Energy and Environmental Indicators Related to Construction of Office Buildings

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Resources, Conservation and Recycling 53 (2008) 8695

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Resources, Conservation and Recycling

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / r e s c o n r e c

Energy and environmental indicators related to constructionof office buildings

A. Dimoudi a,b,, C. Tompa b

a Department of Environmental Engineering, Democritus University of Thrace, Vass. Sofias 12, 67100 Xanthi, Greeceb Hellenic Open University, MSc Environmental Design of Cities and Buildings, Patra, Greece

a r t i c l e i n f o

Article history:

Received 21 July 2008

Received in revised form 8 September 2008

Accepted 16 September 2008

Keywords:

Construction materials environmental

assessment

Embodied energy

Sustainable construction

a b s t r a c t

Buildings construction has a major determining role on the environment through consumption of landand raw materials and generation of waste. It is also a significant user of non-renewable energy and

an emitter of greenhouse gases and other gaseous wastes. As environmental issues continue to becomeincreasinglysignificant, buildings becomemore energyefficient andthe energyneeds for their operation

decreases. Thus, the energy required for construction and consequently, for the material production, isgetting of greater importance. The present paper investigates the role of different construction materials

and quantifies them in terms of the embodied energy and the equivalent emissions of CO 2 and SO2 incontemporary office buildings. It also assesses the importance of the embodied energy of the buildings

structure as compared to the operational energy of the building. It was shown that the embodied energyof the structures building materials (concreteand reinforcement steel) represents the largest component

in the buildings total embodied energy of the examined buildings, varing from 66.73% to 59.57%, whiletheembodiedenergy of thebuildingenvelopesmaterials represents a lower butsignificant proportion ofthe buildings total embodied energy. When the construction elements are examined, the slabs have the

highercontributionat theembodied energyof thestudied buildingsand from theenvelope elements, theexternal wall is contributingthe maximum in theoverallembodied energy of thebuilding. Theembodied

energy correspondence varies between 12.55 and 18.50% of the energy needed for the operation of anoffice building over a 50 years life.

2008 Elsevier B.V. All rights reserved.

1. Introduction

Buildings construction has a major determining role on theenvironment. It is a major consumer of land and raw materials andgeneratesa great amountof waste. It isalsoa significant user ofnon-

renewable energy and an emitter of greenhouse gases and othergaseous wastes (Kospomoulos, 2004). The construction industry isone of the greatest consumers of raw materials, following the foodindustry which is in the top list (Berge, 2000). According to data

from the Worldwatch Institute, the construction of buildings con-sumes 40%of thestone, sand and gravel, 25%of thetimber and 16%of the water used annually in the world (Arena and de Rosa, 2003).The building and construction sector (i.e. including production and

transport of building materials) in OECD countries consumes from25% to 40% of the total energy used (as much as 50% in some coun-

Correspondingauthorat: Department of Environmental Engineering,Democri-

tus University of Thrace, Vass. Sofias 12, 67100 Xanthi,

Greece. Tel.: +30 25410 79 388; fax: +30 25410 79 388.

E-mail address: [email protected] (A. Dimoudi).

tries) (Asif et al., 2007). Buildings through their construction, use

and demolition, consume approximately 50% of the final energyconsumption in the members states of the European Union andcontribute almost 50% of the CO2 emissions released in the atmo-sphere, the basic gasresponsible forthe greenhouse effect. In 2006,

the main construction activities in the 27 Member Countries of theEuropean Union are distributed as 27% in the domestic sector, 30%in the non-domestic sector, 20% in infrastructure works and 23% inrenovation and conservation works (Campogrande, 2007).

Several studies have shown that operational energy accountsfor the main amount of total energy use in dwellings during anassumed service life of 50 years and it is approximately 8595% ofthe total energy use (Thormark, 2006). As environmental issues

continue to become increasingly significant, buildings becomemore energy efficient and the energy needs for their operationdecreases and thus, the energy required for construction and

consequently, for the material production, is getting of greaterimportance. Studies concerning low-energy housing show thatembodied energycan account foras much as4060%of totalenergyuse(Winterand Hestnes, 1999;Thormark, 2002). It was also shown

that in a low-energy building the total energy may be even higher

0921-3449/$ see front matter 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.resconrec.2008.09.008
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A. Dimoudi, C. Tompa / Resources, Conservation and Recycling 53 (2008) 8695 87

than in a building with higher operational energy needs, as largeamounts of energy are needed for production and maintenance ofthe technical equipment (Feist, 1996) and to the fact that high-

embodied energy components are often subject to a wide rangeof replacements (Scheuer et al., 2003).

