a comprehensive framework for assessing the life-cycle energy of building construction assemblies

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This article was downloaded by: [University of Western Ontario] On: 14 November 2014, At: 15:16 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Architectural Science Review Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tasr20 A comprehensive framework for assessing the life-cycle energy of building construction assemblies Robert H. Crawford a , Isabella Czerniakowski a & Robert J. Fuller b a Faculty of Architecture, Building and Planning , The University of Melbourne , Parkville, Australia b School of Architecture and Building, Deakin University , Geelong, Australia Published online: 09 Jun 2011. To cite this article: Robert H. Crawford , Isabella Czerniakowski & Robert J. Fuller (2010) A comprehensive framework for assessing the life-cycle energy of building construction assemblies, Architectural Science Review, 53:3, 288-296 To link to this article: http://dx.doi.org/10.3763/asre.2010.0020 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

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Page 1: A comprehensive framework for assessing the life-cycle energy of building construction assemblies

This article was downloaded by: [University of Western Ontario]On: 14 November 2014, At: 15:16Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office:Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Architectural Science ReviewPublication details, including instructions for authors and subscriptioninformation:http://www.tandfonline.com/loi/tasr20

A comprehensive framework for assessingthe life-cycle energy of building constructionassembliesRobert H. Crawford a , Isabella Czerniakowski a & Robert J. Fuller ba Faculty of Architecture, Building and Planning , The University ofMelbourne , Parkville, Australiab School of Architecture and Building, Deakin University , Geelong, AustraliaPublished online: 09 Jun 2011.

To cite this article: Robert H. Crawford , Isabella Czerniakowski & Robert J. Fuller (2010) A comprehensiveframework for assessing the life-cycle energy of building construction assemblies, Architectural ScienceReview, 53:3, 288-296

To link to this article: http://dx.doi.org/10.3763/asre.2010.0020

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)contained in the publications on our platform. However, Taylor & Francis, our agents, and ourlicensors make no representations or warranties whatsoever as to the accuracy, completeness, orsuitability for any purpose of the Content. Any opinions and views expressed in this publicationare the opinions and views of the authors, and are not the views of or endorsed by Taylor &Francis. The accuracy of the Content should not be relied upon and should be independentlyverified with primary sources of information. Taylor and Francis shall not be liable for anylosses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilitieswhatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantialor systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, ordistribution in any form to anyone is expressly forbidden. Terms & Conditions of access and usecan be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: A comprehensive framework for assessing the life-cycle energy of building construction assemblies

A comprehensive framework for assessingthe life-cycle energy of buildingconstruction assembliesRobert H. Crawford1*, Isabella Czerniakowski1 and Robert J. Fuller21Faculty of Architecture, Building and Planning, The University of Melbourne, Parkville, Australia2School of Architecture and Building, Deakin University, Geelong, Australia

Building environmental design typically focuses on improvements to operational efficiencies such as building thermal

performance and system efficiency. Often the impacts occurring across the other stages of a building’s life are not considered

or are seen as insignificant in comparison. However, previous research shows that embodied impacts can be just as impor-

tant. There is limited consistent and comprehensive information available for building designers to make informed decisions in

this area. Often the information that is available is from disparate sources, which makes comparison of alternative solutions

unreliable. It is also important to ensure that strategies to reduce environmental impacts from one life cycle stage do not come

at the expense of an increase in overall life-cycle impacts. A consistent and comprehensive framework for assessing and

specifying building assemblies for enhanced environmental outcomes does not currently exist. This article presents the initial

findings of a project that aims to establish a database of life cycle energy requirements for a broad range of construction

assemblies, based on a comprehensive assessment framework. Life cycle energy requirements have been calculated for

eight residential construction assemblies integrating an innovative embodied energy assessment technique with thermal

performance modelling and ranked according to their performance.

Keywords: Built environment; construction assemblies; energy; life-cycle assessment

INTRODUCTION

The construction industry worldwide has a significant impact

on the environment. While this impact has been known for

years, those involved in the construction industry often

lack the information necessary to make the decisions

required for a more sustainable outcome. Often these data

are not readily available to building designers or are not pre-

sented in such a way that facilitates the environmental

decision-making process.

An enormous range of construction assemblies for build-

ing wall, floor and roof construction elements currently exist.

