The next green hectare will be vertical

An estimate of the biological suitability of walls in Melbourne’s CBD

Thami Croeser

Supervised by Dr Dominique Hes

Submitted in partial fulfilment of the requirements of the degree of Master of Urban Planning

Faculty of Architecture, Building and Planning

University of Melbourne

October 2014

2

Abstract

This research centres on the following question: “What is the total wall area of Melbourne’s CBD

which could host living plants?”

The answer to this question appears to be substantial; within just the Hoddle Grid, there are at almost

two hectares of wall space with ideal characteristics for greening treatments, and a further seven

hectares where greening could likely be carried out with careful design.

This thesis comes at a time of increasing interest in urban greening within major cities across the

planet. The recognition that plants in urban environments have substantial benefits both in terms of

sustainability and amenity has driven a range of projects and policies to ‘green up’ urban

environments. The City of Melbourne is no exception, having committed to an Urban Forest Strategy

as well as strategies for open space and integrated water management.

However, dense urban areas are highly modified environments, and land attracts high premiums. This

makes urban greening both challenging for plants, which have to face high winds and deep shadows,

and city managers, who face land prices measured in thousands of dollars per square metre.

By pragmatically mapping the physical constraints of walls in the CBD, as well as modelling the urban

microclimate, this research has demonstrated that even in the challenging environment of city

centres, large areas of space exist with potential for greening.

3

Declaration

This thesis does not contain any material that has been

accepted for the award of any other degree or diploma in any

academic institution, and, to the best of my knowledge,

contains no material previously published or written by

another person, except where due reference is made in the

text of this thesis.

Signed:

Date: 31 October, 2014

4

Acknowledgments

This thesis is built on gratitude to many peers, friends and teachers. Of these, six deserve special

thanks:

First, my deep thanks to Dr Dominique Hes, both for the inspirational example she sets in her own

approach to work and teaching, and for her unique supervision. I have made so many exciting

contacts as a result of her guidance.

Second, I am grateful to the Green Infrastructure Research Group for the teaching that inspired this

thesis, and then their eventual involvement in its development.

Third, a big thank you to Christopher Newman, both for your encouragement and for sharing vital

data that formed the foundation of my work

Fourth, to Dr Boon Lay Ong, for demanding that I get organised early, to avoid stress and

compromised research – I owe my current calm state of mind to you.

Fifth, to the City of Melbourne, particularly Gail Hall and Kelly Hertzog, for the encouragement and

including me in their work.

Finally, thank you to Sara Wilkinson at UTS for offering both encouragement and a next step for this

research.

5

Contents

Abstract ................................................................................................................................................... 2

Introduction ............................................................................................................................................ 7

Scope ................................................................................................................................................... 8

Rationale ............................................................................................................................................. 8

Literature Review .................................................................................................................................. 10

Ecosystem services provided by green façades ................................................................................. 10

Risks in applying façade species to buildings ..................................................................................... 12

Methodological Precedents .............................................................................................................. 13

Land Suitability Analysis .................................................................................................................... 13

Modelling the urban microclimate .................................................................................................... 15

Quantifying urban greening potential ............................................................................................... 16

What makes a wall ‘biologically suitable’? ........................................................................................ 17

Methodology ......................................................................................................................................... 20

Physical characteristics of walls in Melbourne .................................................................................. 20

Modelling wind flows ........................................................................................................................ 24

Modelling patterns of shade ............................................................................................................. 25

Synthesis ........................................................................................................................................... 26

Results ................................................................................................................................................... 28

Physical scores ................................................................................................................................... 28

Wind Modelling ................................................................................................................................. 29

Solar Modelling ................................................................................................................................. 32

Synthesis ........................................................................................................................................... 33

Extrapolation ..................................................................................................................................... 34

Discussion .............................................................................................................................................. 36

Limitations ......................................................................................................................................... 37

Further research ................................................................................................................................ 38

References ............................................................................................................................................. 41

6

Figures Figure 1 - Four approaches to vertical greening ...................................................................................... 7

Figure 2 - Location of the Hoddle Grid .................................................................................................... 8

Figure 3 - Effects of English Ivy (Hedera Helix) on wall surface temperature ........................................ 10

Figure 4 - Land Suitability Analysis for wildlife....................................................................................... 14

Figure 5 - Hybrid Land Suitability Analysis ............................................................................................. 15

Figure 6 - Sample of operating CFD model ............................................................................................ 16

Figure 7 - Different types of vegetation produce differing LAI and GPRs .............................................. 17

Figure 8 - Criteria for site analysis ......................................................................................................... 18

Figure 9 – Decision tree for greening a building .................................................................................... 19

Figure 10 - Approach to data collection and analysis. ........................................................................... 21

Figure 11 - Raw data sample ................................................................................................................. 23

Figure 12 - Example of wind tunnel analysis conducted using Autodesk Vasari .................................... 24

Figure 13 - Example of shadow analysis conducted using ESRI ArcScene. ............................................ 26

Figure 14 - Overlay process to combine multiple data types. ............................................................... 26

Figure 15 - Scores for walls surveyed at the northwest corner of the Hoddle Grid. ............................. 27

Figure 16 – Results of physical scoring process for observed walls. ...................................................... 28

Figure 17 - Surveyed walls showed a wide range of physical characteristics. ....................................... 29

Figure 18 - Wind exposure was generally high for observed walls. ....................................................... 29

Figure 19 - Percentage distribution of wind exposure. ......................................................................... 30

Figure 20 - Model outputs for wind exposure, after georeferencing and spectral analysis .................. 31

Figure 21 - Solar scores tended to be low for surveyed walls. .............................................................. 32

Figure 22 - Spatial distribution of solar scores in the city has little relation to building aspect. ............ 32

Figure 23 - Spatial distribution of hybrid score. A score above 6 was considered to be ideal. .............. 33

Figure 24 - Hybrid scores ....................................................................................................................... 34

Figure 25 – Final Result ......................................................................................................................... 34

Figure 26 - Current area purchasable by the open space fund ............................................................ 36

Figure 27 - Green Wall on the Musée du quai Branly, Paris .................................................................. 38

7

Introduction

This thesis will estimate the area of wall space in Melbourne’s CBD which could be covered by green

façades.

The term ‘green façades’ refers to plants that attach directly to walls (such as ivy) as well as species

that require a supporting structure, such as cables, trellises or mesh (such as vines). However, this

term is distinct from ‘green wall’ or ‘living wall’, which refers to the vertical installation of plants that

normally grow in the ground. Figure one contrasts green facades with green walls.

Figure 1 - Four approaches to vertical greening. The examples on the left are green facades; the examples on the right are green walls. This thesis focuses specifically on green facades (IMAP 2014).

This research is based on the recognition that vertical greening offers a range of sustainability benefits

in cities, such as management of heat island effects and pollution control, while increasing the

aesthetic appeal of buildings. In essence, blank walls (with the right characteristics) present an

underutilised opportunity to increase the beauty and sustainability of cities. This thesis will quantify

that opportunity in Melbourne’s CBD, by identifying walls with potential for greening, ranking them

based on their characteristics, and measuring their total area.

Green façades are the focus of this study given their low cost relative to green walls, which tend to

require advanced support and irrigation systems (IMAP 2014). Because façade plants do not require

advanced hydroponic systems or vertical irrigation infrastructure they are both affordable and

resilient, requiring only moderate intervention to be successful if well-designed. Consequently, green

facades present the opportunity for relatively cost-effective, passive urban greening (Hunter-Block et

al. 2014). This potential has not been the subject of substantial research to date (Perini 2013).

8

Scope

This thesis estimates the ‘biological

suitability’ - i.e. the potential for

greening – across the 32 blocks of the

Hoddle Grid, at the heart of

Melbourne’s CBD (depicted in Figure

2). To make this estimate, this study

combines a comprehensive survey of

ten blocks of the CBD with a range of

modelled data to determine the

precise area of wall space within

these ten blocks that is biologically

suitable. Extrapolating on this figure

enables an estimate of the biological

suitability of the full Hoddle Grid.

Rationale

This thesis will consider one opportunity to increase the amount of vegetation in the CBD.

Urban vegetation – often referred to in the literature as ‘green infrastructure’ - offers a range of

benefits to cities, ranging from reduced urban heat island effects and flooding, to increased visual

appeal and psychological wellbeing (Hartig 2008). These are broadly referred to as ‘ecosystem

services’; the literature that surrounds green infrastructure and the ecosystem services it provides is

reviewed briefly in the following chapter.

