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Building and Environment 46 (2011) 1962e1971

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Building and Environment

journal homepage: www.elsevier .com/locate/bui ldenv

Sustainability assessment and rating of buildings: Developing the methodologySBToolPTeH

Ricardo Mateus*, Luís BragançaUniversity of Minho, Department of Civil Engineering, 4800-048 Guimarães, Portugal

a r t i c l e i n f o

Article history:Received 1 October 2010Received in revised form18 March 2011Accepted 5 April 2011

Keywords:Building sustainability assessmentLife-cycleRatingSustainability

* Corresponding author.E-mail addresses: ricardomateus@civil.uminho.pt

uminho.pt (L. Bragança).

0360-1323/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.buildenv.2011.04.023

a b s t r a c t

Although sustainable building is a multidimensional concept, attention to the issue often focuses solelyon environmental indicators, ignoring the substantial importance of social, economic and culturalindicators. Building sustainability involves various relations between built, natural and social systemsand therefore comprises a complex of different priorities that require consideration at each stage ofa building’s life-cycle. To cope with this complexity and to support sustainability systematic, holistic andpractical approaches to building design need to be developed. The main objective of a systematicmethodology is to support the development of a building design that achieves the most appropriatebalance between the different sustainability dimensions, and is, at the same time, practical, transparentand flexible enough to be easily adapted to different types of buildings and technology.

It is the aim of this paper to present an innovative approach for developing building sustainabilityassessment and rating, and to contribute to the evolution of generic methodology and internationalunderstanding by introducing an approach which takes the different dimensions of sustainability intoaccount. The scope of the methodology presented in this paper (SBToolPTeH) is to assess the sustain-ability of existing, new and renovated residential buildings in urban areas, specifically in the Portuguesecontext.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Construction, including the building sector, first began torecognize the impact of its activities on Sustainable Development inthe 1990s [1]. In the construction and real estate sector, sustain-ability issues have global, as well as local and sectorial features. Theconstruction and real estate sector has a strong influence oneconomies and societies, and thus is linked to global environmentalsustainability indexes, such as the ESI scores from the Universitiesof Yale and Columbia which benchmark the ability of nations toprotect the environment worldwide [2]. Agenda 21 on sustainableconstruction [3] emphasized the importance of proceeding withrelated non-technical issues in order to successfully implementimprovement strategies. The fundamental differences betweenthese dimensions have been effectively identified by researchers,for example, Ronchi et al., whose study states that “quality of life isrecognised as the non-physical and non-ecosystem counterpart of anysuitable model of sustainable development” [4].

(R. Mateus), braganca@civil.

All rights reserved.

Due to an increasing awareness of the effects of the contempo-rary development model on climate change and the growing inter-national movement towards high-performance/sustainablebuildings, the current paradigmof building is changing rapidly. Suchchange is affecting both the nature of the built environment as wellthe actual method of designing and constructing a facility. Thisnewly emerging approach differs from established practice in thefollowing important ways: by selecting project team members onthe basis of their eco-efficient and sustainable building expertise;increased collaboration among the project teammembers and otherstakeholders; greater focus on global building performance than onbuilding systems; a strong emphasis on environmental protectionfor thewhole life-cycle of a building; careful considerationofworkerhealth and occupant health and comfort throughout all phases;scrutiny of all decisions for their resource and life-cycle implica-tions; the added requirement of building commissioning, and a realemphasis on reducing construction and demolition waste [5].

A building project can be regarded as sustainable only when allthe different dimensions of sustainability e environmental,economic, social and cultural e are taken into account. The variousissues of sustainability are interrelated, and the interaction ofa building with its surroundings has important ramifications.Common concerns include those of reducing the use of non-

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e1971 1963

renewable materials and water, as well as the production of emis-sions, waste and pollutants. The following goals are thosemost oftenfound on building project agendas: optimization of site potential;preservation of regional and cultural identity; minimization ofenergy consumption; protection and conservation of waterresources; use of environmentally friendly materials and products;healthy and convenient indoor climate, and optimized operationaland maintenance practices [6]. To attain these goals and to supporta sustainable building design, systematic, holistic and practicalapproaches must be properly implemented. Developing and usingbuilding sustainability assessment methods is one solution toexplore in order to promote a more sustainable built environment.

The following paragraphs will present an innovative approachfor developing building sustainability assessment and rating andcontribute to the evolution of generic methodology and inter-national understanding by introducing an approach which takesthe different dimensions of sustainability into account. Thisapproach is based on the state-of-the-art in building sustain-ability assessment, including the latest developments archived bythe above mentioned standardization bodies and in other inter-national fora.

1.1. The state-of-the-art on sustainability assessment methodologies

The purpose of sustainability assessments is to gather and reportinformation for decision-making during the different phases ofconstruction, design and use of a building. The sustainability scoresor profiles based on indicators result from a process in which therelevant phenomena are identified, analyzed and valued. At present,it is possible to identify two opposite trends at work in the process:on the one hand, the indicators commonly used by the differentoperators are characterised by their complexity and diversity while,on the other hand, there is a growing movement towards betterusability through common understanding and simplicity.

