solution to urban flooding because of the commonly assumed effect on rainwater runoff reduction; however, few studies have investigated this effect in humid subtropical areas using long-term monitoring data. In this study, we evaluated two typical types of green roofs, extensive and intensive, in Nanjing City for their capacity to reduce runoff based on empirical hydrological equations calibrated with field measurement data collected over a whole year circle. We analyzed the variations in rainwater retention, evaporation, and runoff with respect to season and rainfall types. Based on paired rainfall-runoff data of 77 events over the year, the curve numbers (CN) of the two green roofs were calculated, and the annual runoff reduction of the city-scale roof greening was assessed. The results showed that annual runoff reduction rates of the extensive and intensive green roofs were 42% and 60.7%, respectively. The runoff reduction magnitude was highest in spring, followed by winter, autumn, and summer, with respective average reduction rates of 78.6%, 47.5%, 33.2%, and 32.9% for the extensive green roof and 98%, 84.3%, 49.5%, and 48.1% for the intensive roof. Soil played a dominant role in rainwater retention, accounting for 52% and 62% of the total runoff reduction for the extensive and intensive green roofs, respectively. Precipitation and rainfall intensity were key factors affecting runoff effects, both being negatively correlated with the runoff reduction rate (P < 0.01). Antecedent soil moisture was negatively correlated with the runoff reduction rate for the extensive green roof (0.01 < P < 0.05) but showed no significant correlation for the intensive green roof. The CNs of the extensive and intensive green roofs were assessed to be 92 and 88, respectively, compared with the value of 98 for conventional impervious roofs. A hypothetical 60% coverage of extensive and intensive greening on all building roofs in the main city of Nanjing might lead to an annual runoff reduction of 2.8×107 m3 and 4.2×107 m3, respectively. These results can provide a scientific basis for urban stormwater management and sponge city construction. 参考文献 相似文献 引证文献

Environmental and operational benefits of green roofs are manifolds; however, their main disadvantages are cost and weight. New technology enabled the use of plastics to reduce the weight of green roof systems to promote their installation. To maximize their potential benefits, green roofs can be installed on existing structures. This study evaluates the influence of green roofs on the seismic response of 3, 6, and 8 storey reinforced concrete ductile moment resisting frames, which were designed according to current seismic standards, however, not designed for green roofs. For each frame, three different types of roofs are considered: gravel flat roof, extensive green roof, and intensive green roof. Nonlinear dynamic time history analysis using an ensemble of twenty real earthquake records was performed to determine the inter-storey drift demand and roof drift demand for each frame. Eigenvalue analysis was also performed to determine the impact of green roofs weight on the elastic and cracked periods of the structure. Results from the analysis demonstrated that intensive and extensive green roofs do not affect the seismic performance of reinforced concrete frame structures.

Experimental comparison of two extensive green roof designs in Northwest Mexico

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

There is growing demand to develop methods that integrate environmental and economic assessment of more sustainable technologies incorporated into commercial and residential buildings. In this paper, we incorporate economic and energy use data obtained for a green roof operating in the Midwest U.S. at latitude 42.94N into an integrated approach to estimate and compare the economic and environmental impacts of an intensive (or extensive) green roof with a built-up roof. The life cycle stages included in the analysis were material acquisition life stage which including the transportation effects from material extraction through manufacturing to the finished products, and the use and maintenance life stage of the building. Environmental impact analysis indicates that green roof emits three times more environmental pollutants than built-up roofs in the material acquisition life stage. However, in the use and maintenance life stage, built-up roof emits three times more pollutants than a green roof. Overall, when emissions from both material acquisition life stage and use and maintenance life stage are combined, the built-up roof contributes almost 3 times more (or 46% more) environmental emissions than green roof over a 45-year building life span. Furthermore the overall energy use, specifically energy involved in the transportation from material extraction through to the finished product indicate that green roof uses 2.5 times less energy than a built-up roof. An Economic Input and Output life cycle assessment (EIO-LCA) was used to estimate the environmental impacts. The economic impact over an assumed 45-year building life was determined using life cycle costing, taking into account Net Present Value (NPV) calculations. Life cycle costing results indicate that green roof costs approximately 50% less to maintain over a 45 year-building life than a built-up roof. A Monte Carlo simulation is also performed to account for any variability in cost data. In addition, the paper presents a method to quantify the value incentive that a decision-maker has in adopting green technology. Results from the study indicate that when a green roof is compared to the Midwest regional NPV of a built-up roof, we find that the cost to maintain it ($35 per square foot) lies well below the average regional NPV of $59 per square foot of a built-up roof.

