Conference Paper

Green roofs in Australia: review of thermal performance and associated policy development

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Abstract

In Australia, there is an increasing interest in using extensive green roofs to make buildings more sustainable and provide a number of social, ecological, aesthetic and thermal benefits to cities. The potential of green roofs to reduce building energy consumption has been extensively studied overseas in a variety of different climates. However, in Australia the green roof industry is relatively new. There is still very little information on the thermal properties of Australian green roofs and their performance. Further, as a relatively new industry, there is a general lack of specific policies and initiatives to promote green roofs. In this paper, we briefly review the research investigating green roof thermal performance in various climates and analyse policies and actions that have been implemented internationally to foster green roofs with an emphasis on their thermal performance. The results showed that most policies were focused on ecological benefits, such as stormwater runoff reduction, rather than thermal benefits. Many green roof policies had difficulty interpreting the thermal performance of green roofs, because of the dynamic nature of green roof R-values. In this study, the effectiveness of overseas green roof policy is discussed and recommendations how they could be adapted for Australian cities are provided.

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... Findings are varied and sometimes in contrast to one another. Common findings are that green roof thermal performance depends on the climate zone, the building materials, the seasonality and the green roof material selection [16,[18][19][20][21][22][23]. For example, in cold climate areas, a thick substrate enhances thermal performance compared to a thin substrate [24]. ...
... Because of these wide ranging results, it is not possible to specify one "optimum" green roof build-up (drainage layer, substrate or growing medium and plants) that will maximise green roof thermal benefits in all countries or climate zones. In situ research is therefore necessary to help select substrates and plants for green roofs in various locations [19]. ...
... Sailor's model comprise many variables and parameters, some relevant to the vegetation layer, and others to the substrate layer, called soil in the model. As a result of a review of the literature [19], we selected three vegetation parameters and three soil parameters as the most relevant to a green roof thermal performance for further investigation. These are: (i) Leaf Area Index (LAI); (ii) Leaf reflectivity (LR); (iii) Minimum stomatal resistance (SR); (iv) Substrate thickness (ST); (v) Conductivity of dry soil (CDS); and (vi) Saturation volumetric moisture content (MC). ...
Article
Full-text available
Green roofs are consistently being used to reduce some of the negative environmental impacts of cities. The increasing interest in extensive green roofs requires refined studies on their design and operation, and on the effects of their relevant parameters on green roof thermal performance. The effects of two design parameters, substrate thickness (ST) and conductivity of dry soil (CDS), and four operating parameters, leaf area index (LAI), leaf reflectivity (LR), stomatal resistance (SR), and moisture content (MC), were investigated using the green roof computer model developed by Sailor in 2008. The computer simulations showed that among the operating parameters, LAI has the largest effects on thermal performance while CDS is a more influential design parameter than ST. Experimental investigations of non-vegetated and sparsely vegetated green roofs in Melbourne were principally used to understand the effect of the substrate and enable better understanding of dominant heat transfer mechanisms involved. Investigated green roofs had three substrate thicknesses (100, 150 and 200 mm), and their performance was compared to a bare conventional roof. In contrast to the computer simulations, the experimental results for summer and winter showed the importance of MC and ST in reducing the substrate temperature and heat flux through the green roof.
... Green roofs can regulate roof surface temperatures through shading, insulation, direct solar reflection and heat loss from the evapotranspiration of leaves and substrates but the benefit of this varies considerably with climate (Pianella et al., 2016a). When irrigated, vegetated green roofs in SE Australia reduce temperatures at the substrate surface and at depth and in summer these are generally cooler than ambient air temperature during the day and warmer at night because of their capacity to retain heat (Razzaghmanesh et al., 2016). ...
... Irga et al. (2017) suggested that government influence can play a significant role in encouraging installation of green roofs, and related the number of green roof installations in different local government areas to the existence and type of green roof policies. However, even with increasing research findings directly relevant to the Australian context, most green roof policies focus on providing information and encouragement for installation, rather than regulating or mandating their inclusion in new developments (Pianella et al., 2016a). Arguably, this period of policy encouragement and support has been important in skilling up and developing industry capacity as well as increasing the 'visibility' and interest in green roofs amongst policy makers. ...
