Green Roof Installation Research Articles

Measurements of nutrients and mercury in green roof and gravel roof runoff

Green roofs are a popular stormwater management technique because they are effective in reducing runoff volume from buildings. However, this does not necessarily result in a reduced pollutant load. Runoff from experimental gravel and green roof plots and two sets of real gravel and green roofs, were analyzed for mercury, nitrogen, phosphorus, and metals. The effects of roof type (green versus gravel) and underlayments (drainage layer, water-retention layer) on runoff volume, pollutant concentration, and pollutant load were evaluated. Although mercury concentrations in runoff were often higher from green roofs than gravel roofs, the reduction in runoff volume from green roofs typically resulted in no significant difference in runoff load. The green roofs also leached significantly higher concentrations of the nutrients phosphorus and nitrogen than the gravel roofs, but reduction in runoff volume did not similarly mitigate the nutrient load. Underlayment type had no significant effect on runoff volume, mercury, or phosphorus concentrations. Plots with a water-retention layer embedded with fertilizer initially leached higher nitrogen, but were similar to other green roof treatments two months following installation. Alum and Ultra-Phos Filter (UltraTech International, Inc.) were also tested for their potential to reduce the phosphorus in runoff. The average reduction in phosphorus in runoff directed through alum-filled pouches was 22%. Based on the elevated nitrogen and phosphorus load running off of the green roofs, caution is recommended when considering the application of fertilizer during installation or maintenance of green roofs. When choosing green building technology, materials and methods must be carefully chosen to match the most critical needs of the local environment.

Environmental Benefits of Retrofitting Green Roofs to a City Block

Although they are widely in use and in many cases are mandated in Europe and North America, the installation of green roofs has been relatively limited in Melbourne and Australia as a whole. A case study is presented that investigates the implementation of green roofs across the Melbourne central business district (CBD) in Australia. The study aims to give an immediately possible and best-case scenario for the benefits achievable depending on the proportion of Melbourne’s roof area covered with green roofs. The following environmental benefits (EBs) of the retrofit are assessed for both scenarios for a city block: (EB No. 1) reduction in urban heat island (UHI) effect (EBUHI), (EB No. 2) reduction in runoff volume (EBR), (EB No. 3) improved water quality (EBL), (EB No. 4) reduction in storm water runoff peak flow (EBPF), and (EB No. 5) greenhouse gas (GHG) emission reduction (EBGHG). These benefits are then scaled up, assuming that the retrofit of green roofs is expanded to cover the entire CBD roof area in the same proportions. This demonstrates the range and scale of benefits that could be achieved under widespread implementation, such as temperature reductions, significantly reducing the UHI effect, and estimated reductions of storm water runoff peak flow, which may mitigate or reduce the frequency and severity of flash flooding.

Habitat connectivity shapes urban arthropod communities: the key role of green roofs.

The installation of green roofs, defined here as rooftops with a shallow soil cover and extensive vegetation, has been proposed as a possible measure to mitigate the loss of green space caused by the steady growth of cities. However, the effectiveness of green roofs in supporting arthropod communities, and the extent to which they facilitate connectivity of these communities within the urban environment is currently largely unknown. We investigated the variation of species community composition (beta diversity) of four arthropod groups with contrasting mobility (Carabidae, Araneae, Curculionidae, and Apidae) on 40 green roofs and 40 extensively managed green sites on the ground in the city of Zurich, Switzerland. With redundancy analysis and variation partitioning, we (1) disentangled the relative importance of local environmental conditions, the surrounding land cover composition, and habitat connectivity on species community composition, (2) searched for specific spatial scales of habitat connectivity for the different arthropod groups, and (3) discussed the ecological and functional value of green roofs in cities. Our study revealed that on green roofs community composition of high-mobility arthropod groups (bees and weevils) were mainly shaped by habitat connectivity, while low-mobility arthropod groups (carabids and spiders) were more influenced by local environmental conditions. A similar but less pronounced pattern was found for ground communities. The high importance of habitat connectivity in shaping high-mobility species community composition indicates that these green roof communities are substantially connected by the frequent exchange of individuals among surrounding green roofs. On the other hand, low-mobility species communities on green roofs are more likely connected to ground sites than to other green roofs. The integration of green roofs in urban spatial planning strategies has great potential to enable higher connectivity among green spaces, so that eventually even communities of low-mobility species become connected. Furthermore, improving the design of green roofs (composition and configuration of vegetation and soil types) could enhance the ecological value, particularly for low-mobility species.

