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Keywords:

  • sustainability assessment;
  • sustainable development indicators;
  • construction sector;
  • green buildings;
  • rating systems;
  • performance measurement

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References

The increasing attention to sustainability is pushing the construction sector to build more sustainable buildings. In this scenario, several sustainable development indicators have been proposed. The worldwide diffusion of sustainability rating systems and that of their structures are considered as proxy variables for the evaluation of sustainable constructions. Available rating systems span from energy consumption evaluation systems to life cycle analysis and total quality assessment systems. In these last systems, a multi-dimensional approach is proposed, as several building ratings are evaluated separately before being considered together. The description of assessment results from a sample of 490 buildings provides data to discuss construction characteristics that, currently, aim at being defined as sustainable. The paper shows that building energy performance is considered the most important criterion in sustainability rating systems, and the least achieved one in sustainability assessments. In contrast, other performance ratings of the building, such as water efficiency or indoor air quality, are achieved with a high rate of success in sustainability assessments. Copyright © 2011 John Wiley & Sons, Ltd and ERP Environment.


Introduction

  1. Top of page
  2. ABSTRACT
  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References

The increasing attention to sustainability is pushing the construction sector towards rapid changes. Policies, laws and regulations around the world are asking the sector to adopt sustainable innovation in terms of products and processes to encourage more sustainable buildings (Hellstrom, 2007; Steurer and Hametner, 2011). This attention for the building sector arises from its energy consumption and GHG emissions, which, in developed countries, are 30 and 40% of the total quantities, respectively (IPCC, 2007). Forecasts of the EIA (2010) show that energy consumption in buildings is increasing at a rate comparable to those of the industrial and transportation sectors. However, according to IPCC (2007), the building sector has the highest energy saving and pollution reduction potential, given the flexibility of its demands. IPCC showed that, in countries that are not members of the Organisation for Economic Cooperation and Development (non-OECD) and in economies in transition, potential CO2 saving in buildings could be 3 and 1 Gt CO2-eq per year respectively in 2030. A total possible reduction of almost 6 Gt CO2-eq per year is then possible worldwide in the next 20 years if the building sector embraces sustainability. This highlights why sustainable buildings are often considered a priority for a sustainable world (IPCC, 2007; Butera, 2010). Assessment of sustainable development is an essential prerequisite to its promotion, and for this large difficulties exist producing sustainable development indicators (Mitchell, 1996). Sustainability assessment can be defined as the process of identifying, predicting and evaluating the potential impacts of initiatives and alternatives (Devuyst, 2000). The possibility to assess products and processes is particularly important for a sector as inertial and conflicting as that of construction (Winston, 2010).

The main scope of this paper is to review sustainability assessment practices for buildings describing both existing sustainability rating systems and assessment results in a sample of buildings. The paper focuses on the evaluation criteria of rating systems. An analysis of building assessments through a sustainable rating system enables the discussion of certain characteristics of sustainable constructions. The paper does not aim at presenting a complete theory, and it does not follow the classic theory–test structure of scientific papers, but it endeavors to discuss the current state of sustainability assessment in the construction sector through a review of current practices. The following section contains an introduction to the sustainability assessment. This implies describing the diffusion of sustainability assessment worldwide and possible approaches for building assessment. The next section contains a description of several assessment systems. The fourth section reports and discusses sustainability assessment results in a sample of buildings. This highlights the structure of a multi-dimensional sustainability rating system. Statistics around sustainability assessments enable a discussion of current practices. Finally, trends of sustainability assessment in the construction sector are discussed.

Sustainability Assessment

  1. Top of page
  2. ABSTRACT
  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References

Diffusion of Sustainability Assessment

According to many studies, sustainability assessment is necessary to increase the diffusion of sustainable buildings (Cheng et al., 2008; Ding, 2008). Unfortunately, the construction sector is unfamiliar with performance measurements, and although many assessment systems already exist worldwide their diffusion is still low in absolute terms. Sustainability measurements in the building sector are capturing much attention worldwide, rapidly moving from fashionable certifications to current practices. In 2010, 650 million square meters obtained a sustainability certification throughout the world, with projections for 1100 million square meters in 2012 and for more than 4600 million square meters in 2020 (Bloom and Wheelock, 2010). Sustainability building certification programs and rating systems are used worldwide, with the only exceptions being Africa (except South Africa) and Latin America (except Brazil).

