Analysis of the most widely used Building Environmental Assessment methods

Abstract

Building Environmental Assessment (BEA) is a term used for several methods for environmental assessment of the building environment. Generally, Life Cycle Assessment (LCA) is an important foundation and part of the BEA method, but current BEA methods form more comprehensive tools than LCA. Indicators and weight assignments are the two most important factors characterizing BEA.

From the comparison of the three most widely used BEA methods, EcoHomes (BREEAM for residential buildings), LEED-NC and GBTool, it can be seen that BEA methods are shifting from ecological, indicator-based scientific systems to more integrated systems covering ecological, social and economic categories. Being relatively new methods, current BEA systems are far from perfect and are under continuous development. The further development of BEA methods will focus more on non-ecological indicators and how to promote implementation.

Most BEA methods are developed based on regional regulations and LCA methods, but they do not attempt to replace these regulations. On the contrary, they try to extend implementation by incentive programmes.

There are several ways to enhance BEA in the future: expand the studied scope from design levels to whole life-cycle levels of constructions, enhance international cooperation, accelerate legislation and standardize and develop user-oriented assessment systems.

Keywords:

• Building Environmental Assessment
• LCA
• BREEAM
• LEED
• GBTool
• soft systems methodology

1. Introduction

1.1 Research category

Building Environmental Assessment (BEA) is a term used for several methods of environmental assessment of building environments including indoor climate, single building and building group – community. BEA is different to the environmental assessment of industrial products; it evaluates not only general environmental impact issues such as energy, water, waste, material, etc., but also issues such as lighting, ventilation, noise, parking, etc. related to living performance including occupant health and satisfaction.

Most BEA methods are developed based on Life Cycle Assessment (LCA), which is a technique for assessing the environmental aspects associated with a product over its life cycle. LCA is an integrated ‘cradle to grave’ approach used to assess the environmental performance of products and services (ISO 14040, 1997; Baumann & Tillman 2004). Many LCA tools are also implemented in BEA. However, in that they consider buildings as industrial products, these tools examine the raw material and energy issues only and cannot consider the social aspects of buildings. They are not the main objects discussed in this article, instead so-called ‘criteria-based BEA’ methods (Assefa et al. 2006) or ‘credit-weighting’ scale (Lee et al. 2002) are discussed. Figure 1 displays the boundaries of LCA and BEA.

Figure 1 LCA and BEA – different boundaries.

The goal of BEA is to identify and evaluate the environmental impacts of building development or operation. On the one hand, for a new construction, the conclusion of the assessment could support decision making and promote sustainable design and plan. On the other hand, for an existing building, an objective assessment is a useful starting point for the identification of disadvantages and for reforming design. Whatever the style of the object, these assessments do not determine decision making, but they do influence the process. The role of BEA is a technical service.

Generally, BEA has functions such as:

	presenting a set of quantitative environmental measures and evaluating methods for sustainable buildings and communities;
	promoting official policies and regulations aimed at sustainable construction;
	raising consumer awareness of environmental issues and standards;
	recognizing and encouraging environmental design for buildings, and stimulating the market for sustainable construction;
	improving environmental management of the built environment; and
	forcing the building market to pay more attention to ecological issues.

From a scientific perspective, BEA methods have been developed after several years of research. Both theoretical elements and operational methods have been constructed. Many countries have special institutions or committees co-operating with national authorities to deal with BEA issues. BEA rating systems from registration, documentation to evaluation and certification are at an advanced stage of development in several countries.

1.2 Most widely used BEA methods

1.2.1 BREEAM (UK)

BREEAM (BRE Environmental Assessment Method), launched in 1990, was the first BEA method in the world (Prior 1991). It has been the most widely used means of assessing the environmental performance of buildings in the UK and is increasingly accepted in the UK construction and property sectors as offering practice in environmental design and management. BREEAM assesses the performance of buildings with respect to management, energy use, health and well-being, pollution, transport, land use, ecology, materials and water (BREEAM 2005).

1.2.2 LEED Green Building Rating System (USA)

The LEED (Leadership in Energy and Environmental Design) Green Building Rating System is the USA's most widely used BEA system using a voluntary and consensus-based national standard. It was developed by the US Green Building Council (USGBC) over the period from 1994 to 1998. The newest version is LEED 2.1. USGBC member committees are actively collaborating on new and existing LEED standards (Scheuer & Keoleian 2002). In contrast with other BEA methods, LEED is a relatively simple rating system. It has no complicated algorithms. Furthermore, USGBC provides credit interpretation and training workshop services, which has contributed to LEED's dominant position in the USA.

1.2.3 GBTool (international)

The Green Building Challenge (GBC) is an international collaborative research effort aimed at developing a BEA tool to evaluate the environmental impact of buildings. The ‘GBTool’ is the method used to assess the potential energy and environmental performance of the case-study projects in the Green Building Challenge process.