Building sustainability assessments based on a life-cycleapproach can produce important long-term benefits for bothbuilding owners and occupants [7], namely: helping to minimizeenvironmental impacts; solving existing building problems; creatinghealthier, more comfortable andmore productive indoor spaces, andreducing building operation and maintenance costs. Life-cycleanalysis considers all the inputs and outputs of acquiring, owning,and disposing of a building system. This approach is particularlyuseful when project alternatives, which fulfil the same performancerequirements, but differ with respect to initial costs and operatingcosts, have to be compared in order to select the one that maximizesnet savings [7].

The development of assessment methods and the respectivetools is a challenge both for the academia and in practice. An issueof prime importance is that of managing the flows of informationand knowledge between the various levels of indicator systems.An important constraint to these methods is that the specificdefinition of the terms “sustainable building” or “high perfor-mance building” is complex, since different actors in the building’slife-cycle have different interests and requirements [8]. Forinstance, promoters will give more attention to economic issues,whereas the end users are more interested in health and comfortissues [1].

During the last two decades a significant number of environ-mental and sustainability assessment tools for buildings have beendeveloped. The first commercially available environmental assess-ment tool for buildings was the Building Research EstablishmentAssessment Method (BREAM) [9,10]. This method was establishedin the UK in 1990 and together with the following two rating andcertification systems it provides the basis for the other approachesused throughout the world: Sustainable Building Tool (SBTool),

developed through the collaborative work of representatives from20 countries [11]; and the Leadership in Energy and EnvironmentalDesign (LEED�), developed in the U.S.A. [12]. In general, thesemethods are characterized by assessing a number of partialbuilding features and aggregating these results into an environ-mental rating or sustainability score [13].

In the SBTool the approach is to weight different indicators,taking into account weighting factors that are fixed at the nationallevel. Each “score” is the result of the comparison between thestudied building and the national reference. This scheme allows aninternational comparison of buildings from different countries.Other tools, for instance, BREEAM and LEED, are based upon credits.The maximum number of credits available for each indicator isrelated to its weight in the overall score, which is expressed bya rating (e.g. from Pass to Excellent in BREEAM).

There are also LCA-based tools available that are especiallydeveloped to address the building as whole, such as, for example,Eco-Quantum (Netherlands) [14], EcoEffect (Sweden) [15], Env-est2 (U.K.) [16], BEES 4.0 (U.S.) [17] and ATHENA (Canada) [18]. Inthe existing literature, comparative studies of contextual andmethodological aspects of tools have been made, for example,Forsberg and Malmborg [19]. Haapio and Viitaniemi [1] also per-formed a study that analysed and categorised a group of sixteenenvironmental impact assessment tools. The majority of thesetools are developed according to a bottomeup approach, i.e.a combination of building materials and components add up toa building, even though they are designed to consider the wholebuilding, including energy demand, etc [20]. Tools to supportdecision-making in accordance with principles of performance-based design have also been developed, mainly in researchcommunities.

Sustainability assessment tools are constantly evolving in orderto overcome their various limitations. The main goal, at present, isto develop and implement a systematic methodology to supporta building design which achieves the most appropriate balancebetween the different sustainability dimensions, and which is, atthe same time, practical, transparent and flexible enough to beeasily adapted to different kinds of buildings and to the constantevolution of technology. There are many countries that alreadyhave or are in the process of developing domestic assessmentmethods, which means that examples of international exchangeand coordination are increasingly evident.

Sustainability assessments are usually based on indicators.These indicators provide information about the main influencesof the industry as a whole and about the impacts of constructionand operation of buildings and other built assets [21]. In trying toestablish a list of generally accepted indicators, it seems thatdevelopment leads to different parameters and weighting factorsin different countries [22]. This finding can be regarded as a realresponse to the actual needs of decision-making as both theessential indicators and their weights are highly dependent onthe environmental, social and economic contexts of their use.

1.2. The ongoing standardisation work

The use of a different list of indicators in different approachesmakes a definitionof the term, “Sustainable Construction”, subjectiveand causes difficulties in comparing results from different tools. Inorder to overcome these constraints, both the International Organi-zation for Standardization (ISO) and the European Committee forStandardization (CEN) have worked actively in the last few years todefine standard requirements for the environmental and sustain-ability assessments of buildings.

As a result of the ISO Technical Committee (TC) 59, “Buildingconstruction”, and its Subcommittee (SC) 17, “Sustainability in

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e19711964

building construction”, four new technical specifications and stan-dards were published:

- ISO/TS 21929-1:2006, Sustainability in building construction e

sustainability indicators e Part 1: Framework for the devel-opment of indicators for buildings [23];

- ISO 21930:2007, Sustainability in building construction e

environmental declaration of building products [24];- ISO 15392:2008, Sustainability in building construction e

general principles [25];- ISO 21931-1:2010, Sustainability in building construction e

framework for methods of assessment of the environmentalperformance of construction works e Part 1: Buildings [26].