New building construction systems and materials are con-

stantly being developed, with many of these aimed at

improving the thermal performance of buildings. Less

common is development aimed at reducing the impacts

associated with the manufacturing stage of these materials.

Previous studies have shown that these ‘indirect’ impacts

can be as significant as those associated with the operation

of a building (Treloar et al., 2001). The impacts occurring

across the entire life cycle of a building need to be con-

sidered. This includes those impacts associated with material

production, building operation, maintenance and end-of-life.

Architects and building designers require detailed environ-

mental performance data in their efforts towards reducing

the environmental impacts associated with the buildings

that they are designing.

Energy rating tools are now used nationally to help build-

ing designers reduce the impacts associated with building

operation through improvements to the thermal performance

of the individual elements of the building envelope. These

tools fail to consider the effect that these operational

improvements have on the impacts associated with the

other stages of the building life cycle, such as the manufac-

turing stage. An integrated approach to environmental

impact assessment is essential to ensure that issues are not

shifted from one life-cycle stage to another.

Few designers are aware of the source of the materials that

they specify and the energy consumed during the manufacture

of those materials, the source of that energy or the long-term

*Corresponding author: Email: [email protected]

ARCHITECTURAL SCIENCE REVIEW 53 | 2010 | 288–296doi:10.3763/asre.2010.0020 #2010 Earthscan ISSN: 0003-8628 (print), 1758-9622 (online) www.earthscan.co.uk/journals/asre

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Page 3: A comprehensive framework for assessing the life-cycle energy of building construction assemblies

environmental implications of their decisions. Furthermore,

there is a lack of information and resources needed to trans-

late designers’ awareness into decisions and practical out-

comes. While there is growing interest from clients and

designers to deliver projects with a lower environmental

impact, despite their intentions, the most intelligent resol-

utions and designs will not be reached if they are based on

unreliable or incomplete data.

The aim of the study was to develop a comprehensive fra-

mework for analysing the life-cycle energy requirements of

building construction assemblies and rank them based on

their performance. The application of this framework is

demonstrated through a life-cycle energy analysis of eight

common residential construction assemblies. The findings

from this study will form part of a much larger project that

will involve developing a comprehensive database of the

life-cycle energy performance of a large range of construc-

tion assemblies for various building typologies across the

various climate zones within Australia. The database will

enable information on the life-cycle implications of using

particular materials and construction assemblies to be pre-

sented in a comprehensive manner but also to be more

readily available to building designers, with the aim of mini-

mizing building environmental impacts.

BACKGROUND

Numerous studies have investigated the life-cycle energy

requirements of buildings (including inter alia Adalberth,

1997; Fay et al., 2000; Foster et al., 2000). These studies

have typically assessed individual buildings and not necess-

arily the impacts attributable to individual construction

assemblies. Studies to have considered the energy require-

ments of assemblies have typically focused on either their

embodied energy (EE) (e.g. Lawson, 1996; Venkatarama

Reddy and Jagadish, 2003; BRE, 2008; Iyer-Raniga et al.,

2008) or thermal performance (e.g. Bouchlaghem, 2000;

Al-Sanea, 2002; Thorsell and Bomberg, 2008), but not both

simultaneously. Within all of these studies, many gaps and

the use of unreliable, potentially erroneous data are apparent.

Lawson (1996) assessed the initial embodied energy of 40

floor, wall and roof assemblies, providing an embodied

energy value (in MJ) per square metre of assembly. The

BRE (2008) Green Guide provides a ranking of the environ-

mental performance of a wide range of assemblies based

on their initial embodied energy per square metre of

assembly. A similar project conducted by RMIT (Iyer-

Raniga et al., 2008), known as the Building Assemblies

and Materials Scorecard also provides a ranking of a

range of assemblies based on their initial embodied energy

and other environmental parameters. For each of these

studies, the focus from an energy perspective is limited

to the initial embodied energy of the building assemblies

considered, excluding energy requirements associated

with replacement, operation and maintenance. The

ATHENA EcoCalculator for Assemblies (ATHENA,

2007), developed by the ATHENA Sustainable Materials

Institute, provides environmental performance data for

common construction assemblies and includes both initial

and recurring embodied energy requirements but excludes

operational energy.