A feature of GBTool that differs from other BEA systems is that the method is designed from the outset to reflect the different priorities, technologies, building traditions and even cultural values that exist in various regions and countries. The members of national GBC teams and others are free to draw from it in whole or part for use in the creation of assessment tools (iiSBE 2005a).

1.3 Other criteria-based methods

1.3.1 CASBEE (Japan)

CASBEE (Comprehensive Assessment System for Building Environmental Efficiency) is a Japanese integrated BEA system that has been developed by committees in the academic, industrial, and government sectors. CASBEE is a variety of assessment tools for the various phases of the building under evaluation: planning, design, completion, operation, and renovation. CASBEE is currently one of the most complex BEA systems. It covers almost every aspect during construction, which indicates the power of this method on the one hand, however on the other hand it also means it is extremely difficult to implement (Murakami et al. 2002; Huang et al. 2003).

1.3.2 Green Star and NABERS (Australian)

Green Star, announced by the Green Building Council, is a national voluntary rating system that evaluates the environmental performance of buildings. Rating tools are under development for a range of building types and phases. The tool addresses the largest segment of the commercial office market, existing buildings, and helps building owners to assess the environmental merits of their existing or future assets (Green Building Council of Australia, accessed 15 June 2005).

NABERS (National Australian Built Environment Rating System) is Australia's first comprehensive built environment rating system that has been developed in consultation with industry and other stakeholders by the Australian Government Department of the Environment and Heritage. NABERS is a performance-based rating system that measures an existing building's overall environmental performance during operation against a set of key impact categories (NABERS 2005).

1.3.3 Ecoprofile (Norway)

Ecoprofile is a BEA method based on two earlier methods: Ecoprofile for Buildings and Environmental and Resource Effective Commercial Buildings (ERCB) in Norway. The Ecoprofile of a building is divided into three principal components: External environment, Resources and Indoor climate. Eventually a class 0 will be included that will represent a sustainable construction, but there is currently no basis for defining such a level (Pettersen 2000).

1.3.4 PromisE (Finland)

The PromisE system was developed in Finland for environmental assessment and classification of existing buildings. It has a classification structure divided into four main categories: human health; use of natural resources; ecological consequences; and environmental risk management. These main categories are then described as subsystems with their content explained in more detail. The system is designed to meet different demands arising from three building types: apartment buildings, office buildings and retail premises. The classification structure is generic, but tailored to meet the specific needs of different building types at a low level (Andresen et al. 2004).

1.3.5 Green Mark for Buildings (Singapore)

The Green Mark for Buildings was developed by the Building and Construction Authority, Singapore, as a strategic programme to encourage sustainability in urban areas. The Green Mark for Buildings is also supported by the National Environment Agency. It assesses five areas of concern globally: energy efficiency; water efficiency; project development and management for new buildings; indoor environmental quality; and environmental innovations (Building and Construction Authority 2005).

1.4 LCA methods implemented in BEA categories

In addition to integrated BEA tools, many LCA tools are implemented in the building categories focusing on raw material and energy. Their assessment scopes are relatively narrow compared with other BEA system but they do represent more quantitative approaches. This article will not discuss them in detail.

1.4.1 BEAT 2002 (Denmark)

BEAT 2002 is a LCA tool for performing environmental assessment of products, building elements and buildings that has been developed by the Danish Building Research Institute. The tool, a relational database built with Microsoft Access, consists of a database containing environmental data and a user interface with an integrated inventory and assessment tool. The database contains environmental data for unit processes. Based on these data the inventory tool can calculate environmental impact. Furthermore, a number of other indicators are also included (Andresen et al. 2004).

1.4.2 Eco-Quantum (Netherlands)

Eco-Quantum is a LCA-based computer tool developed by IVAM in 1997. IVAM is an innovative research agency active in many environmental areas affiliated to the University of Amsterdam. Eco-Quantum provides architects and project developers with an instrument to measure the environmental performance of buildings. Eco-Quantum shows the quantified environmental impact of the dwelling using the four (in future five) environmental indicators for buildings. These indicators are resource depletion, gaseous emissions, energy consumption and waste generation (hindrance with biodiversity and land use will be included in future) (W/E Consultants Sustainable Building 2000).

1.4.3 ATHENA, GaBi, SimaPro, etc

There are many famous LCA tools, such as ATHENA, GaBi, SimaPro, etc. with specialized databases that can be used for building categories. These have been widely implemented in many industrialized countries, for instance Germany, France, Italy, Switzerland, and Spain, etc. (Hui 2002).