Referring to the model for innovation diffusion, proposed by Rogers and reinterpreted in Crossing the Chasm (Moore, 1991), sustainability assessment diffusion has reached visionaries, the number of early adopters is increasing and the subject is becoming common in specialized press and journals (Bloom and Wheelock, 2010), but, even in active countries, it still needs to become a mature practice (McGraw-Hill Construction, 2008). In the innovation diffusion theory (Rogers, 2003), communication is generally the most important element for the introduction of a new paradigm among members of its social systems. For this, sustainability assessments and sustainability rating systems represent the framework for sustainable constructions. Proof of this was given by the European Directive EPBD, which required the placement of energy consumption certificates and plaques in the assessed buildings (EC, 2003).

The increasing number of certified buildings shows that awareness of sustainability is increasing. Moreover, the assessment scale allowed by many rating systems, which permit definition of several sustainability grades, has shown a trend towards higher sustainability levels in the last few years. For example, few buildings among first assessed projects were rated as LEED platinum buildings (best rated ones) from 1999 to 2002. Then, in 2003, some buildings were rated platinum, and currently this rating is common among sustainable buildings (Bloom and Wheelock, 2010).

Possible Approaches

Sustainable buildings have been broadly defined as buildings that encompass environmental, social and economic standards, together with technical aspects (Rwelamila et al., 2000). It is often unclear how to categorize and recognize sustainable buildings. In fact, a frequently discussed topic regards how sustainability should be measured (Steurer and Hametner, 2011). After the energy crisis in the 1970s, regulations promoted energy consumption limits for buildings around the world. As a result, energy consumption evaluation became the sustainability measure for building assessment. Meanwhile, sustainability consciousness has evolved, and nowadays assessments generally consider energy consumption as just one among other parameters. The complexity of a building often suggested a multidisciplinary approach in sustainability assessment (Langston and Ding, 2001). This is also because buildings cannot be considered as assemblies of raw materials, but they are generally high order products that incorporate different technologies assembled according to unique processes (Ding, 2008). The sustainability of a building should, therefore, be evaluated for every subcomponent, for the integration among them in functional units and assembled systems (e.g. the air conditioning system, the envelope), as well as for the building in its entirety. Finally, it is becoming more and more evident that a building cannot be considered an island, but its sustainability should be considered and assessed by looking at the surrounding environment.

A possible approach to sustainability evaluation is through the sustainability assessment of building products. This approach is internationally established for many kinds of product, and only regards environmental evaluations. Three types of product environmental label exist and are defined in ISO 14020 (2000). These are the eco-certification environmental labels (type I), the self-declared environmental claims (type II) and the environmental declarations (type III). Among these, type III is the most common label for building products. However, environmental evaluations of products are rarely performed by manufacturers, and the diffusion of environmental product declarations (EPDs) in the building sector is low (McGraw-Hill Construction, 2008). Product eco-certification assessment systems have been developed in different countries: among others, there is the American Green Seal, the European Eco-Label, the French NF Environment Mark, the German Blue Angel and the Japanese Eco Mark. Moreover, specific evaluations for building products exist, especially for timber and concrete based ones. The above mentioned labels have a binary evaluation and indicate a sustainable product without the ability to measure its greenness.

Since 2011, the new European Construction Products Directive (CPD) states that a sustainable resource use evaluation is part of the assessment for the CE mark (CPR, 2011), which should imply a larger diffusion of environmental assessments for the construction sector, at least in Europe.

Energy labels represent another way of assessing product sustainability, although they are only useful for equipment (e.g. heat pumps). Finally, the adoption of certified sustainable materials is not sufficient to obtain a sustainable building, because the complexity of such requires a holistic and integrated evaluation (Ding, 2008). For example, the sustainability assessment of a building product needs to consider difficulties in predicting factors such as transportation distance or wastes. In this sense, product labels only constitute a database for a sustainability analysis. Construction is a complex input–output sector where the material flux is difficult to standardize and rarely a priori programmed (Cole, 1998). Some research states that building sustainability can be better evaluated by looking at the building as a process because it never finishes, but evolves through occupancy. Weather, orientation and local parameters continually influence the operational needs of the building. Moreover, buildings are constructed according to a specific design defined according to clients' requests. These aspects prevent buildings from being considered as manufacture standardized products. Finally, construction stakeholders constitute a variegated network of subjects (de Blois et al., 2011) and differences among them imply several possible points of view in sustainability assessment. In this sense, Cole (1998) stated that sustainability varies according to stakeholders: a community aims at low construction wastes whereas an occupant looks at indoor environmental quality. Given that sustainability assessment should include the evaluation of social and economic parameters, definition of a universally accepted assessment system is a long way away.