Given that many green façade species are resilient, quick to grow, tolerant of heavy pruning and

require limited root space (Hunter-Block et al. 2014), this study has the potential to identify pragmatic

opportunities for cost-effective urban ecosystem service provision.

This thesis coincides with a period of growing interest in green infrastructure and its benefits.

At an international level, calls for improved integration of green infrastructure into our cities have

highlighted the central role of urban planners. Ensuring urban ecosystem services are delivered is

increasingly considered a serious objective of urban development (Secretariat of the Convention on

Biological Diversity 2012; ARUP 2014).

Local policy suggests clear recognition of the value of these services in Melbourne. This is evident in

strategies seeking to improve drainage regimes through water-sensitive urban design (the Total

Watermark: Cities as Catchment Strategy) as well as canopy cover through tree planting (The Urban

Forest Strategy) (City of Melbourne 2012b; City of Melbourne 2014). The City of Melbourne’s Open

Space Strategy includes a number of detailed plans to increase the number of open spaces in urban

renewal areas, and this is explicitly justified by the benefits that open spaces provide (City of

Melbourne 2012a).

Projects supporting the increased uptake of green walls, roofs and façades in Melbourne are in

development, as evidenced by a review of policy options for urban greening produced by the IMAP

(Inner Melbourne Action Plan) alliance of councils late in 2013, as well as their ‘Growing Green Guide’

which offers advice on how to plan, finance and construct green walls, roofs and facades (IMAP 2014).

Figure 2 - Location of the Hoddle Grid, the focus of this study (Google Earth 2014).

9

While this research focuses solely on identifying and quantifying the opportunity for greening, this

identified opportunity could in turn be used to determine the quantity and value of ecosystem

services that green façades could provide in the CBD. From a planning perspective, this research could

support projects or policies that seek to systematically improve the city’s provision of urban

vegetation, and in turn the benefits that accrue from this vegetation. The relatively small amount of

research on green façades in urban environments also justifies this research; studies of green roofs

are much more abundant, despite vertical surfaces being a greater total area in dense urban areas

(Rayner et al. 2010).

10

Literature Review

This chapter outlines the ecosystem services that are be provided by façade plants, before briefly

reviewing the risks of façade greening. The study then turns to the methodological literature to

establish a foundation for the techniques employed in this study.

Ecosystem services provided by green façades

Urban vegetation provides a number of valuable services to people who live and work in cities – from

direct, tangible services like cooling, pollution reduction and flood mitigation to more indirect benefits

like encouraging exercise, reducing stress and increasing aesthetic appeal of the urban environment

(Hartig 2008). In recent years, the term ‘ecosystem services’ has emerged to collectively refer to

these services (Farber et al. 2002; Costanza et al. 2014).

While the literature pertaining specifically to the benefits of green facades is relatively limited, Rayner

et al. (2010) outline the following benefits:

Thermal regulation of the urban environment

Attenuation of noise

Reduction of smog and particulate pollutants

Habitat provision

Improved aesthetic value

Collectively, these benefits highlight the potential for façade greening to address challenges of urban

change mitigation and adaption, as well as increasing the property values and general appeal of

Melbourne’s CBD (IMAP 2014).

The most developed area of the green façade literature concerns the potential for façade plants to

manage heat in urban environments. There is an emerging body of evidence that suggests green

facades can aid in moderating internal building temperatures, and reducing urban heat island effects,

both through transpiration and reducing solar heat gain to walls (Holm 1989; Sternberg et al. 2011;

Perini et al. 2011; Sheweka & Mohamed 2012; Hunter et al. 2014; Cameron et al. 2014). Figure 3

shows data from a study conducted by Sternberg et al. (2011), demonstrating the effects of ivy on the

surface temperature of walls in England.

Figure 3 - Effects of English Ivy (Hedera Helix) on wall surface temperature (Sternberg et al. 2011, p.295).

The figure above demonstrates the ability of façade planting to reduce thermal gains and losses on

building surfaces. This supports modelling by Kontoleon & Eumorfopoulou (2010) which suggests that

11

green facades admit less than one eighth of the solar energy that strikes them, the rest being

reflected or absorbed by the plant. This ability becomes significant when this results in reduced heat

island effects, or when façades reduce heat transfers through building facades, effectively insulating

the buildings so they require less air conditioning and heating. These cooling effects are well-

established for urban greenery in general (IMAP 2014), and the use of façade planting to keep

buildings cool is a well-established practice in some countries, such as Japan (Koyama et al. 2013).

However, researchers have pointed out that the quantification of thermal performance of green

façade systems in urban environments remains a developing field of research, with many knowledge

gaps and methodological inconsistencies. While studies suggest potential for energy savings produced

by green facades, there is insufficient evidence to be certain of how substantial or consistent these

effects may be in the urban environment (Hunter et al. 2014; Perini et al. 2011, Ip et al. 2010).

Beyond thermal benefits, studies on the ecosystem services provided specifically by green facades are

rare. Those that exist have found that green facades reduce traffic noise (Van Renterghem et al.

2013), insulate buildings against cold conditions (Bolton et al. 2014; Sternberg et al. 2011), absorb

particulate pollutants (Sternberg et al. 2011) and are considered to improve visual quality of buildings

(White & Gatersleben 2011).

No studies to date have seriously considered the potential for vertical planting to moderate

hydrological regimes; this is remarkable given that the horizontal use of plants for this purpose is a

substantial field of technical endeavour, bringing together science, engineering, software

development and urban management. The integration of natural drainage systems into urban

planning and design is referred to as Water Sensitive Urban Design (Water by Design 2014). This field

has demonstrated that integrating plants into drainage systems can offer benefits in terms of flood

mitigation as well as improved quality of stormwater runoff from cities, while increasing urban

amenity (Raja Segaran et al. 2014; van Roon 2007; City of Melbourne 2014)

In terms of the general ability of green infrastructure to reduce peak stormwater flows, much of the

empirical evidence focuses on green roofs. These studies demonstrate that rooftop soil is effective in

detaining stormwater long enough that peak flows to sewers are reduced, thereby substantially

reducing risks of serious flooding in urban environments (Wong & Jim 2014; IMAP 2014).

The City of Melbourne has identified Elizabeth Street (which floods regularly) as a ‘flagship project’ for

flood mitigation through water sensitive urban design measures (City of Melbourne 2014). This study

found that many walls in Hoddle grid include downpipes that drain large roof areas directly into

laneways or streets; there may be potential for these to drain into soil instead, effectively supporting

the growth of façade plants while slowing stormwater in the manner described above. Drainage

systems that are not visible from the street were not recorded, but there may be further potential to

retrofit these to drain into soils supporting façade plants. While this is an exciting prospect, the

literature on the hydrological performance of urban green façades is unfortunately nonexistent.

Beyond direct studies of ecosystem benefits, a richer literature exists demonstrating that encounters

with nature are important to human health. A range of studies have demonstrated that natural

environments facilitate ‘psychological restoration’ (Kaplan 1996; Hartig & Staats 2006). These studies

have produced empirical evidence that natural stimuli (or even images of nature) result in

improvements in physiological indicators of stress (e.g. heartbeat, muscle tension, skin conductivity);

stress recovery is enhanced even when the ‘natural’ features (like trees and grass) exist in an urban

setting (Ulrich et al. 1991). Attention Restoration Theory has produced evidence indicating that the

ability to direct attention following mentally exhausting activity (such as driving or studying) is

12

restored by nature, or views of nature. (Kaplan 1996; Taylor et al. 2002; Hartig 2004). With increasing

evidence linking depression and cardiovascular disease to workplace stress, these findings are

particularly significant (World Health Organisation 2009).

Ulrich (1986) found that patients with views of trees, rather than brick walls, enjoyed better recovery

from surgery, had shorter hospital stays and used smaller quantities of painkillers. Anxiety associated

with dental work was found to be lower when a large mural of a natural scene was placed in the

clinic; this was reflected both in self-ratings and heart-rate data (Ulrich 1991). Prisoners with a view to

a natural scene required less healthcare (Taylor et al. 2002).

Worker productivity improves, and stress levels decrease, when workers have a view to nature; job

satisfaction was found to be higher (Kaplan 1993). Access to natural or green space appears to be

important in the decision to exercise; the size, location and quality of open spaces all appear to be

significant (Sugiyama et al. 2013; Giles-Corti et al. 2005). This is significant when we consider that as

of 2008, an estimated 1.4 billion adults globally were overweight; of these, 500 million were obese

(World Health Organisation 2014).

Overall this review of the benefits of urban greening has revealed that these benefits are diverse, and

that the depth of scholarship in this field is quite variable; façade greening remains an uncommon

topic of study, with emergent methodologies that are not always optimal or consistent (Rayner et al.