2 Formulation of BEA methods criteria

General LCA tools can be developed for BEA with special inventory data in built environmental categories, e.g. ATHENA, GaBi, SimaPro, etc. Integrated BEA methods are developed from environmental design guidelines adopting LCA principles, e.g. BREEAM, LEED, etc. This kind of BEA method is similar to a three-step computer program: input, calculation and output. As long as users input the required information – many different parameters – the methods will output the result credits for rating. Consequently, BEA methods may be regarded as data-processing systems that enable movement from written guidelines to computer programs.

Generally, the final credit of a BEA method can be expressed as:

where C is the final credit, C _i is the credit of single indicator, f _i is the weighting factor (between 0 and 1) of the indicator, and n = number of indicators.

BEA methods confirm some categories to be assessed, for example energy, water, materials, pollution, indoor climate, etc. Each category has a number of subdivisions, and each subdivision has one or several indicators. Actually, the function of BEA methods is transforming these different parameters into uniform credits by the application of a set of criteria. The differences between BEA methods are essentially indicator selections and their weighting. BEA methods provide users with the opportunity to assess the sustainability of building projects using simple credits, rather than many complex scientific parameters (Watson et al. 2005).

As the core of the BEA method criteria, the algorithms decide the final results of assessments. Current BEA tools have two algorithm types. Some BEA tools, for instance LEED, list assessed items. As long as the evaluated item is up to the reference, it will be awarded the credit, and vice versa. The final credits are the sum of achieved credits. Other BEA tools, for instance BREEAM, use a slightly more complex algorithm. Not equally shared in every aspect, the primary items may cost more credits and secondary items may cost less credits.

The different ratings are assigned to the assessed objects according to their final credit total. A distinctive difference between BEA methods and LCA tools is that the BEA methods not only calculate the numerical values of different indicators, but also estimate them, which means the methods have more subjective features depending on reference values. The rated grade depends on both the hard parameters of ecological loads and the criteria used for weighting assignments, while the general LCA calculates the ecological loads but usually does not combine them with some criteria.1 The higher scores of important indicators will help projects to obtain higher ratings in a BEA system.

The criteria of indicator selection and weight assignment are the main points to be analysed.

3 Comparison of three most widely used BEA methods

Here, three widely used BEA methods are compared: EcoHomes 2005 (BREEAM for residential buildings) (BREEAM Office 2004a,b), LEED-NC version 2.2 (USGBC 2005b), and GBTool 2005 (iiSBE 2005b). BREEAM is the oldest BEA method, LEED is slightly younger, and GBTool is the youngest method.

3.1 Indicators used in assessment methods

BEA methods are rating systems using some given criteria. The final weighted credits are the sum of many indicator credits. Generally, the BEA indicators are no more than issues of site plan, energy, transport, materials, water, pollution, indoor climate, etc. Various BEA methods have their own set of chosen indicators, which is the first factor that should be compared.

The second factor that should be compared is the weighting of these indicators. Although most indicators are alike in the different BEA methods, they are allocated different weights. This allows the emphasis of the different BEA methods to be summarized.

Table I lists the indicators of the three most widely used BEA methods, which are sourced from BRE, USGBC and iiSBE's official guidelines (BREEAM Office 2004a,b; USGBC 2005b, iiSBE 2005b). EcoHomes and GBTool have offered the indicator's per cent of total score in their rating checklist. LEED does not use percentages. The full score is 69 points and almost every indicator is 1 point (a few indicators are more than 1 point). Here they are converted into percentages, so most indicators' weight is 1/69 = 1.45%.

Table I. Indicators of the three most widely used BEA methods and their weighting, sourced from BRE, USGBC and iiSBE's official guidelines (BREEAM Office 2004a,b; USGBC 2005; iiSBE 2005b).