Sustainability Rating Systems

  1. Top of page
  2. ABSTRACT
  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References

According to ISO 15392 (2008), construction sustainability includes ‘considering sustainable development in terms of its three primary aspects (economic, environmental and social), while meeting the requirements for technical and functional performance’. More than 600 sustainability assessment rating systems are available worldwide (BRE, 2008). New systems are continually proposed and the most diffused ones receive a yearly update. This evolving situation has led to release of the standards Sustainability in Building Construction – Framework for Methods of Assessment of the Environmental Performance of Construction Works – Part 1: Buildings (ISO 21931–1, 2010) and Sustainability of Construction Works – Sustainability Assessment of Buildings – General Framework (ISO 15643–1, 2010).

Systems for sustainability assessment span from energy performance evaluation to multi-dimensional quality assessment. According to Hastings and Wall (2007), they can be grouped into

  • cumulative energy demand (CED) systems, which focus on energy consumption
  • life cycle analysis (LCA) systems, which focus on environmental aspects
  • total quality assessment (TQA) systems, which evaluate ecological, economic and social aspects.

The above division should not be considered strictly as many assessment systems do not fit perfectly into one category. CED systems are often mono-dimensional and aim at measuring sustainability of the building through energy related measurements. LCA systems measure the impact of the building on the environment by assessing the emission of one or more chemical substances related to the building construction and operation. LCA can have one or more evaluation parameters, whereas TQA systems are multi-dimensional as they assess several parameters. The first two categories of systems have a quantitative approach to the assessment, whereas a TQA system generally has a qualitative or quantitative approach for different criteria. In the following sections CED, LCA and TQA systems are described.

Cumulative Energy Demand Systems

CED systems measure and evaluate the energy consumption of the building. Energy is furnished to buildings to cover needs such as heating, ventilation, air conditioning, water heating, lighting, entertainment and telecommunications. The specification of the energy request is of primary importance as CED systems can refer to just some of the above consumptions (often, just heating and hot water consumption) or can consider all needs without distinction regarding the final use.

CED systems evaluate the energy consumption over a time unit, which generally corresponds to one year. However, monthly or semi-annual evaluations have been proposed (Marszal et al., 2011). Energy consumption for residential buildings in developed countries at middle latitudes assumes values of some hundreds of kilowatt hours per square meter net floor surface per year (kW h/m2 a): for example, heat consumption of traditional European and US buildings is 300 kW h/m2 a on average (Butera, 2010). Referring to traditional buildings, operating energy demand dominates the building CED during the life cycle, being 80% of the total energy consumption (Suzuki and Oka, 1998). A small energy percentage is consumed for material manufacture and transportation, construction and demolition. Consequently, energy saving policies have typically only given attention to operation energy performance (EC, 2003). Energy consumption requirements of new buildings are greatly decreasing under the pressure of more stringent requirements (Figure 1).

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Figure 1. Energy requirements for heating in some European building codes over the years (data taken from national regulations)

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In the US, zero energy buildings (or ZEBs) are discussed in the Energy Independence and Security Act (EISA, 2007), whereas the recast of the European Energy Performance of Buildings Directive (EC, 2010) has established that only ZEBs should be built after 2020. A ZEB can be defined as a building with a very high level of energy efficiency, so that the overall annual primary energy consumption is equal to the onsite energy production from renewable energy sources. A universally accepted definition of ZEBs is still lacking (Marszal et al., 2011), and several proposed methodologies for ZEB calculations differ for the metric of the analysis (energy, CO2 emission, costs), the balancing time and the type of energy use considered in the assessment.

As highly efficient buildings are built, the energy needs during construction and demolition processes, together with the embodied energy in construction materials, become relatively more significant. Hernandez and Kenny (2010) have defined the life cycle zero energy building (LC-ZEB) concept for energy consumption equity in a whole life perspective. A life cycle evaluation of energy use implies enlarging time and space boundaries in the assessment (Suzuki and Oka, 1998), and represents the trend for energy based sustainability assessment in the construction sector.

CED systems are a mono-dimensional analysis, which considers the energy flux. Apart from an energy analysis, some researchers have accounted for other measurement units, such as exergy (Tronchin and Fabbri, 2008) or emergy (Pulselli et al., 2007). Exergy is the maximum useful work that brings the system into a heat reservoir equilibrium, whereas emergy is the available solar energy directly and indirectly used in a transformation. These units of measurement are related to thermodynamic principles of resource use, and may be more appropriate than energy to evaluate building consumption (Marszal et al., 2011), although energy data are more common in the literature.

