DECARBONISING THE AUSTRALIAN HOUSING STOCK FOR CLIMATE … · DECARBONISING THE AUSTRALIAN HOUSING STOCK FOR CLIMATE CHANGE JOHN J. SHIEL BE MENGSC MAPPSC PhD Candidate ... for the

AIRAH and IBPSA’s Australasian Building Simulation 2017 Conference, Melbourne, November 15-16.

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DECARBONISING THE AUSTRALIAN HOUSING STOCK FOR CLIMATE

CHANGE

JOHN J. SHIEL BE MENGSC MAPPSC PhD Candidate

University of Newcastle

Principal, EnviroSustain

PO Box 265 Jesmond, NSW 2299

[email protected]

BEHDAD MOGHTADERI PHD Professor and Head of Chemical Engineering

Director of Priority Research Centre for Frontier Energy Technologies & Utilisation

Newcastle Institute for Energy and Resources


University Drive, Callaghan, NSW 2308

[email protected]

RICHARD M. AYNSLEY PHD Principal, Building Energetics,

PO Box 219

Pomona, Qld 4568

[email protected]

ADRIAN PAGE PHD Emeritus Professor


University Drive, Callaghan, NSW 2308

[email protected]

JOHN M. CLARKE Research Team Leader, Regional Projections

CSIRO Climate Science Centre

PB1 Aspendale, Vic 3195

[email protected]

ABOUT THE AUTHORS

John J. Shiel is the Principal of EnviroSustain which conducts sustainability audits and consults on

low carbon buildings and precincts. He is a Ph.D. candidate at the University of Newcastle,

Australia and a member of iiSBE, with IT, civil, structural and foundation engineering

qualifications. John was formerly a Civil Engineer designing power station structures, and IT

Consultant with a transnational.

Professor Behdad Moghtaderi is the Head of Chemical Engineering, the Director of the Priority

Research Centre for Frontier Energy Technologies & Utilisation, and the Director of VTara Clean

Energy Technology Centre at the University of Newcastle. He collaborates with industry and

government in energy and environment, and has 5 patents and published over 300 articles.

mailto:[email protected]






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Dr Richard Aynsley is a retired architect academic and consultant with over forty years of

international experience and has authored numerous publications. He has held the positions of

UNESCO Professor of Tropical Architecture, served on the US ASHRAE Standard 55 Thermal

Comfort committee, and is a life member of ASHRAE and associate member of ASCE.

Emeritus Professor Adrian Page is an internationally recognized researcher in the field of structural

masonry at the University of Newcastle, and has been involved in both the applied and fundamental

aspects of masonry research for more than 30 years. He has close links with industry, is the Chair of

the Australian Masonry Structures Code committee and has over 300 publications related to the

structural and building science aspects of masonry design and construction.

John Clarke is the Acting Research Group Leader, Projections, Products and Services,

CSIRO Climate Science Centre. He has over 25 years’ experience in the fields of climate change

impacts and adaptation, and in conservation ecology, and coordinated the development of the latest

version of the Climate Change in Australia website. His team develops climate change projections

and tailored datasets used by practitioners and researchers in Australia and internationally, to

quantify impacts and plan appropriate responses.

ABSTRACT

Australia has committed to the global effort to keep temperature rises below 1.5 Kelvin but has a

building stock with one of the world’s worst carbon emissions per person. This paper presents PhD

findings that rank the cost-effectiveness of retrofits to lower heating and cooling energy and carbon

emissions for three existing representative Australian houses. The method modelled the Adelaide

climate in 2050, carried out thermal simulation modelling of 50 affordable retrofits with the

AccuRate package, considered best practice decarbonisation approaches, and used a do-it-yourself

(DIY) simple payback period cost benefit analysis. The results show that the most cost-effective

single retrofits are 1) partial conditioning of the house; 2) ceiling insulation; 3) optimum weather-

stripping; and 4) cavity insulation of the external wall, with others depending on the type of house

construction. The cost-optimal retrofit combinations were medium payback periods for all house

types, with energy savings from 25% to 80% costing between $2,000 and $7,000 DIY. Strategies

and government incentives were found for tenants including using small payback periods with a

cost of less than $1,500 for energy savings up to 50% across all house types. So, the Australian

housing stock can be rapidly decarbonised by adopting best practice infrastructure decarbonisation

approaches; by undertaking retrofit combinations with small and medium payback period; by

encouraging retrofits for the active renovation movement; and by providing government incentives.