Indicators	EcoHomes	LEED	GBTool∗
Site and planning
Site selection		1.45%
Building density	3.33%	1.45%	1.90%
Building on land of inherently low ecological value	1.67%	1.45%
Protection of ecological features	1.67%	1.45%	2.30%
Ecological enhancement	1.67%		1.10%
Change of ecological value of site	6.67%	1.45%
Stormwater design	4.28%	2.90%	2.10%
Heat island effect		2.90%	1.50%
Wind conditions around tall buildings			0.80%
Daylight or solar energy			1.20%
Limit cumulative thermal changes to water			2.40%
Local cultural values			0.50%
Maintenance of heritage buildings			1.30%
Total	19.29%	13.05%	15.10%
Energy
Greenhouse gas emissions	10.71%		3.30%
On-site renewable energy	2.14%	4.35%	1.90%
Green power		1.45%	1.90%
Building energy performance	5.36%	14.49%	3.30%
Energy efficiency goods	2.14%	1.45%^†	1.10%
External lighting	2.14%
Drying space	1.07%
Enhanced commissioning		1.45%	2.10%
Measurement and verification		1.45%
Predicted electrical peak demand			1.00%
Total	23.56%	24.64%	14.60%
Transport
Public transport	2.14%	1.45%	2.50%
Green vehicles		1.45%
Parking capacity		1.45%
Bicycle storage	2.14%	1.45%
Local amenities	3.21%		1.50%
Home office	1.07%
Total	8.56%	5.80%	4.00%
Materials
Building reuse		4.35%	2.00%
Construction waste management		2.90%
Materials reuse	2.90%	2.90%
Recycled content		2.90%	1.60%
Regional materials		2.90%	1.10%
Rapidly renewable materials		1.45%
Timber	4.35%	1.45%	1.70%
Cement substitutes in concrete			1.50%
Environmental impact of materials	7.73%
Solid waste			3.20%
Total	14.98%	18.85%	11.10%
Water
External water use	1.67%	2.90%	1.30%
Wastewater technologies		1.45%
Internal water use	8.33%	2.90%	1.60%
Total	10.00%	7.25%	2.90%
Pollution
Light pollution reduction	2.14%	1.45%	0.80%
Atmospheric emissions	6.43%^‡		3.40%
Minimize danger of hazardous waste			1.20%
Stormwater and sewage pollution			1.20%
Total	8.57%	1.45%	6.60%
Indoor climate and functionality
Increased ventilation		1.45%	5.50%
Outdoor air delivery monitoring		1.45%
Air quality management		2.90%	3.80%
Low-emitting materials		5.80%
Indoor chemical pollutant		1.45%
Controllability of systems		2.90%	5.70%
Daylight and illumination	5.46%	2.90%	3.60%
Sound insulation	7.52%		2.90%
Thermal comfort		2.90%	2.30%
Space utilization	1.88%		1.90%
Maintenance of core functions			0.50%
Total	15.04%	21.75%	26.20%
Others
LEED-accredited professional		1.45%
Innovation in design		5.80%
Maintenance of performance			4.20%
Flexibility and adaptability			7.00%
Cost and economics			4.50%
Social aspects			3.80%
Total	0	7.25%	19.50%
∗The data weights of different projects should show slight changes.
^†Only includes refrigerant management, not other home appliances.
^‡Only includes NO x emissions.

As these three BEA methods have different category sets in their own settings, some indicators may be moved into unified categories in the table, which creates slight imprecision, but does not change the results as a whole.

EcoHomes has the fewest indicators and GBTool has most, which reflects the more recent the development period, the more complex the method. In fact, GBTool has more sub-indicators to cover the whole range of building design and planning, not only environmental issues, but also social and economic issues. Compared with GBTool, EcoHomes is more a simple environmental assessment method rather than a comprehensive building environmental impact calculation.

3.2 Indicator weight assignment

In order to compare the weights of indicators they are grouped into six categories: site plan; energy (energy and transport); raw materials (materials and water); pollution; indoor climate; and others. Site plan indicates the general environmental factors; energy, raw materials and pollution are main ecological assessment indicators; indoor climate indicates the living quality of buildings. In addition to these basic BEA indicators, some other parameters are presented in LEED and GBTool as additional encouragements. Figure 2 displays the weight assignments of the three methods in these six categories.

Figure 2 Weight assignments of dominant BEA methods in six categories.

The site plan is the only category that all the three methods award similar weight, although they still show subtle differences. EcoHomes and LEED's parameters are direct ecological indicators; however GBTool has some ecology-irrelevant parameters, such as cultural value and heritage preservation. It appears that GBTool is more comprehensive than the others.

The issues of energy and raw materials are EcoHomes and LEED's focal points, which is not the case for GBTool. Little attention is given to pollution issues as civil buildings usually emit much smaller pollution levels than industrial buildings. Energy, water and pollution are usually important factors in general environmental assessment methods because of their strong eco-relation. Here GBTool displays its distinctive attitude to these general ecological problems – it does not place them as the most important problems; they have the third and fifth greatest weights.

Indoor climate is the most important element for GBTool. This is mostly related to living conditions and human behaviour, i.e. GBTool considers social factors more.

EcoHomes has no other parameters beyond the basic five categories. LEED gives innovation of design and accredited professionals an additional couple of credits. GBTool puts a relatively high weight on this category compared to the other two methods – nearly one-fifth of total credits. All the parameters are social and economic indicators.

Here, indicators are grouped into three levels: direct ecological indicators, indirect ecological indicators and non-ecological indicators. The direct ecological indicators are those using the strict ecological perspective, for instance protection of ecological features, greenhouse gas emissions, etc. The indirect ecological indicators are the indicators that influence ecological systems indirectly, for instance energy efficiency, material recycling, public transport, water recycling, etc. The non-ecological indicators are indicators that would not influence ecological systems but would influence the quality of developments, for instance maintenance of heritage buildings, cost and financial situation. Table II lists the weight assignments in three levels.