Life Cycle Analysis Systems

Several systems have been developed for the environmental assessment of manufactured products, such as Environmental Risk Assessment (ERA), Material Flow Accounting (MFA), Input–Output Analysis (IOA) and Life Cycle Analysis (LCA). These systems generally break down products and processes into elementary parts. LCA is the most commonly used of the above systems. It divides a building into elementary activities and raw materials to assess the environmental impact over a life cycle from manufacture and transportation to deconstruction and recycling (Seo et al., 2006). LCA is a robust methodology refined on the basis of manufacturing sector experiences. LCA assessments consist of four phases (ISO 14040, 2006): the goal and definition phase, the life cycle inventory, the life cycle impact assessment and the improvement assessment phase. LCA systems allow the comparison of products on the basis of the same functional quality. This describes the quality of a product service as well as its duration, e.g. square meters of a building element with a substitution rate every 50 years. The scientific rigor of LCA is inherent to assessments from cradle to grave phases, although it is limited by uncertainties in collecting data relating to building processes. LCA diffusion in the building sector is limited by a lack of information (Seo et al., 2006). In fact, the specificities of the construction processes require data for every building material in any region. Databases have been created for LCA evaluations and implemented in specifically designed software in several geographic areas: BEES in the US, BOUSTEAD and ENVEST in England, SIMAPRO and Eco-Quantum in the Netherlands, Ecoinvent in Switzerland and GaBi in Germany. However, these databases are only valid for assessments in a specific region. The United Nations Environment Program's Sustainable Buildings and Climate Initiative (UNEP-SBCI) has recently adopted the Common Carbon Metric. This system allows emissions from buildings around the world to be consistently assessed and compared. The assessment reports the Carbon Intensity, which is the evaluation in weight of carbon dioxide equivalent emitted per square meter per year (kg CO2-eq/m2 a). The assessment is mainly based on the operational consumption, but it can be extended to the whole life cycle of the building.

An obstacle for LCA diffusion is its specialist structure: outputs of LCA systems are represented by environmental impacts expressed through chemical substances, which are not easily understood by construction sector actors (Langston and Ding, 2001).

LCA systems assess the environmental paradigm of sustainability without considering social and economic impacts. To fit this limit, some studies relate the disaggregation analysis necessary for an LCA to an evaluation of economic costs. Such an approach is interesting for the building sector, as life cycle cost (LCC) analysis represents a familiar paradigm to construction stakeholders. Combined LCA–LCC can, hence, be useful to evaluate environmental and economic aspects in life terms by assigning a price to chemical elements. For example, BEES and GaBi systems already permit the selection of cost-effective environmentally preferable products.

Total Quality Assessment Systems

TQA systems aim at considering the three aspects of sustainability of buildings: environmental issues such as GHG emission and energy consumption, economic aspects such as investment and equity and social requirements such as accessibility and quality of spaces. The most common TQA systems are the multi-criterion systems. They are greatly increasing the attention for sustainable assessment of buildings, as they are well related to market interests and stakeholders' culture (Newsham et al., 2009). Multi-criterion systems base the evaluation on criteria measured by several parameters, and compare real performances with reference ones. Each criterion has a certain number of available points over total assessment and the overall evaluation of sustainability comes out by summing the results of assessed criteria. A critical aspect of multi-criterion systems is their additional structure, as they assign scores for positively evaluated elements (Hahn, 2008). Multi-criterion systems are generally easy to understand and can be implemented in steps for each criterion. Moreover, a step implementation is allowed during the analysis: in fact, these systems enable the assessment of the building at several stages, from the concept design to the final construction, and can be used during construction too.

Several multi-criterion systems exist to assess building sustainability worldwide. As many are just adaptations of more famous ones to regional level or for specific scopes, only the most adopted systems are considered here. These are BREEAM, LEED, CASBEE, SBTool and Green Globes. Other famous rating systems are the Australian Building Greenhouse Rating (ABGR), the Green Home Evaluation Manual (GHEM), the Chinese Three Star, the US Assessment and Rating System (STARS) and the South African Sustainable Building Assessment Tool (SBAT).

The United Kingdom was the first country to release a multi-criterion system for sustainability assessment before this concept entered into the agenda of international policies with the Rio Conference. The British Building Research Establishment Environmental Assessment Method (BREEAM) was planned at the beginning of the 1990s by the British Research Establishment, and was released in 1993. The system has a large diffusion in the United Kingdom, where almost 10 000 buildings have been certified.1 Since 2009, as a consequence of the worldwide attention garnered by this system, an international version has been released, and currently BREEAM has adapted versions for Canada, Australia and Hong Kong. The system is differentiated for 11 building typologies and its evaluations are expressed as a percentage of successful over total available points: 25% for pass classification, 40% for good, 55% for very good, 70% for excellent, 85% for outstanding. The evaluation categories are management, health and wellbeing, energy, transport, water, materials, land use, ecology, pollution and innovation.