One of the few studies that have modelled both the oper-

ational and embodied energy of construction assemblies is

that of Pierquet and Bowyer (1998). This study assessed

the life-cycle energy implications of various wall systems,

concluding that in all cases the thermal performance of a

building was able to be improved, but at the cost of an

increase in the initial embodied energy requirement. Pierquet

and Bowyer’s study differs from that proposed in this study

in that the results obtained included an estimate for single-

season heating energy, simulated using ‘HOT-2000’ soft-

ware, as opposed to quantifying the annual operational

energy requirements for the lifetime of the assembly.

The Green Building Initiative (Bryan and Trusty, 2008) is

currently undertaking a project to develop a national green

building rating standard for the US incorporating both embo-

died energy, using the ATHENA EcoCalculator and oper-

ational energy modelling.

At best, studies to have assessed the embodied energy of

assemblies have used incomplete methods of embodied

energy analysis, known to exclude up to 87% of the

energy requirements associated with construction (Crawford,

2005). Never before has a model utilizing a systemically

complete system boundary been used to assess the embodied

energy associated with a broad range of construction assem-

blies. Due mainly to the known deficiencies in the methods

of analysis used, the knowledge gained from previous

studies provides little support to industry in their need for

building life-cycle energy data to inform design decision-

making. This information needs to be available during the

design phase so that decisions can be made early to have

the most beneficial environmental outcome.

All of the studies listed above (Lawson, 1996; Pierquet

and Bowyer, 1998; BRE, 2008; Bryan and Trusty, 2008;

Iyer-Raniga et al., 2008) use a process analysis method to

quantify the energy embodied in a range of construction

assemblies. Process analysis suffers from a systemic incom-

pleteness, which is due to the delineation of the assessed

system by the finite boundary, and the omission of contri-

butions outside this boundary. The arbitrary truncation of

the system boundary also limits the comparability of

results. Hybrid analysis methods have been developed in

an attempt to minimize the limitations and errors of tra-

ditional embodied energy assessment methods. National

average statistics that model the financial flows between

sectors of the economy, referred to as input–output (I–O)

data, can be used to fill the gaps that are caused by system

boundary incompleteness (Proops, 1977). These hybrid

methods combine process data and I–O data in a variety

of formats (inter alia Proops 1977; Duchin 1992; Treloar

1997; Lenzen 2001; Suh and Huppes, 2002).

A comprehensive framework for assessing the life-cycle energy of building construction assemblies 289

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In a tiered hybrid approach (Suh and Huppes, 2002)

‘upstream’ truncation error is eliminated. But this technique

uses I–O analysis as a black box, relying on the consultant to

decide which processes are important and require analysis.

This technique can only resolve the upstream truncation

error for items that the user decides are relevant. If the user

chooses to start the I–O analysis at the highest point in the

supply chain, for example, the building construction, to

avoid truncation error, all opportunities are lost for integrat-

ing potentially available and more accurate process data, due

to the ‘black box’. As the supply chain is disaggregated to

allow the integration of process data, the potential exists

for ‘sideways’ and ‘downstream’ truncation error, as demon-

strated for a brick veneer wall assembly in Figure 1. The

magnitude of these truncation errors depends on the type

of product or activity, but can be in the order of 50–80%

(see e.g. Hendrickson et al., 1998; Lenzen and Dey, 2000;

Crawford, 2005).

The hybrid model developed by Treloar (1997) (known

as input–output-based hybrid analysis) addresses many

of these problems by starting with a disaggregated

I–O model to which available process data are integrated.

This avoids the possibility for sideways and down-

stream truncation errors discussed above, in addition to

upstream truncation. Initially, the I–O model can be used

to scope a product’s system boundary to identify the most

important inputs. It is then possible to target efforts

towards collecting or sourcing process data of particular

inputs or processes.

The current study extends on similar previous studies by

providing a more comprehensive assessment of the energy

embodied in a range of construction assemblies (resolving

substantially the issue of system boundary incompleteness).

This information is integrated with thermal performance data

for these assemblies. The outcomes of this project will be

valuable to industry generally as they strive to implement

sustainable design more rigorously. The information pro-

vided by this project will facilitate the design decision-

making process, and the balance between construction and

operational impacts will be able to be better evaluated in

order to create buildings that are optimized across the build-

ing life cycle.

METHODOLOGY

This section outlines the assemblies analysed in this initial

study and the methods used to assess their life-cycle

energy requirements over a 50-year period.