Table II. The BEA method weight assignments, in three levels.

Indicators	EcoHomes	LEED	GBTool
Direct ecological indicators	43.0%	27.4%	28.3%
Indirect ecological indicators	41.2%	55.1%	35.6%
Non-ecological indicators	15.8%	17.5%	36.1%

EcoHomes and LEED use a similar proportion of ecological indicators to non-ecological indicators. The difference between them is that LEED has less direct ecological indicators. Compared with EcoHomes and LEED, GBTool considers non-ecological indicators more. This again demonstrates that GBTool is a more comprehensive BEA method.

3.3 Evaluation and summaries

EcoHomes is an ecological, indicator-based BEA method. BREEAM is the first environmental building rating system in the world, so it is rational that it is developed based on experience of other environmental assessment methods.

LEED was developed later and has similar weight assignments to EcoHomes except the encouraging credits for innovation design and accredited professionals. However, it increases the weight of indirect ecological indicators as compared to direct ecological indicators.

GBTool is the newest BEA method among those considered here. It is a more comprehensive BEA method that has more social and economic parameters. GBTool is designed as a generic framework, and requires a third part to adjust it to suit the unique conditions applicable to certain building types in various regions. It is not only an environmental assessment method, but also a sustainability assessment method. Consequently, parameters cover sustainable building issues within the three major areas – the environmental, social and economic sectors. It should be noted that this system is under continuous development (iiSBE 2005a). Although it is still to be completed, the preliminary framework has covered more categories than the other BEA methods.

Apart from their differences, all these BEA methods include the following elements:

3.3.1 Comprehensive rating systems

BEA is not a specialized assessment, but an integrated assessment system. It not only grades different sustainable aspects, but also unifies these aspects into an overall credit. If BEA is a pure LCA tool, it is possible to confirm the coefficients of different factors with modern mathematic LCA algorithms, although it is quite difficult in many aspects: goal definitions, system boundary definitions, environmental impact level, etc. However, even the most ecological indicator-based BEA method, BREEAM, also includes some non-ecological factors that are hardly used in the LCA method. The more non-ecological indicators involved the less objective the BEA becomes. It is this subjectivity of current BEA methods that provides the flexibility to suit different regions – different users can adjust the weight assignments according to their requirements, which is a main advantage of the GBTool. However, this makes the comparison of buildings across the world almost impossible, so it is also a disadvantage of GBTool in another perspective.

3.3.2 Complex methods

The objective of BEA is built environment, i.e. architecture in its broad sense. Architecture has large numbers of attributes in various categories. Consequently BEA has to define many indicators in order to cover different categories, which is a common method of scientific research. With the development of BEA, indicators increase and evaluating systems become more complex. There are more than twice as many GBTool indicators as there are in LEED (iiSBE 2005b).

There is no doubt that strict quantitative assessments make the final rating credits robust, as long as fundamental data are precise and full. However on the other hand, this makes the preparation work difficult and detailed and users tend to recoil at the sight of the thick guidelines and bulky tables. Even if users have enough courage and vigour to face the documentation, collecting the necessary information is also hard work. Most BEA methods are so complex that they are not easy to use for a non-professionally trained person, especially for architects who tend to be artists rather than engineers.

3.3.3 Specialization

Initially, most methods were general. Now they are moving to more specialized structures that can be adapted to any situation. For instance, LEED has installed, or is currently developing, six sub-aspects: new commercial construction and major renovation projects (LEED-NC); existing building operations (LEED-EB), commercial interior projects (LEED-CI); core and shell projects (LEED-CS); homes (LEED-H); and neighbourhood development (LEED-ND) (USGBC 2005a).

The specialized BEA tools are more professional and aim at different kinds of built environments, which do not make the assessment more (or less) accurate than generic tools, but they allow for more comprehensive and user-friendly interfaces. However, these specialized BEA methods also make it difficult to compare credits with each other.

3.3.4 Regional, based on local regulations

BEA methods are developed for regional users because buildings cannot move. It may use local data that also makes comparisons difficult. BEA is not the national standard and it must exercise under the frame of national codes. Consequently most BEA is based on local standards first (BREEAM 2005).

For instance, in the second factor of EcoHomes – Building Fabric applicability:

‘Homes built to the following regulations should achieve improvements according to column I:

	England and Wales 2002 Building regulations Part L1
	Scotland Part J of the Technical Standards (6th amendment)

Homes built to the following regulations should achieve improvements according to column II:

	Scotland Part J of the Technical Standards (4th and 5th amendments)
	Northern Ireland Building Regulations Part F
	All refurbishments (independent of country)’

It is obvious that EcoHomes can only be implemented outside UK if countries use British regulations as well. Since all BEA methods are based on local regulations, there is no international BEA tool at present. GBC is an international BEA programme and the GBTool provides the basics for member countries concerning the creation of assessment tools, but GBC does not recommend the direct use of GBTool as a national BEA method. It should be improved in order to cover each practical situation (iiSBE 2005a).