Other studies have investigated the role of different buildingmaterials on the overall energy balance and environmental influ-

ence of the buildings construction sector. The main materialsinvestigated in different national case studies are wood, concrete,steel, brick, with wood based constructions resulting at the lowestenergy needs and CO2 emissions compared to the other materi-

als(Koch, 1992; Buchanan and Honey, 1994; Cole and Kernal, 1996;Buchanan and Levine, 1999; Lenzenand Treloar, 2002; Perez-Garciaet al., 2005; Gustavsson and Sathre, 2006). Studies of Dutch resi-dential constructions revealed that an increase in wood use could

reduce CO2 emissions by almost 50%, compared with traditionalDutch constructions (Goverse et al., 2001). Selection of low envi-ronmental impact materials can result at a reduction up to 30% ofCO2 emissions in the construction phase, as concluded from a case

study of terraced houses in Spain (Gonzlez and Navarro, 2006).Other studies have investigated the environmental impact of localconstruction materials and practices (Venkatarama et al., 2003).

When the relevant contributionof the different building materi-

alswas assessed in a typical semi detached three-bedroomhouseinScotland, it was found that concrete, timber and ceramic tiles arethe three major energy intensive materials used in the building,with concrete alone consuming about 65% of the total embodied

energy of the home. Since concrete has been used in large quan-tity, it was proved that concrete and mortar are responsible for 99%of the total CO2 resulting from the house construction (Asif et al.,2007).

Different factors affect the energy and CO2 balances associ-ated with building materials over their lifecycle. According toGustavsson and Sathre (2006), some of these can be described asuncertainties, resulting from stochastic variations or from lack of

knowledge of precise parameter values. Examples of sources of

uncertainty in CO2 balance related to building materials includethe growth rate of a particular forest stand and the decomposi-tion dynamics of land filled wood. Uncertainty in energy balance

can be caused,for example, by natural differences in physical prop-erties of raw materials such as wood or stone, requiring differentamounts of processing energy. Other factors that influence energyand CO2 balances can be described as variability, determined by

human decisions and management methods. Examples include theprocess technology used to manufacture cement, the fuel used todriveproduction processes,and thechoice ofusingprimary orrecy-cled steel. Combinations of uncertainty and variability that may

be difficult to separate can also affect energy and CO2 balances.For example, different factories may produce identical productsusing physical processes of different efficiency (i.e. with variabil-

ity) but when aggregated in the marketplace or building stock itmaybe impossible to distinguish the differences (i.e. uncertainty ispresent).

The effect on the overall environmental performance of

buildings of different manufacturing procedures and end-of-lifealternatives of the building materials was also investigated in sev-eral studies. The effects of land use and end-of-life alternatives ofbuilding materialswereassessedfor thecase of wood andconcrete-

framed buildings and it was concluded that wood-framed buildingshave lowerenergy useand greenhouse gasemission than concrete-framed buildings (Borjesson and Gustavsson, 2000). Consideringwood substitution in the case of Swedish and Norwegian stud-

ies it was found that wood construction consistently results inlower greenhouse gas emission than non-wood materials, with

the amount depending on material waste management and how

forest carbon flows are considered (Petersen and Solberg, 2005).For the cases of a wood and a concrete-framed building, a varia-tion of key parameters in the manufacture (e.g. clinker production

efficiency, blending of cement, crushing of aggregate, recycling ofsteel, lumber drying efficiency) and use of the materials (e.g. mate-rial transportation distance, carbon intensity of fossil fuel, recoveryof logging, sawmill, construction and demolition residues for bio-

fuel, growth and exploitation of surplus forest not needed forwoodmaterial production) were considered and it was concluded thatthe use of wood building material instead of concrete, coupledwith greater integration of wood by-products into energy systems,

would be an effective means of reducing fossil fuel use and net CO2emission to the atmosphere (Gustavsson and Sathre, 2006).

The need for considering not only the operational energy of abuilding but also the energy attributable to activities being under-

taken by actual users of a building as well as common activities ofhouseholds for a couple over a 30-year period was examined in anexample of an Australian two bedroom residential building. It wasfound that the amount of primary energy simulated for the oper-

ational energy of the house and the petrol used in motor vehiclesrepresented only 30% of the total life cycle energy, showing that theindirect energycomponent of the life cycle energyof the house andthe households activities is more important than the direct energy

component (i.e. for house operation and car operation). (Treloar etal., 2000).

Use ofanymethodcan onlybe assuccessfulas the validity oftherespective database and thus, any results drawn from an environ-

mental study for a building have to be accompanied by a detailedstatement on the origins of the basic data used for the evaluationof the building components (Papadopoulos and Giama, 2007).

The embodied energy related to construction of office buildings

was evaluatad by Cole and Kernal (1996) for construction practicesin Canada. Reviewingpreviousrelevant workfor office buildings (inN. Zealand, Australia, Japan, Canada, U.S., U.K.), theyshowed that bigdifferences on estimated values between the different case studies

existvariation by up to 10 times.