Limitations with the simulation assumptions mean that adjustments may be required to apply these

findings, particularly with regard to occupancy intensity and the conditioning of most rooms, but

the ranking of retrofits should remain the same per house type.

Keywords: affordable retrofits, low-carbon retrofits, existing houses, climate change, simulation

Theme: Building Energy Simulation: Research

1. INTRODUCTION

World surface temperatures are still rising at an accelerated rate (Nuccitelli, 2016) and natural

disasters have tripled in the last 35 years with around $4 trillion dollars in property damage


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(MunichRe et al., 2015, pp. 43–44). With the volume of greenhouse gases already released into the

troposphere, temperatures will continue to accelerate, leading to more severe natural disasters.

Australia has committed to keep temperature rise below 1.5 Kelvin at the 2015 Paris Conference of

Parties (COP21) which implies a zero carbon economy by 2050 (ASBEC, 2016, p. 21). However,

Australia’s building stock has one of the world’s worst carbon emissions per person (WRI, 2005;

ASBEC, 2008, p. 8), and the residential sector makes up 50% of the carbon emissions of the

building sector.

It is therefore important to rapidly lower the carbon emissions of existing housing and to adapt it to

global warming (Ren, Wang and Chen, 2014; Blumer and Mayers, 2017). In reality however, this

can be a difficult problem due to issues such as:

• the large number of stakeholders in the residential sector (WBCSD, 2009),

• split incentives for landlords and tenants, where those paying for energy efficiency upgrades

do not enjoy the benefits (WBCSD, 2009, p. 20; ASBEC, 2016, p. 97), and

• the large renovation movement in Australia (HIA, 2016) which includes few retrofits (Pears,

1998).

Performance upgrades are more likely to be adopted if they are convenient and affordable (Bond,

Pacifici and Newman, 2011). In this respect, do-it-yourself (DIY) retrofits can keep costs low

(Williams et al., 2013), and the first author has had requests for these during energy auditing.

So the aim of this paper is to find affordable DIY retrofits to reduce operational carbon emissions in

2050 for existing Australian housing for a warm temperate climate in which around 50% of the

population lives (BZE et al., 2013, p. Appendix 2), based on the findings of a retrofit PhD program

(Shiel, 2017).

2. METHOD

Figure 1 shows the methodology used in this study with 1) the AccuRate 2050 weather input files

from climate change modelling; 2) housing and retrofit energy analyses; and 3) a carbon and cost

benefit analysis.


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Source: Shiel

Figure 1. The method for estimating house retrofit cost benefits, including climate change scenarios

2.1 Modelling climate change

Climate change modelling (Shiel, 2017) was carried out for 2050 using the Australian Climate

Futures (ACF) on-line tool (CSIRO and BoM, 2015), for two scenarios:

• Extreme Climate Change, where emissions follow the current path of “business as usual”

(Peters et al., 2013, p. 5). This assumes fossil fuels are plentiful and corresponds with the

IPCC’s AR5 RCP8.5, where RCP is a Representative Concentration Pathway (RCP) (van

Vuuren et al., 2011), and

• Scarce Resources (reported here) where resource depletion can cause prices to rise for

energy and materials (including those for construction), which slows economic growth and

therefore carbon emissions (Victor, 2008; Heinberg, 2011; Klare, 2012).

The climate change modelling developed annual hourly weather input files for the AccuRate

simulation program to represent Adelaide in 2050 by selecting a General Circulation Model (aka a

Global Climate Model; GCM); finding the projected change in the ‘temperature’ and ‘humidity’

climate parameters for 2050; and transforming the global climate projection to a regional level

using a downscaling method. The Change Factor Method (CFM) was used for downscaling, where

Belcher’s “morphing” technique (Belcher, Hacker, and Powell 2005) was used with Adelaide’s

weather data from NatHERS’ 1990 Reference Meteorological Year (RMY) climate file.