4 Discussion

4.1 The strength and weakness of LCA-based BEA

LCA is a methodology whereby all material and energy flows of a system are quantified and evaluated. Usually, LCA tools in the construction industry are less developed than in other industries (Scheuer & Keoleian 2002). More LCA tools are currently under development for BEA; for instance, the Environment Priority Strategies in Product Design (EPS) method that developed in Sweden, the Environmental Theme Method that developed in the Netherlands, and the Ecological Scarcity Method that developed in Switzerland (Jönsson 2000).

4.1.1 Robust quantitative assessment method

In the scientific area LCA has been acknowledged as one of the most powerful methods (Baumann & Tillman 2004). Its advantage is the ability to calculate the consequences of specific combinations of building materials, building designs and local utility options, for example energy supply, material and energy use for indoor climate equipment, waste management, transport type, etc. (Assefa et al. 2006). The LCA quantitative assessment method is very different from the ranking method of the criteria-based methods. It is an accurate calculation instead of the rough rating system.

For example, LEED uses a total of 69 credits. Most credits have a relevant indicator. If the object can meet the lowest requirement of this indicator then it will be awarded the credit. In fact, each indicator has only two statuses, positive or negative, which indicates that it is merely a qualitative assessment method, while LCA methods not only judge the good or bad, but also judge the level of the good.

Since the LCA-based BEA methods have such powerful abilities, they are used widely in civil engineering and planning. Unfortunately, they are usually applied in the scientific research areas. So far, LCA tools have rarely been carried out in large-scale, practical building projects and administrative decision making. This is due to two reasons:

(1) Conflicts between depth and applicability. The validity of LCA is in direct proportion to its depth and in inverse proportion to its complexity and applicability (Jönsson 2000; Scheuer & Keoleian 2002). For instance, the rough calculation of the energy consumption of a house is the sum of energy consumption in the construction and operation phases. The deeper calculation should add the energy consumption during the production phases of building materials. The much deeper calculation would consider the distance from the material production locations to the building and the transport methods, because the same materials may consume different energy in a certain building due to different transportation methods. It is evident that calculations will increase rapidly with increasing depth, which means more time, manpower and financing. However, all building projects face limited financing and time. The project may be hardly changed at all if it receives poor LCA results. These conflicts form the major barrier to applying LCA in BEA categories.

(2) The uncertainty and independence of buildings. The other factors that interfere with the application of LCA are two characteristics of buildings – uncertainty and independence. Uncertainty means the construction and operation processes of buildings cannot follow the scientific plans strictly. Independence means almost every building is unique – even though two buildings could have the same hardware, they still differ in operation with different users for different functions.

For instance, the inhabitants' behaviour patterns will influence water consumption in a building – a person may shower three times every day or only once every 3 days. This is the uncertainty. If buildings are mass-produced units, the mean values from samples could be used. Actually, almost every building is unique. If the LCA is for the entire construction industry, this does not matter. However, now it is applied to every single building project. The average value cannot replace the actual value.

4.2 BEA strategies

Since LCA methods have fatal weaknesses in their application, BEA methods have developed a new approach, which was named the Middle Path by some researchers (Scheuer & Keoleian 2002).

4.2.1 Not a scientific method

Although most BEA methods are developed from LCA methods, they are different. BEA methods are not absolutely scientific; otherwise their indicators would be the same and have the same weights. The different weight assignments are decided by experts in the organizations that established them, according their own opinions and experience. Since these experts are able to stipulate weights, others can do the same. The GBTool has implemented this idea, more or less.

The GBTool provides numbers of indicators covering a wide domain. Users may choose indicators according to project conditions and indicator weights may be slightly changed as well. The GBC also encourages members to develop their own BEA methods based on GBTool.

According to scientists and engineers, a scientific approach is necessary to assess sustainability. However, BEA methods involve features of consensus-based tools. Consensus is not a scientific base and tells us little about sustainability. It is interesting that a sustainability assessment system does not assess sustainability as an absolutely objective standard. BEA methods' developers have to consider social and economic factors as important as scientific assessment in practice. A rough qualitative assessment is enough in a BEA system. More accurate quantitative assessment can be done by LCA tools. BEA's task is not only sustainability assessment, but also to guide the direction of actions, and it is hard to avoid the fact that this guide represents the method developers' subjective thinking.