A widely spreading rating system is LEED (Leadership in Energy and Environmental Design), which was released in 1998 by rthe US Green Building Council (GBC).2 This system is currently available for ten building typologies. There are six evaluation categories to obtain the 69 possible points of the standard in version 2: sustainable site (14 points), water efficiency (5), energy and atmosphere (17), material and resources (13), indoor environment quality (15) and innovation and regional specificities (5). LEED points accumulated are divided into the following categories: at least 26 points for certified buildings, 33 for silver, 39 for gold and 52 for platinum. Although released in the US, GBC has been diffused worldwide over the years, and recently the World GBC has opened regional chapters in countries in Europe, Africa, America and Asia. Almost 20 000 buildings are registered for certifications, and current requests for new certifications regard buildings in 110 countries2.

CASBEE (Comprehensive Assessment System for Building Environmental Efficiency)3 is a Japanese rating system developed in 2001, also available in English. CASBEE covers a family of assessment tools based on a life cycle evaluation: pre-design, new construction, existing buildings and renovation. This system is based on the concept of closed ecosystems and considers two assessment categories, building performance and environmental load. Building performance covers criteria such as indoor environment, quality of services and outdoor environment, whereas environmental loads cover criteria such as energy, resources and materials, reuse and reusability, and off-site environment. By relating the previous two main criteria, CASBEE results are presented as a measure of eco-efficiency on a graph with environmental loads on one axis and quality on the other, so that sustainable buildings for CASBEE have the lowest environmental loads and highest quality. Fewer than 100 buildings have been certified with this system, although the number is rapidly increasing.

At the end of the 1990s, the Sustainable Building Council promoted an internationalization of rating systems under the leadership of Natural Resources Canada (NRC). Towards this initiative a common protocol, SBMethod, was developed. Using the general scheme, several countries then proposed national versions of this system, such as Verde in Spain, SBTool PT in Portugal and SBTool CZ in the Czech Republic. In Italy, this protocol was implemented in 2000 as SBTool IT, it was updated in April 2011 and it is now known as ITACA. Moreover, ten Italian regions have adopted modified versions of the system to better cover regional specificities. In 2005, adapting the Canadian version of BREEAM, the Green Building Initiative (GBI) launched a new rating system, known as Green Globes. Criteria of this include project management, site, energy, water, indoor environment, resource, building materials and solid waste.

A critical aspect of multi-criterion systems regards the selection of criteria and weight given to each criterion: in fact, reasons behind choices are not explicit. In this paper, among the aspects through which a comparison of sustainability rating systems could be done, criteria and weights were selected. This shows which aspects of building performance are given more consideration in sustainability assessments. Figure 2 shows weights assigned by the above six systems, grouping the criteria of each into seven main categories. Selection of these categories was based on main sustainability building aspects (Langston and Ding, 2001): site selection, energy efficiency, water efficiency, material and resources, indoor environmental quality, waste and pollution. The category ‘others’ contains criteria that do not fit into the other six categories. When more than one version of the same system existed, the one applicable to new construction was selected. The attribution of each system criterion into previous categories resulted in some difficulties because the system structures were not always easily accessible and criteria among systems did not perfectly overlap. For this reason, the attribution was performed by the author, and then repeated by two sustainability experts to check coherence in attribution of criteria in the seven categories. Credits assigned in the LEED system for low-emitting materials (6 points out of 69) were assigned to the IEQ category; however, they could also be assigned to the waste and pollution category, which in Figure 2 has not received any weight. Management and innovation criteria have been included in the category ‘others’. For example, LEED assigns 7% of its credits to innovations, BREEAM has 15% for construction management and Green Globe has 12.5% for project management. Moreover, in the category ‘others’ there are points given by CASBEE for mitigation and off-site solar energy and by GBTool for the cultural perception of sustainability. The result of the weight comparison among rating systems agrees with similar studies (Fowler and Rauch, 2006, BRE, 2008).

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Figure 2. Comparison of the weights assigned by six sustainable rating systems, grouping the respective criteria into seven categories

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It is interesting to note that energy efficiency among assessment systems in Figure 2 is always considered the most important category (weight average among the six systems 25.5%), followed by IEQ (17.7%), waste and pollution (15.9%), sustainable site (13.2%) and material and resources (11.5%). Green Globes assigns a higher percentage of its assessment weight to energy efficiency (36%): this is established by the inclusion of criteria that are not presented in other systems, such as the correct size energy efficient system or energy efficient transportation.