The present paper investigates the role of different constructionmaterials and quantifies them in terms of the embodied energyandthe equivalent emissionsof CO2 andSO2 in contemporary office

buildingsin Greece. It also assesses theimportance ofthe embodiedenergy of the buildings structure as compared to the operationalenergy of the building. The environmental impact of two officebuildings in Greece, following contemporary construction practice

was evaluated for the construction phases of a building, work thatcorresponds at about 5560% of the total budget of the project.

The aims of the current paper are to:

investigate whether there are significant differences in initialembodied energy of different construction practices in officebuildings in Greece:a more conventional one and one with more

contemporary materials, investigate the order of magnitude of the embodied energy of

the construction materials compared with the overall energyperformance of the building. Thus, the analysis proceeded intocomparing the embodied energy and the relevant environmen-

tal indicators (CO2, SO2 emissions) of the construction materialswith the operational energy of the buildings,

highlight the importance of embodied energy of the structural

materialsas compared with the operationalenergyneeds of officebuildings based on current and future energy needs of officebuilding in Greece.

The analysis of the contribution of the different building ele-ments andmaterials on theoverallembodiedenergy of thebuilding

aimed at identifying those components and materials with the


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88 A. Dimoudi, C. Tompa / Resources, Conservation and Recycling 53 (2008) 8695

higher contribution on the energy embodied in the constructionof office buildings and thus, at exploring possible proposals onminimizing them.

In this particular case study, only the emissions of CO 2 and SO2have been studied (gases which contribute to global warming andatmospheric acidification respectively) but the same study can alsobe extended to other harmful environmental implications imposed

by the construction industry: for example, the emission of heavymetals to the atmosphere and water, the use of non-renewableenergy sources, the effects on eutrophication and on water con-sumption.

2. Case study office buildings

The construction practicesin twocontemporary officebuildings,located at Athens, Greece, were investigated. The two examinedoffice buildings are of different morphology and size, nevertheless,

both buildingsare constructed accordingto thesame national stan-dards (e.g. Thermal Insulation Regulation,Building Codes,ConcreteCodes and Fire-protection regulation). The buildings envelopematerials differ but they can be considered as typical construc-

tion solutions for contemporary office buildings in Greece. Theselection of these two typical office buildings was made in orderto compare and quantify the environmental impact of differ-ent building materials and elements in the construction of office

buildings.The 1st examined building is a five-storey, office building with

2 basements and a flat roof. The total usable area of the build-ing (including the basement) is 1891 m2. The support frame of

the building is constructed of reinforced concrete (category classC16/20) according to the current national concrete standards. Theexternal and internal walls were constructed of brick and mortar.External walls are double brickwalls (0.27 m thickness) with core

thermal insulation, a 5-cm thick extruded polystyrene layer. Theexternal concrete building elements (columns, beams, structural

walls) were also externally thermally insulated with a 5-cm thickextruded polystyrene layer. The envelope of the basement is not

thermally insulated but water resistance layers were applied. Theflat, reinforced concrete roof of the building was insulated with a5-cm extruded polystyrene layer. The flooring material is ceramictiles in the office spaces and marble in the corridors and staircases.

The 2nd examined building is a three-storey, office buildingwith a basement and a flat roof. The total usable area of the

building (including the basement) is 400 m2. The support frame

of the building is constructed of reinforced concrete (categoryclass C16/20) according to the national standards. The externaland internal walls were constructed of brick and mortar. Theexternal walls are double brickwalls (0.27 m thickness), with core

thermal insulation of a 5-cm thick mineral wool layer. The exter-nal concrete building elements (columns, beams, structural walls)

were externally insulated with a 5-cm thick extruded polystyrenelayer. The basement is not thermally insulated but water resis-

tant protection was applied. The flat reinforced concrete roof ofthe building has a 5-cm extruded polystyrene layer. The build-ing facades are covered with aluminium cladding, an elementthat is used in the last years in the construction of modern style

office buildings. The aluminium composite panel (4 mm thick-ness and density 1425kg/m3) consists of two aluminium sheets(0.50 mm thickness and density 2700 kg/m3) with a polyethylene

core (3 mm thickness and density 1000 kg/m3). The flooring mate-rial is vinyl tiles in the offices and marble in all corridors andstaircases.

3. Methodology

Each building was analysed in the different building elementsthat constitute it, according to the project drawings. The build-

ing elements were in turn analysed into their constituent materiallayers. The data for the environmental parameters of the differentbuilding materials were collected from the international literature(SIA, CBPR) as presented in Bikas, 2001 (Table 1), since there is no

data available in Greece. As far as the aluminium composite panelis concerned, data were not available and in order to calculate itsenvironmental attributes, the material was analysed according toits constituent layers.