Construction assembliesThis study modelled the life-cycle energy associated with

eight standard residential construction assemblies. This

included two floor assemblies, four external wall assemblies

and two roof assemblies. The functional unit considered was

a one square metre area of each assembly over 50 years

(Table 1).

Life-cycle energy analysisThe life-cycle energy associated with construction assem-

blies includes their initial embodied energy, the energy

embodied in subsequent replacement and maintenance of

components or materials (recurrent embodied energy), the

energy associated with the demolition and disposal of

materials and the energy required to maintain a comfortable

internal temperature (operational energy). The life-cycle

embodied energy associated with the assemblies is calcu-

lated based on the anticipated life of the building in which

they are used (for the purpose of this study this was

assumed to be 50 years for residential buildings). It is essen-

tial that the recurrent embodied energy is determined due to

the considerable variability across different assemblies. For

example, the need for numerous replacements of an

energy-intensive material in a particular assembly may

have a significant impact on the total embodied energy

requirement over the life of a building.

The energy associated with the end-of-life demolition and

disposal of materials has not been included in this study.

Crowther (1999) has shown that the energy associated with

this stage of a building’s life represents less than 1% of the

building’s life-cycle energy requirement. The reuse or

recyclability of materials has significant potential to reduce

building embodied energy. However, the value of the

material for reuse at the end of its life is a relatively small

factor in the overall life cycle of the product, especially con-

sidering the length of time needed to realize the benefit of the

reuse and the fact that the embodied energy credit should go

to the reuse, and not be subtracted from the initial installation

(Treloar, 2000). Therefore, this study includes only the initial

and recurrent embodied energy and the energy required for

maintenance and building operation. Despite this, the study

represents a much more comprehensive approach than has

been undertaken previously.

Figure 1 | Upstream, downstream and sideways truncationerrors in the brick wall assembly system boundary

290 Crawford, Czerniakowski and Fuller

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Page 5: A comprehensive framework for assessing the life-cycle energy of building construction assemblies

Embodied energyEmbodied energy accounts for the energy associated with the

manufacture of products and materials, including those

resulting from the manufacture of goods and services used

during this process. For example, the energy embodied in

timber products typically comprises energy for harvesting,

transporting and milling the lumber, and finishing and

delivering the products. Many factors (including technology,

fuel supply structures, climate, region, product specification

and analysis methods) can contribute to considerable varia-

bility in embodied energy data.

The embodied energy assessment was performed using an

input–output-based hybrid analysis. This method is applied

using an I–O model of Australian energy use. The base I–

O data were taken from the Australian National Accounts

(ABS, 2003) and combined with energy intensity factors by

fuel type. The combination of these two sources comprises

the I–O model. The model includes the value of capital pur-

chased in previous years, and capital imported from other

countries, amortized over the capital items life (as described

and analysed in Lenzen and Treloar, 2004). Capital refers

to the equipment and machinery used to make products.

The I–O model was used as the basis for the embodied

energy analysis of the eight assemblies. The best available

process data were incorporated for specific materials manu-

facturers as per the input–output-based hybrid approach

(Treloar, 1997). Process-specific data for the energy from

the manufacture of specific materials were obtained from

the latest available Simapro Australian database (Grant,

2002). Eventually, this may be replaced with data from the

CSIRO-led AusLCI database project as it becomes available.

The calculation of the energy embodied in the assemblies

was based on the material energy intensities from Table 2,

which includes the energy from fossil fuel consumption.

These intensities were compiled using the input–output-

based hybrid method, combining available process data for

the specific materials with I–O data. The use of I–O data

here resolves any upstream truncation errors for these

materials.

The quantities of the materials used in a one square metre

area of each assembly were multiplied by their respective

energy intensities. The sum of these results gave the total

process-based hybrid embodied energy for the different

assemblies. These values then had to be substituted within

the overall I–O model, to complete the system boundary.

The total energy intensity value of the I–O pathways, for

which physical quantity data were obtained, is deducted

from the total energy intensity of the ‘residential construc-

tion’ sector (for residential buildings) to give the ‘remain-

der’. The ‘remainder’ thus corrects ‘sideways’ and

‘downstream’ truncation error (Figure 1), at least in terms

of the Australian economic system as defined by the Austra-

lian Bureau of Statistics (ABS, 2003).