The above averages do not have a rigorous meaning, standard deviations among systems are high and percentages change if other versions of the systems or other assessment systems are considered. However, studies have shown many similarities among sustainability rating systems (Smith et al., 2006). Finally, it should be remembered that evaluation criteria and weights are just one of the ways to compare systems. Fowler and Rauch (2006) compared the above mentioned systems for other properties (applicability, usability, communicability), again finding some similarities. Differences among the systems have led to creation of the Sustainable Building Alliance in order to establish common evaluation categories and to improve comparability among systems in sustainability assessments.

Many studies have discussed the limits of rating systems; however, only limits for weight and criteria are considered here. Unscientific criteria selection has been criticized by both Rumsey and McLellan (2005) and Schendler and Udall (2005). Bower et al. (2006) stated there was a lack of overall life cycle perspective in evaluations. On the same topic, the US National Institute of Standards and Technology (NIST) analyzed the LEED system from an LCA perspective, leading to the conclusion that it is not a reliable sustainability assessment system (Scheuer and Keoleain, 2002).

From Figure 2, it is clear that, in the selection of assessment criteria, environmental aspects in existing systems receive much more attention than economic and social ones (Sev, 2009). Recently, some multi-criterion rating systems more closely related to a TQA have been released. For example, the Deutsche Gesellschaft für Nachhaltiges Bauen (DGNB), available since 2009, aims at evaluating sustainability through the quality of the building: economic aspects emerge explicitly, and, in the category of technical quality, paradigms such as performance, durability and ease of cleaning, as well as dismantling and recycling, are considered. More attention is paid to social aspects than in other rating systems. Finally, functional aspects such as space efficiency, safety, risk of hazardous incidents, handicap accessibility, suitability for conversion, public access, and art and social integration are considered.

Characteristics of Certified Buildings

  1. Top of page
  2. ABSTRACT
  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References

In the present section sustainability rating systems are used as a proxy variable to analyze the characteristics of certified buildings. The results of constructed buildings can be more useful to understand the state of the art of sustainability assessment in the building sector than policies, regulations and rating systems. In fact, scores obtained by assessed buildings provide for discussion of their real sustainable characteristics.

Sustainable rating systems are, generally, voluntary standards, and their adoption is, hence, partially motivated by signaling factors. This means that the construction firm or the owner of the building decides to perform a sustainability assessment also to communicate something to the outside world (Mlecnik et al., 2010). According to King and Toffel (2007), signaling and intrinsic benefits are mixed together when sustainable rating systems are used. In their analysis, this clearly emerged from the decreasing number of buildings that obtained a larger number of credits than the minimum one for a given certification level. Buildings generally aim at an established certification level, and rarely show higher performance than the minimum ones for the given certification level. However, considering motivations other than sustainability, results of assessed buildings enable the comprehension of the most common choices in the construction of sustainable buildings.

In this section, a rating system is chosen to discuss aspects of sustainable buildings by looking at statistics of achieved points in certified buildings. Although there is space for improvement in LEED (Bower et al., 2006; Hahn, 2008; Newsham et al., 2009), this is the most diffused system worldwide, and hence it has been chosen for the analysis. A sample of 490 buildings was selected in the GBC database,4 from already built projects were assessed with version 2 of LEED. The sample was composed by buildings which had allowed diffusion of their evaluation data. Selected buildings belonged to several typologies, with a large majority of commercial (52%) and residential (30%) buildings. The time of construction was very similar among buildings, from 2002 to 2009, hence, a diachronic analysis could not be performed. Figure 3 shows points earned on average over the total possible points. The data suggest several considerations.

  • Sustainable sites is an important category in the overall evaluation (14/69 available points); however, assessed buildings reach fewer than 50% of the available points on average. The selection of a sustainable site is often influenced by property possibilities, municipal policies and previous land uses, making a free selection difficult.
  • Energy and atmosphere is the category with the largest number of points (17/69 points). The ratio of successful points to possible ones is the lowest among categories (38%).
  • Indoor environmental quality is the second category for available points but the first contributing to the total score, as average earned points are 56% of available ones.
  • Water efficiency receives only a few points in the standard (5/69), despite its importance for a sustainable building. The most probable reason for this is that few actions can lead to a significant efficiency in the use of this resource and, in fact, buildings obtained 62% of the available points on average.
  • The material and resources category has a considerable number of available points but effectively earned ones are few, with an average of 40%.
  • The innovation and design process category has a low number of available points, and on average buildings are successful in this category on 66% of the available points, which means that sustainable buildings are generally able to fulfill requirements in this category.

With the largest number of achievable points but third in absolute earned points and last in relative earned points to the total achievable ones, the energy and atmosphere category shows abnormal percentages. This suggests that energy requirements are still difficult to achieve, and also that projects aimed at sustainability certification under-adopt performances within this category. The low result of energy and atmosphere scores can probably be justified by the very low preparedness and the low awareness of this category among constructors (Son et al., 2011).