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2.2 Housing and retrofit energy analyses

Thermal simulations were conducted on models of three existing Australian houses (see Figure 2)

with the NatHERS accredited AccuRate software package, for the Warm Temperate climate of

Adelaide. The houses were selected to match the three eras of 1950s, 1980s and 2010, having

appropriate floor types, and the three most common wall construction types in Australia:

weatherboard lightweight walls (House 1), cavity brick walls (House 2), and brick veneer walls

(House 3) (DEWHA, 2008, p. 104).

Source: (Shiel, 2017)

Figure 2. Existing houses chosen to represent 3 eras and common construction types for Australia.

Over 50 single retrofits were selected and costed from a suite of around 70 retrofits for each house,

and these were simulated, energy savings calculated and ranked by simple payback period (SPP).

Passive solar principles governed the retrofit designs, including solar access for northerly windows;

window shade control; perimeter insulation; optimum infiltration levels; optimum thermal mass;

and cross-ventilation. In addition, consideration was given to the low exergy principles of using the

lowest quality energy from sources such as the sun to heat occupants in a similar manner to passive

solar principles, or from the wind or rain (Aynsley and Shiel, 2017; Alterman, 2017) to naturally

cool occupants. This is contrasted with relying on high quality energy such as electricity which

needs three times the delivered or final energy of home appliances in primary energy generated

from centralised power stations, and including transmission and appliance energy losses.

Infiltration levels were estimated in AccuRate using an unsealed exhaust fans approach (MEFL,

2010, pp. 107–108) to find the volume of air exchange required for a room based on its size and the

air changes per hour (ACH).


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The main retrofit categories simulated were:

• partial air conditioning (of the living room and kitchen only),

• insulation of the perimeter,

• radiation changes with window treatments,

• weather-stripping, and

• extra thermal mass.

2.3 Carbon and cost benefit analysis

The savings in energy costs and carbon emissions per year were estimated for each retrofit using a

split system air conditioner popular in South Australia (ABS, 2014). The state’s electricity carbon

intensity factor of 0.64 kgCO2-e/kWh (DEE, 2016) was used with an electricity rate of $0.35 per

kWh.

A simple payback period (SPP) approach was used for the cost benefit analysis, although it does not

take into account future energy price increases; replacement, repair or refinishing costs; or inflation.

The SPP was estimated from the DIY capital costs and the annual cost savings (Shiel, 2017).

2.4 Selecting cost-effective retrofits

Affordable practical retrofits were simulated based on the primary author’s experimental results,

and the advice of Architects and product suppliers. These included standard retrofits such as bulk

and reflective foil insulation for the ceiling and roof, as well as novel retrofits such as exterior

corrugated galvanised iron cladding; tree and vegetation shading; and shrubs for wing walls. Some

of these novel retrofits did not meet NatHERS protocols, but were used to lower temperatures rather

than gain a better star rating.

The retrofits were ranked as those most cost-effective, but some retrofits which were assumed to

have a zero DIY cost (e.g. if they were hobbies or already part of the house e.g. aquariums, wine

racks, or a PV system) were included although they had low carbon savings.

2.5 Combining retrofits

Retrofits were combined using a unique approach of selecting multiple cost-effective single retrofits

that affected internal temperatures for the same envelope component, such as a ceiling or floor. This

approach contrasts with others that conform to star-rating protocols where a few single retrofits are

selected on an intuitive basis, or many retrofits are simulated using a brute force computer search

approach. The retrofits were combined for three sets of costs with small, medium and large payback

periods to suit the occupant categories (see the Appendix):

• tenants (T), those who would like to carry out a few retrofits, or those with low disposable

incomes e.g. owners with a large mortgage, with an SPP less than 3 years,

• owners (O) with some mortgage, landlords who may wish to keep expenses low, or those

wanting to do more retrofits than above, with an SPP greater than 3 years but less than 10

years, and

• those desiring deeper retrofits (D), or with more disposable income, or with a long-term

occupancy with an SPP greater than 10 years but perhaps less than 20 years.


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2.6 Best practices for rapidly decarbonising

With the high demand for housing in Australia, a life-cycle carbon analysis should be undertaken

before retrofitting a house, since older houses on large lots close to public transport may justify

consolidated development (Norman, MacLean and Kennedy, 2006; Randolph et al., 2007; Iyer-

Raniga, 2010).