The constructiondetails together with quantitydata of theenvi-ronmentalattributes to7 ofthe main buildingelements (per 1 m2 ofexternal area), covering 5 elements of the building envelope (insu-

lated)and 2 internal building elements (uninsulated) are presentedin Tables 2a and 2b (Tompa, 2005). The table illustrates the con-struction details of each element, description of each material layerwith its corresponding thickness and in the last column the energyand environmental characteristics of each building element. The

reinforcement steel was considered in the estimations of the build-ing element involving reinforcement concrete. The constructiondata for Building 1 were used.

Table 1

Environmental attributes (embodied energy and equivalent CO2 and SO2 emissions) of building materials.

Material Embodied energy (MJ/kg) Equivalent CO2 (g CO2/kg) Equivalent SO2 (g SO2/kg) Lifetime Data source

Mortar 0.5 74 0.29

Cement flooring tiles 1.2 123 0.4 80Light concrete (for slopes) 0.4 68 0.25 80 SIA

Concrete (structure) 0.7 123 0.4 80 SIA

Reinforcement steel 9.9 474 1.79 SIA

Extruded polysterene 90.7a 1914a 17.57a

Mineral wool 15.9 1042 4.22 40

Brick 2.7a 247 0.94 80

Ceramic tiles 2.5 225 1.09

Internal plaster 1.4 181 0.61 40 SIA

External plaster 1.4 182 0.63 40 SIA

PVC membrane 51.6 2043 14.27 25 SIAAluminium sheet 312.7 11815 94.83 SIA

Polyethylene 103b

Vinyl tiles 79.1b

Source: Bikas, 2001.a Bikas and Milonas, 1999.b

Centre for Building Performance Research, Victoria University of Wellington, New Zealand, http://www.vuw.ac.nz/cbpr/documents/pdfs/ee-coefficients.pdf .
http://www.vuw.ac.nz/cbpr/documents/pdfs/ee-coefficients.pdfhttp://www.vuw.ac.nz/cbpr/documents/pdfs/ee-coefficients.pdfhttp://www.vuw.ac.nz/cbpr/documents/pdfs/ee-coefficients.pdf


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Table 2a

Environmental attributes of building elements (Reinforcement steel was considered in estimations).

4. Results and discussion

4.1. Buildings embodied energy assessment and relevant

environmental indicators

Thevalues of theembodied energyand theequivalent emissions

of CO2 and SO2 in terms of total values and per square meter ofoverall floor area of each building are presented in Table 3 and in

graphical form in Figs. 13.

The embodied energy of building 1 reaches the value of 3647 GJwhilefor building 2 thecorrespondingvalue is 1309GJ, correspond-

ing with 378 tn CO2 and 1.5tn SO2 for building 1 and 116 tn CO2and 0.5 tn SO2 for building 2. It is shown that although the totalvalue of embodied energy, equivalent CO2 and SO2 emissions forbuilding 1 are greater than building 2 (Table 3), the correspond-

ing specific values expressed per floor area are greater for building2 (Figs. 13) (Tompa and Dimoudi, 2007). The relevant contribu-

tion of the different materials on the environmental performance


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Table 2b

Environmental attributes of building elements (Reinforcement steel was considered in estimations).

Table 3

Embodied energy and equivalents CO2 and SO2 of buildings 1 and 2.

Embodied energy (GJ) Equivalent CO2 (kg) Equivalent SO2 (kg) Embodied energy/m2 (GJ/m2) Equivalent CO2 (kg/m2) Equivalent SO2 (kg/m2)

Building 1 3647 377899 1469 1.93 199.84 0.78

Building 2 1309 115759 464 3.27 289.40 1.16

of the two building is analysed and discussed in the followingsections.

4.2. Building materials

Each building was analysed into its construction materialsin order to analyse and compare the energy and environmen-

tal attribute of each one of the two construction practices. Thecommon building materials in both buildings were concrete, rein-forcement steel, bricks, extruded polysterene for the insulation ofstructural building elements and forthe insulation of flatroof,plas-

ter, mortar,cement flooring tiles, PVC membrane.Building materials that differ concern insulation of the external

brickwalls (building 1: extruded polysterene, building 2: min-eral wool), the facade cladding (building 1: plaster, building 2:

cladding with aluminium composite panel) and the flooring mate-rials (building 1: ceramic tiles, building 2: vinyl tiles). The totalquantitiesand the environmental parameters of each material used

Fig. 1. Embodied energy per m

2

of total floor area of the building.

in every building are presented in Table 4 for building 1 and inTable 5 for building 2.