4.2.2 Influencing building designs

In life-cycle thinking, building is a process rather than a result. The purpose of environmental assessment is to decrease environmental impact. LCA can calculate the scale of environmental loads, and compare several technical solutions in order to improve the situation. However, LCA has little influence on the building process. How do stakeholders transform LCA awareness into environmental improvement? BEA's methodology is to influence building design and then to control the entire life cycle of buildings (Figure 3).

Figure 3 BEA's methodology and building life cycle.

As mentioned above, user behaviour patterns are uncertain. What the LCA tools can do is to use mean values to forecast environmental load during the operations phase, but it does not fit each individual building. BEA methods present a new way not to control, but to influence people's behaviour. For instance, many BEA methods would consider bicycle storage in order to encourage the wider use of bicycles as transport (EcoHomes – Section Tra2, LEED-NC – Credit 4.2, GBTool – A3.6); while no LCA tools will include this issue. BEA methods use a large quantity of indirect ecological parameters. Although they are not the direct ecological indicators and are calculated differently, they would influence the actual environmental impact. Moreover, these guidelines are more significant to architects than are abstract figures, and architects play a central role in the building design process.

4.2.3 Market transformation

Much environmental identification concerns political behaviour, such as the EU Energy Star label. However, most BEA systems have been commercialized or are being commercialized. There are two reasons: BEAs are not regulations administered by authorities, and the BEA process generates high costs due to the complex steps and the necessity of a large numbers of professionals.

There have been many mandatory standards in building industries. If developers do not comply, the buildings are illegal. However, BEA is not a part of mandatory standards. The path that BEA tools are taking is more in the nature of industry collaboration: voluntary market-based standards. Many BEA organizations are developing incentive programmes to extend the implementation of BEAs. For instance, at the end of 2003, the Australian Department of the Environment and Heritage (DEH) began a process to commercialize NABERS and called for Expressions of Interest (EoI) from suitably resourced, experienced and committed organizations to undertake the commercialization phase – including the market rollout, promotion, implementation and ongoing administration of NABERS. In August 2004 the Sustainable Energy Development Authority of NSW (SEDA) was awarded the contract to make NABERS a commercial reality (NABERS 2005).

Figure 4 shows the USGBC's estimate of green building markets (Watson 2003). Most BEAs use a similar operational process: Eligibility, Registration, Documentation, Credit Interpretation and Certification. Commercial operation can stimulate building project teams to consider more environmental aspects as certification can increase commercial benefits.

Figure 4 Green building markets estimated by USGBC (Watson 2003).

4.2.4 International cooperation

The global environmental impact is an international issue. When BEA methods were first developed there was no international cooperation among countries. Each country developed their own BEA methods, which were not compatible with each other.

In October 1998 an international conference entitled Green Building Challenge ‘98 (GBC ‘98) was held in Canada. It was a significant milestone in the world's collective understanding of BEA. The conference included around 90 technical papers by international experts on issues of importance to green building and its assessment. After GBC ‘98, GBC has been held three times in the period up to 2005. As a result, the GBTool research process involves a multinational team that determines what should be used as standards for measures. The software program is flexible enough to account for the climatic differences of each country using the tool (iiSBE 2005a).

International cooperation will not replace national assessment methods, but it can provide a general system as a foundation and an interface between different methods.

4.3 Two trends

By the end of 2005, approximately 390 million square feet and 3000 projects have been registered with USGBC in order to become LEED certified (USGBC News 2005). About 4% of new commercial constructions have been completed under LEED guidelines (in the USA) (Associated Press 2004). LEED has one of the best market operations, but still few buildings are built according to LEED, let alone other BEA systems. It is obvious that BEA methods cannot play the leading role in the transformation of the entire construction industry. Currently, two BEA trends are developing.

4.3.1 Legislation and standardization

One reason for BEA methods not being implemented widely is that BEA methods are not mandatory regulations. Here we can compare this with the EU automobile emission regulation. The EU automobile emission regulation has four levels. In 1992 Euro 1, in 1996 Euro 2, in 2000 Euro 3 and in 2005 Euro 4 began mandatory implementation in EU countries (Euro 5 planned for 2010) (Vogel et al. 2005). The later standards are stricter than the previous ones. If there were no EU agenda aimed at limiting automobile emissions, it is unimaginable that the producers would consciously reduce the automobile emission levels of their products.

However, the situation in construction is not exactly similar to automobiles. The building industry is not monopolized by a few manufacturers. Normally, construction companies are relatively small-scale and even families or individual people may build houses. Consequently, many stakeholders feel that construction is a private issue and they have the freedom to take decisions on the level of specifications for each building.

It is true that the stakeholders have the right to decide their building's level, but this should be within the private sphere only. The buildings may use cheap plaster or expensive stone, which does not matter, but they may also use electricity, water and produce solid waste and waste water, which demands support from municipal infrastructures. In these aspects, buildings are the same as automobiles.