Recurrent embodied energyThe energy associated with material or component replace-

ment and periodic maintenance during the life of a building

can represent up to 32% of its initial embodied energy

(Treloar et al., 2000). The extent of this depends on a

number of factors, including the useful life of the building,

Table 1 | Description of modelled assemblies

Element Assembly Description

Roof Timber frame,concrete tile

20mm concrete roof tiles,50 × 35 hardwood battens,250 × 50 hardwood beams,90 × 35 softwood joists,RFL, R3.0 fibreglassinsulation, 10mmplasterboard, water-basedpaint

Timber frame,steel sheet

As for ‘Timber frame,concrete tile’, corrugatedsteel replaces 20mmconcrete roof tiles

Externalwalls

Polystyrene,timber frame

50mm expandedpolystyrene, 4mm cementrender, 90 × 45 softwoodframe, RFL, R2.0 fibreglassinsulation, 10mmplasterboard, water-basedpaint (external and internal)

Brick veneer,timber frame

Standard clay bricks,90 × 45 softwood framing,RFL, R2.0 fibreglassinsulation, 10mmplasterboard, water-basedpaint

Brick veneer,steel frame

As for ‘Brick veneer, timberframe’, steel framingreplaces timber framing

Timberweatherboard

25mm hardwoodweatherboards, 90 × 45softwood frame, RFL, R2.0fibreglass insulation, 10mmplasterboard, water-basedpaint (external and internal)

Floor Elevated timberfloor

Steel reinforcement, 25MPaconcrete footings and piers,R2.0 fibreglass insulation,100 × 75 bearers and100 × 50 joists (hardwood),20mm hardwood flooring,two coats sealer

Concreteslab-on-ground

Membrane, expandedpolystyrene waffle-pods,steel reinforcement, 110mm25MPa concrete, ceramictiles

A comprehensive framework for assessing the life-cycle energy of building construction assemblies 291

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anticipated life of the assembly and the individual material or

component life. A building with a high initial embodied

energy may provide greater long-term value if that building

is also expected to have a longer life.

The recurring embodied energy for the assemblies

included the additional requirements for building materials

used in maintenance and repairs over the estimated life of

a residential building of 50 years. This was calculated by

assigning replacement rates to materials used in the initial

construction. For example, paint had a replacement rate of

10 years. So at Year 10, and each multiple of 10, the

energy embodied in the initial application of paint in the

assembly was added to the assembly’s initial embodied

energy to determine the life-cycle embodied energy

requirement.

Little data currently exist for the anticipated life of con-

struction materials in Australia. For the purposes of this

study, maintenance and replacement periods for materials

have been estimated with consideration of the likely

exposure to deteriorating effects for each assembly. The esti-

mated useful life or replacement periods for the materials

used in the eight assemblies analysed in this study are

shown in Table 3, assuming they are periodically

maintained.

The life-cycle embodied energy of a particular assembly,

including initial and recurring embodied energy, was calcu-

lated using equation 1.

LCEEa ¼XM

m¼1

ULb

ULm

� EEm

� �ð1Þ

where LCEEa is the life-cycle embodied energy of the build-

ing assembly a; ULb the useful life of the building; EEm the

embodied energy of material m; and ULm the useful life or

replacement period of material m.

Operational energyThe operational energy associated with each of the eight

assemblies was calculated with a computer model,

developed using TRNSYS software. A 250m2 ‘box’ with

3m high walls was set up and the properties of the individual

materials that make up each assembly were determined

(including thickness, density, thermal conductivity and

specific heat), based on AIRAH (1989). The size of the

box chosen is representative of the average new house size

in Australia (ABS, 2008). Sensitivity analysis was conducted

on three different-sized boxes to determine whether there

was a significant difference in the heating and cooling

requirements (per square metre of floor area) for boxes of

Table 2 | Energy intensity of materials

Material Unit Energy intensity(GJ/unit)

Material Unit Energy intensity(GJ/unit)