In 2005, CEN set up the Technical Committee (TC) 350,“Sustainability of construction works”, which aims to developvoluntary horizontal standardization of methods for the assess-ment of the sustainability aspects of new and existing constructionworks and standards for the environmental product declarations(EPD) of construction products [27]. As a result of the work carriedout to date the following pre-standards and standards have beenproduced:

- EN 15643-1:2010, Sustainability of construction works e

Sustainability assessment of buildings e Part 1: Generalframework [28];

- CEN/TR 15941:2010, Sustainability of construction works e

Environmental product declarations e Methodology forselection and use of generic data [29];

- prEN 15643-2:2009, Sustainability of construction works e

Assessment of buildings e Part 2: Framework for the assess-ment of environmental performance [30];

- prEN 15643-3:2008, Sustainability of Construction Works e

Assessment of buildings e Part 3: Framework for the assess-ment of social performance [31];

- prEN 15643-4:2008, Sustainability of Construction Works e

Assessment of buildings e Part 4: Framework for the assess-ment of economic performance [32];

- prEN 15978:2010, Sustainability of construction works e

Assessment of environmental performance of buildings e

Calculation method [33];- prEN 15942:2010, Sustainability of construction works e

Environmental product declarations e Communication formate Business to business [34].

1.3. Aim of the study

This paper presents an innovative approach to develop buildingsustainability assessment and rating. The main objective of thispaper is to develop a systematic methodology to support buildingdesign that achieves the most appropriate balance between thedifferent sustainability dimensions, and which is, at the same timepractical, transparent and flexible enough to be easily adapted todifferent kinds of buildings and technology.

This new approach is intended for use in the assessment ofexisting, new, and renovated residential buildings and its bench-marks are especially adapted to the Portuguese context. Further-more, this methodology will allow future rating and labelling ofbuildings, in parallel with the Energy Performance of BuildingsDirective.

This paper also aims to establish a definition of the term,“Sustainable Construction”, by drawing up an objective list ofindicators, easily understandable by all stakeholders, in order to

promote further sustainable design, construction, operation andmaintenance of buildings.

2. Development of the methodology SBToolPTeH

2.1. Definition

This paper presents a methodology for supporting sustainablebuilding design as well as predicting the sustainability of residen-tial buildings. The methodology here discussed is primarily basedon the international Sustainable Building Tool (SBTool) method andis complemented by the ongoing work of CEN TC350 and by thework performed by ISO TC59. The SBTool method is the result of thecollaborative work of several countries, begun in 1996 and waspromoted by the International Initiative for a Sustainable BuiltEnvironment (iiSBE). This international involvement is whatdistinguishes the SBTool from the others methodologies: it wasspecifically designed to allow users to reflect on different prioritiesand to adapt it to the environmental, socio-cultural, economic andtechnological contexts of different regions.

The Portuguese version of SBToole SBToolPTe is the result of thework performed both at the University of Minho and iiSBE Portugal(the Portuguese chapter of iiSBE), whose aim was to develop andpropose a generic methodology to assess the sustainability ofexisting, new and renovated buildings in urban areas, specifically inthe Portuguese context. In this methodology all three dimensions ofsustainable development are considered and the final rating ofa building depends on the comparison of its performance with twobenchmarks: conventional practice and best practice. This method-ology has a specific module for each type of building.

As a first step, a methodology to assess the sustainability ofresidential buildings was developed. The reasoning for this prioritywas the fact that most of the impacts from the construction sectorare related to the housing sector. The acronym given to the meth-odology is SBToolPTeH (Sustainable Building Tool for Housing inPortugal). The following priorities were defined in the developmentof the SBToolPT:

- To develop a list of parameters wide enough to be meaningfuland to comprise themost relevant building impacts, and, at thesame time, limited enough for practical use;

- To develop a building-level assessment method based uponexisting state-of-the-art of methodologies and taking intoaccount ongoing standardization;

- To establish an appropriate balance between all differentdimensions of sustainable development (environmental, socialand economic);

- To limit or exclude the subjective and/or qualitative indicatorsthat are hard to validate (e.g. aesthetics and technicalinnovation);

- To improve reliability through the use of accepted LCAmethods for environmental performance assessment;

- To produce an assessment output and certification label that iseasy for building users to interpret and understand and equallyeasy for clients and designers to work with.

The proposed methodology is able to compare the overallperformance of various construction projects and to rank thesignificance of the various sustainability indicators of each of theseprojects. The list of indicators and the related weighting system areable to highlight particular aspects during the earlier design stage,which then means that design teams can provide a range ofmeasures for mitigating adverse impacts. In this methodology, theoverall performance is a relative score which makes it possible tocompare the performance of the building under assessment with

Table 1List of categories and sustainability indicators for the SBToolPTeH methodology.

Dimension Categories Sustainability indicators

Environment C1 e Climate changeand outdoor air quality

P1 e Construction materials’embodied environmentalimpact

C2 e Land use andbiodiversity

P2 e Urban densityP3 e Water permeability of thedevelopmentP4 e Use of pre-developed landP5 e Use of local floraP6 e Heat-island effect

C3 e Energy efficiency P7 e Primary energyP8 e In-situ energy productionfrom renewable sources

C4 e Materials and P9 e Materials and products

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two benchmarks: conventional practice and best practice. Further-more, this methodology is also able to compare performance at thelevel of a particular sustainability category in various constructionprojects.