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Figure 3. Earned points over the total possible in each assessment category for different classes of LEED rated buildings

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Figure 3 represents the percentages for buildings of different classes, for certified, silver, gold and platinum buildings. In platinum buildings, the percentage of earned points in the energy and atmosphere category increases with respect to other classes of buildings, becoming the category contributing most to the overall score in absolute value (78% of points obtained, with an average of almost 14 points over the 69 available). However, if compared with the total available points in this category, those obtained have a lower percentage than in other categories. The material and resources category also suffers from obtaining a high percentage of points for any class of buildings and, in particular, in platinum ones this category represents a less successful one (62%). The high percentage of success in the innovation category can be justified by the freedom the LEED system allows for points in this category. Moreover, it is interesting to look at the results for the water efficiency category: the importance of this resource, together with the ease of designing and building systems of water harvesting, suggest that water efficiency represents an achievable target that can be reached, almost independently from the rate of sustainability certification.

The comparison between achieved points in silver and gold buildings shows that the improvement in the assessment is lightly influenced by the material and resources category. In fact, average earned points in this category are similar among buildings. Conversely, a larger improvement occurs between silver and gold buildings in the energy and atmosphere and water efficiency categories.

Figure 4 disaggregates the statistics in Figure 3 by representing the earned points for any criterion. This shows which points in each category are more often reached. In the indoor environmental quality category, criteria from IEQ 1.0 to 5.0 are earned by a high percentage of buildings in any class: these criteria correspond to the air monitoring system, an increase in ventilation, management of air quality during construction, use of low emitting materials and control of pollutant source. This suggests that sustainable buildings have nowadays learned how to achieve a good indoor quality, or on the contrary that the required target levels are in line or below the common practice of sustainable buildings.

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Figure 4. Percentages of earned points over the total possible in several categories of the LEED system in buildings of different classes

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Energy related criteria are among the less achieved ones. In particular, the percentage of buildings with renewable energy production is low for any class of buildings, with only 1% of certified buildings able to produce 20% of energy from renewable sources (E&A 2.3). A high energy performance (E&A 1) is partially achieved, and many buildings make only limited choices towards optimization: high success rates for E&A 1.1, 1.2 (optimize energy performance through lighting power and lighting controls), while low ones for E&A criteria 1.3, 1.4, 1.5, which are related to the HVAC, equipment and appliances energy savings, respectively.

Urban and brownfield redevelopment criteria (SS 2.0, 3.0) have low success rates: this suggests that the possibility of selecting land is of secondary importance in respect to the construction priority. In contrast, criteria about alternative transportation (public transportation access SS 4.1 and bicycle storage and changing rooms SS 4.2) have a high success rate. Moreover, they are relatively inexpensive (Morris and Matthiessen, 2007), as changes in the building design are minimal. A similar discourse is valid for other criteria in the sustainable site category, such as the mitigation of the heat island effect (SS 7.2).

In the water efficiency category, water use reduction has a high percentage of success among all certification levels, with values that, in certified buildings, go from 60% for 20% reduction in water use (WE 3.1) to 37% for 30% reduction (WE 3.2). Limitation in irrigation needs (WE 1.1) is, generally, obtained through an appropriate selection of grass design. In contrast, the implementation of innovative wastewater technologies (WE 2.0) represents a complicated target even for best-rated buildings. According to Morris and Matthiessen (2007), this could probably be justified, as on-site wastewater treatment adds significant costs.

Finally, criteria in the material and resources category have a different behavior. In fact, high success percentages are reached for construction waste management (M&R 2.1, 2.2) and use of local and regional materials (M&R 5.1, 5.2) in any class of buildings. In contrast, other criteria in this category show a low success rate even in platinum buildings: among these are criteria for adoption of building reuse materials (M&R 1.1, 1.2, 1.3) and rapidly renewable materials (M&R 6.0). This suggests that sustainable buildings are generally able to reduce the impact of their material and resource uses, although this ability is shown by selecting new virgin materials more than looking at using recycled or low energy embodied ones.

Obviously, the choice to use the LEED protocol, limiting the evaluation to one rating system, means the analysis is influenced by its structure as well as by its criteria. Further analysis should test the above results in different and larger samples of buildings, while looking at the results in buildings of different typologies should help to understand certification differences among typologies. Finally, assessment results with other rating systems should be compared in order to obtain a larger validity of the above findings and to limit the influence of the rating system structure.