공공건물 옥상녹화와 설치태양광(PV)의 효율향상 상관관계 연구

This study aims to investigate advantages of complex installation of green roof and PV system in a public building, to analyze the impact of green roof on the efficiency of PV power generation, and to consider the correlation between green roof and PV power generation. When the temperature and power generation of the modules installed in the green roof and non-green roof of the public building were measured for 3 days, the average temperature of the green roof was 23.6 degrees, and it was 36.1 degrees in the non-green roof which increased by nearly 53%. Overall, the module temperature in the green roof was lower. On the other hand, in relation to the PV generation depending on temperature reduction during the same period, the mono-crystalline module and the poly-crystalline module in the green roof showed an increase in generation at nearly 222.2W and 341.6W, and the efficiency rose by 5.5% and 6.2%, respectively, compared to the modules in the non-green roof. Therefore, it is analyzed that green roof has a positive influence on PV power generation. Finally shows the efficiency of the installed on the Green Roof PV system (complex Installation) higher than on the concrete roof PV system. Thus, the complex PV systems as well as the usual benefits of green roofs will provide greater synergies.

The promise [and uncertainties] of Biochar

The promise [and uncertainties] of Biochar

Evaluation of green roof as green technology for urban stormwater quantity and quality controls

Promoting green design, construction, reconstruction and operation of buildings has never been more critical than now due to the ever increasing greenhouse gas emissions and rapid urbanizations that are fuelling climate change more quickly. Driven by environmental needs, Green Building Index (GBI) was founded in Malaysia to drive initiative to lead the property industry towards becoming more environment-friendly. Green roof system is one of the assessment criteria of this rating system which is under category of sustainable site planning and management. An extensive green roof was constructed in Humid Tropics Center (HTC) Kuala Lumpur as one of the components for Stormwater Management Ecohydrology (SME) in order to obtain scientific data of the system. This paper evaluates the performance of extensive green roof at Humid Tropics Center with respect to urban heat island mitigation and stormwater quantity and quality controls. Findings indicate that there was a reduction of around 1.5°C for indoor temperature of the building after installation of green roof. Simulations showed that the peak discharge was reduced up to 24% relative to impervious brown roof. The results show an increment of pH and high concentration of phosphate for the runoff generated from the green roof and the runoff water quality ranged between class I and II under INWQS.

Green-Roof Effects on Neighborhood Microclimate and Human Thermal Sensation

Green roofs have been recognized as an effective sustainable design tool to mitigate urban heat island (UHI) effects. Previous studies have identified green-roof benefits in cooling and energy-conservation at the building scale, with limited exploration of the wider influence on neighborhood microclimate and human thermal comfort (HTC). This paper investigated the impacts of community-scale green-roof installation on air temperature and HTC in five typical residential neighborhoods of subtropical Hong Kong. The microclimate models ENVI-met and RayMan permitted studies of two main green-roof scenarios, namely extensive (EGR) and intensive (IGR). Microclimatic monitoring data from a local experimental green-roof site validated the modeling methods. The results verified that green-roof cooling effects were not restricted to rooftops, but extended to the ground to improve neighborhood microclimate. EGR reduced pedestrian-level air temperature by 0.4–0.7 °C, and IGR by 0.5–1.7 °C, with maximum effect in open-set low rise sites. Coverage by building footprints and building height dampened lateral and vertical advection of cool air generated by green roofs. Roof greening also improved notably the rooftop-podium level HTC. Diurnal duration of high heat stress was reduced by 6–9 h for EGR scenarios, and 9–11 h for IGR. The findings indicated that large-scale green-roof installation could bring neighborhood-wide cooling, mitigate urban heat island effect, and furnish more comfortable thermal environment for urban residents.