2010; Hunter-Block et al. 2014). Nevertheless, the general range of ecosystem services arising from

urban vegetation is well-studied, with a number of literature reviews offering solid overviews of the

field (Dobbs et al. 2014; Dobbs et al. 2011; Wang et al. 2014; Gómez-Baggethun & Barton 2013). This

review now considers the risks that are inherent to growing plants directly on walls.

Risks in applying façade species to buildings

Very few plants that attach themselves to buildings are destructive, despite this being a widely-held

perception. English Ivy (Hedera Helix) is generally benign, but has the potential to drive its roots

through gaps in deteriorating brickwork. Light, deciduous species like Boston Ivy (Parthenocissus

Tricuspidata) do not appear to pose this risk. Sound masonry is not damaged by any common ivy

species, even Hedera Helix (Royal Horticultural Society 2014).

In fact, by shading walls and blocking rainfall, ivy reduces damage to walls from normal weathering

processes:

“We now have strong evidence that ivy reduces the threats of freeze-thaw, heating

and cooling and wetting and drying (and salt weathering) through its regulation of the

wall surface microclimate. (…)We also have strong evidence that ivy will reduce the

impact of rain-based chemical weathering”

(English Heritage 2010, p.35-36)

Where climbing plants do damage walls, this damage is generally superficial; loss of paint on removal

of directly-attaching façade plants can be expected. Structural damage may occur over timescales of

centuries, in the absence of building maintenance. Species selection can assist in minimising risks;

plants climb or twine on mesh or trellises are particularly low-risk, though appropriately durable

support structures for these plants are important (IMAP 2014).

Beyond the small literature specific to the risks and ecosystem disservices associated with green

facades, it is important to recognise that all urban green infrastructure will have some level of

associated disservice that must be managed. Natural growth of plants is not orderly; this can lead to

13

perceptions of messiness or lack of maintenance (Loder 2014). Other common disservices include

allergens, falling leaves and branches, root damage to pavements, and provision of habitat for animals

such as snakes, rodents and insects (Gómez-Baggethun & Barton 2013; Dobbs et al. 2014). Dense

vegetation can also be associated with perceptions of poor safety, especially at night (Sreetheran &

van den Bosch 2014).

Methodological Precedents

At the time of writing, no study has sought to estimate the potential for vertical greening of buildings

at the city scale. However, the use of spatial analysis to assess the suitability of land for various uses is

well established. This study is novel in its focus on façade greening, as well as its consideration of

vertical surfaces in the urban microclimate, which requires 3D analysis and a range of modelling tools.

Aside from these new dimensions, the methodology used in this study is consistent with suitability

analysis techniques that have been in use for some decades (e.g. McHarg (1969)).

While the body of literature immediately concerned with mapping and measuring potential for urban

greening is very small, a number of studies seeking different outcomes have used techniques that are

highly relevant to the task at hand. This section describes three areas of research that are relevant to

this paper:

Studies employing Land Suitability Analysis and GIS

Urban microclimatic modelling in 3D

Studies that seek to quantify opportunities for urban greening.

Land Suitability Analysis

Land suitability analysis has been applied to a wide range of spatial research tasks; from finding

habitat for wolves in Switzerland (Glenz et al. 2001) to identifying optimal development locations in

Beijing (Liu et al. 2014) to explaining the distribution of hot-tub cabins in Applachian Ohio (Van Berkel

et al. 2014).

Despite the very divergent range of applications of this methodology, the spatial application of

qualitative and quantitative decision criteria is a common theme in these studies. Generally a range of

pertinent factors to the suitability analysis will be identified, scored and mapped; often a hybrid

indicator will be used that effectively represents the sum of all the factors considered in the suitability

analysis. This can then be used to determine the relative merit of various locations or land parcels

within the study area. In this respect, suitability analysis can be considered a spatial application of

multicriteria decision analysis (MCDA); just like an MCDA, a spatial suitability analysis can include

variable weightings for some criteria to reflect higher importance or user preferences (Curran et al.

2014).

The potential for green façade retrofits to existing buildings has not been studied in Melbourne;

indeed, this is a an area that has had very little investigation globally (Perini 2013). However, the

literature does offer a few examples of suitability analysis for other types of urban greening.

In Prescott Valley, Arizona, Miller et al. (1998) employed GIS-based analysis as a core element of a

‘greenway development plan’, which identified linear corridors of land that could be vegetated to

support recreational and environmental values. While the fields of GIS, modelling and remote sensing

have developed substantially since 1998, this study transparently outlines the steps in suitability

analysis which remain central to modern studies.

14

The study assembled spatial data for a number of biophysical and socioeconomic criteria within the

115km2 study area, then employed a panel of experts to determine appropriate weightings to the

data to ensure the analysis reflected each dataset’s impact on the specific desired outcomes of the

process; these were wildlife habitat, riparian function and recreation. Community input was also

sought on some weightings. Once data collection was finalised and weightings were established, GIS

was used to combine the many layers of spatial data in this study. This produced a map which showed

the optimal locations for prospective greenways in Prescott for each of the desired functions; the

combination of these results produced a final ‘multi-objective greenway suitability map’ that

accounted for all key considerations (Miller et al. 1998).

Figure 4 below shows the output map for wildlife habitat; figure 5 shows the final multi-objective

greenway suitability map that the project produced.

Figure 4 - Land Suitability Analysis for wildlife (Miller et al. 1998, p101).

15

Figure 5 - Hybrid Land Suitability Analysis (Miller et al. 1998, p104).

Modelling the urban microclimate

More recent studies have demonstrated the potential for computer models and remote sensing

techniques as powerful analytical tools in the urban environment. In a study of a public square in

Chania, Greece, Maragkogiannis et al. (2013) used both aerial photographs and terrestrial laser

scanners to create a detailed digital 3D model of the square and its urban context. Software now

exists that simulates wind-flow in 3D environments; this is referred to as Computational Fluid

Dynamics (CFD) software.

By modelling typical local wind flows around the 3D model, the authors were able to determine the

likely levels of thermal comfort enjoyed by users of this public space. Figure 6 shows an example of

the CFD simulation employed by the authors.

16

Figure 6 - Sample of operating CFD model (Marakogiannis et al. 2014, p.5).

Solar analysis was also used to determine heat gains within the various materials of the square. As

the authors point out, this kind of modelling is valuable both in terms of understanding current urban

microclimates and designing systems to mitigate problematic microclimatic issues (such as the Urban

Heat Island Effect)(Maragkogiannis et al. 2013).

Quantifying urban greening potential

In a recent study, Wilkinson et al. (2014) analysed rooftops within the Melbourne CBD to determine

their potential for green roof retrofits. The results of this analysis were used as the basis for flood

modelling, to consider the effectiveness of rooftop greening as a flood mitigation strategy. The

potential for green roofs to reduce localised flooding effects by retaining water is well-established

(Claus & Rousseau 2012). By applying a set of decision criteria, Wilkinson et al. (2014) were able to

identify the total roof area with potential for greening in the CBD, and then model the flood

mitigation effects that such a roof area might offer. This study found that around 15% of buildings in

the CBD had potential for this kind of retrofitting, but these buildings tended to be too far from areas

of localised flooding to have a major impact on inundation levels.

Beyond studies that directly identify opportunities for greening, a number of frameworks have

emerged to conceptualise and measure the benefits that plants offer to urban areas.

Ong (2003) developed the Green Plot Ratio (GPR) as a normalised means of quantifying the amount of

vegetation within an area. This is a tool that has been applied to urban planning in Singapore,

particularly in assessing the merits of large residential developments.

The GPR effectively compares the size of a property parcel to the total leaf area of all plants on that

site (which is known as the Leaf Area Index, or LAI). LAI is a common biological parameter which is

useful because it is more efficient than land area in representing the likely level of ecological

processes (such as transpiration or photosynthesis) that are happening at a given location. For

example, two landscaped sites of 100m2 each may have very different total leaf area, because one is

simply covered in grass while the other is densely planted with mature trees. Thus, we can expect that

17

the densely vegetated plot will conduct more photosynthesis and transpiration because it has a larger

leaf area (Ong 2003).

The LAI neatly encapsulates this idea by recognising that the LAI of the grassed site is 1 while the

vegetated site may be 4 (i.e. the total leaf area of plants on the site is four times the size of the site).

Since photosynthesis and transpiration are key processes for the production of oxygen and removal of

latent heat, it is important that the potential of these processes is measured in a normalised way that

recognises the differences between different kinds of vegetation.