2.2. Boundaries of assessment

Most of the Portuguese construction market is related to theresidential sector. This study therefore prioritises the developmentof a methodology to support and to rate sustainable residentialbuildings.

The object of assessment is the building, including its founda-tions and external works, within the area of the building site. Theimpacts of the building upon its surroundings and the urbanenvironment are not considered. Some authors have concludedthat restricted scales of study (corresponding to a single buildingfor example) are too limited to correctly take into accountsustainable development objectives [35]. Nevertheless, sustainableurban planning is normally limited to municipalities and regionalauthorities and therefore it is more rational and straightforward tolimit the physical system boundary to the building itself (or part ofit) together with the site. As a result, the methodology excludesconstruction works outside the construction site (includingnetworks for communication, energy, and transportation). The useof this boundary is in accordance with prEN 15643-2:2009 [30].

The time boundary should represent the whole life-cycle stagesof a building. In a new building, all life-cycle stages, fromconstruction to final disposal, are considered; and in existingbuildings, the temporal boundary is marked from the moment ofintervention until to the final disposal.

2.3. Structure and assessment steps

The methodology is supported by an assessment guide and theassessment procedure follows four steps (Fig. 1):

i) Quantification of performance of the building at the level ofeach indicator;

ii) Normalization of parameters;iii) Aggregation of parameters;iv) Sustainable score calculation and global assessment.

waste management reusedP10 e Use of materials withrecycled contentP11 e Use of certified organicmaterialsP12 e Use of cement substitutesin concreteP13 e Waste managementduring operation

2.4. Sustainability categories, indicators and parameters

After defining the boundaries the next step was to define thecategories, indicators and related parameters within the threesustainable development dimensions that were going to be used to

Fig. 1. Framework of the SBToolPT methodology.

assess the objectives of a project. Each category is defined bya number of indicators and each indicator is defined by a number ofparameters.

After analyzing the main characteristics of several buildingsustainability assessment systems in different countries andstudying the local context, authors defined nine categories for theassessment tool. A category is a global indicator that summarisesthe performance of a building at the level of a key-sustainabilityaspect. SBToolPT has nine sustainability categories (Table 1): C1 e

Climate change and outdoor air quality; C2 e Land use and biodi-versity; C3 e Energy Efficiency; C4 e Materials and wastemanagement; C5 e Water efficiency; C6 e Occupant’s health andcomfort; C7 e Accessibilities; C8 e Education and awareness ofsustainability; and C9 e Life-cycle costs. Each assessment categoryis identified by one or more indicators.

An indicator is a sign or a signal that relays a complex message,from potentially numerous sources, in a simple and useful manner[36]. Therefore, the three main objectives of the indicators are:simplification, quantification and communication [37]. SBToolPTeHhas a total of twenty-five indicators (Table 1). The number andnature of the indicators vary from one category to another accordingto the category itself and its importance to the Portuguese context.The list of indicators is based on the commonly accepted life-cycleassessment (LCA) methods, the main indicators used in severalbuilding sustainability assessment systems in different countries(mainly in the international SBTool method), and in the ongoing

C5 e Water efficiency P14 e Fresh water consumptionP15 e Reuse of grey andrainwater

Society C6 e Occupant’s healthand comfort

P16 e Natural ventilationefficiencyP17 e Toxicity of finishingP18 e Thermal comfortP19 e Lighting comfortP20 e Acoustic comfort

C7 e Accessibilities P21 e Accessibility to publictransportationP22 e Accessibility to urbanamenities

C8 e Education andawarenessof sustainability

P23 e Education of occupants

Economy C9 e Life-cycle costs P24 e Capital costP25 e Operation cost

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e19711966

work at the CEN TC350 standardization body. In addition, eachindicator is defined according to a number of parameters. A param-eter is a measurable or observable property which provides infor-mation about a phenomenon/environment/area with a significanceextending beyond that directly associated with a value [38]. As anexample, the parameter used in SBToolPTeH to measure theperformance at the level of indicator “P7 e Primary Energy” is theannual primary energy (in kilogram of oil equivalents per squaremeter of net area) used for heating, cooling and hot water produc-tion, according to the Portuguese thermal regulation methodology.Indicators and related parameters are the basis of the methodology,since objectives and results will be conditioned by them.

This methodology has a total of nine sustainability categoriesand twenty-five sustainability indicators within the three sustain-ability dimensions.

In SBToolPT, assessment of embodied impacts related to buildingmaterials is based on the same list of environmental impactsexpressed by the impact categories of LCA, which are normallydeclared in the Environmental Product Declarations (EPDs). The listof environmental categories and environmental parameters wasextended so that it would be possible, in a holistic approach, toaccess the main life-cycle environmental impacts, according tonational priorities. Therefore, the methodology uses a list of fifteenparameters and considers all the environmental impacts expressedby the impact categories of LCA as well as all environmental aspectsexpressed by data derived from LCI and not assigned to the impactcategories of LCA that are listed in the prEN 15643-2:2009 [30].