Article
Australian cities have been slow to implement green roofs. This is because there are many potential barriers to their widely acceptance as a nature based solution that can make cities more liveable and help them adapt to, and mitigate, climate change. Due to significant differences in rainfall, temperature, available substrates and suitable vegetation relying on northern hemisphere research and experience is problematic as many of the environmental and economic benefits of green roofs are location specific. This paper aims to 1. synthesise a decade of Australian green roof research that has sought to overcome these barriers, 2. assess the current status of the Australian green roof industry and remaining knowledge gaps, and 3. provide a roadmap for future progress developed in multidisciplinary industry workshops. Many of these insights will be applicable to areas with similar seasonally hot and dry climates or emerging green roof markets. We identified that significant progress has been made in addressing the barriers to green roofs in Australia. Research has focused on developing green roofs for local conditions and quantifying their benefits. Substrate research has investigated the suitability of locally available materials with a focus on how water retention additives and organic waste materials can increase plant available water and therefore survival. By taking a plant physiology approach Australian researchers have gained a strong functional understanding of suitable green roof plants and the benefits they provide, considerably expanding the available palette beyond the succulents commonly used internationally. Research has quantified green roofs’ stormwater retention and building insulation and energy benefits and provided evidence that they benefit well-being and performance, important for employee productivity.
... However, many studies have shown that building energy savings from green roofs are strongly dependant on climate and location [17], as well as building characteristics and existing insulation [18,19]. Given that Australia is conventionally divided into eight different climate zones [20], the thermal performance and consequent building energy savings would be different across the country, and specific recommendations on the best green roof build-up should be tested and provided locally [21]. ...
... However, we recognise that further studies are required to model the thermal performance of buildings using these substrates across Australia climate zones [21]. We also understand that the green roofs should be judged on the multiple benefits they provide, and not only for their insulating properties. ...
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There has been growing interest in using extensive green roofs for commercial and residential buildings in urban areas. Green roofs provide many benefits, including adding an additional insulation layer. The potential of this benefit depends on many factors, including the thermal properties of the green roof substrate. Thermal conductivity values of three substrates comprised primarily of scoria, crushed roof tile and bottom-ash were measured with steady-state and transient techniques under three moisture conditions. Specific heat capacities of the green roof substrates were also measured with a transient technique. Steady-state measurements were performed with a “k-Matic” apparatus while transient measurements with KD2 Pro needles. In general, the steady-state measurements showed more consistency than transient measurements. Thermal conductivity differed among the three substrates: crushed roof tile had the highest conductivity values across all moisture contents. Substrate moisture content consistently increased thermal conductivity across all substrates, but this was significantly greater for the crushed roof tile substrate. Steady-state thermal conductivity curves were fitted using the thermal conductivity model for green roof substrates adopted by Sailor (2011). The coefficients obtained are presented and can be used in green roof models to quantify the thermal performance of green roofs and building energy savings.
... These cities have different drivers for the implementation of green roofs and walls, most often related to issues of increasing the resilience and livability of the city. Cities with more developed living architecture industries have a range of policy approaches to encourage and/or mandate green roofs and walls (Pianella et al. 2016). The approaches adopted in these cities are expanded and critiqued in the Case Study report accompanying this report. ...
Technical Report
Full-text available
A large-scale and coordinated effort to retrofit green infrastructure into our built environment could see residential property values increase by 6 to 15 per cent as well as providing social, health and environmental benefits. A team of researchers at the University of Technology Sydney analysed the business case for green roofs and walls in Australia. The literature review included a US Cost Benefit Analysis (CBA) which found a viable case for boosting urban greenspace. It showed increases in residential property values with good amounts of green infrastructure between 6 and 15%. The review also found that widescale adoption of green roofs in Toronto, Canada could reduce temperatures in urban areas by up to 5 degrees Celsius. ‘Expanding the Living Architecture in Australia’ explores whether a mandatory or voluntary approach to green roofs and walls would work best in Australia, and draws on scientific literature and international case studies to illustrate how it could work in a localised setting. It found green roofs and walls offer great potential to expand living architecture in Australia and could deliver a suite of benefits from improved air quality and reduced storm water impacts, in addition to boosting community interaction and urban aesthetics.
... Because of these wide ranging results, it is not possible to specify an 'optimum' green roof build-up (plants and substrate or growing medium) that will maximise green roof thermal benefits in any country or climate zone. In situ research is therefore necessary to help select green roof materials in different areas (Pianella et al., 2016a). ...