The GPR applies this idea to urban spaces, and has been used as a mechanism of assessing residential

designs. For example, a development with 75% site coverage and a lawn area of 25% effectively has a

GPR of 1:4. However, if that same lawn area was densely vegetated, the total GPR of the site may be

1:1 (because the leaf area of plants on the site is equal to the site area, even though the plants only

occupy a quarter of the site) (Ong 2003).

This concept is illustrated by figure 7.

Figure 7 - Different types of vegetation produce differing LAI and GPRs (Ong 2003, p.206).

The GPR is an interesting concept when considering the potential for vertical and rooftop greening to

add leaf area to buildings with very high site coverage. The GPR’s ability to act as a more consistent

proxy indicator of ecological processes such as photosynthesis is important, when considering the

literature on ecosystem services, discussed above. Attempts to quantify ecosystem services in urban

environments often primarily use trees (e.g. Dobbs et al. 2011), effectively excluding other types of

urban vegetation. Concepts of LAI and GPR are therefore important to this study, because they offer a

means of measuring vegetation of all types, including green facades.

What makes a wall ‘biologically suitable’?

Literature describing the key factors that determine the success or failure of green facades in urban

environments is very sparse. Informal discussions with a number of urban horticulture researchers at

the University of Melbourne’s Green Infrastructure Research Group have suggested that these

specific parameters are important, but remain unknown.

However, a study by Rayner et al. (2010) in Melbourne focused on the performance of façade plants

on the CH2 building, and yielded a number of insights that are of relevance to this study.

18

CH2’s northern face was planted with 164 façade plants, from five species, in 2006. In 2008, Rayner et

al. (2010) returned to study the success of these plants, and found that more than half of the plants

had died, or failed to cover even a small area of their trellis backing. The reasons for this high rate of

failure are instructive to this thesis.

Failures suggested plants were stressed by a combination of low light, inadequate maintenance, wind

burn and irrigation failure; the variance in these impacts between the species used is of particular

instructive value (for example, this study shows that Jasmine had very poor tolerance of low light,

despite its ability to handle these conditions outside highly urbanized environments).

While this experience does not yield specific guidance on the tolerances of façade plants, it does

indicate that façade plants on walls with good access to water and light but limited exposure to the

wind are more likely to be successful. This insight is corroborated by the Growing Green Guide (IMAP

2013), which suggests that while there are no ‘hard and fast rules’ about the climatic tolerances of

plants in urban environments, an understanding of environmental gradients (i.e. locations with more

or less wind, sun and rainfall) is sufficient to make design decisions.

The Growing Green Guide also offers a number of practical guidelines for site analysis, which include

characteristics of particular walls that must be considered in determining their suitability for façade

greening. These are presented in figure 8.

Figure 8 - Criteria for site analysis (IMAP 2014, p.32).

A number of these practical considerations have informed the methodology employed in this paper.

Walls with greening potential in the CBD are often in close proximity to pathways or other services

(e.g. bins) and may include fire exits, firefighting equipment or water and electricity meters. Many

19

walls also have windows. These are all factors that can reduce available space for planting, and

increase requirements for support structures, as well as ongoing maintenance costs.

Perini (2013) describes a green building retrofit in Italy, where a number of these factors are fed into

a customised ‘decision tree’ to determine which kinds of treatments are appropriate for each wall –

see figure 9.

Figure 9 – Decision tree for greening a building, incorporating physical and microclimatic factors (Perini 2013, p.272)

Perini’s decision framework it is not appropriate to the scale or scope of this study because it focuses

on the complete greening of every surface of a single building, on the side of a forested hill. However,

its approach demonstrates how systematic decisions about greening can be made once a set of

constraints is identified.

The following chapter outlines how this study established a series of rules, derived from the literature

reviewed above, to interpret a series of datasets (both gathered and modelled) to determine which of

the CBD’s walls are most suited to façade greening.

20

Methodology

The methodology employed in this paper is effectively a multicriteria suitability analysis (exemplified

by Miller et al. (1998)) that integrates 3D microclimatic modelling of sunshine and wind velocity

(exemplified by Maragkogiannis et al. (2013)) to discern optimal locations for greening treatments in

Melbourne’s CBD (exemplified by Wilkinson (2014)) so that the GPR of sites in the CBD can be

increased (Ong 2003), with corresponding ecosystem service benefits (Dobbs et al. 2011).

This analysis will enable the rigorous identification of walls that are not only large, blank and easy to

maintain, but also have sufficient light and access to soil, and are not located in areas subject to high

winds. These criteria draw on the Growing Green Guide (IMAP 2013), as well as reflecting the insights

of Rayner et al. (2010) in their critical analysis of the façade plants on the CH2 building. These are

discussed in greater detail in the previous chapter.

This chapter describes the three components of the methodology, in terms of why they were selected

and how each was carried out. The three key areas of research were as follows:

Mapping of physical characteristics of each wall

Modelling of solar access to each wall

Modelling of windflows around each wall

This chapter concludes with a description of how these components were integrated into a single

index of biological suitability.

Physical characteristics of walls in Melbourne

This component of the methodology involved a direct survey of every wall in ten of the 32 blocks of

Melbourne’s CBD. This involved preparing a map of every wall in the city, using a GIS layer which

recorded the footprint of each building, and assigned that wall a code.

This enabled me to record the characteristics of each wall against its corresponding code during a

foot survey. Early methodological testing revealed that mapping all characteristics of all walls in the

CBD is impractical, as only 15% had any potential for façade greening, meaning that large amounts of

data would be collected for walls with no retrofit potential.

21

Therefore, data is only recorded for walls that have some potential for façade greening; walls that are

completely unfeasible are eliminated at the point of data collection, and no further information is

gathered on their properties. Figure 10 demonstrates how this simplifies the process.

The following factors triggered immediate elimination of a wall:

Glazed facades (any wall where windows form more than 50% of the wall)

Architectural facades

Walls with no access to the ground (e.g. due to an overhanging balcony or adjoining building)

Heritage facades (sides of buildings are not subject to this trigger)

Art (excluding ‘tagging’ but including street art)

Once a wall was observed that did not have any of these ‘dealbreaker’ characteristics, the

characteristics in table 1 were checked and noted:

Figure 10 - Approach to data collection and analysis.

22

Table 1. Survey criteria employed to determine physical characteristics of walls.

Question Rationale

1. Does the wall have soil at its base? Planter boxes require additional investment and space.

2. Is the wall next to a narrow walkway or driveway?

This will determine maintenance requirements and may require more sophisticated planter design

3. Does the wall have any windows? (walls with less than 50% glazing are recorded)

This determines maintenance requirements. Windows also reduce the area with potential to be greened.

4. Does the wall have a drainage pipe at its base?

Walls with a drainage pipe nearby can be passively watered by rainfall more effectively

5. Is this an area where waste bins are stored?

Greening may require relocation of bins or designs to avoid conflicts with bins or garbage trucks

6. Is there a fire exit on this wall? Fire exits cannot become overgrown; these walls will require additional maintenance and/or design for non-attaching creepers.

7. Is the wall used for any other services (eg. firefighting equipment, electricity meters)

Services cannot become overgrown; these walls will require additional maintenance and/or design for non-attaching creepers.

Survey criteria were selected after reviewing the Growing Green Guide’s guidelines for site analysis,

outlined in figure 9. I confirmed the adequacy of this framework by participating in workshops with

the City of Melbourne’s Urban Landscape team, where a number of specialists in urban horticulture

discussed criteria that should be considered when greening laneways. I also undertook

methodological testing to ensure that there were no wall characteristics outside the literature that

may be significant.

However, one criterion that could not be assessed as part of the foot survey was weight loading.

Assessing the capacity of each wall to support the weight of façade plants was not possible, as this

requires the services of a structural engineer. This was placed outside the scope of this study,

recognising that most buildings in the CBD are large and robust, but that there is potential that

structural integrity could be a concern for a portion of the walls considered, and appropriately light

greening responses may need to be adopted.

On completion of surveys, the data was cleaned and manually entered into a spreadsheet, then linked

to a digital map in ESRI’s ArcMap. Each of the seven surveyed characteristics produced a map that

could be used in the suitability analysis. Figure 11 shows an example of a map for one of the

characteristics surveyed.

23

Figure 11 - Raw data gathered at the block between Exhibition, Lonsdale, Russell and La Trobe Streets

24

Modelling wind flows

Modelling of wind in urban environments is a critical element of this study, as wind stress is a key

limiting factors for urban plants. Wind can be physically damaging to plants, but it also has a

dehydrating effect on leaves (Hunter-Block et al. 2014). This means that plants in windy locations will

require different irrigation arrangements and some species may not be viable (IMAP 2013).