The list of social parameters includes three categories and eightparameters. This list was developed in order to include the mainaspects of the building occupants’ health and comfort and includesother aspects relating to the mobility of building occupants andtheir access to the main urban amenities. It also reflects the func-tional requirements of a residential building, according to nationalbuilding codes. A further important aspect that is also consideredhere is the occupants’ education and awareness of sustainability,since the real performance of a building, during the operationphase, is largely dependent on the occupants’ behaviour.

The economic performance indicators were defined in order toinclude the most relevant life-cycle costs. This list thereforeincludes two indicators: one for the costs of the building up untilthe end of the construction phase and another for the costs (energyand water) during the operation phase. Operation cost is the NetPresent Value (NPV) of energy and water costs calculated on annualbasis and assuming a life-cycle of at least fifty years.

Table 2Environmental impact categories declared in the built-in LCA database for buildingtechnologies.

Environmental impact categories Unit/declared unit LCA methods

Depletion of abiotic resources [kg Sb equiv.] CML 2 baseline 2000Global warming potential (GWP) [Kg CO2 equiv.] IPCC 2001 GWP 100aDestruction of atmospheric

ozone (ODP)[Kg CFC-11 equiv.] CML 2 baseline 2000

Acidification potential (AP) [Kg SO2 equiv.] CML 2 baseline 2000Eutrophication potential (NP) [Kg PO4 equiv.] CML 2 baseline 2000Photochemical ozone

creation (POCP)[Kg C2H4 equiv.] CML 2 baseline 2000

Non-renewable primary energy [MJ equiv.] Cumulative EnergyDemand

Renewable primary energy [MJ equiv.] Cumulative EnergyDemand

2.5. Quantification of parameters

The assessment guide presents the methodologies that shouldbe used by the assessor in order to quantify the performance of thebuilding at the level of each sustainability indicator.

To facilitate the quantification of environmental performance,SBToolPT uses the same environmental categories declared in theEnvironmental Product Declarations (EPDs). However, there are, atpresent, some limitations to this approach due to the scarcity ofavailable EPDs. The solution proposed to overcome this problemwas to develop and use databases with the LCA data for the mostcommonly used buildingmaterials and components. Therefore, thismethodology includes an LCA database that is continuously upda-ted and covers: common building technologies for each buildingelement (floors, walls, roofs, windows and doors); the mostcommonly used building materials; and the impacts from theoperation of the most common HVAC equipment. This databasecovers the six environmental impact categories presented inTable 2. The environmental impact categories were quantified

using the SimaPro software [39] and Table 2 presents the LCAmethods used.

Fig. 2 presents how the information is organized in the LCAdatabase for a building component and both the list of environ-mental indicators and LCA methods used to quantify it [40]. Thefunctional unit used for the building components database is onesquare metre (m2) of area and one unit of mass (kg) for the mate-rials database.

At the level of social performance, the assessment guide pres-ents the analytical methods that should be used to quantify theparameters. If the assessment is being carried out during thebuilding operation, in-situ measurements can also be used.

Measuring the economic performance of a building is morestraightforward than measuring, for instance, the environmentalperformance. Standardized methodologies and quantitative pub-lished data are readily available for the Portuguese context.Economic performance is based on the market value of the dwell-ings and on their operational costs (costs relating to water andenergy consumption).

2.6. Normalization and aggregation

The objective of the normalization of parameters is to avoidscale effects in the aggregation of parameters inside each indicatorand to solve the problem of some of the parameters being of thetype “higher is better” and others being “lower is better”.Normalization was done using Diaz-Balteiro [41] Equation (1).

Pi ¼Pi � P*iP*i � P*i

ci (1)

In this equation, Pi is the value of ith parameter. P*i and P*i arethe best and worst values of the ith sustainable parameter. The bestvalue of a parameter represents the best practice in use in thePortuguese building sector and the worst value represents thestandard practice or the minimum legal requirement. Thesebenchmarks are updated in an annual basis or whenever a newregulation enters into force.

In addition to making the value of the parameters considered inthe assessment dimensionless, normalization converts the valuesbetween best and conventional practices into a scale boundedbetween 0 (worst value) and 1 (best value). A building designwhichperformance is above the best practice benchmarks will havea score above 1 and performances below the conventional will havea negative normalized value. This equation is valid for both situa-tions: “higher is better” and “lower is better”.

For example, the normalization of the primary energy used forheating (hot water heating included) was done as presented inTable 3 and Equation (2).

Fig. 2. Part of the SBToolPT LCA database [37].

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e1971 1967

Eh ¼ Eh� Eh*Eh* � Eh*

¼ 100� 14035� 140

¼ 0:38 (2)

As presented in Table 4, the normalized values of each param-eter are converted into a graded scale bounded between E (lesssustainable/below the conventional practice) and Aþ (moresustainable/above the best practice) in order to facilitate theinterpretation of results. In this graded scale, level D is equivalent tothe conventional practice and A to the best practice. The gradedscale was defined assuming a linear evolution in the buildingperformance between the upper limit of grade D and grade A. Thismethodology considers that a building which performance is until10% higher than the conventional practice has a similar perfor-mance to a conventional one.