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The research deals with the experimental assessment of the yearly thermal performance of a green roof compared to other passive cooling technologies under temperate climate. All roofs are installed on highly insulated slabs (U-value < 0.25 W/m2 K), in order to understand whether in summer the passive cooling effects are inhibited by the low thermal transmittance recently introduced in many southern Europe countries to meet the demands of the energy saving regulations for the winter heating season. Even though many studies have focused on the performance of green roofs, there is little knowledge regarding their potential in highly insulated roofs. Most of the studies derived from analytical simulations, but the thermal behaviour of a green roof is a complex phenomenon and involves combined heat and mass transfer exchanges difficult to assess with analytical models, while more experimental data are necessary. Optical properties of the roofs covering materials were experimentally measured, and the thermal transmittance of the roofs was experimentally evaluated. Field measurements show how in winter the green roof is able to guarantee further insulation even in saturation conditions. In summer, the green roof mitigates incoming heat fluxes and ceiling temperatures. Its performance is however partially hindered by high insulation.
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Air pollution problems caused from the development of infrastructures are getting serious, in which air flow is reduced and heat is trapped among high-rise buildings. In order to mitigate these problems, various methods have been developed in previous studies. Extensive green roof has been identified as one of the most important means to mitigate these problems and implement sustainable development principles in the building features. Governments world-wide have been introducing various policies and regulations for promoting extensive green roof particularly for building projects. However, the existing buildings in many large cities such as Hong Kong display few extensive green roof features. Hong Kong is one of the most densely populated cities with many high-rise buildings. This paper examines the major barriers encountered in promoting extensive green roof systems for the existing buildings in Hong Kong. Case study approach is adopted to investigate how and why the barriers can hinder the implementation of extensive green roof features. Research results show that lack of promotion and incentives from governments and the increase maintenance cost are identified as the top barriers to the implementation. The paper concludes by providing further suggestions and actions that can help mitigate these existing barriers.
Article
Modular green roofs were investigated to better understand surface and membrane level temperature expectations of unirrigated green roofs during hot summer conditions in south-central Texas. We used three succulent monocultures, Sedum kamtschaticum, Delosperma cooperi, Talinum calycinum syn. Phemeranthus calycinus and one unplanted control module, each replicated 3 times. Media surface and below media temperatures were monitored, as well as soil water content and general weather conditions (RH, air temperature). Temperatures at the surface and below the media surface were compared with temperatures of a standard roof surface. We found that diurnal surface temperature reductions were very stable throughout the summer. Much larger temperature reductions were achieved below the modules than at the soil surface. Temperature reductions at the soil surface were predominantly driven by soil volumetric water content (VWC) and, to a lesser degree, air temperature while species and percent cover had small modifying effects through interactions with VWC and air temperature. Temperature reductions below the modules were driven by surface soil temperature, while increasing VWC led to a small decrease in temperature reductions at the membrane level. Mean daily temperature reductions achieved were 18.0 °C at the soil surface and 27.5 °C below the module, thus demonstrating that unirrigated, succulent-based green roofs can provide significant rooftop temperature reductions during hot, dry summer conditions.
Article
This paper presents the results of a comparative study aiming to investigate the suitability of materials used in outdoor urban spaces in order to contribute to lower ambient temperatures and fight heat island effect. The study involved in total 93 commonly used pavement materials outdoors and was performed during the whole summer period of 2001. The thermal performance of the materials was measured in detail using mainly infrared thermography procedures. The collected data have been extensively analysed using statistical techniques. Comparative studies have been performed in order to identify the major advantages and disadvantages of the materials studied. Materials have been classified according to their thermal performance and physical properties into 'cool' and 'warm' materials. The impact of color, surface roughness and sizing has been analysed as well. The study can contribute to selection of more appropriate materials for outdoor urban applications, and thus assist to fight the heat island effect, decrease the electricity consumption of buildings and improve outdoor thermal comfort conditions.