The percentage participation of the weight and environmental

parameters of building materialsembodiedenergy, equivalent CO2and SO2 emissions in the entire building is presented in Fig. 4 for

building 1 and in Fig. 5 for building 2.By examining the results of the analysis we can see that:

The embodied energyof the structures building materials (rein-forced concrete) representsthe largest component in the buildingstotal embodied energy for both buildings, representing 66.73%for building 1 (42.43% for concrete and 24.3% for reinforcement

steel) and 59.57% for building 2 (35.78% for concrete and 23.79%for reinforcement steel). The embodied energy of building enve-lopesmaterials represents a lowerbut significant proportion of thebuildings total embodied energy. In case of the conventional con-

struction (building 1) brickshave the higher embodied energythanthe other envelope materials, with a contribution of 10.70%. In caseof themore modern constructionwith aluminiumcladding,the sit-

Fig. 2. Equivalent CO2 emissions per m

2

of buildings total floor area.


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Table 4

Structural materials and environmental parameters of building materialsbuilding 1.

Material Volume (m3) Density (kg/m3) Weight (kg) Embodied energy (MJ) Equivalent CO2 (kg) Equ ivalent SO2 (kg)

Concrete 930.795 2400 2233908 1547467 234593 885

Reinforcement steel 11.332 7900 89521 886258 42433 160

Bricks 103.236 1400 144530 390231 35699 136

Cement flooring tiles 9.038 2400 21691 26029 2668 9

Mortar 29.154 1800 52477 26239 3883 15

Internal plasters 88.434 1800 159181 222853 28812 97External plasters 17.891 1900 33993 47590 6187 21

Ceramic tiles 30.794 2000 61588 153970 13857 67

Extruded polystyrene 67.533 35 2364 214415 4525 42

PVC membrane 2.566 1000 2566 132406 5242 37

Total 3647458 377899 1469

Fig. 3. Equivalent SO2 emissions per m2 of buildings total floor area.

uationis quitedifferentas thealuminium claddingshavethe higherembodied energy fromall otherenvelopematerials (11.14%) despite

its small total weight compared to the overall weight of materialsused in the building. The application of aluminium claddings also

influences the relevantcontribution of plaster in the totalembodiedenergy. The percentage participation of plaster (internal and exter-

nal) is 7.41% for building 1, while for building 2 is only 4.07%, as thebuilding facades are covered with aluminium cladding. This rela-tively low percentage participation of bricks is due to the fact thatthe internal brickwalls are limited in both buildings and especially

in building 1, as the partitins are constructed of plasterboard, acommon practice in office buildings. Anyway, in residential build-ings, the percentage participation of bricks in the buildings totalembodied energy is much higher, resulting at much lowerpercent-

age participation of concrete and of reinforcement steel.The percentage participation of the insulation materials,

extruded polystyrene for both buildings and additional mineral

wool forbuilding2, is significantlylower(5.88%and 4.96% forbuild-ings 1 and 2 respectively), as well as the percentage participation

of PVC membrane (3.63% for building 1 and 5.51% for building 2),despite the very high values of the materials embodied energy, asthey are used in very small quantities in both buildings. As far asthe flooring materials are concerned, in building 2, the percent-

age participation of vinyl tiles is relatively high (6.54%) if we takeinto consideration their small thickness while in building 1, thepercentage participation of ceramic tiles is 4.22%.

When the paints are also analysed, it is found that they con-

tribute with less than 1% in the overall balance of the embodiedenergy of the buildings, the values ranging from 0.88% for building1 to 0.49% for building 2.

The CO2 equivalent emissions of the structures building mate-

rials (concrete and reinforcement steel) represent a dominantproportion of the buildings total equivalent CO2 emissions forboth buildings, representing 73.30% for building 1 (62.08% for con-crete and 11.22% for reinforcement steel) and 75.30% for building 2

(62.42% for concrete and 12.88% for reinforcement steel). The CO 2equivalent emissions of building envelopes materials represent a

lower proportion of the buildings total CO2 equivalent emissions,about the one fourth of the total CO2 emissions from the building.

Bricksare thegreater contributor from theenvelopematerialin CO2emissions, withpercentage of 9.45% and 7.30% forbuildings 1 and 2respectively. The percentage participation of plaster is significantlylower, 9.26% for building 1 and 5.94% for building 2, while the per-

centage participation of aluminium composite panel is 4.15%. Thepercentage values of the extruded polystyrene and the PVC mem-brane are lower, despite the very high values of the materials CO 2equivalent emissionsbecause they areused in very small quantities

in the buildings.The SO2 equivalent emissions of the structures building mate-

rials (concrete and reinforcement steel) represent a dominant

Table 5

Structural materials and evironmental parameters of building materialsbuilding 2.