Green roofs are being created in various purposes to use spaces. Most of them have been built with a goal as a resting place. However, the use of the green roofs needs to be raised. Otherwise, maintenance and administration of green roofs can be loosened. In addition, budget or cost involved can be wasteful. Therefore, this study makes a proposition if the satisfaction of green roofs is higher, the use of green roofs could be increased more. We are willing to analyze how beneficial the awareness can affect for the satisfaction with regard to green roofs. The findings can be helpful to provide a foundation data for raising the use of green roofs. We believe that the awareness benefits and satisfaction could be different depending on the facility`s status on green roofs. Therefore, we classified green roofs of 11 department stores, in Seoul, into four types. Among them, we paid attention to five department stores that were able to represent each type. We analyzed the awareness benefits and satisfaction depending on the type of green roofs. We analyzed casual relationships between them using Structural Equation Modeling. We expect that the landscape architecture scholars will expand research on the various determinants in using green roof. een Roof; Type of Green Roof; Benefit Awareness; Satisfaction; Structural Equation Modeling;

The extensive or intensive green roofs are today the common solution for roofs at new and retrofitted buildings in different climatic regions. In terms of region where the building is located the thermal insulation in the roof is or not. In the direction from the equator further the thermal insulation in the roof is important to decrease the heat flow from the building to the exterior during winter months. The presence of thermal insulation on the roof also influences the heat load of rooms under the roof during summer months. What is the impact of green roofs on the cooling of rooms under the roof. The analysis in this article is comparing two different approaches to evaluate the energy efficiency of green extensive roof in the climatic conditions of Slovakia. The comparison is based on the results from the computer simulation of the multi-dwelling house in the software DesignBUILDER v7. On one side the decrease of solar heat through the green roof is analyzed in comparison with roof without substrate layer. On the other side the decrease of energy demand for cooling for the room under the green roof is analyzed in comparison with roof without substrate layer. The results for the evaluation of energy efficiency of green roofs are very different. The decrease in energy demand for cooling rooms under the green extensive roof is under 5 %. The decrease of the solar heat through the green extensive roof is in the range 22 � 33 % depending on the roof construction, if it is lightweight or heavyweight roof structure. The energy demand for cooling of room considers all impacts such as solar heat gains through the glass of windows or opaque constructions but also internal heat gains. We can say that it is a complex evaluation of the impact of green roofs on the building. The assessment of the impact of green extensive roofs that is based on the decrease of heat load through the roof is a very isolated approach and so, it is not proper for the evaluation of the energy efficiency of green extensive roof during summer.

It is of great significance to analyze the runoff pollution load characteristics of different roof materials to improve the estimation accuracy of urban non-point source pollution loads. Yangzhou City was selected as the study area. There, three types of roofs were chosen for rainfall-runoff monitoring, including a Chinese style tile roof, cement tile roof, and concrete flat roof. The pollutant concentrations, scour law, and first flush effect of the three types of roofs were compared. The results show that the event mean concentration (EMC) of total nitrogen (TN), total phosphorus (TP), permanganate index, and total suspended solids (TSS) in the runoff of Chinese style tile roofs are around 4-9 times that in the runoff of cement tile roofs. The rainfall intensity exhibits stronger effect on the change in pollutant concentrations of runoff from the Chinese style tile roof than that from the cement tile roof. The Pearson correlation coefficients (r) of rainfall intensity against TP and TSS in time series were 0.853 and 0.822, respectively. The first flush intensities of the three types of roof materials were in the order cement tile roof > concrete flat roof > Chinese style tile roof. It was found that 60.0% of the roof runoff pollution load could be reduced by intercepting 31.5%, 58.0%, and 60.4% of the initial runoff for the Chinese style tile roof, the cement tile roof, and the concrete flat roof, respectively. The actual emissions of TN, TP, and TSS, and the permanganate index in rainstorm events would be significantly underestimated when roof materials are not distinguished. This would have negative effects on the pollution control of urban non-point sources. It is demonstrated that the fine distinction of roof materials is able to improve the estimation accuracy of urban non-point source loads.

Performance evaluation and development strategies for green roofs in Taiwan: A review

Bioeconomy helps to move towards a renewable, fossil-free future. The environmental impact is significantly reduced when replacing fossil-based products with bio-based alternatives. In a bioeconomy, all products are made from renewable and biogenic resources. In the building sector examples for biogenic sources are traditionally wooden building structures, while green roofs are becoming more popular. The goal of the present project was to assess the amount of biogenic carbon stored in green roofs and wooden buildings overall. The question is whether green roofs are improving the biogenic carbon usage of buildings and find out how that can be improved. The methods used are based on construction modelling, life cycle assessment and standardised environmental product declaration (EPD). The results indicate that wooden building structures are not enough for a complete biogenic building to move to a renewable, fossil-free future. Furthermore, the green roofs do add more biogenic carbon to the building than conventional roofs, while seen over the whole building these benefits are negligible. The results are presented as renewable and nonrenewable energy as well as biogenic carbon and greenhouse gas emissions. These are compared with conventional roofing based on non-renewable standard roofs in Sweden.