Green roofs in Melbourne - potential and practice

In Melbourne, green roofs are increasingly being included in the new and retrofitted buildings that claim to be ‘sustainable’ or ‘green’. This enthusiasm follows overseas experience where a variety of benefits have been recorded; these include a reduction in heating and cooling loads. This benefit is of particular importance because of the urgent need to reduce the greenhouse gas emissions associated with air conditioning. What is the potential for such savings and to what extent are some of the existing green roofs likely to achieve these benefits? This paper begins with a review of the overseas experience to reduce conditioning loads, particularly cooling, in temperate climates. Some observations on the potential and practice of green roofs in Melbourne is then presented. The results of measurements of plant canopy, soil and hard surface temperatures on two green roofs in the Melbourne Central Business District are discussed and future on-going work is outlined.

The effect of green roofs on pedestrian level air temperature

Man made alterations have resulted in higher air temperatures in cities, compared to their surrounding rural areas. There are many attempts to modify the urban design elements to ameliorate urban heat island effect. One among them is the concept of green roofs. There is a potential to incorporate vegetation to the large roof area of the buildings. Several studies investigated the effect of micro and macro scale implementation of green roofs. Most of these studies examined the impact of green roofs on the air temperature variation at the roof level, whereas studies are lacking on the effect of green roof at the pedestrian level. Therefore, this study aims to explore the impact of green roofs on the air temperature at pedestrian level, in the central business district (CBD), using Melbourne as a case study. A generic layout of Melbourne's CBD is modelled using ENVI-met 3.1 BETA 4. A number of different scenarios with different green roof coverages and building heights are examined. It was found that green roofs did not have significant impact on the temperatures at pedestrian level.

A pixel-based approach to estimation of solar energy potential on building roofs

Precise estimation of solar energy on building roofs plays a critical role in sustainable development and renewable energy consumption of high-density human habitats. Conventional solar radiation models based on costly Light Detection and Ranging (LiDAR) data are only adequate for existing buildings, not for future construction areas. In this paper, a pixel-based methodology is constructed for estimating solar energy potential over roofs. Buildings with flat roofs in a newly planned construction area are chosen as a case study. The solar radiation at a certain cell is mathematically formulated in the pixel unit, and its yields over a certain time period are calculated by considering multiple instantaneous solar irradiances and are visually presented by image processing. Significant spatial and temporal variations in solar radiation are measured. Within the study area, the maximum and minimum annual radiation yields are estimated at 4717.72 MJ/m2/year and 342.58 MJ/m2/year respectively. Radiation contour lines are then mapped for outlining installation ranges of various solar devices. For each apartment building, around 20% of roof areas can obtain 4500 MJ/m2/year or more solar radiation yields. This study will benefit energy investors and urban planners in accurately predicting solar radiation potential and identifying regions with high radiation over building roofs. The results can be utilised in government policies and urban planning to raise awareness of the use of renewable energy sources.

Conservation management and diets of Powerful Owls (Ninox strenua) in outer urban Melbourne, Australia

The Powerful Owl Ninox strenua is Australia’s largest owl, and is mainly found east of the Great Dividing Range on the mainland in tall-open forests. The species is considered rare, both nationally and in the State of Victoria; and threatened in the Greater Melbourne area. Recovery plans for the future conservation management of N. strenua are being prepared in 2 states.

Historically, Powerful Owls have been thought to require large homes ranges (about 1000 ha per pair) in suitable old-growth forest, which provides nest hollows for the owls and their arboreal marsupial prey. Recent research, however, has found N. strenua may be more numerous and breed more successfully in a wider range of habitats than previously believed. In particular, the birds have been found living in forests and woodlands within the greater metropolitan areas of cities. The most extreme case is where a nest tree has been found within 800m of urban settlement and 6km from the centre of Brisbane.

In this paper we report on the diet, habitat use, and conservation management by a number of breeding pairs of owls in outer urban Melbourne. Study sites range from a relatively undisturbed rainforest habitat 80km from central Melbourne, through dry sclerophyll, eucalyptus-dominated open forest with some disturbance to a site 8km from central Melbourne in highly disturbed urban parkland.