Wind in urban environments shows complex behaviour; simply checking the aspect of a wall does not

fully assess its exposure to prevailing winds, as buildings have a strong role in creating localised wind

patterns by either blocking winds or channeling them. Altitude is also a significant variable in

considering urban winds; taller buildings are often exposed to very powerful winds, with gusts

regularly exceeding 100km/h (Hunter-Block et al. 2014).

To account for these localised idiosyncracies, modelling software must be used. Computerised

modelling of wind is common in the fields of architecture and engineering, and a range of software

exists for this purpose. This study used Autodesk’s ‘Vasari’, which includes a virtual wind tunnel

(Autodesk 2014)

Modelling tested a topographically-correct 3D model of the city in Vasari’s wind tunnel. Vasari was

calibrated to test wind patterns resulting from the three most typical wind directions and speeds

through the year, using standard Bureau of Meteorology data. In each instance a wind speed of

10m/s was used, as this was a typical speed for the three wind directions considered. Figure 12 shows

the operation of the virtual wind tunnel.

Figure 12 – Wind model in operation. Image prepared using Autodesk Vasari.

At the time of writing, Vasari did not have capacity to export directly to GIS software packages;

indeed, no CFD software appears to be capable of this task. However, by capturing and

georeferencing images of the model’s results for each of the three wind tests, it was possible to

import the modelled data with relatively high accuracy.

Analysis of the imported model data followed a series of steps. Spectral analysis enabled the software

to convert each shade of the colour-coded model output into a category which represented a varying

25

intensity of wind speed; categorise were assigned a score of 0-10 depending on wind speed. As a

result of this analysis, scores for local wind exposure were known for every location in the Hoddle

Grid, for three different prevailing wind directions.

Modelling patterns of shade

Access to light is another critical limiting factor for plants in urban environments. Tall building result in

deep shade that is challenging even for plants that are typically shade-tolerant. There are almost no

studies that specifically consider the performance of façade species in urban canyons (Hunter-Block et

al. 2014). However, it is possible to use modelling to examine gradients of light and shadow in urban

environments, and score locations on their relative access to sunshine. This study scores walls

positively for access to light, both because it is important to the success of plants, and because

buildings with substantial exposure to the sun will enjoy the greatest cooling benefits when shaded by

foliage (Kontoleon & Eumorfopoulou 2010).

This study considers the average level of shade experienced in the CBD by calculating the location of

shadows at 9am 12pm and 3pm on September 22, the Spring Equinox. The equinox is used because it

represents the perfect average of shadows throughout the year, since this is the day where both night

and day-time are of equal length. Shadow calculations in this precise configuration are commonly

used in assessing overshadowing impacts in new developments (Department of Transport Planning

and Local Infrastructure 2014)

To determine the fall of shadows within the CBD, a three-dimensional model of the city was imported

into ESRI’s ArcScene, a software package that enables 3D GIS analysis. By using the ‘Sun Shadow

Volume’ tool in this program, a three-dimensional ‘volume’ for shadows at 9am 12pm and 3pm were

produced; an example of shadow volumes are shown in figure 13.

26

Figure 13 - Example of shadow analysis conducted using ESRI ArcScene. Yellow shapes respresent morning shadows (9am); blue shapes represent afternoon shadows (3pm) on the spring equinox.

By intersecting these shadow volumes with the walls identified in the foot survey, it became possible

to know whether each wall was in full shade, partial sun or full sun at each of the studied times. This

in turn could be converted to a score; shade received a score of zero, partial sun received a score of 1,

and full sun received a score of 2. Because three time periods were studied, this effectively gave each

wall a score of 0-6, with 0 representing no light at any part of the day, and 6 representing full sun

throughout the day. The use of a simple score that can be mapped enabled synthesis with other

datasets developed by this study.

Synthesis

Following direct data collection, the walls identified in each of the ten city blocks served as the basis

for subsequent data analysis. GIS enables the overlay of many different layers of data; ultimately, this

Figure 14 - Overlay process to combine multiple data types.

27

study collated the full range of modelled and collected data into a single GIS map, with layers

corresponding to each of the criteria considered by the study. Figure 14 demonstrates the essential

steps of this overlay process.

Firstly, scoring physical suitability involved developing an equation to reward walls for positive

physical characteristics, and penalise them for negative characteristics. The equation is as follows:

𝑥 = 5 − (𝑠𝑢𝑚 𝑜𝑓 𝑛𝑒𝑔𝑎𝑡𝑖𝑣𝑒 𝑐ℎ𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑖𝑠𝑡𝑖𝑐𝑠) + (𝑠𝑢𝑚 𝑜𝑓 𝑝𝑜𝑠𝑖𝑡𝑖𝑣𝑒 𝑐ℎ𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑖𝑠𝑡𝑖𝑐𝑠)

This equation assigns a score of 1 for each of the seven characteristics surveyed (refer to figure 14

above). The two positive characteristics were access to soil, and the presence of a nearby downpipe.

All other characteristics were considered negative. This equation is designed so that the minimum

score a wall can receive is zero (if it has all five negative characteristics and no positive characteristics)

and the maximum is 7. By applying this equation, the map in figure 15 was produced.

Figure 15 - Scores for walls surveyed at the northwest corner of the Hoddle Grid. This index is simple, awarding points for soil and drainage infrastructure, and removing points for windows, fire exits, services or narrow walkways.

As the methodology progressed, modelled data was added to the map in figure 15. The three wind

intensity maps were combined; each map scored wind intensity on a scale of zero to ten, resulting in

a combined wind score of zero to thirty for each wall. The solar map, as discussed above, effectively

assigned a solar score of zero to six to each wall.

Each of these maps and datasets is useful in its own right, particularly for selection of plants and

planting design for individual greening projects. However, this study seeks to produce a final map that

incorporates all data to show the relative suitability of all walls in the study area. Therefore it is

necessary to develop an index capable of being influenced by all scores.

28

To combine the scores results for wind, solar and physical properties of each wall, simple addition

would not work, as this would result in a score which would be strongly influenced by wind.

Therefore, each score was normalised down to a score out of three. To do this, the following equation

was applied:

𝑥 = (𝑝ℎ𝑦𝑠𝑖𝑐𝑎𝑙 𝑠𝑐𝑜𝑟𝑒 ∗

67

2) − (

𝑤𝑖𝑛𝑑 𝑠𝑐𝑜𝑟𝑒

10) + (

𝑠𝑜𝑙𝑎𝑟 𝑠𝑐𝑜𝑟𝑒

2)

After applying a rounding function, each wall received a final score that ranged between zero (least

suitable) and nine (most suitable).

The following chapter reports the results of mapping this index, as well as exploring the outputs of

each component of the analysis.

Results

This study found that there are likely to be almost two hectares of wall space in the CBD which have

optimal characteristics for green façade treatments. A further seven hectares is likely to be feasible

with more careful design and species selection. In total, this suggests that a vertical area larger than

Melbourne’s Flagstaff Gardens has potential for greening in Melbourne’s CBD.

These estimates are the product of extrapolation, and a combined index which accounts for both

microclimatic and physical factors. This chapter details the results of each of these component

analyses, then describes the process by which these results have been extrapolated to produce the

estimates described above.

Physical scores

Of the total number of walls surveyed, 330 individual walls (9%) with a total length of 7314m showed

potential for façade greening. Within this sample, the distribution of scores for physical properties

shown in figure 16 was observed.

Figure 16 – Results of physical scoring process for observed walls.

This distribution suggests that a large area of wall space in the CBD is relatively lacking in physical

constraints; most walls had one or two constraints. This distribution underlines the need for planting

designs that can address these individual site-specific issues. For example, planters with a narrow

29

profile could facilitate greening of tight spaces and thoroughfares, and support structures could be

designed to minimise the need for maintenance to keep windows and fire exits clear.

The most common problems with walls in

the studied blocks included:

A lack of direct access to soil

Limited space for planting

Windows that could be obscured

by façade growth

The full range of physical characteristics

are outlined in figure 17.

These results also suggest a significant

potential to cheaply leverage existing

rooftop drainage systems using existing

downpipes. Given that Rayner et al. (2010) found that irrigation failure was a common reason for

façade plant death, this is an important positive characteristic for walls.

Wind Modelling

Analysis of wind results, shown in figure 18 reveals that very few walls are sheltered from wind from

all directions, and much of the area surveyed is exposed to relatively high-velocity wind in most

conditions.

Figure 18 - Wind exposure was generally high for observed walls.