Article
Singapore is a Garden City. On the other hand, with increasing population and limited territory, the government had to adopt a high-density and high-rise residential strategy. The high concentration of buildings in cities has resulted in many environmental issues, such as the Urban Heat Island effect. The rising ecological concerns for building design attempt to create harmony between buildings and their surroundings through mitigating their negative impact on the environment. The greening of buildings is essentially one of the ecological measures. The National Parks Board (NParks) launched a skyrise greenery approach/programme recently to promote the greening of buildings.To explore the thermal benefits, a before and after measurement and an experiment were carried out. The green roof tends to experience lower surface temperature than the original exposed roof surface, especially in areas well covered by vegetation. A maximum temperature difference of 18 °C was observed. However, the substrate temperature measured can exceed the surface temperature of the original exposed roof when the substrate is very dry. In areas that tend to be sparsely covered by vegetation, the peak temperature recorded was up to 73.4 °C during the day time. Ambient air temperature, correspondingly, at 300 mm above the substrate surface can reach 40 °C. This is worsened by the lower wind speed recorded after the measurements. The resulting substrate moisture, when the green roof systems are well covered by vegetation, will tend to keep substrate temperature lower than the original exposed bare roof. The heat flux through the roof structure was greatly reduced due to the installation of extensive systems. Maximally, over 60% of heat gain was stopped by the system. The impact of different types of vegetation may vary as well. Those with relatively extensive greenery coverage led to better thermal performance.
Article
Measurements of the thermal behaviour of two residential buildings equipped with a green roof system have been performed in Athens, Greece. Experimental data have been used to calibrate detailed simulation tools and the specific energy and environmental performance of the planted roofs system has been estimated in detail. Simulations have been performed for free-floating and thermostatically controlled conditions. The expected energy benefits as well as the possible improvements of the indoor thermal comfort have been assessed. It is found that green roofs have a limited contribution to the heating demand of insulated buildings operating under the Mediterranean climate. On the contrary, the green roof system is found to contribute highly to reduce the cooling load of thermostatically controlled buildings. For the considered residential buildings, a cooling load decrease of about 11% has been calculated. In parallel, it is found that green roofs contribute to improve thermal comfort in free-floating buildings during the summer period. The expected maximum decrease of the indoor air and roof surface temperatures is close to 0.6°C. Such a decrease contributes to reduce by 0.1 the summer absolute Predicted Mean Vote Comfort Index levels in the building. Copyright © 2009 John Wiley & Sons, Ltd.
Article
Globally, buildings are responsible for approximately 40% of the total world annual energy consumption. Most of this energy is for the provision of lighting, heating, cooling, and air conditioning. Increasing awareness of the environmental impact of CO2 and NOx emissions and CFCs triggered a renewed interest in environmentally friendly cooling, and heating technologies. Under the 1997 Montreal Protocol, governments agreed to phase out chemicals used as refrigerants that have the potential to destroy stratospheric ozone. It was therefore considered desirable to reduce energy consumption and decrease the rate of depletion of world energy reserves and pollution of the environment. One way of reducing building energy consumption is to design building, which are more economical in their use of energy for heating, lighting, cooling, ventilation and hot water supply. Passive measures, particularly natural or hybrid ventilation rather than air-conditioning, can dramatically reduce primary energy consumption. However, exploitation of renewable energy in buildings and agricultural greenhouses can, also, significantly contribute towards reducing dependency on fossil fuels. Therefore, promoting innovative renewable applications and reinforcing the renewable energy market will contribute to preservation of the ecosystem by reducing emissions at local and global levels. This will also contribute to the amelioration of environmental conditions by replacing conventional fuels with renewable energies that produce no air pollution or greenhouse gases. The provision of good indoor environmental quality while achieving energy and cost-efficient operation of the heating, ventilating and air-conditioning (HVAC) plants in buildings represents a multi-variant problem. The comfort of building occupants is dependent on many environmental parameters including air speed, temperature, relative humidity and quality in addition to lighting and noise. The overall objective is to provide a high level of building performance (BP), which can be defined as indoor environmental quality (IEQ), energy efficiency (EE) and cost efficiency (CE). - Indoor environmental quality is the perceived condition of comfort that building occupants experience due to the physical and psychological conditions to which they are exposed by their surroundings. The main physical parameters affecting IEQ are air speed, temperature, relative humidity and quality. - Energy efficiency is related to the provision of the desired environmental conditions while consuming the minimal quantity of energy. - Cost efficiency is the financial expenditure on energy relative to the level of environmental comfort and productivity that the building occupants attained. The overall cost efficiency can be improved by improving the indoor environmental quality and the energy efficiency of a building. This article discusses the potential for such integrated systems in the stationary and portable power market in response to the critical need for a cleaner energy technology. Anticipated patterns of future energy use and consequent environmental impacts (acid precipitation, ozone depletion and the greenhouse effect or global warming) are comprehensively discussed in this paper. Throughout the theme several issues relating to renewable energies, environment and sustainable development are examined from both current and future perspectives.