The experience from EU automobile emission regulation shows that legislation and standardization is one important approach to promoting environmental production. Incentive programmes are useful to extend the concept, but availability is limited. The development of BEA methods is the basis of future regulations in a sense.

4.3.2 User-oriented development

BEA methods are integrated systems involving both environmental and social aspects. In the environmental aspect, they will be transformed into mandatory regulations step by step; in social aspects, they will be transformed into user-oriented methods.

LCA is a kind of Hard Systems Methodology whose main concept is a trilogy: observing world, analysing world and reconstructing world. Hard System Methodology considers that the raw world is structured and mechanical. Humans can identify the rules of this world and use them in practices. However, there are many indefinite factors in the human world, so traditional engineering is weak in areas such as social, cultural, educational, health issues and management. The soft systems thinking presents a different thinking mode which does not consider the world to be mechanical and can be absolutely controlled by humans. However, humans can influence and organize the world by using limited, internalized actions, which is an iterative process of interaction and communication between problem solver or manager and real-world problem situation, rather than a result (Checkland 1999). Figure 5 displays hard and soft system stances.

Figure 5 Hard and soft systems stances (Checkland 1999).

Modern management theory includes soft systems methodology for solving social problems. BEA should not only try to ‘control’ the project, but also ‘influence’ the process. User-oriented methods mean that indicators and their weights are decided by stakeholders instead of using pre-assigned indicators. However, if every stakeholder is allowed to prescribe his own set of weights, then communication between stakeholders becomes impossible and comparison of buildings and solutions is impossible as well. For instance, you can never compare an EcoHomes' grade with a LEED's grade. Different assessment results have little comparability. So BEA is an exponent of new solutions but it may never replace the position of local codes and regulations in building market. BEA's main function is demonstration rather than broad implementation, which is regulations' function. It is unpractical to place all hope of building sustainability on the BEA.

The current BEA systems are developed by academic groups, so theoretical ecological issues are the most important issues in these systems. However, other stakeholders, such as planners, developers, inhabitants and contractors may have different interests to pursue. For instance, to most inhabitants, energy efficiency is important usually for monetary reasons rather than environmental reasons. Consequently, if the inhabitants could make their own BEA system, the indicators must be different from the academic BEA system. Even the same indicators may have different considerations. For instance, the experts state that bicycle storage is to save fossil fuel, while the inhabitants consider it more as a lifestyle factor.

Current BEA methods, especially those such as GBTool, have established frameworks which are flexible enough to adapt to user-oriented requirements. Future BEA methods may be developed on the basis of current frameworks and focus on different stakeholders' interests.

5 Conclusions

BEA is a kind of comprehensive environmental assessment system for the built environment. Generally, LCA is an important foundation and part of a BEA method, but it may not be entirely equal to BEA. Current BEA methods are complex and professional. Most BEA tools are developed based on regional regulations; however they do not try to replace these regulations. On the contrary, they try to extend implementation using incentive programmes instead of forcible orders.

From the comparison of the three most widely used BEA methods, it can be found that BEA methods are shifting from ecological, indicator-based scientific systems to more integrated systems covering ecological, social and economic categories. As a fresh method, current BEA systems are far from perfect and are under continuous development. Actually, as a foundation for BEA systems, LCA methodology has been relatively developed.

LCA can be used as a robust quantitative assessment method but cannot be applied for large quantities of various building projects. However, BEA methods are not absolutely scientific. BEA's methodology is to influence sustainable design and then to control the entire life cycle, which is a type of soft systems thinking. Most BEA systems have been commercialized or are being commercialized. Commercial operation can stimulate building project teams to consider more environmental aspects as certification can increase commercial benefits.

In many European countries, especially in the Netherlands, Germany and Nordic countries, LCA tools have been researched and developed to quite an advanced level, and have been applied widely in many industrial areas. People prefer to use LCA, and criteria-based BEA methods have little implementation, which may be related to European rational character. On the other hand, in North America, UK and Asian countries, criteria-based BEA methods are relatively more acknowledged and applied cases keep on increasing. In the USA, thousands of projects have been certificated by LEED (USGBC News 2005). It seems that BEA methods are developing in a way that is different from normal scientific approaches. No one knows if it will be successful and if it will achieve real sustainability. But, there are several obvious ways to enhance BEA methods in the future:

	expanding the scope from the design level to the whole life-cycle level of constructions;
	paying more attention to non-ecological indicators and different stakeholders' interests;
	enhancing international cooperation;
	accelerating legislation and standardization; and
	developing user-oriented assessment systems.

Notes

¹ With the development of LCA methods, today weighting methods have been introduced into most LCA methods too. The criteria of weighing are to convert different environmental loads into one parameter, for instance, CO₂ emissions. However, to ensure accurate conversion needs a great deal of basic data and calculations.