Although building sustainability assessment crosses differentfields and involves the use of numerous indicators and parameters,in the communication of the global evaluation of a design approach,the use of a long list of indicators with their associated levels ofperformance is useless. The reasoning for this is the fact that if theperformance is communicated using several grades it is difficult tounderstand the overall performance and therefore to comparedifferent design approaches. To overcome this, the best method isto combine indicators within each category and sustainabilitydimension in order to obtain the respective performance levels[42]. Consequently, the inclusion of a weighting system of indica-tors is a necessary stage in the process of developing assessmenttools. This system can define the importance of each indicatoraccording to the local context in which the tool is developed [7].

This process should consider and integrate different methodol-ogies such as: Experts panel, Endpoint method, Economy method,

Table 3Example of benchmarking for normalization.

Parameter Primary energy used for heating(hot water heating included)

Notation EhUnit kWh/m2/yearValue 100Reference value 140Best practice 35

Analytic Hierarchy Process (AHP) method, among others [7]. Thefinal result should be obtained by considering the advantages andavoiding the constraints of each method [7]. Such a process impliessubjectiveweighting, which is subject to a number of shortcomings,as discussed, for instance, by Finnveden [43].

The methodology uses a complete aggregation method for eachindicator, according to Equation (3).

Nj ¼Xn

i¼1

wi$Pi (3)

The indicator Nj is the result of the weighting average of all thenormalized parameters Pi;wi is theweight of the ith parameter. Thesum of all weights must be equal to 1.

Difficulties in this method lie in the setting of the weight of eachparameter and in the possible compensation between parameters.Since weights are strongly linked to the objectives of the projectand to the relative importance of each parameter in the assessmentof each indicator, higher weights must be adopted for parameters ofmajor importance in the project. In this approach, the possiblecompensation between parameters is limited inside each indicator.

The following aspects have been considered in the developmentof the system of weights:

- The system of weights of other building sustainability assess-ment methodologies: the work included an analysis of themain methodologies in order to indentify the parameters ofgreatest importance;

Table 4Conversion of the quantitative normalized parameters into a qualitativegraded scale.

Grade Values

Aþ Pi > 1:00A (Best practice) 0:70 < Pi � 1:00B 0:40 < Pi � 0:70C 0:10 < Pi � 0:40D (Conventional practice) 0:00 < Pi � 0:10E Pi � 0:00

Table 5Relative importance weight (%) of each impact category according to SAB study[44,45],

Impact category Relative importance weight (%)

8 impacts 12 impacts

Global warming 24 16Acidification 8 5Eutrophication 8 5Fossil fuel depletion 8 5Indoor air quality 16 11Habitat alteration 24 16Water intake 4 3Criteria air pollutants 6Smog 6Ecological toxicity 11Ozone depletion 5Human health 11

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e19711968

- The actual state-of-the-art concerning the importance of eachenvironmental impact category in the whole-building environ-mental impact assessment: different LCA methods and theopinions of LCA experts were analysed and taken intoconsideration;

- The opinion of different stakeholders: besides considering theopinion of academic experts, the approach adopted for thisstudy considered the opinions of different intervenients in thebuilding life-cycle (designers, sustainability consultants,contractors and users).

During this phase of the study, it was possible to verify a highlevel of consensus among the different intervenients on the relativeimportance of each sustainability indicator in the assessment of theglobal sustainability of a building.

At the environmental level, there are no national impact scoresconcerning theweight foreachenvironmental parameter in termsofits relative importance to overall performance. Nevertheless, thereare some internationally accepted studies that have established analmost complete definition. Two of the most consensual lists ofvalues are based on a US Environmental Protection Agency’s ScienceAdvisory Board (SAB) study [44,45], and a Harvard University study[46]. SBToolPT uses the SAB’s approach and allocates the listedenvironmental parameters in the impact categories of that method,according to the contribution of each environmental parameter tothe extension, intensity and duration of the impact category. Table 5presents the relative importance of each impact category, accordingto the US EPA’s Science Advisory Board (SAB) study.

Table 6Weight of each environmental indicator and category in the assessment of environment

Categories Sustainability indicators

C1 e Climate change and outdoor air quality P1 e Construction materials’ em

C2 e Land use and biodiversity P2 e Urban densityP3 e Water permeability of theP4 e Use of pre-developed landP5 e Use of local floraP6 e Heat-island effect

C3 e Energy efficiency P7 e Primary energyP8 e In-situ energy production

C4 e Materials and waste management P9 e Materials and products reP10 e Use of materials with recP11 e Use of certified organic mP12 e Use of cement substituteP13 e Waste management duri

C5 e Water efficiency P14 e Fresh water consumptionP15 e Reuse of grey and rainw

Table 6 presents the results of the methodology used to definethe weight of each environmental indicator and category in theassessment of environmental performance (NA).

Although it is easy to quantify the functional parameters, theway in which each parameter influences the user’s health andcomfort, and therefore the overall sustainability of the project, isnot consensual. An assessment of this kind involves subjectiverating and depends, above all, on the type of solution and on thevaluator’s social-cultural and economic status. Several buildingsustainability assessment methodologies consider an empiricaldistribution of weights to assess the social performance ofa building. In order to overcome this problem, we developeda scientific-based methodology in order to study the relativeimportance (wi) of the most prominent comfort stressors, namely,thermal environment (Ptc), acoustics (Pac), air quality (Paq) andvisual comfort (Pvc), in the perceived global comfort (Gc), accordingto the model presented in Equation (4).