Material Volume (m3) Density (kg/m3) Weight (kg) Embodied energy (MJ) Equivalent CO2 (kg) Equ ivalent SO2 (kg)

Concrete 283.573 2400 680575 468373 72259 261

Reinforcement steel 3.980 7900 31442 311424 14911 56

Bricks 24.450 1400 34230 92421 8455 32

Cement flooring tiles 4461 2400 10706 12848 1317 4

Mortar 2.230 1800 4015 2008 297 1

Internal plasters 19.594 1800 35269 49377 6384 22External plasters 1.455 1900 2765 3871 503 2

Vinyl tiles 0.722 1500 1083 85665 2213 15

Mineral wool 5.468 100 547 8694 570 2

Extruded polystyrene 17.740 35 621 56316 1188 11

PVC membrane 1.397 1000 1397 72085 2854 20

Aluminium panel 0.506 1425 721 145845 4809 38

Total 1308927 115759 464


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Fig. 4. Contribution of the different materials in the embodied energy, equivalent CO2 and SO2 emissions in building 1.

proportion of the buildings total equivalent SO2 emissions for

both buildings, representing 71.18% for building 1 (60.27% for con-crete and 10.91% for reinforcement steel) and 68.29% for building

2 (56.16% for concrete and 12.13% for reinforcement steel). The SO2equivalent emissions of building envelopes materials represent a

significant proportion of the buildings total SO2 equivalent emis-sions, with bricks contributing with 9.25% and 6.93% forbuildings 1and 2 respectively. The percentage participation of plasters is 8.07%for building 1 and 5.01% for building 2, while the percentage par-

ticipation of the aluminium composite panel in the building 2 issignificantly higher (8.14%), because of the very high value of thematerials SO2 equivalent emissions (94.83 g SO2/kg). The percent-age values of insulation and PVC membrane are lower, despite the

very high values of the materials SO2 equivalent emissions as theyare used in very small quantities in buildings.

The percentage values of the environmental attributes of thestructures building materials and of brick in the envelope do not

present considerable differentiation in both buildings, despite theirdifferent morphology, because the quantities of materials usedare proportional to the floor area. The percentage participation ofconcrete is of great importance for the buildings total embodied

energy, as it rises to 42% and, if we include the reinforcement steel,it rises to 66%, while the percentage participation of concrete inthe entire building values of the equivalent SO2 is even more sig-nificant. Concrete as a material has smaller values of embodied

energy and environmental impacts as compared to other construc-

tion materialssuch as aluminium, ceramic andvinyl tiles. However,

since concrete is used in a very large quantity in any construc-tion, it becomes responsible for a large share of the gross embodied

energy and environmental impacts. Given the fact that buildings inGreece are mainly built of reinforced concrete and that buildings

total embodied energy is proportional to the amount of the mate-rial used and to the value of the materials embodied energy, thefirst priority should be the choice of construction practices whichsave quantities of material.

Another priority should be the use of building elements withlow embodied energy and equivalent pollutant emitters (CO2, SO2).Among materials with comparable properties, one must choosethe material not only with the lower embodied energy but also

with the lower environmental impact, even when this materialis present in small quantities and its participation in the entirebuilding values does not seem significant. So, ceramic tiles arepreferable to vinyl tiles and plaster is preferable to aluminium

composite cladding panels. However, it can be argued that alu-minium composite cladding panels have the advantage of a longerlife span and they may also be produced from recycled aluminium.Ceramic tiles have longer life duration than vinyl tiles and their

replacement may not be required during the assumed buildinglife span. Materials, that are present in very small quantities in abuilding, such as insulation and PVC membrane, however, havedisproportionate environmental impact due to their production

procedures.

Fig. 5. Contribution of the different materials in the embodied energy, equivalent CO2 and SO2 emissions in building 2.


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Fig. 6. Contribution of the different building elements in the overall embodied energy, equivalent CO2 and SO2 emissions in building 1.

4.3. Building elements

The estimation of the embodied energy and the equivalent CO 2and SO2 emissions of the building construction elements (beams,columns, shear walls, slabs, flat roof, staircase, foundation) whichare constituted from reinforced concrete, was based on the values

of the total weight of reinforcement steel and concrete, as takenfrom the records of the construction company and the construc-tion details of the different building elements. The total quantity ofsteel was equally distributed at each building element according

to the volume of concrete corresponding at each element con-structed of reinforced concrete. The relevant contribution of themain structural elements in the embodied energy and environ-mental emissions, CO2 and SO2, are illustrated in Figs. 6 and 7 for

buildings 1 and 2 respectively.When the constructionelements are examined,we observe that

slabs have the higher contribution at the embodied energy in both

buildings with a proportion of 35.0% and 27.0% for buildings 1 and2 respectively. According to the comments made in the previoussection, this can be attributed at the high quantities of reinforcedconcrete used in this building component. Shear walls have alsoa high contribution in the overall performance. This conclusion

is in accordance with previous relevant studies for buildings inGreece (Bikas, 2001). It should be stated that construction prac-tices in Greece due to strict standards for earthquake protection ofbuildings demand big surfaces of support frame elements made of

reinforced concrete.