Aluminium, reflective foil m2 0.14 Mortar T 2.0

Bricks m2 0.56 Plasterboard (10mm) m2 0.21

Cement render (4mm) m2 0.032 Steel, decking m2 0.59

Concrete 25MPa m3 4.57 Steel, structural t 85.5

Concrete roof tile (20mm) m2 0.25 Tiles, ceramic m2 0.29

Expanded polystyrene (50mm) m2 0.36 Timber – hardwood m3 21.3

Fibreglass insulation R2.5 m2 0.22 Timber – softwood m3 10.9

Membrane (1mm) m2 0.51 Water-based paint m2 0.096

Table 3 | Useful life/replacement periods for assemblymaterials

Material Usefullife

Material Usefullife

Aluminium,reflective foil

50^ Mortar 50^

Bricks 50^ Plasterboard(10mm)

30*

Cement render(4mm)

20^ Steel, decking 30+

Concrete 25MPa 50^ Steel, structural 50^

Concrete roof tile(20mm)

25^ Tiles, ceramic 25*

Expandedpolystyreneinsulation (50mm)

25^ Timber –hardwood(external)

25#

Fibreglassinsulation R2.5

50^ Timber –softwood(internal)

50#

Membrane (1mm) 50^ Water-basedpaint

10*

NB. based on 50-year building life.Source: *Treloar et al. (2000), +Ding (2004), #FWPA (2007),^assumed.

292 Crawford, Czerniakowski and Fuller

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different volumes with the results showing that the difference

was negligible. TRNSYS parameters were set, such as initial

zone temperature (208C), initial humidity (50%), tempera-

ture band (18–248C) and climate zone. Ventilation, heat

gains from people, computers and artificial lighting were

excluded. Hourly solar radiation, dry bulb temperature, rela-

tive humidity and Melbourne climatic data were used to

determine the approximate heat loss/gain through each

assembly and therefore the energy required annually to main-

tain the predetermined internal temperature. Boundary con-

ditions were applied to five surfaces of the box so that no

heat gain or loss occurred through these surfaces. The sixth

surface (varies depending on the element being analysed)

was specified as the assembly to be modelled. The

TRNSYS simulation was then run to calculate annual

energy requirements for heating and cooling the ‘box’ (in

GJ/box). The annual energy requirements for the ‘box’

were divided by the area of modelled element to determine

energy requirements attributable to one square metre of

assembly for the particular element (GJ/m2 assembly).

These steps were repeated for all eight assemblies.

RESULTS

This section presents the findings of the life-cycle energy

analysis and ranking of the eight construction assemblies.

Embodied energyFigure 2 shows the life-cycle embodied energy requirements

(including recurrent embodied energy due to replacement

and maintenance) for a one square metre area of each of

the eight assemblies, over a 50-year period.

Operational energyFigure 3 shows the operational energy per square metre of

each of the eight assemblies over a 50-year period.

Assembly rankingThis section presents the ranking of the eight assemblies

based on their life-cycle energy results (from lowest to

highest life-cycle energy requirement) among assemblies

for each building element (Table 4). Initial and recurrent

embodied energy (EE) and operational energy are also

shown separately. Errors associated with the modelling tech-

niques and assumptions used in this study may influence the

findings. Further research will be conducted to determine the

influence of potential errors in both embodied energy and

operational energy on the ranking of assemblies.

DISCUSSION AND CONCLUSION

This article presents a method for ranking building assem-

blies based on their life-cycle energy performance. The

initial findings of a study that aims to compile a database

of the life-cycle energy requirements associated with a

large range of building construction assemblies, for use in

various climate zones across Australia, have been presented.

The potential importance of incorporating embodied impacts

with operational impacts is shown in Table 4. While a par-

ticular assembly may have a higher initial embodied

energy requirement than an alternative assembly, the poten-

tial for improved thermal performance of that assembly and

reduced material replacement requirements may result in a

lower net energy requirement over the life of a building.

While Treloar et al. (2000) have shown that embodied

energy associated with the replacement of building materials

can represent up to 32% of the initial embodied energy of a

building, this study has shown that for particular building

assemblies, the energy embodied in material replacement

can represent between 7 and 110% of the initial embodied

energy of each assembly. A ranking of assemblies within

each element group was seen to be most useful output

from this study, considering the difficulties in drawing

Figure 2 | Life-cycle embodied energy per square metre of assembly

A comprehensive framework for assessing the life-cycle energy of building construction assemblies 293

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Page 8: A comprehensive framework for assessing the life-cycle energy of building construction assemblies

generic conclusions from the operational energy figures

obtained. The figures given are meaningless beyond the

case assessed in this study, as every building will have differ-

ent operational energy requirements based on orientation,

internal gains, windows, operating hours, etc. It is anticipated,

however, that the ranked order of assemblies would hold true

when considering the various options for a specific building.