Article
The advantages of the planned roofs are undoubtedly numerous from both the ecological and the social point of view. They act positively upon the climate of the city and its region, as well as upon the interior climate of the buildings beneath them. They give protection from the solar radiation, which is the main factor in passive cooling. By reducing thermal fluctuation on the outer surface of the roof and by increasing their thermal capacity, they contribute, to the cooling of the spaces below the roof during the summer and to the increase of their heat during the winter. Due to the decrease of the thermal losses, the green roofs save the energy consumption.This paper refers to the analysis of the thermal properties and energy performance study of the green roof. The investigation were implemented in two phases: during the first phase, extended surface and air temperature measurements were taken at the indoor and outdoor environment of the buildings where the green roof had installed and during the second phase of the study, the thermal properties of the green roof, as well as, the energy saving were examined, through a mathematical approach.
Article
In a very hot climate equivalent to a Japanese summer, the reduction of heat coming into rooms is very important with respect to thermal comfort and energy efficiency. The objective of this study is to investigate the evaporative cooling effect from roof lawn gardens planted in non-woven fabric as one mode of passive cooling. It was confirmed by field measurements during the summer that the amount of heat coming into the rooms was reduced by a roof lawn garden. That is, the surface temperature of the roof slab decreased from about 60 to 30°C during day time, which was estimated to be followed by a 50% reduction in heat flux into the room by simple calculation. The evaporative cooling effect from roof lawn gardens is considered to play an important role in reducing heat flux. In order to evaluate the evaporative cooling effect of a roof lawn garden, analysis of the heat and moisture transport in the lawn garden is required. Thus, along with those field measurement, a wind tunnel experiment in a room was carried out in order to obtain the basic information for understanding and predicting the heat and moisture transport in the lawn. Furthermore, a numerical calculation by a simultaneous transport model of heat and moisture was carried out using the results of the wind tunnel experiment. The calculated results were in fairly good agreement with the measured values, and the evaporative cooling effect by the roof lawn garden was shown. For more accurate and quantitative evaluation and prediction, sensitivity analysis of the transport parameters and the examination of the proposed model including measurements are required.
Article
Green roof utilisation has been known since ancient times both in hot and cold climates. Nowadays, it has been reconsidered at issue of energy saving and pollution reduction. In this paper, some measurement sessions on a green roof installed by the Vicenza Hospital are described. A data logging system with temperature, humidity, rainfall, radiation, etc. sensors surveyed both the parameters related to the green roof and to the rooms underneath. The aim is to evaluate the passive cooling, stressing the evapotranspiration role in summer time. Furthermore, the enhanced insulating properties have been tested during winter time. A predictive numerical model has been developed in a building simulation software (TRNSYS) to calculate thermal and energy performances of a building with a green roof, varying the meteorological dataset for a specific geographic zone.
Article
There is increasing public, industry and government interest in establishing green roofs in Australian cities due to their demonstrated environmental benefits. While a small number of green roofs have been constructed in Australia, most are roof gardens or intensive green roofs. Despite their potential as a climate change adaptation and mitigation tool and their widespread use in the northern hemisphere, there are very few examples of extensive green roofs in Australia. One of the major barriers to increasing the prevalence of extensive green roofs in Australia is the lack of scientific data available to evaluate their applicability to local conditions. Relying on European and North American experience and technology is problematic due to significant differences in climate, available substrates and plants. This paper examines green roofs in Australia, discusses the challenges to increasing their use and the major information gaps that need to be researched to progress the industry in Australia.
Article
Energy consumption in the residential and tertiary sectors is especially high in developed countries. There is a great potential for energy savings in these sectors. Energy conservation measures are developed for newly constructed buildings and for buildings under refurbishment. However, to achieve a significant reduction in energy consumption apart from the standard energy-efficiency methods, innovative technologies should be implemented, including renewable energy. Coherency of standard, modern energy efficiency and renewable options becomes necessities. To approach the idea of sustainable buildings, a few developmental steps are needed, regarding energy, water, land and material conservation, together with environmental loading, and the qualities of the indoor and outdoor environments.