Urban particulate pollution reduction by four species of green roof vegetation in a UK city

Urban particulate pollution in the UK remains at levels which have the potential to cause negative impacts on human health. There is a need, therefore, for mitigation strategies within cities, especially with regards to vehicular sources. The use of vegetation as a passive filter of urban air has been previously investigated, however green roof vegetation has not been specifically considered. The present study aims to quantify the effectiveness of four green roof species – creeping bentgrass (Agrostis stolonifera), red fescue (Festuca rubra), ribwort plantain (Plantago lanceolata) and sedum (Sedum album) – at capturing particulate matter smaller than 10 μm (PM10). Plants were grown in a location away from major road sources of PM10 and transplanted onto two roofs in Manchester city centre. One roof is adjacent to a major traffic source and one roof is characterised more by urban background inputs. Significant differences in metal containing PM10 capture were found between sites and between species. Site differences were explained by proximity to major sources. Species differences arise from differences in macro and micro morphology of the above surface biomass. The study finds that the grasses, A. stolonifera and F. rubra, are more effective than P. lanceolata and S. album at PM10 capture. Quantification of the annual PM10 removal potential was calculated under a maximum sedum green roof installation scenario for an area of the city centre, which totals 325 ha. Remediation of 2.3% (±0.1%) of 9.18 tonnes PM10 inputs for this area could be achieved under this scenario.

Weather effect on thermal and energy performance of an extensive tropical green roof

This study investigated the weather effect on thermal performance of a retrofitted extensive green roof on a railway station in humid-subtropical Hong Kong. Absolute and relative (reduction magnitude) ambient and surface temperatures recorded for two years were compared amongst antecedent bare roof, green roof, and control bare roof. The impacts of solar radiation, relative humidity, soil moisture and wind speed were explored. The holistic green-roof effect reduced daily maximum tile surface temperature by 5.2°C and air temperature at 10cm height by 0.7°C, with no significant effect at 160cm. Green-roof passive cooling was enhanced by high solar radiation and low relative humidity typical of sunny summer days. High soil moisture supplemented by irrigation lowered air and vegetation surface temperature, and dampened diurnal temperature fluctuations. High wind speed increased evapotranspiration cooling of green roof, but concurrently cooled bare roof. Heat flux through green roof was also weather-dependent, with less heat gain and more heat loss on sunny days, but notable decline in both attributes on cloudy days. On rainy days, green roof assumed the energy conservation role with slight increase instead of reduction in cooling load. Daily cooling load was 0.9kWhm−2 and 0.57kWhm−2, respectively for sunny and cloudy summer days, with negligible effect on rainy days. The 484m2 green roof brought potential air-conditioning energy saving of 2.80×104kWh each summer, equivalent to electricity tariff saving of HK$2.56×104 and upstream avoidance of CO2 emission of 27.02t at the power plant. The long-term environmental and energy benefits could justify the cost of green roof installation on public buildings.

SIMULATION OF HEAT EXCHANGE PHENOMENA AND WATER REGIME IN GREEN ROOF SUBSTRATES

Installation of intensive or extensive green roofs increases in Western European and North American cities. It is estimated that 12% of all flat roofs are green in Germany and the roof industry is growing at a rate of 10% per year in the EU. Apart from the aesthetic point of view, the main objective is to reduce heating (by increasing thermal resistance value) during winter and cooling (by evaporation) during summer. Most researches are conducted on specific plant species for green roof establishment. The major purpose of this work is to evaluate the theoretical approach of thermal properties (heat capacity and thermal conductivity) of wet substrates and to propose a simulation modelling of the interactions of the processes of water transport and heat flow and exchanges. Water flow properties using the van Genuchten approach and heat flow equation are applied in 1D simulation to different substrates and configurations. The main result is that the water retention properties of the substrate are the main parameter to consider but with different effects between winter and summer. The geometry of installation (height, support) is an important aspect of installation. Heat diffusion phenomena stay limited vs. latent heat exchanges in summer.