The ability to provide such a comparison between any

construction assembly will provide architects and building

designers with a powerful tool that will support them as

they strive towards designing more environmentally sustain-

able buildings. With this, architects and building designers

will be in a better position to make more informed choices,

selecting individual or combinations of construction assem-

blies for the various building construction elements that rep-

resent the greatest opportunity for improving environmental

performance across the building life cycle. This level of

information is crucial when it comes to understanding and

optimizing the life-cycle environmental performance of

buildings.

Comparison to previous studiesWhile previous studies have assessed the energy

embodied in construction assemblies, these have typically

been based on incomplete methods of assessment, such as

process analysis. Using these methods can lead to consider-

able errors in any findings. The previous study published

by Lawson (1996) presented the initial embodied energy

for a range of construction assemblies, based on process

analysis. Table 5 compares the initial embodied energy

for the assemblies analysed in this study to those presented

by Lawson.

As can be seen from Table 5, the assembly embodied

energy figures from this study are significantly higher than

those published in the previous study by Lawson. This

may be due to a combination of factors, but includes the

use of a wider system boundary. The embodied energy has

not been previously calculated for a range of building assem-

blies using a comprehensive embodied energy assessment

method, namely input–output-based hybrid analysis. As

embodied energy makes up a significant proportion of the

Table 4 | Ranking of assemblies based on life-cycle energy per square metre of assembly

Assembly InitialEE (GJ)

RecurrentEE (GJ)

Operationalenergy (GJ/annum)

Life-cycleenergy (GJ)

Rank

Timber frame, concrete tile roof 1.58 0.84 0.03 3.78 1

Timber frame, steel sheet roof 2.05 1.18 0.03 4.59 2

Polystyrene, timber frame 1.21 1.40 0.30 17.81 1

Brick veneer, timber frame 1.26 0.59 0.43 23.28 2

Brick veneer, steel frame 1.34 0.59 0.43 23.36 3

Timber weatherboard 1.35 1.51 0.49 26.76 4

Concrete slab on ground 3.98 0.29 0.02 5.48 1

Elevated timber floor 2.89 1.68 0.07 8.09 2

Figure 3 | Life-cycle operational energy per square metre of assembly

294 Crawford, Czerniakowski and Fuller

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Page 9: A comprehensive framework for assessing the life-cycle energy of building construction assemblies

life-cycle energy requirements of any building, variation in

embodied energy findings may have a considerable impact

on any conclusions drawn.

The findings from the initial study presented in this

article will be used to further develop the ranking system

in order for it to be applied to a much broader range of

assemblies. This will form the basis of a detailed database

that can then be used by architects and building designers

to compare alternative construction assemblies for particular

building types, elements and locations. The operational

energy requirement for a square metre area of each assem-

bly will be analysed for all Australian climate zones. Oper-

ational energy requirements will vary considerably

depending on the specific characteristics of the external

building envelope and the building location, due mainly

to climatic differences, internal loads, conditioning require-

ment, operating hours and the typical fuel mix to supply

energy for heating and cooling, specific to each state.

Embodied energy requirements may also vary considerably

depending on the source of materials, replacement and

maintenance periods and building life.

Architects and building designers will be able to optimize

the life-cycle environmental performance of buildings by

selecting assemblies (based on their ranking) that result in

the lowest life-cycle energy requirement. This will ultimately

lead to a reduction in energy consumption and greenhouse

gas emissions from the construction sector.

ACKNOWLEDGEMENTS

The late A/Prof. Graham Treloar is gratefully acknowledged

for his many years of encouragement, support and guidance.

The authors also acknowledge Prof. Manfred Lenzen, The

University of Sydney, for his work in developing the base

I–O model used in the study. This work is supported by a

University of Melbourne Strategic Research Initiative Fund

Research Development Grant and a Chartered Institute of

Building Research Development Grant, and the authors

would like to thank both of these bodies for their support

of this project.

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Lawson(1996)

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Timber frame, steel sheetroof

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Polystyrene, timber frame 1.21 –

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Elevated timber floor 2.89 0.24

A comprehensive framework for assessing the life-cycle energy of building construction assemblies 295

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