Gc ¼ Ptc$wtc þ Pac$wac þ Paq$waq þ Pvc$wvc (4)

This methodology involved subjective evaluation (question-naires to building users) and parallel experimental evaluations.During the experimental evaluations, the methodology includedthe assessment if four parameters: resultant temperature (Tr),average illuminance (lx), CO2 concentration (ppm) and weighted Aequivalent continuous noise level (Leq). The subjective and experi-mental data collected were processed using the multivariablelinear method. Both the weight of the other three social indicatorsand the weight of each societal category were based on the opinionof different stakeholders and building users.

Table 7 shows the results of the methodology used to define theweight of each society indicator and category in the assessment ofsocial performance (NS).

At the level of economic performance (NE), according toa questionnaire conductedwith different stakeholders and buildingusers, it was possible to conclude that the best trade-off is archivedwhen an equal weight is given to the two indicators. These resultsare presented in Table 8.

2.7. Representation and global assessment of a project

As a rule, most stakeholders prefer a single, graded scalemeasure to represent the overall score for a building. Such a scoreshould be easy for building occupants to understand and interpretbut should also be easy for clients, designers and other stakeholders

al performance (NA).

Weight (%)of the indicator

Weight (%)of the category

bodied environmental impact 13 13

8 20development 1

344

16 32from renewables 16

used 9 29ycled contend 9aterials 7s in concrete 3ng operation 1

3 6ater 1

Table 7Weight of each social indicator and category in the assessment of the social performance (NS).

Categories Sustainability indicators Weight (%)of the indicator

Weight (%)of the category

C6 e Occupant’s health and comfort P16 e Natural ventilation efficiency 7 60P17 e Toxicity of finishing 7P18 e Thermal comfort 19P19 e Lighting comfort 15P20 e Acoustic comfort 2

C7 e Accessibilities P21 e Accessibility to public transportation 17 30P22 e Accessibility to urban amenities 13

C8 e Education and awareness of sustainability P23 e Education of occupants 10 10

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e1971 1969

to work with. Therefore, the last step of the methodology is tocalculate the sustainable score (NG). The NG is a single index thatrepresents the global sustainability performance of a building; it isevaluated using Equation (5).

NG ¼ wA � NAþwS � NSþwC � NC (5)

Where, NG is the sustainability score, Nj is the performance at thelevel of the dimension j and wj is the weight of the dimension jth.

The weight of the environment, society and economy dimen-sions in the assessment of global performance is, respectively, 40%,30% and 30%. This value considers the following aspects: theimportance of environmental issues for the survival of humanbeings and other species; the harmonious coexistence between thethree sustainability dimensions, according to the sustainabledevelopment aims; and the opinions of academic experts,construction stakeholders and building users.

The labelling system for the SBToolPT methodology is similar tothat used in the existing labelling schemes such as the EU energylabelling scheme for white goods and the European DisplayTM

Campaign posters [47]. In this study, however, due to the possiblecompensation between categories, the global performance ofa building is not communicated by using only the overall score. Inthis methodology the performance of a building is measuredagainst each category, each of the three sustainable dimensions andthe global performance (sustainable score). Building performanceis ranked on a scale from Aþ to E. Fig. 3 represent the output of theSBToolPT methodology for a hypothetical case study at the level ofthe sustainability dimensions and global score.

From the outputs of this building sustainability assessmentmethod it is possible to monitor and compare the performance ofthe solution in study with the benchmarks of the methodology:conventional solution (D grade) and best practice (A grade). Thenearer to grade Aþ the performance of the solution is, the moresustainable it is. If the solution shows a grade E in one parameter orcategory, it has obviously performed worse than the referencesolution at that level, therefore identifying an issue that requiresspecial attention.

3. Discussion

The usability, reliability and fitness for purpose of the differentsustainability assessment tools has been carefully evaluated by

Table 8Weight of each economic indicator and category in the assessment of economicperformance (NE).

Categories Sustainabilityindicators

Weight (%) ofthe indicator

Weight (%) ofthe category

C9 e Life-cycle costs P24 e Capital cost 50 100P25 e Operational cost 50

researchers in the area, leading to the publication of some impor-tant conference and journal papers in recent years. To date, scoringof the indicator systems is best developed in methods that useenvironmental information for single properties like LCA tools.These tools may be linked to different phases of the building designprocess, from the initial definition or technical design phase toa building in use, in order to obtain an overall picture of theattainment of sustainability targets. These include tools for theperformance-based design and building approach and otherbuilding rating schemes.

The whole-building evaluation may also be done on the basis ofperformance of the completed building with respect to its space,structural and technical systems and their interaction. The toolsavailable are, for example, modelling of energy flows, lighting andaccessible routes.