0

100

200

300

400

500

600

700

800

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Distribution of Wind Scores (m)

Figure 17 - Surveyed walls showed a wide range of physical characteristics.

30

Indeed, figure 19 shows that only 5% of the studied

wall area is relatively sheltered. This has substantial

implications for species selection and façade design,

and suggests that almost all scored walls will

experience a penalty of 2-3 points out of a possible

three for wind exposure in the calculation of the

suitability index. Only 392 metres of the surveyed

walls escape this penalty.

Figure 19 - Percentage distribution of wind exposure.

31

The maps in Figure 20

demonstrate the variable

exposure that walls in

Melbourne face through

the year; northerly winds

(180 degrees) appear to

be the most effective in

penetrating the CBD’s

structure. Again, this kind

of mapping is useful in

design at the site scale,

as it enables prediction of

the wind angles that will

most threaten façade

plants at individual sites.

This can then be

responded to through

selection of appropriate

supporting structures and

species.

Figure 20 - Model outputs for wind exposure, after georeferencing and spectral analysis in ArcMap. A score of 9 represents the greatest wind exposure.

32

Solar Modelling

Figure 21 demonstrates that on the equinox, the majority of the walls surveyed receive little or no

sunlight. By far the largest score category is zero – this indicates that over 3000m of the selected walls

are in constant shadow for at least half of the year.

Figure 21 - Solar scores tended to be low for surveyed walls.

Many of these walls are in laneways, or at the bases of large south-facing buildings. If façade greening

seeks to reduce thermal gains, this analysis effectively shows the walls that will benefit most from the

thermal protection that façade greening offers. The distribution of these walls also proved to be

unpredictable; large north-facing walls often were not the locations with the highest solar scores, due

to overshadowing effects from adjacent buildings – as demonstrated in figure 22.

Figure 22 - Spatial distribution of solar scores in the city has little relation to building aspect.

33

With solar and wind modelling successfully completed and mapped, it becomes possible to combine

all data in a single GIS layer, and make final estimates of the biological suitability of walls in the CBD.

Synthesis

Applying the scoring equation (described in the previous chapter) produces a relatively simple map

that clearly indicates the locations best suited for façade greening. The directly-surveyed blocks show

very heterogeneous results after the combined score, with the combined effect of variable shading

and wind exposure meaning that many individual walls have segments with quite different scores.

This presents both benefits and challenges; walls with low scores along some sections will not always

be biologically unsuitable, because there are other sections that enable access to light and shelter

from wind. On the other hand, the heterogeneity of scores even within walls makes it more difficult

to be certain that a high score necessarily represents a contiguous greening opportunity.

Figure 23 - Spatial distribution of hybrid score. A score above 6 was considered to be ideal.

Figure 24 demonstrates the final distribution of scores. Challenging microclimatic conditions across

much of the city helped drive the distribution downwards, and out of a total of nine points, very few

walls scored more than six points.

34

Figure 24 - Hybrid scores were generally average or poor, with just over one in ten walls scoring well.

Extrapolation

The results described above are measured in metres of wall – but the focus of this thesis primarily

area, not length. Therefore, it is necessary to assume a level of vertical growth on each wall. Common

façade plant species are capable of growing as high as 20-25m (Hunter-Block et al. 2014). However,

this study assumes a height of 7 metres, recognising that a number of the surveyed walls were

approximately two storeys tall, and this represents a reasonable height that a plant could cover in a

few seasons.

This study considered ten blocks in Melbourne’s CBD; the full Hoddle Grid consists of 32 blocks. This

requires the results to be extrapolated to estimate the area with potential for greening. While

thorough statistical analysis is outside of the scope of this analysis, a basic upscaling of the observed

ten blocks is possible, simply requiring the study results to be multiplied by 3.2. This upscaling, along

with a universal assumed wall height of 7m, produces the results presented in figure 25.

Figure 25 - The final result of this thesis: an estimate of the area of wall space in the Hoddle Grid with potential for facade greening, ranked by suitability.

Unsuitable91.9ha

Good(6+), 1.9ha

Average(4-5), 7.0ha

Poor (0-4), 7.5ha

Potential16.4ha

35

While simple, this figure represents the final synthesis of this research; it is an estimate of vertical

greening potential for the CBD, suggesting substantial areas are suitable for this kind of treatment.

36

Discussion

This study has identified a substantial area of vertical space in Melbourne’s CBD with potential for

greening.

Discovery of an area of potential vertical green space this large is valuable. The City of Melbourne has

a clear intention to green up the city, but is currently struggling to afford new land for parks and open

spaces; the city’s current fund for open spaces is currently at $11 million, enough to purchase just

550m2 of space in the CBD (The Age 2014). For ease of comparison, figure x demonstrates a 550m2

parcel in relation to Flagstaff Gardens.

Figure 26 - Even with a budget of $11000000, the open space fund would barely buy an area the size of a netball court in Melbourne's CBD.

This thesis has estimated that the Hoddle Grid has 18, 754m2 of wall space that is highly suited for

greening with façade plants. A further 70,316m2 of wall space that received ‘average’ suitability

scores may also present opportunities. In this respect, vertical greening appears to offer a means to

green up the city while bypassing the fierce competition of the Melbourne property market.

Green walls do not offer the same recreational benefits as parks; as one council officer remarked,

‘one cannot walk a dog on a green wall’. However, vertical greening can aid in the provision of many

ecosystem services in the city. These are outlined in some detail in chapter two; they range from

mitigation of heatwaves to aesthetic and health benefits. These benefits have potential to support a

number of the city’s key policy initiatives that apply to the city, including the Open Space Strategy, the

Urban Forest Strategy and the Total Watermark Strategy.

In addition to supporting council’s vision of a greener city, the results of this study could feed into

existing scholarship in the field of urban ecology. For example, the Green Plot Ratio (Ong 2003) could

be adapted to include vertical greening, and used as a means of assessing development proposals, as

has been the case in Singapore. Alternately, the area identified by this study could be the subject of

calculations to quantify ecosystem service provision, in the style of Dobbs (2011). Valuing these

37

quantified urban ecosystem services in financial terms would in turn become possible, enabling cost-

benefit analysis of large urban greening initiatives.

Beyond the positive finding that the city does have substantial potential for vertical greening, it is also

important to reflect on the finding that microclimatic factors are often unfavourable to plants in the

CBD. This not only underlines the need to be selective in façade greening initiatives, but also to

preferentially select plants that tolerate high winds, high evaporative demands (related to high winds)

and deep shade. While this is a challenge, it is also an opportunity; this thesis assigned low suitability

rankings to over 7.5ha of wall space, which could also potentially be greened if suitable species and

planting designs can be implemented (albeit with higher risks, costs and maintenance requirements).

The finding that a large number of walls with potential for greening may include windows, fire exits

and other services is also significant; species selection will be important in responding to these

constraints. In many cases, twining façade species, which can be trained along carefully-placed mesh

or cabling may be preferable to aggressive self-attaching creepers like English Ivy (Hedera Helix).

Limitations

While the findings of this study are potentially significant, they are also limited by a number of factors.

Access to data was a critical issue; the City of Melbourne’s head GIS administrator was unable or

unwilling to furnish me with the spatial data that I required to carry out this study, having failed to

respond to a number of requests both from myself and his colleagues. After much searching, I was

able to source building footprint and height data from 2002 through a helpful academic contact; this

required substantial cleaning and modification to be useable, and may retain some errors and

anachronisms.

As discussed above, the methodology of this paper could not incorporate structural assessment of

walls. While my surveys left me with the impression that much of the CBD’s building stock is large and

thoroughly engineered, my inability to assess structural integrity means that my recommended

locations for greening may be compromised by structural issues in some cases. This means that this

study’s estimates of potential greening may be exaggerated. Similarly, discussions with City of

Melbourne staff have suggested that in some instances underground cabling may be a barrier to in-

soil planting; this was not accounted for in this study.

A lack of scholarly literature describing the behaviours and tolerances made it impossible to discern

any clear point at which a wall becomes ‘biologically suitable’. While this would vary between species,

any information about the tolerances of even one common façade plant in terms of minimum

daylight, or maximum wind speeds, would have helped as a benchmark for development of

quantitative indices. Fortunately the Growing Green Guide (IMAP 2013) explicitly recognises this as an

issue, and suggests a gradient-based approach (as adopted in this report). However, the hybrid index

adopted is relatively lacking in refinement; all criteria are weighted equally, whereas some may in fact

be more important than others. Of course these weightings would again vary from plant to plant, and

a truly sophisticated set of quantitative indices for biological suitability would require very extensive

research and development.