Best practice strategies continue to evolve (Shiel, 2009) but based on current climate science and

expert opinion (Snow and Prasad, 2011; IPCC-AR5, 2015; Larson and iiSBE, 2017), it is important

to maintain infrastructure which:

• has the greatest longevity;

• is in reasonable condition;

• is 20m above sea level;

• is located near public transport;

• is in regions with high population; and

• has high fuel carbon intensities e.g. for electricity, the states of Victoria and NSW/ACT.

So, housing with these characteristics, and which has the largest operational carbon emissions and

the best solar access for a photovoltaic (PV) system should have the highest priority for retrofits.

3. RESULTS

The Scarce Resource scenario and DIY costings are reported here, and the retrofit contractor

costings and the Extreme Climate Change scenario are in the dissertation (Shiel, 2017).

3.1 Climate change

The HadGEM2-ES GCM was selected as the most appropriate GCM for both scenarios, and Table

1 shows the projected changes in temperature and humidity from 1995 to 2050.

Pathway Projected annual mean change in

the monthly surface temperature

(Kelvin)

Projected annual mean change

in Humidity (%)

RCP4.5 1.2 -1.1

Table 1. The projected changes in Adelaide temperature and humidity, from 1995 to 2050 for the

Scarce Resources scenario

Source: Shiel with data from ACF (CSIRO and BoM, 2015)

3.2 Single retrofits

The carbon savings of the single retrofits compared to the base case house configuration are plotted

against the DIY simple payback period (SPP), together with a label identifying that SPP in:

• Figure 3 for the 1950s weatherboard timber floor (House 1), including a colour code for the

type of retrofit,

• Figure 4 for the 1980s cavity brick timber floor (House 2), and

• Figure 5 for the 2010 brick veneer concrete floor (House 3).

Each figure also contains a table listing each of the effective retrofits ranked in SPP order.


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3.3 Retrofit combinations

Figure 6 shows the percentage of conditioned energy saved by retrofit combinations against their

cost for each house type, while Figure 7 shows the carbon savings of those retrofit combinations

against payback periods. Figure 7 also includes the indicative occupant categories for each payback

period separated by dashed lines, for all house types.

The Appendix contains Table 2 which shows the retrofit combination details for each of the houses,

payback periods and occupant categories, including which retrofits are applicable.

Source: Shiel

Figure 3. The carbon savings by payback period for single DIY retrofits of House 1, a 1950s

weatherboard timber floor house for the Adelaide 2050 Scarce Resource scenario. The retrofits are

colour coded for thermal mass (dark blue bolded), roof and ceiling insulation (light blue), sealing

(bolded black), floors (brown), cavity walls (purple bolded), wall cladding (purple), vegetation

(green), and other (black).

4. DISCUSSION

4.1 Climate change

The Scarce Resource scenario was selected based on the critical status of some socio-economic and

earth system indicators from the Anthropocene research (Steffen et al., 2015) and from other

researchers, as cited in Shiel (2017). These include fresh water availability per person and

domesticated land for crops, grazing and cities. This appears to be driven by the growth in spending

(real GDP) (Zovanyi, 2013, p. 25) and by the rapid expansion of the middle class on a finite planet


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(Kharas, 2017; Shiel, 2017), which could lead to further price rises as resources diminish (Rubin,

2009, p. 22).

From Table 1, while there is little change in humidity from 1995 to 2050, the 1.2 K increase in

projected temperature is very significant, for this scenario with a lesser degree of climate change.

This is because measurements have already shown a 1 K increase in average global temperatures

since 1850 (IPCC-AR5, 2015, p. 3), and with another 1.2 K, the COP21 target of keeping the

temperature rise below 1.5 K level will be exceeded by 30% in 2050 ((2.2-1.5)/2.2*100).

Source: Shiel

Figure 4. The carbon savings by payback period for single DIY retrofits of House 2, a 1980s cavity

brick timber floor house for the Adelaide 2050 Scarce Resource scenario.

4.2 Single retrofits

The most cost-effective single retrofits across all house types (see Figures 3-5) for the Scarce

Resource scenario in 2050 for Adelaide are 1) partial conditioning of only the living room and

kitchen; 2) ceiling insulation; 3) optimum weather-stripping; and 4) cavity insulation of the external

wall. For houses with access to a concrete floor, an internal brick wall is cost-effective for thermal

mass, and for older timber-floored houses, extra roof and underfloor insulation and galvanised iron

cladding to the external wall are also cost-effective.