Although there are subjective aspects to the majority ofassessment tools, hindering their adoption, they still have animportant role to play, not only in evaluating the impacts of anactual building, but also, and evenmore importantly, in guiding theappropriate design for the attainment of performance objectives.The greatest constraint to sustainability assessment is that assess-ment involves subjective rating and depends above all on theplanned function of the building, as well as on its socio-economicand cultural heritage context. Additionally, one of the mostimportant aspects influencing the results is the list of indicators andtheir respective parameters, since the result relies on the perfor-mance obtained in each indicator. The definition of a list of indi-cators and respective parameters to be adopted on an internationalscale is one solution to explore in order to make the evaluationmethods more objective.

Another important constraint is that although there are severalrecognized LCA tools, most building sustainability assessment andrating systems are not comprehensive or consistently LCA-based. Thereasons for this failure are above all related to the complexity of thestages of anLCA. Besides being complex, the LCAapproach is alsoverytime consuming and therefore mainly used by experts at academiclevels. For these reasons most of the building sustainability assess-ment methods rely on single material proprieties or attributes, suchas recycled content, recycling potential or distances travelled fromthe point of manufacture [48]. This situation causes some distortionin both the interpretation of the results from the environmentalperformance assessment and the comparison of these results withdifferent building sustainability assessment and rating systems.

Due to the above mentioned reasons, and despite numerousstudies in the area of building sustainability assessment, there isa lack of a commonly accepted methodology to assist architects andengineers in the design, construction and refurbishing stages ofa building. Nevertheless, in spite of the limitations of the differentmethods, the increasingly widespread use of assessment methodsis having direct and indirect impacts on the promotion of sustain-able building design. Many countries either have or are in the

Fig. 3. SBToolPT output for a hypothetical building e performance of the solution presented at the level of the three sustainable dimensions and the sustainable score.

R. Mateus, L. Bragança / Building and Environment 46 (2011) 1962e19711970

process of developing domestic assessment methods, which ismaking the need for international exchange and coordinationincreasingly relevant. Sustainability in the building sector hasgained an international forum and the Green Building Challenge,for example, is organizing several major international conferenceswhich are having a noticeably positive effect on the promotion ofthis concept. Furthermore, both the International Organization ofStandardization (ISO) and the European Committee for Standardi-zation (CEN) are making important progress towards the stan-dardization of sustainability indicators and horizontal methods inbuilding sustainability assessment.

This paper has attempted to present an approach to buildingsustainability assessment that can contribute to the evolution ofgeneric methodology. The methodology is based on the actuallimitations of the existing building sustainability assessmentmethods and on the work currently being developed in interna-tional fora, including standardization bodies.

The methodology presented in this paper (SBToolPTeH) isintended to foster more sustainable building design, construction,operation, maintenance and disassembly/deconstruction bypromoting and making possible a better integration of environ-mental, societal, functional and cost concerns with other traditionaldecision criteria. This methodology can be used to support thesustainable design, since it defines the sustainable constructionconcept through a list of sustainability indicators and relatedperformance objectives. Additionally it can be used to evaluate theoverall sustainability performance. According to this methodology,a sustainable building is the onewhich performance is optimized atthe level of the twenty five indicators presented in Table 1 and hasan overall average performance level at least 10% higher than theconventional building practice.

SBToolPTeH is based on the international SBTool approach, sinceit uses the same core indicators and normalization system to assessthe sustainability of a building (the performance of a building iscompared with two benchmarks: best practice and conventionalpractice). This international involvement distinguishes it fromother methodologies. Another important contribution to the actualstate-of-the-art is the way in which environmental performance isassessed, since SBToolPT’s approach is based on a standardised LCAmethod. The integrated LCA database is also an important tool forguiding designers in their selection of materials and buildingcomponents with a stronger environmental performance. TheSBToolPT system can also be used to certify the sustainability ofbuildings, since it includes a certification label. This label uses thesame approach as energy certification schemes and is quitedifferent from the other approaches developed to date; mostmethodologies use only one overall score to communicate thesustainability of a building, while in SBToolPT performance is alsocommunicated at the level of nine sustainability key-issues. This

transparency is useful both to designers and end users and isessential for greater objectivity in the assessment process.

4. Conclusions

The sustainable design, construction and use of buildings arebased on the best trade-off between environmental pressure(relating to environmental impacts), social aspects (relating tousers’ comfort and other social benefits) and economic aspects(relating to life-cycle costs). Sustainable design strives for greatercompatibility between the artificial and the natural environmentswithout compromising the functional requirements of the build-ings and the associated costs.

Many countries either have or are in the process of developingdomestic assessment methods, which makes the need for interna-tional exchange and coordination increasingly relevant. This papercontributes to the evolution of generic methodology and interna-tional understanding by introducing an approach that takes thedifferent dimensions of sustainability into account and incorporatesa standardised LCAmethod to assess the environmental dimension.

This paper presented the SBToolPTeH methodology, whosescope is to assess the sustainability of existing, new and renovatedresidential buildings in urban areas, specifically in the Portuguesecontext. Although this paper only presented the SBToolPT module toassess the sustainability of residential buildings, the approach usedin the other modules is based in the same framework.

SBToolPT methodology is intended to boost sustainable buildingin Portugal. It supports steps towards sustainable design andconstruction through the definition of a list of objectives that areeasily understandable by all intervenients in the constructionmarket and is compatible with the Portuguese construction tech-nology context.

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