Finally, it must be acknowledged that the potential for greening is not the same as the intention to

green. The hectares of wall space identified by this study are held by a great diversity of individuals,

with what is likely to be a range of attitudes to urban greening, often coloured by exaggerated fears of

building damage from ivy (as identified by English Heritage (2010)). Therefore, it must be recognised

that this potential for greening would be very difficult to realise without a raft of incentives, support

and landholder engagement.

38

Further research

This study raises a number of questions that could be answered by further research.

As discussed above, research that specifies the tolerances of urban vegetation would be particularly

valuable. This appears to be a very substantial gap in the literature.

There may also be scope to use the results of this study to consider possibilities for greening that go

beyond façade planting. Green facades are the explicit focus of the study, as façade plants have

potential to be relatively passive. Intensive green walls (in the style demonstrated in figure 27) are

substantially more expensive and sensitive than green facades, but further analysis of the data

presented by this study could identify locations where this kind of greening may be most suitable.

Even at an estimated $900-1200 per square metre, this kind of wall treatment is relatively cheap

compared to the price of land in the CBD, which currently is in the region of $20,000 per square

metre (The Age 2014; Greenwall Australia 2014).

Figure 27 - Green Wall on the Musée du quai Branly, Paris (Blanc 2005).

This research revealed the current limits of 3D GIS software for urban modelling applications. While

improvised modelling techniques proved effective in this study, a more sophisticated means of

integrating 3D wind and solar microclimatic data into a virtual city could produce more accurate

results. The technique this study employed to derive my 3D city was also relatively basic; simply

extruding building footprints to their maximum heights results in an approximation of building

dimensions rather than a precise representation. The use of laser scanning (demonstrated by ) or

LIDAR to more accurately represent the urban environment would also offer the chance to replace

some or all elements of the foot survey, for example by automatically detecting which walls had

39

windows. Thermal images taken during a heatwave, combined with this 3D data, could provide a 3D

representation of the city could add an additional dimension to the analysis, by determining which

walls are most susceptible to radiative heat gain and which locations are most in need of cooling.

This study revealed that a number of buildings have drainage infrastructure that could passively water

façade plants. Of course, this is not the only source of water in the urban environment – large

amounts of water are used in buildings. Further research could determine the potential for greywater

to provide a relatively consistent water supply to façade plants.

Research by Ong et al. (2013) suggests that landholders in the CBD are not entirely averse to building

greening, but also that Council may need to incentivise and or legislate to promote this behaviour to

produce useful results. Research to quantify the distribution of attitudes towards façade greening

within the landowner community of the CBD could be highly useful to this field, particularly if it could

reflect willingness-to-green under different policy configurations. With a suitably large sample, an

index of landowner acceptance could be developed. This would enable estimated potentials for urban

greening (as produced by this study) to be moderated, to reflect realistic likelihoods of landowners

acting to green their buildings.

40

Conclusion

This paper has identified a substantial potential for vertical greening in Melbourne’s CBD, with a

conservative estimate of just under 2ha of vertical space in the CBD likely to be well-suited to façade

greening treatments. A further 7ha is likely to have potential for greening with more careful species

selection and planting design. An even larger area is likely to be difficult to green, but with further

horticultural research and disciplined applications of site-specific design, even this area may yield

some opportunities.

The method applied in this study is both innovative and traditional; the use of land suitability analysis

is well-established, but the integration of modelled data and the focus on vertical space is novel. The

resulting research findings therefore represent a unique addition to the literature. While basic and

somewhat improvised, the ability of this method to support urban greening projects in three

dimensions shows potential both for expanded application and methodological refinement.

This thesis has also highlights the need for further research into the tolerances of plants in urban

environments, as well as designs for planting that respond to the specific challenges and

opportunities of of the urban environment – including strong winds, deep shade, narrow

thoroughfares and downpipes with potential to irrigate plantings. Development of these solutions is

important to minimise requirements for maintenance and irrigation of vertical greening treatments,

as well as reducing risks, maintenance costs and plant failures.

This thesis was inspired by the common aphorism ‘what gets measured, gets done’; it is hoped that by

quantifying an opportunity, this research might help contribute towards its realisation, perhaps

through eventual integration with the City of Melbourne’s existing and planned urban greening

strategies and projects.

41

References

ARUP, 2014. Cities Alive, Available at: http://www.arup.com/homepage_cities_alive.aspx.

Autodesk, 2014. Vasari Beta. Available at: http://autodeskvasari.com/ [Accessed October 31, 2014].

Van Berkel, D.B., Munroe, D.K. & Gallemore, C., 2014. Spatial analysis of land suitability, hot-tub cabins and forest tourism in Appalachian Ohio. Applied Geography, 54, pp.139–148. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0143622814001684 [Accessed October 7, 2014].

Blanc, 2005. Quai Branly Museum | Vertical Garden Patrick Blanc. Available at: http://www.verticalgardenpatrickblanc.com/realisations/paris/quai-branly-museum [Accessed October 31, 2014].

Bolton, C. et al., 2014. Effectiveness of an ivy covering at insulating a building against the cold in Manchester, U.K: A preliminary investigation. Building and Environment, 80, pp.32–35. Available at: http://linkinghub.elsevier.com/retrieve/pii/S036013231400170X [Accessed June 11, 2014].

Cameron, R.W.F., Taylor, J.E. & Emmett, M.R., 2014. What’s “cool” in the world of green façades? How plant choice influences the cooling properties of green walls. Building and Environment, 73, pp.198–207. Available at: http://www.sciencedirect.com/science/article/pii/S036013231300351X [Accessed March 26, 2014].

City of Melbourne, 2012a. Open Space Strategy: planning for future growth,

City of Melbourne, 2014. Total Watermark - City as a Catchment.

City of Melbourne, 2012b. Urban Forest Strategy,

Claus, K. & Rousseau, S., 2012. Public versus private incentives to invest in green roofs: A cost benefit analysis for Flanders. Urban Forestry & Urban Greening, 11(4), pp.417–425. Available at: http://linkinghub.elsevier.com/retrieve/pii/S1618866712000854 [Accessed August 28, 2014].

Costanza, R. et al., 2014. Changes in the global value of ecosystem services. Global Environmental Change, 26, pp.152–158. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0959378014000685 [Accessed May 24, 2014].

Curran, R.W., Bates, M.E. & Bell, H.M., 2014. Multi-criteria Decision Analysis Approach to Site Suitability of U.S. Department of Defense Humanitarian Assistance Projects. Procedia Engineering, 78, pp.59–63. Available at:

42

http://linkinghub.elsevier.com/retrieve/pii/S1877705814010261 [Accessed October 7, 2014].

Department of Transport Planning and Local Infrastructure, 2014. City of Melbourne Planning Scheme. Available at: http://planningschemes.dpcd.vic.gov.au/schemes/melbourne [Accessed June 5, 2014].

Dobbs, C., Escobedo, F.J. & Zipperer, W.C., 2011. A framework for developing urban forest ecosystem services and goods indicators. Landscape and Urban Planning, 99(3-4), pp.196–206. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0169204610002793 [Accessed July 14, 2014].

Dobbs, C., Kendal, D. & Nitschke, C.R., 2014. Multiple ecosystem services and disservices of the urban forest establishing their connections with landscape structure and sociodemographics. Ecological Indicators, 43, pp.44–55. Available at: http://linkinghub.elsevier.com/retrieve/pii/S1470160X14000594 [Accessed May 6, 2014].

English Heritage, 2010. Ivy on Walls,

Farber, S.C., Costanza, R. & Wilson, M.A., 2002. Economic and ecological concepts for valuing ecosystem services. , 41, pp.375–392.

Giles-Corti, B. et al., 2005. Increasing walking: how important is distance to, attractiveness, and size of public open space? American journal of preventive medicine, 28(2 Suppl 2), pp.169–76. Available at: http://www.ncbi.nlm.nih.gov/pubmed/15694525 [Accessed July 9, 2014].

Glenz, C. et al., 2001. A wolf habitat suitability prediction study in Valais ( Switzerland ). , 55.

Gómez-Baggethun, E. & Barton, D.N., 2013. Classifying and valuing ecosystem services for urban planning. Ecological Economics, 86, pp.235–245. Available at: http://linkinghub.elsevier.com/retrieve/pii/S092180091200362X [Accessed June 2, 2014].

Greenwall Australia, 2014. Green Walls. Available at: http://greenwallaustralia.com.au/greenwalls-custom/ [Accessed October 31, 2014].