Diets of the families of owls were determined by analyzing remains in regurgitated pellets. The data confirm that arboreal marsupials constitute the major prey items, especially the Common Ringtail Possum Pseudocheirus peregrinus. There were differences in diets depending on the availability of prey species, which suggest a level of opportunism not previously suspected. Our study is also the first to confirm the owls capture adult Common Brushtail Possums Trichosurus vulpecula (15% of pellets containing the remains of this large opossum have bones of mature adults at 1 site) and thus take prey up to two and a half times their own weight. As well our data suggest Powerful Owls are not restricted to hollow-dwelling prey, as in some sites the marsupials rested during the day either in leafy nests called dreys (P. peregrinus) or in house roofs (T. vulpecula).

In the most heavily disturbed sites, breeding success has been reduced, and we have evidence that in one particular year the young were eaten by one of the parents. This followed construction of a bicycle track under the nest during the breeding season. Recommendations are made for the future conservation and habitat management of Powerful Owls in the Yarra Valley corridor.

Green roof retrofit potential in the central business district

Purpose – The purpose of this paper is to illustrate the potential for green roof retrofit to commercial buildings in a city centre to property managers and other property professionals.

Design/methodology/approach – This paper addresses the research question: what is the potential of existing buildings in the CBD to accommodate a retrofitted green roof? Furthermore, it questions how many buildings are suitable for green roofs? The researchers compile a unique building database incorporating information about 536 commercial buidings and evaluate the potential suitability of each building to undergo a green roof retrofit. Assisted by other commercially available databases and software, the researchers are able to assess each roof based on criteria derived from an extensive literature review.

Findings – A relatively small proportion of roofs are found to be suitable, partly a result of local climate conditions and rainfall patterns, and the physical property stock. On a purely physical assessment, only a very small proportion of CBD stock is found to be suited. These buildings are most likely to be in low secondary locations, ungraded or B grade buildings, privately owned, concrete framed and not overshadowed by adjoining properties.

Practical implications – Property managers and other property professionals can now determine the potential of their portfolio stock for green roof retrofit based on the review of building attributes required for success adaptation in this paper. It possible that greater potential for green roof retrofit exists in the suburbs or regional towns where lower rise buildings may reduce the amount of overshadowing found in city centres. Follow-up research could focus on a comparison of regional and suburban developments.

Originality/value – This is the first study of its kind and has assessed such a large number of buildings for their suitability for green roof retrofit; the findings provide a reliable guide for policymakers regarding the potential number of city centre buildings which would be possible to retrofit. Such findings should influence policymaking and incentives to target effective sustainability policies with regards to existing buildings.

Measuring eco-roof mitigation on flash floods via GIS simulation

Purpose: The rapid and ongoing expansion of urbanised impervious areas could lead to more frequent flood inundation in urban flood-prone regions. Nowadays, urban flood inundation induced by rainstorm is an expensive natural disaster in many countries. In order to reduce the flooding risk, eco-roof systems (or green roof systems) could be considered as an effective mechanism of mitigating flooding disasters through their rainwater retention capability. However, there is still a lack of examining the stormwater management tool. The purpose of this paper is to evaluate the effects on flooding disaster from extensive green roofs. Design/methodology/approach: Based on geographical information system (GIS) simulation, this research presents a frame of assessing eco-roof impacts on urban flash floods. The approach addresses both urban rainfall-runoff and underground hydrologic models for traditional impervious and green roofs. Deakin University’s Geelong Waurn Ponds campus is chosen as a study case. GIS technologies are then utilised to visualise and analyse the effects on flood inundation from surface properties of building roofs. Findings: The results reveal that the eco-roof systems generate varying degrees of mitigation of urban flood inundation with different return period storms. Originality/value: Although the eco-roof technology is considered as an effective stormwater management tool, it is not commonly adopted and examined in urban floods. This study will bring benefits to urban planners for raising awareness of hazard impacts and to construction technicians for considering disaster mitigation via roof technologies. The approach proposed here could be used for the disaster mitigation in future urban planning.