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4.2.1 Optimum infiltration levels

A retrofit with a recommended optimum level of infiltration (Lstiburek, 2002; Ambrose et al., 2013,

p. 59) of ten air changes per hour (10ACH50) was simulated, as well as an ultra-sealed level, which

corresponded to minimum gap settings because NatHERS rewards tightly sealed house designs with

higher star ratings. The ultra-sealed level was developed as two retrofits, since they were costed

with and without an Energy Recovery Ventilation (ERV) system. Envelopes sealed below 10ACH50

have greater carbon savings, but can have poor indoor air quality without an ERV unit, affecting

occupant health (Aynsley and Shiel, 2017). When the cost of an ERV unit is added, the ultra-sealed

level is less cost-effective, whereas the optimum infiltration level remains affordable. So this

optimum level of infiltration was an important retrofit for climate change because older houses tend

to have high infiltration rates (Ambrose et al., 2013), which is detrimental to good thermal

performance.

Source: Shiel

Figure 5. The carbon savings by payback period for single DIY retrofits of House 3, a 2010 brick

veneer concrete floor house for the Adelaide 2050 Scarce Resource scenario.

4.2.2 High thermal mass but low embodied energy materials

To keep internal temperatures constant for a conditioned house with dynamic external temperatures,

a low conductivity envelope is required. However, if the goal is to reduce the conditioned energy

with a free running or naturally conditioned house, a low diffusivity envelope is needed (Barrios et

al., 2011), where diffusivity is conductivity divided by thermal mass.


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Hence high thermal mass retrofits are needed for temperate and subtropical climates with large

diurnal temperature swings, but the challenge is to find retrofits with low or negative embodied

energy. Options include:

• hempcrete and solid timber, which sequester carbon and are carbon negative (Envirotecture,

2015; FWPA and Dewsbury, 2016);

• zero carbon bricks (Clarke, 2014, p. 71);

• removing carpet from a concrete floor; and

• low carbon earth-walls, second hand bricks and pavers, and liquids e.g. stored in aquariums

or wine racks.

Liquids, carpet removal from concrete floors and new brick walls were simulated in this research.

The aquariums and wine racks had a small effect and were assumed to have zero cost because the

occupant enjoys those activities. Also, an internal wall retrofit proved to be cost-effective even with

new bricks, and so second-hand bricks would be even more cost-effective.

4.2.3 Comparison of retrofits across house types

Figures 3-5 show similar retrofits across each house type, with the most cost-effective retrofits

ranked in the table in each figure for particular house constructions. The most cost-effective retrofit

across all houses is the partial air-conditioning retrofit (Number 56).

The ceiling insulation had interesting effects across the houses. R2 m2K/W ceiling insulation

reduced the conditioned energy by 29% and 32% for the 1950s and 1980s houses respectively, but

only by 12% for the 2010s house type. This is because the 2010s house type already had R1 ceiling

insulation, whereas the other houses had no insulation. However, increasing the insulation value to

R3 only reduced the conditioned energy by a further 1-2% for the 1950s and 1980s houses but by a

more substantial 5% for the 2010s house. Finally, increasing the ceiling insulation further to R4 and

R5 had a negligible effect on the conditioned energy savings of all houses.

Another retrofit which had unusal effects across houses was underfloor insulation e.g. retrofit

number 18 which used R2.5 polystyrene batts. This reduced the conditioned energy of the 1950s

house by 15% whereas the reduction for the 1980s house was only 3%, and of course did not apply

to the 2010s house with a concrete slab.


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Source: Shiel

Figure 6. Percentage energy saved from DIY retrofit combinations by cost, for house type, where

the labels are the simple payback periods (years).

4.3 Retrofit combinations for rapid decarbonisation

Figure 6 shows the percentage energy saved from DIY retrofit combinations by cost and for the

large payback period retrofit combinations, it shows:

• an 85% reduction in conditioned energy for the 1950s weatherboard house for $12,500 (see

Figure 7 for more accurate costs) with an 8-year payback period,

• almost an 80% reduction in conditioned energy for the 1980s cavity brick house for around

$15,000 with a 13-year payback period, and

• almost a 30% reduction in conditioned energy for the 2010s brick veneer house for $6,000,

also with a 13-year payback period.