Article
This paper deals with the experimental investigation and analysis of the energy and environmental performance of a green roof system installed in a nursery school building in Athens. The investigation was implemented in two phases. During the first phase, an experimental investigation of the green roof system efficiency was presented and analysed, while in the second one the energy savings was examined through a mathematical approach by calculating both the cooling and heating load for the summer and winter period for the whole building as well as for its top floor. The energy performance evaluation showed a significant reduction of the building's cooling load during summer. This reduction varied for the whole building in the range of 6–49% and for its last floor in the range of 12–87%. Moreover, the influence of the green roof system in the building's heating load was found insignificant, and this can be regarded a great advantage of the system as any interference in the building shell for the reduction of cooling load leads usually to the increase of its heating load.
Article
Vegetation strategically placed on roofs and walls can be considered as a complement of urban greens. It is actually an ecological solution to the concrete jungle in cities. The benefits of green roofs are unquestionable from the thermal point of view. But some quantitative data on this subject are still needed in the context of tropical climate. Therefore, a field measurement was conducted in Singapore to investigate the thermal impacts of rooftop garden. From the derived data, it has been confirmed that rooftop gardens contribute thermal benefits to both buildings and their surrounding environments.
Article
Traditional construction practices provide little opportunity for environmental remediation to occur in urban areas. As concerns for environmental improvement in urban areas become more prevalent, innovative practices which create ecosystem services and ecologically functional land cover in cities will be in higher demand. Green roofs are a prime example of one of these practices. The past decade has seen the North American green roof industry rapidly expand through international green roof conferences, demonstration sites, case studies, and scientific research. This study evaluates existing international and North American green roof policies at the federal, municipal, and community levels. Green roof policies fall into a number of general categories, including direct and indirect regulation, direct and indirect financial incentives, and funding of demonstration or research projects. Advantages and disadvantages of each category are discussed. Salient features and a list of prompting standards common to successfully implemented green roof strategies are then distilled from these existing policies. By combining these features with data collected from an experimental green roof site in Athens, Georgia, the planning and regulatory framework for widespread green roof infrastructure can be developed. The authors propose policy instruments be multi-faceted and spatially focused, and also propose the following recommendations: (1) Identification of green roof overlay zones with specifications for green roofs built in these zones. This spatial analysis is important for prioritizing areas of the jurisdiction where green roofs will most efficiently function; (2) Offer financial incentives in the form of density credits and stormwater utility fee credits to help overcome the barriers to entry of the new technology; (3) Construct demonstration projects and institutionalize a commitment greening roofs on publicly-owned buildings as an effective way of establishing an educated roofing industry and experienced installers for future green roof construction.
Green Roof Policies-A guideline for decision makers and Green Roof supporters
  • W Ansel
Ansel, W. (2015) Green Roof Policies-A guideline for decision makers and Green Roof supporters,History of the Future: 52nd World Congress of the International Federation of Landscape Architects, IFLA 2015-Congress Proceedings, 396-400.
Past-Present-Future: Green Roof Techniques in Changing Times, Green Roofs-Bringing Nature Back to Town. International Roof Congress
  • R Appl
Appl, R. (2009) Past-Present-Future: Green Roof Techniques in Changing Times, Green Roofs-Bringing Nature Back to Town. International Roof Congress, Berlin, 25-27 May, 7-14.
Growing green guide: a guide to green roofs, walls and facades in Melbourne and Victoria, Australia, Victorian Department of Environment and Primary Industries
  • Depi
DEPI (2014) Growing green guide: a guide to green roofs, walls and facades in Melbourne and Victoria, Australia, Victorian Department of Environment and Primary Industries, Melbourne.
Growing green guide: green roofs, walls & facades policy options background paper
IMAP (2014) Growing green guide: green roofs, walls & facades policy options background paper, ed., Inner Melbourne Action Plan, Melbourne.
Thermal performance of green roofs through field evaluation
  • K B Liu
Liu, K. B., B. (2003) Thermal performance of green roofs through field evaluation, Proceedingsfor the First North American Green Roof Infrastructure Conference, Awards and Trade Showm Chicago IL.