Game-Theory Approach for Resident Coalitions to Allocate Green-Roof Benefits

Roof greening in cities provides a range of environmental, economic, and social benefits. However, the lack of motivation among property owners in high-rise buildings poses an intractable obstacle to its wide implementation in compact cities. Cooperation amongst stakeholders, from individual-building to city-block scales, could facilitate adoption of green roofing, with implications for urban sustainability. This study is an attempt to evaluate the net gain from roof greening in terms of apportioned collective costs and benefits to a group of property owners. With government tax exemption to encourage green-roof installation, a fair-allocation scheme, based on the Shapley value, is adopted to distribute the net gain in a partnership structure. A case study in Hong Kong serves to illustrate the application of the method to allocate theoretically the sharable gain of roof greening translated into monetary terms. The results verify the importance of individual owners in different coalition configurations in moulding the benefit profile. The crux of the financial incentive scheme is the enhanced rewards to optimized cooperation, and the pump-priming triggering of cooperation and action. The benefits of green roofs could be maximized by their widespread and contiguous, rather than piecemeal, installation. Green roofs could reduce both capital and recurrent public expenditures in stormwater management, healthcare, and green-space provision, the savings from which would be more than enough to fund the tax-exemption scheme. The findings yield convincing justifications for government financial incentives to promote public–private partnerships and cooperative coalitions of stakeholders in roof greening in compact urban areas.

The role of Green Roofs on Reducing Heating and Cooling Loads: A Database across Chinese Climates

This paper aims to use detailed modelling techniques and develop a database for assessing in a quick and easy way the energy performance of green roof designs across a range of Chinese climates. The focus is on heating and cooling loads by calculating indoor temperatures using the EnergyPlus simulation tool. The study covers 5328 configurations by varying model parameters such as location, climate, seasonal periods, glazing type, wall insulation levels, roof insulation, soil thickness and condition, and vegetation density characteristics. It was found from the results that green roofs can offer significant energy savings for heating and cooling loads if they are applied on roofs without insulation but only limited energy savings where heavy insulation on the roof is also applied. This database can prove to be a useful tool to the practitioners who want to perform rapid assessments of the potential energy savings that could be gained from a green roof installation in a Chinese location.

Chemistry of growth medium and leachate from green roof systems in south-central Texas

Installation of intensive and extensive green roofs is becoming popular for reducing runoff from impervious surfaces in many cities around the world. Most studies on runoff quality from green roofs have been conducted in cooler northern climates. We examined the losses and gains of nutrients, cations and selected anions in planted and unplanted growth medium and compared these to initial growth medium (IGM) typically used for green roof modules in south-central Texas. Water extracts of growth medium and leachate from three replicates of unplanted growth medium and three planted species (Sedum kamtschaticum, Delosperma cooperi and Talinum calycinum) were examined. During the first 6 months after establishment we observed high losses of nitrate (25 to 44 mg kg−1), dissolved organic carbon (DOC: 155 to 190 mg kg−1) and nitrogen (DON: 9.0 to 11.2 mg kg−1) and orthophosphate-P (1 to 2 mg kg−1). Average leachate concentrations based on four rain events 6 months after establishment ranged from 0.3 to 6.6 mg L−1 in planted modules and 6.3 mg L−1 in unplanted modules for nitrate-N, 38 to 42 mg L−1 in planted modules and 32 mg L−1 in unplanted modules for DOC, 2.1 to 3.1 mg L−1 in planted modules and 2.1 mg L−1 in unplanted modules for DON and 0.27 to 0.37 mg L−1 in planted modules and 0.40 mg L−1 in unplanted modules for orthophosphate-P. We suggest that after the establishment of green roofs, leachate losses may contribute some runoff concentrations of nitrogen, carbon and phosphorous in urban areas.

Green Roofing in Indiana: Case Studies and Design Notes

Green roof technology and implementation are taking root in North America at an accelerating pace. Growing recognition of the benefits of green roofs and increasing interest in green infrastructure are leading to expansion of green roof technologies that have been in use for decades in Europe and elsewhere. While some regions have adopted the use of green roofs on a large scale, other areas are warming up to the concept more slowly. Large-scale implementation of green roofs has not yet occurred in Indiana, but a number of exemplary projects have been constructed, and there are signs that interest in the technology is increasing in the state. The purpose of this article is to provide an overview of green roof technology, analyze selected green roofs in Indiana, explore trends in the state, and address issues for future development of green roof technology in the region. A variety of green roofs were investigated throughout the state. Discussions were held with individuals involved in each project to obtain technical and logistical details of green roof design, installation, and performance.