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Source: Shiel

Figure 7. Carbon savings of combined retrofits by payback period for house type, with labels being

the retrofit combination DIY costs (AUD dollars). This provides a rapid housing decarbonisation

approach to suit house types and match selected occupant categories – See the Appendix for details.

Figure 7 shows cost-effective retrofit combination carbon savings for payback periods to suit each

occupant category. It shows that occupants desiring deep retrofits can save per annum:

• almost 3 tonnes of CO2-e for the 1950s weatherboard house,

• around 2 tonnes of CO2-e for the 1980s cavity brick house, and

• around 0.9 tonnes of CO2-e for the 2010s brick veneer house.

On the other hand, while tenants in 1950s weatherboard houses and the 1980s cavity brick houses

can save around 1.5 tonnes of CO2-e per year, tenants in the 2010s brick veneer houses can only

save around 0.8 tonnes of CO2-e per year.

The optimum energy- and carbon-saving level of retrofit combinations from a purely cost point of

view for each house type, is indicated in Figure 6 by the retrofit combinations with a medium

payback period due to the asymptotic nature of each curve. For example, for House 1, with

weatherboard walls and timber floor, around 77% of the conditioned energy can be saved with the

medium payback period DIY retrofit combination costing $7,300 (from Figure 7). However for

85% savings in conditioned energy, $12,500 is required, ie. around $5,000 extra is needed for a

further 8% saving in energy. However, this introduces a dilemna for tenants who may not be

motivated to undertake this level of retrofit combination due to the larger investment or length of

time for payback.

To assist with the split incentives issue, tenants could negotiate a lease at a constant rental tariff

longer than the payback period of the retrofits they undertake, or else negotiate a lower rental tariff

for the duration of the payback period.


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If the government introduced Mandatory Disclosure for dwellings (where a star rating is needed

when the property is sold or leased), which is under consideration, this would encourage landlords,

as well as owners, to undertake retrofits.

So tenants could invest less than $1,500 to retrofit all house types with the retrofit combination with

a small payback period to save between 0.8 tonnes (22% of the conditioned energy) and 1.5 tonnes

(55% of the conditioned energy) of CO2-e per year (from Figures 6 and 7). This could be at a small

profit if the lease terms above were negotiated, assisting to overcome the split incentives problem.

If the landlord carried out retrofits as well, then the retrofit combinations could approach the

medium payback period levels of retrofits.

So the cost-optimum retrofit levels for all house types are:

• the retrofit combinations with medium payback period, for owners, deep retrofit households

and the government, and

• the retrofit combinations with a small payback period for tenants.

The best practice rapid decarbonisation approach mentioned above should be considered to

prioritise the selection of houses for the retrofits identified here, and the active renovation

movement should be encouraged to adopt them as well.

4.4 Government assistance and incentives

Government subsidies and rebate schemes could be introduced to encourage retrofits since they can

assist in meeting local, state and federal government greenhouse gas targets; in reducing energy

poverty and deprivation (Liu and Judd, 2017); and also in reducing the peak power requirements of

each state’s electricity network.

In particular, government incentives may be required to encourage retrofits for tenants, particularly

if rental agreements such as those described above cannot be negotiated or the landlord does not

permit retrofits to be carried out.

4.5 The reliability of the approach

The climate was modelled to 2050 because durable houses have up to a 100 year lifespan (Snow

and Prasad, 2011) and therefore houses of the 1950s era may not have much longevity past 2050.

Another factor was because Global Climate Model projections are quite reliable in the short term,

but become more uncertain beyond 15 years (CSIRO and BoM, 2015, p. 88).

Limitations were found with the NatHERS protocol (Shiel, 2017) for thermal simulation modelling

regarding:

• its occupancy assumptions where a large number of rooms are assumed to be conditioned,

over extended time periods, which may not match actual occupant patterns,

• its inability to model in ratings mode thermal lined curtains, phase change materials, and

vegetation benefits other than shading e.g. evapotranspiration effects on walls.

• the modelling of cladding, where the 0.4mm corrugated galvanized iron sheeting is very

effective, but may be overestimated since the minimum AccuRate material thickness is

1mm, and corrugations cannot be accurately modelled.