Sustainability Assessment Trends and Conclusions

  1. Top of page
  2. ABSTRACT
  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References

Trends of sustainability assessment systems have been of interest since the study by Crawley and Aho (1999). As seen above, single- and multi-dimensional systems exist. Sustainability assessment was originally based on a single, often energy related, parameter. However, assessments through a single dimension have received much criticism (Nijkamp et al., 1990; Janikowski et al., 2000), as a single criterion is generally unable to measure the sustainability complexity. An increasing awareness of externalities, risk and long-term effects have suggested a larger diffusion for multi-criterion systems. Available multi-criterion systems have been accused of a lack of completeness as they neglect some criteria: for example, they rarely take into account the economic dimension of the development. This lack prevents the evaluation of the economic consequences of sustainable choices and, therefore, constitutes a great limit for sustainability rating systems (Ding, 2008). In fact, by neglecting the evaluation of economic aspects, sustainability rating systems contradict one of the development dimensions and allow the additive logic for adoption of sustainable choices, which can surely be criticized. The paper has shown that this limit affects any system, as almost no system incorporates economic and social evaluations.

The importance of economic and social evaluations has recently emerged in defining systems for developing countries, where it is more evident that the environment cannot be the only assessment category, but economic and social equity are fundamental (Gibberd, 2005). This should re-establish a sustainability perspective to assessment systems which actually seem too focused on the environment. A comprehensive approach to the evaluation has led to design systems that require much detailed information. For example, the last version of GBTool comprises more than 120 criteria. The complexity of criteria has been pointed out as a limit for the diffusion of sustainable rating systems (Mlecnik et al., 2010). Complexity is one of the barriers highlighted by Rogers in his innovation diffusion theory (2003), and if sustainability rating systems, and sustainability itself, are perceived as too complex by building stakeholders then sustainability practices will be adopted slowly. A balance between completeness in coverage and simplicity of use is hence necessary to spread sustainability building assessment systems. The greater diffusion of multi-criterion TQA systems than LCA ones is probably due to their simplicity and check list structure. In fact, although LCA analyses are often more rigorous than multi-criterion systems, they are still complex to understand and their diffusion is limited to a few specialists. The importance of simple systems is also emerging as a factor in making them useful as design tools. In order to introduce sustainability rating systems early in the construction process they must be structured not to need detailed information before they are generated.

An open aspect of sustainability rating systems regards possible regional adaptations in assessment criteria. The Italian experience of SBC-ITACA shows that regions are adapting the original system to local characteristics and priorities with regional criteria. It is evident that sustainability evaluation needs site adaptations, in order to fit sustainable requirements with contextual aspects. This approach is shared more and more worldwide. For example, the new version of the LEED system, version 3, has introduced points for regional priority to assess local aspects too. However, local aspects, priorities and benchmarks are complex to establish, especially when it is necessary to manage weights and optimal performance values as in multi-criterion systems.

Review among some sustainability rating systems has shown a trend for whole life perspective analysis as the assessment is moving to cover the construction and operation phases, and sometimes the dismantling phase.

Limits of sustainability assessments suggest that more complete rating systems are necessary to assess the multi-dimensional aspects of sustainability and to improve the triple bottom line of buildings.

An important trend in sustainability assessment is seen in the increasing attention to the neighborhood and construction site. First assessment systems considered the building as a manufactured product, and evaluated it almost in isolation. However, the importance given to the surrounding site is greatly increasing; for example, available points for sustainable sites have increased from 15 to 23% from version 2.2 to version 3 of LEED. Energy requirements have also become stronger in the latest versions of this and others assessment systems. This can certainly be motivated by the more rigid requests of energy regulations worldwide, but also by the greater attention being given to energy saving in buildings.

This paper has shown that energy performance is generally considered the most important criterion in building sustainability assessment, being the only one in CED and the most important one in every TQA system. Results of certified buildings have shown that energy performances are well below the optimal ones even in sustainable buildings: reasons for this are often the high cost of energy saving measures and the low preparedness of construction actors. In contrast, indoor environmental quality, which is highly considered among criteria of sustainability rating systems, is generally reached at a high rate by sustainable buildings.

The paper has reviewed the current status of sustainability assessment in the construction sector, describing and, often, criticizing most diffused systems. Although there has been a large and rapid diffusion of these systems, room for their improvement exists. The paper has indicated the necessity of improving the communicability of the assessment systems and encouraging a more inclusive approach, which could take into account externalities, long term (or life-cycle) effects and economic and social aspects, without increasing the complexity of the assessment systems.

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  3. Introduction
  4. Sustainability Assessment
  5. Sustainability Rating Systems
  6. Characteristics of Certified Buildings
  7. Sustainability Assessment Trends and Conclusions
  8. References
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