Hartig, T., 2008. Green space, psychological restoration, and health inequality. Lancet, 372(9650), pp.1614–5. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18994650 [Accessed July 10, 2014].

Hartig, T., 2004. Restorative Environments. Encylopedia of Applied Psychology, 3, pp.273–279.

Hartig, T. & Staats, H., 2006. The need for psychological restoration as a determinant of environmental preferences. Journal of Environmental Psychology, 26(3), pp.215–226.

43

Available at: http://linkinghub.elsevier.com/retrieve/pii/S0272494406000521 [Accessed July 15, 2014].

Holm, D., 1989. T h e r m a l I m p r o v e m e n t b y m e a n s o f L e a f Cover o n E x t e r n a l Walls - - A S i m u l a t i o n M o d e l. , 14, pp.19–30.

Hunter-Block, A.M. et al., 2014. Quantifying the thermal performance of green façades: A critical review. Ecological Engineering, 63, pp.102–113. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0925857413005211 [Accessed January 23, 2014].

IMAP, 2014. Growing Green Guide. Available at: http://www.growinggreenguide.org/ [Accessed June 12, 2014].

Ip, K., Lam, M. & Miller, A., 2010. Shading performance of a vertical deciduous climbing plant canopy. Building and Environment, 45(1), pp.81–88. Available at: http://linkinghub.elsevier.com/retrieve/pii/S036013230900122X [Accessed June 11, 2014].

Kaplan, R., 1993. The role of nature in the context of the workplace. Landscape and Urban Planning, 26(1-4), pp.193–201. Available at: http://linkinghub.elsevier.com/retrieve/pii/0169204693900167.

Kaplan, S., 1996. THE RESTORATIVE BENEFITS OF NATURE : TOWARD AN INTEGRATIVE FRAMEWORK. , (1995), pp.169–182.

Kontoleon, K.J. & Eumorfopoulou, E. a., 2010. The effect of the orientation and proportion of a plant-covered wall layer on the thermal performance of a building zone. Building and Environment, 45(5), pp.1287–1303. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0360132309003382 [Accessed June 3, 2014].

Koyama, T. et al., 2013. Identification of key plant traits contributing to the cooling effects of green façades using freestanding walls. Building and Environment, 66, pp.96–103. Available at: http://www.sciencedirect.com/science/article/pii/S0360132313001315 [Accessed April 3, 2014].

Liu, R. et al., 2014. Land-use suitability analysis for urban development in Beijing. Journal of environmental management, 145, pp.170–9. Available at: http://www.ncbi.nlm.nih.gov/pubmed/25036557 [Accessed October 7, 2014].

Loder, A., 2014. “There”s a meadow outside my workplace’: A phenomenological exploration of aesthetics and green roofs in Chicago and Toronto. Landscape and Urban Planning, 126, pp.94–106. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0169204614000097 [Accessed September 30, 2014].

44

Maragkogiannis, K. et al., 2013. Combining terrestrial laser scanning and computational fluid dynamics for the study of the urban thermal environment. Sustainable Cities and Society. Available at: http://www.sciencedirect.com/science/article/pii/S2210670713000851 [Accessed April 3, 2014].

McHarg, I., 1969. Design With Nature, The Natural History Press.

Miller, W. et al., 1998. An approach for greenway suitability analysis. Landscape and Urban Planning, 42, pp.91–105.

Ong, B.L., 2003. Green plot ratio: an ecological measure for architecture and urban planning. Landscape and Urban Planning, 63(4), pp.197–211. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0169204602001913.

Ong, B.L. et al., 2013. Report on Urban Greenery in the Private Realm for the City of Melbourne,

Perini, K. et al., 2011. Greening the building envelope , façade greening and living wall systems. Open Journal of Ecology, 1(1), pp.1–8.

Perini, K., 2013. Retrofitting with vegetation recent building heritage applying a design tool—the case study of a school building. Frontiers of Architectural Research, 2(3), pp.267–277. Available at: http://www.sciencedirect.com/science/article/pii/S2095263513000319 [Accessed April 3, 2014].

Raja Segaran, R., Lewis, M. & Ostendorf, B., 2014. Stormwater quality improvement potential of an urbanised catchment using water sensitive retrofits into public parks. Urban Forestry & Urban Greening, 13(2), pp.315–324. Available at: http://linkinghub.elsevier.com/retrieve/pii/S161886671400003X [Accessed May 12, 2014].

Rayner, J.P., Raynor, K.J. & Williams, N.S.G., 2010. Façade Greening : a Case Study from Melbourne , Australia. , (2008), pp.709–714.

Van Renterghem, T. et al., 2013. The potential of building envelope greening to achieve quietness. Building and Environment, 61, pp.34–44. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84871782935&partnerID=tZOtx3y1 [Accessed March 20, 2014].

Van Roon, M., 2007. Water localisation and reclamation: steps towards low impact urban design and development. Journal of environmental management, 83(4), pp.437–47. Available at: http://www.ncbi.nlm.nih.gov/pubmed/16837124 [Accessed April 28, 2014].

Royal Horticultural Society, 2014. Ivy on Buildings. Available at: http://www.rhs.org.uk/advice/profile?PID=258 [Accessed June 12, 2014].

45

Secretariat of the Convention on Biological Diversity, 2012. Cities and Biodiversity Outlook,

Sheweka, S.M. & Mohamed, N.M., 2012. Green Facades as a New Sustainable Approach Towards Climate Change. Energy Procedia, 18, pp.507–520. Available at: http://linkinghub.elsevier.com/retrieve/pii/S1876610212008326 [Accessed February 28, 2014].

Sreetheran, M. & van den Bosch, C.C.K., 2014. A socio-ecological exploration of fear of crime in urban green spaces – A systematic review. Urban Forestry & Urban Greening, 13(1), pp.1–18. Available at: http://linkinghub.elsevier.com/retrieve/pii/S1618866713001350 [Accessed May 16, 2014].

Sternberg, T., Viles, H. & Cathersides, A., 2011. Evaluating the role of ivy (Hedera helix) in moderating wall surface microclimates and contributing to the bioprotection of historic buildings. Building and Environment, 46(2), pp.293–297. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0360132310002222 [Accessed May 27, 2014].

Sugiyama, T. et al., 2013. Initiating and maintaining recreational walking: a longitudinal study on the influence of neighborhood green space. Preventive medicine, 57(3), pp.178–82. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23732245 [Accessed July 10, 2014].

Taylor, A.F., Kuo, F.E. & Sullivan, W.C., 2002. Views of Nature and Self-Discipline: Evidence From Inner City Children. Journal of Environmental Psychology, 22(1-2), pp.49–63. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0272494401902415 [Accessed July 15, 2014].

The Age, 2014. Melbourne can’t afford new parks. Available at: http://www.theage.com.au/victoria/melbourne-cant-afford-new-parks-20140913-10g7fz.html [Accessed October 31, 2014].

Ulrich, R.S., 1986. Human responses to vegetation and landscapes. Landscape and Urban Planning, 13, pp.29–44. Available at: http://linkinghub.elsevier.com/retrieve/pii/0169204686900058.

Ulrich, R.S. et al., 1991. Stress recovery during exposure to natural and urban environments. Journal of Environmental Psychology, 11(3), pp.201–230. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0272494405801847.

Wang, Y. et al., 2014. Effect of ecosystem services provided by urban green infrastructure on indoor environment: A literature review. Building and Environment, 77, pp.88–100. Available at: http://linkinghub.elsevier.com/retrieve/pii/S036013231400081X [Accessed May 28, 2014].

Water by Design, 2014. What is Water Sensitive Urban Design? Available at: http://waterbydesign.com.au/whatiswsud/ [Accessed July 15, 2014].

46

White, E. V. & Gatersleben, B., 2011. Greenery on residential buildings: Does it affect preferences and perceptions of beauty? Journal of Environmental Psychology, 31(1), pp.89–98. Available at: http://linkinghub.elsevier.com/retrieve/pii/S027249441000099X [Accessed June 11, 2014].

Wong, G.K.L. & Jim, C.Y., 2014. Quantitative hydrologic performance of extensive green roof under humid-tropical rainfall regime. Ecological Engineering, 70, pp.366–378. Available at: http://linkinghub.elsevier.com/retrieve/pii/S092585741400278X [Accessed July 15, 2014].

World Health Organisation, 2014. Factsheet: Obesity and overweight. Available at: http://www.who.int/mediacentre/factsheets/fs311/en/ [Accessed July 15, 2014].

World Health Organisation, 2009. Global health risks. Available at: http://www.who.int/healthinfo/global_burden_disease/global_health_risks/en/ [Accessed September 12, 2014].