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5. CONCLUSION

If the Scarce Resource scenario projected temperature rise of 1.2 Kelvin eventuates, natural

disasters could increase, and price rises may add to the urgency of retrofitting to lower emissions.

Affordable low-carbon single retrofits for all Australian house types were found to be 1) partial

conditioning of the house; 2) ceiling insulation; 3) optimum weather-stripping; and 4) cavity

insulation of the external wall, and others that depend on the type of house construction. Retrofits

for optimum infiltration and added thermal mass were identified as important for climate change.

The cost-optimum retrofit combination levels for all house types are 1) those with medium payback

period for owners, deep retrofit households and the government where the energy savings were

from around 25% to 80% at an optimal DIY cost of between $2,000 and $7,000, and 2) those with a

small payback period for tenants with energy savings from 20% to 50% at a cost of less than

$1,500. The latter may be able to assist with the split incentives issue if leasing strategies are

successful or if the government provides incentives.

This study suggests that rapid decarbonisation of housing is feasible by using the best practice

infrastructure decarbonisation approaches identified; by undertaking the two cost-optimum DIY

retrofit combinations identified for tenants and owners; by commencing Mandatory Disclosure for

residential properties to encourage landlords and owners to adopt retrofitting measures; by

encouraging more retrofitting for the active renovation movement; and by providing government

incentives.

Limitations with the simulation assumptions mean that adjustments may be needed e.g. with regard

to occupancy intensity and the conditioning of most rooms although the ranking of retrofits should

not be affected.

ACKNOWLEDGEMENTS

The authors would like to thank CSIRO’s Dr Dong Chen for NatHERS assistance; Architect

Graham Hunt for assistance with AccuRate modelling; retrofit suppliers particularly 4Seasons’

Ross Kestle for insulation advice and rates; and the reviewers for their practical insights.


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7. APPENDIX – RETROFITS FOR EACH COMBINATION

ID Retrofit Description Retrofits for each house combination

House 1 2 3

Combination Retrofit ID 201 301 501 202 302 502 203 303b 503

SPP (years) 1 5.4 8.3 1.9 7.1 12.9 2.7 5.4 12.5

Occupant category (T-Tenants, O-Owners, D–

Deeper) T O D T O D T O D

76 Lstiburek sealing approx. 10ACH50 Y Y Y Y Y Y Y Y Y

35 Parasol roof in N and W (PV panels) Y Y Y Y Y Y Y Y Y

32 Low-e film applied to all windows

Y

34 Low-e film tint to non-North windows

Y

49 1.4m dia Ceiling fans to living & bed rooms

Y

42 8 wine racks (564 bottles) in living room Y Y Y Y Y Y Y Y Y

44 2 large Aquariums in Liv Rm Y Y Y Y Y Y Y Y Y

45 1 large Aquarium in Liv Rm Y Y Y Y Y Y Y Y Y

10 Liv/Garage wall R1.5 insulation & Ceiling R2

(not garage) Y Y Y

Y Y

2 Ceiling R3

Y

Y

Y

3 Ceiling R4 Y

Y

Y Y

5 Roof sarking Rfoil & ceiling R1.3 Expanded

Polystryrene + Rfoil Y

53 Roof R1 insulation (No double-sided Rfoil) Y

58 500 dble-foil backed polyethylene foam to roof Y Y

59 Foil batts in roof under battens Y Y Y Y Y

60 Foil batts in ceiling (over battens) Y Y

62 Foil batts stapled under floorboards

Y Y

Y Y

16 Underfloor 90mm gap & 1500 bubble Insulation

with dbl-sided Rfoil Y

18 R2.5 polystyrene batts under timber floor

Y

67 Add carpet to timber floor

Y Y

72 Polystyrene cubes insulation to wall cavity

Y Y

Y Y

74 140mm Polystyrene cubes insulation to full

wall cavity with NO sisalation on studs Y

65 Corrugated galv. iron sheeting as ext wall

cladding (not garage) Y

Y

66 Corrugated galv. iron sheeting as ext North wall

cladding only Y

55 Green ivy on North & West walls - shade only

Y Y

26 5m high deciduous trees 3m from North, East &

West windows Y

Table 2. The retrofits for each house and combination’s payback period with occupant category,

sorted by retrofit type and colours as per Figure 3. (Source: Shiel)

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