Cost-Effectiveness of Green Roofs

Life-cycle assessment was used to evaluate the widespread installation of green roofs in a typical urban mixed-use neighborhood. Market prices of materials, construction, energy conservation, storm-water management, and greenhouse gas (GHG) emission reductions were used to evaluate private and social costs and benefits. Results suggest green roofs are currently not cost effective on a private cost basis, but multifamily and commercial building green roofs are competitive when social benefits are included. Multifamily and commercial green roofs are also competitive alternatives for reducing greenhouse gases and storm-water runoff. However, green roofs are not the most competitive energy conservation techniques. GHG impacts are dominated by the material production and use phases. Energy impacts are dominated by the use phase, with urban heat island (UHI) impacts being an order of magnitude higher than direct building impacts. The quantification of private and social costs and benefits should help guide green roof policy. Results should encourage green roof enthusiasts to set appropriate life-cycle assessment boundaries, including construction material impacts and UHI effects.

Unsaturated 2D modelling of subsurface water flow in the coarse-grained porous matrix of a green roof

Summary The analysis of the interactions between hydrologic processes and green roof installations in the urban environment requires to improve the understanding of the unsaturated water flow in the coarse-grained porous media usually employed in such technological solutions. In order to base our research on experimental evidences, a monitoring program was carried out at the green roof experimental site of the University of Genoa (Italy). A continuous acquisition system is available at the experimental site for rainfall intensity and subsurface water flow measurements at 1 min resolution. Soil water content is also measured at the same resolution in time by four TDR probes located along a vertical profile. The SWMS_2D model, based on Richards’ law and the Van Genuchten–Mualem functions, is here applied to simulate the variably saturated flow within the green roof system. The model was calibrated and validated using rainfall–runoff events observed at the experimental site. The calibration and validation strategy involved comparing predicted and measured outflow hydrographs. The model adequately reproduces the hydrographs, as demonstrated by the limited relative percentage deviations obtained for the total discharged volume, the peak flow and the hydrograph centroid. Furthermore the predicted water content closely matches the observed one at various depths along the vertical profile where measurements are available, thus confirming that the model correctly describes the variably saturated flow field within the green roof. The mechanistic model, based on a single porosity approach, here employed to describe the variably saturated flow within the thin stratigraphy, is demonstrated to suitably describe the hydrologic performance of a green roof, which is typically realized with high hydraulic conductivity and coarse-grained porous media.

Quantifying air pollution removal by green roofs in Chicago

The level of air pollution removal by green roofs in Chicago was quantified using a dry deposition model. The result showed that a total of 1675 kg of air pollutants was removed by 19.8 ha of green roofs in one year with O 3 accounting for 52% of the total, NO 2 (27%), PM 10 (14%), and SO 2 (7%). The highest level of air pollution removal occurred in May and the lowest in February. The annual removal per hectare of green roof was 85 kg ha −1 yr −1. The amount of pollutants removed would increase to 2046.89 metric tons if all rooftops in Chicago were covered with intensive green roofs. Although costly, the installation of green roofs could be justified in the long run if the environmental benefits were considered. The green roof can be used to supplement the use of urban trees in air pollution control, especially in situations where land and public funds are not readily available.

Growing Green Roofs, City by City

Green roofs—rooftops that are partially or completely covered with vegetation growing in soil medium over a waterproof membrane—have gained momentum over the past six years as building owners recognize their advantages over conventional roofing in terms of better energy efficiency and reduced rain runoff. Now local governments are exploring incentives for moving the practice into the mainstream. A look at cities that are leading the country in green roof coverage reveals a growing range of policy tools.

Establishment and Persistence of Sedum spp. and Native Taxa for Green Roof Applications

Although the economic, environmental, and aesthetic benefits of green roofs have been recognized for decades, research quantifying these benefits has been limited—particularly in the U.S. Green roof usage and research is most prevalent in Germany, but can also be seen in several other European countries and Canada. If green roof installations are to be successful in Michigan and the rest of the U.S., then a better understanding of what specific taxa will survive and thrive under harsh rooftop conditions in this geographic area is required. Nine simulated rooftop platforms containing three commercially available drainage systems were installed at Michigan State University. Eighteen Michigan native plants planted as plugs and nine Sedum spp. planted as either seed or plugs were evaluated over three years for growth, survival during both establishment and overwintering, and visual appearance. All Sedum spp. tested were found to be suitable for use on Midwestern green roofs. Of the eighteen native plant taxa tested, Allium cernuum L., Coreopsis lanceolata L., Opuntia humifosa Raf., and Tradescantia ohiensis L. are suitable for use on unirrigated extensive green roofs in Michigan. If irrigation is available, then other native species are potential selections.