From the envelope elements, the external wall is contributingthe maximum with 1214% in the overall embodied energy of the

building. As the studied buildings are office buildings which areusually open plan buildings, without internal walls, the externalwalls are the dominant envelope element regarding their environ-mental performance.

4.4. Overall energy assessment of the two buildings

The embodied energy of the building construction materials arecompared with the energy needed to operate an office building in

the area of Athens (climatic zone B). Studies on the energy per-formance of office buildings based on energy audit data of officebuildings in different regions of Greece (Santamouris et al., 1994)and verified by comparing them against the actual annual energy

balance data reported bythe Hellenic Ministry of Development givethat the overall energy consumption of an office varies according

to the construction period of the building and the climatic zone itis located (Gaglia et al., 2007). The specific annual overall energy

consumption (in kWh/m2), covering both thermal and electricalenergy consumption, for office buildings in each of the 4 climaticzones (AD) is presented in Table 6. The mean overall energy con-sumptionfor a buildingconstructed inthe last decade(period2001)

is 131kWh/m2 while for buildings to be constructed in the future(period 2010) the expected energy consumption is estimated at141 kWh/m2. By comparing the embodied energy of the two build-ings (Table 3) with the expected operational energy (Table 6), for

Fig. 7. Contribution of the different building elements in the overall embodied energy, equivalent CO2 and SO2 emissions in building 2.


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Table 6

Equivalent years between embodied energy and operation energy for the 2 office buildings.

Climatic zone (construction period: 2001) Mean value Climatic zone (construction period: 2010) Mean value

A B C D A B C D

Annual overall energy consumption

(kWh/m2)

119 126 140 158 131 136 137 147 166 141

Equivalent yearsBuilding 1 6.91 6.53 5.87 5.20 6.28 6.05 6.00 5.59 4.95 5.83

Building 2 10.19 9.62 8.66 7.67 9.25 8.91 8.85 8.25 7.30 8.60

% Contribution (over expected life period)

Building 1 13.82 13.05 11.75 10.41 12.55 12.09 12.00 11.19 9.91 11.66

Building 2 20.37 19.24 17.31 15.34 18.50 17.82 17.69 16.49 14.60 17.19

buildings constructed in the decade of 2000, this corresponds at

6.91 years for the climatic zone A (regions with high ambient tem-peratures) to 5.20 years for the climatic zone D (regions with thelowest ambient temperatures), with a valueof 6.28 yearsfor a meanstructure in Greece. For buildings to be constructed in the near

future (period 2010), the corresponding values vary from 6.05 to4.95 years with a mean value of 5.83 years.

For the morecontemporary construction(building 2), the equiv-alent years are much higher, as they vary from 10.19 to 7.67 years

with a mean value of 9.25 years for the construction period 2001while for a future construction these values vary form 8.91 to 7.30with a mean value of 8.60 years.

For a life cycle of a building of 50 years, the embodied energy of

the two buildings corresponds at 13.05% and 19.24% of the overallenergyconsumption of the buildings for the climatic zone B, wherethe studied buildings belong. In average, the embodied energycorrespondence varies between 12.55% and 18.50% of the energy

needed for the operation of an office building constructed in thelast decade.

A significant parameter that affects energy consumption ofbuildings and the overall ecological balance is heat island. Energy

consumption for cooling of buildings shows an increasing trend

worldwide not only in countries that are characterized by hot cli-matic conditions but also in cities suffering from the heat islandeffect. Urban heat islands with daytime average air temperatures

25 C higher than the surrounding rural areas are present inmany cities around the world while in Athens, Greece, the dailyheat island intensity under the canopy was found to be closeto 10 C (Santamouris, 2007). Heat islands attribute not only to

thermal discomfort but also the increased air temperatures, raiseair-conditioning energy consumption in buildings and peak elec-tricity demand.

Innovative materials, like cool building materials, have been

developed during the last years, achieving decrease of the demandfor air conditioning of buildings (Akbari et al., 1992; Synnefa et al.,2007). In the existence of available data of the embodied energy of

these materials, the assessment of the overall energy performanceof buildings will give valuable results.

5. Conclusions

This papers has studied the contribution of building materialsin the overall environmental performance of office buildings by

examining 2 office buildings in Athens, Greece.The embodied energyof the structures building materials(con-

crete and reinforcement steel) represents the largest componentin the buildings total embodied energy of the examined build-

ings, representing 66.73% for building 1 and 59.57% for building2 while the embodied energy of the building envelopes materials

represents a lower but significant proportion of the buildings total

embodied energy. The percentage participation of the insulation

materials and flooring materials is significantly lower despite thevery high values ofthe materials embodiedenergy,as they areusedin small quantities in both buildings. In case of the more modernconstruction with aluminium cladding, the aluminium claddings

have the higherembodied energyfrom allotherenvelope materials(11.14%) despite their small total weight compared to the over-all weight of materials used in the building. The application ofaluminium claddings also influences the relevant contribution of

plaster in the total embodied energy.The CO2 equivalent emissions of the structures building mate-

rials represent a dominant proportion of the buildings totalequivalent CO2 emissions for both buildings, representing 73.30%

for building 1 and 75.30% for building 2 while the building enve-lopes materials represent a lowerproportion of the buildings totalCO2 equivalent emissions, about the one fourth of the total CO 2emissions from the building.

Concrete as a material has smaller values of embodied energyand environmental impacts as compared to other constructionmaterials such as aluminium, ceramic and vinyl tiles. Given thefact that buildings in Greece are mainly built of reinforced con-

crete and that the buildings total embodied energy is proportional

to the amount of the materials used and to the value of the mate-rials embodied energy, the first priority should be the choice ofconstruction practices which save quantities of material.

When the construction elements are examined we observe thatslabs have the higher contribution at the embodied energy in bothbuildings, with a proportion of 35.0% and 21.0% for buildings 1 and2 respectively.

From the envelope elements, the external wall is contributingthe maximum with 1213% in the overall embodied energy of thebuilding. As the studied buildings are office buildings which areusually open plan buildings, without internal walls, the external

walls are the dominant envelope element regarding their environ-mental performance.

The embodied energy of the shell of the two office buildings,

support frame and envelope, corresponds at 6.53 and 9.62 years ofthe expected energy consumption for the operation of these build-ing in the climatic zone B, with a value of 6.289.25 years for amean structure in Greece for buildings 1 and 2 accordingly. For a

life cycle of a building of 50 years, the embodied energy of the twobuildings corresponds at 13.05% and 19.24% of the overall energyconsumption of the buildings for the climatic zone B, where thestudied buildings belong. In average, the embodied energy corre-

spondence varies between 12.55%and 18.50% of the energyneededfor the operation of an office building. Considering that buildingsbecome more energy efficient and energy standards imposed inthe different countries will result to lower energy consumption in

buildings, we conclude that the contribution of the initial embod-ied energy and environmental parameters (equivalent CO2 and SO2

emissions) of the building materials will become more important


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in the overall environmental performance of buildings in future.It should be mentioned that this study was based on data from

the international literature and many figures may change in the

existence of national, more representative data on the embod-ied energy and the environmental parameters for the materialsand manufacturing processes applied in Greece. It is evident thatnational data may differ between different countries as the com-

ponents involved in estimation of the environmental attributeslike primary material sources, transportation, manufacturing pro-cesses, energy production may significantly affect the absolutefigures of embodied energy and equivalent emissions. As men-

tionedin previousstudies aswell,published studies provide a guideto typical ranges of the initial embodied energy of buildings and itis difficult to interpret and compare the studies because of lackof detailed pieces of information on the origins of each material

estimations.Comparison between different studies is not always straight-

forward as the components included in the embodied energyestimation may differ between the studies e.g. some studies apart

from the structure and envelope incorporate relevant estimationsfor site work, services and construction for the building. Thus, itgets difficult to explain the differences between estimated values,given the limited description of what constitutes the parts of esti-

mations in the different case studies. It should be also stressedthat construction practices differ from country to country, espe-cially between different continents. Variation in estimated valuescan also be attributed at the different materials used in different

construction practices, different data used for the same material(e.g. for embodied energy, density), on the definition of the differ-ent construction components taken into account in the analysis, onthe size of the building and the structure (e.g. existence or not of

underground parking).The materials choice in the construction of buildings is deter-

minant for the energy required for the construction of buildingsand for the environmental implications. Contemporary materi-

als used in modern buildings (e.g. aluminium panels) are more

energy intensive and with higher environmental emissions. Forgiven construction practice, the buildings totalembodied energy isproportional to the amount of the material used and to thevalue of

the materials embodied energy. Therefore, the first priority shouldbe the choice of construction practices which save quantities ofmaterial.This priority is valid, especially forthe reinforcedconcrete,because of its very high participation in the buildings embodied

energy and correspondingly in the entire building values of theequivalent CO2 and SO2 and given the fact that buildings in Greeceare mainly built of reinforced concrete.

Also priority should be the use of building elements with low

embodied energy and equivalent pollutant emitters (CO2, SO2).Among materials with comparable properties, one must choosenot only the material with the lower embodied energy but also

with the lower environmental impact. As far as construction prac-tices are concerned, additional criteria should be considered likethe lifetime of building materials, the compatibility of the lifetimeamong the layers building materials, the kind of assembly of differ-

ent materials and of the different layers, their maintenance needsover the building life cycle. In the existence of available data of theembodied energy of innovative materials, like cooling materials,the assessment of the overall energy performance of buildings will

also give valuable results.

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Energy and Environmental Indicators Related to Construction of Office Buildings