Sustainability Assessment of Buildings Indicators

Abstract

The building sector is responsible for a high environmental impact, namely during construction, maintenance, demolition, and lifetime. It is then urgent to develop tools for guiding all stockholders to make buildings more sustainable. In order to make the sustainability assessment of a building, it is necessary to make a survey of the most appropriate parameters for this analysis and organize them hierarchically. The first sustainability certification rating tools were developed in the 90′s of the last century, namely Leadership in Energy and Environmental Design (LEED) and Building Research Establishment Environmental Assessment Methodology (BREEAM), which allow for the quantitative sustainability assessment of different types of buildings. After the first developments, many authors joined in the endeavor of producing easier-to-use and more accurate sustainability assessment systems using sustainability indicators and their respective weights. This work provides a rational pathway throughout the relevant literature on sustainability indicators, comparing indicators proposed by different authors and different sustainability certification systems.

1. Introduction

In 1992 the United Nations declared sustainability as the guiding principle for the 21st century [1]. It all stems from the acclaimed report Our Common Future by the World Commission on Environment and Development, released in 1987 [2]. In it, several concerns regarding the future of mankind are discussed, including food security, species and ecosystem protection, poverty as well as energy, among others. Sustainable development, according to the report, is the idea of fulfilling the essential needs of all individuals while also providing them with the chance to improve their lives without hindering future generations’ ability to fulfill their own needs. The three pillars of sustainability are Environmental, Social and Economic (see Figure 1).

The evolution of sustainable development was paired with advancements in technology as well as political actions [3]. An important landmark is the 1992 United Nations Conference on Environment and Development, also known as the Earth Summit, in which 27 principles for sustainable development were established [4]. Later, in 2002, the sustainability agenda was further pushed at the World Summit on Sustainable Development [5], where changes in consumption and production were recognized, as well as the eradication of poverty and the protection and maintenance of natural resources.

Since then, the globalization of sustainable development has been verified across several industries. Examples of such can be found in agriculture [6], energy storage [7], fuel production [8,9], supply chain management [10], chemistry [11], materials [12,13,14,15], water [16], and urban development [17,18], among others.

The Circular Economy has received attention and focus as a viable tool for sustainable development [19]. It helps establish connections between industries where residues can be used in a different process, generating economic value and contributing to the reduction of waste and consumption of materials [20]. The relationship between Circular Economy and sustainability has been studied by Geissdoerfer et al. [21], who found different types of relationships in the literature. Nevertheless, there is a beneficial relationship between both topics.

Buildings and construction have been one of the most fundamental and ancient needs since humanity became sedentary. In the 1990s, the sector was responsible for 40% of the world’s materials and energy consumption [22]. Development of principles for the attainment of sustainable construction was started in this decade, with the development of certification tools like Building Research Establishment’s Environmental Assessment Method (BREEAM) and Leadership in Energy and Environmental Design (LEED)–which will be discussed further below. At the same time, authors started making their proposals, such as Hill and Bowen [23], in 1997. A proposal for sustainable construction under four pillars was made–Social, Economic, Biophysical and Technical. The proposal was criticized by Ofori in the following year, but an agreement on the urgency of consensus and raising awareness of the industry regarding sustainable construction was needed [24]. To date, a consensus on a common taxonomy, namely the number of categories, levels of hierarchy and indicator weighting, has not been achieved. These assessment systems are still in their infancy when compared with the rating tools due to the lack of wide empirical field information.

Presently, the construction sector is still responsible for a significant amount of energy and material consumption [25]. A joint effort from different practitioners in the building field has been achieved to develop new strategies and methods with sustainability in mind. Akadiri et al. [6] proposed three main objectives when developing a sustainable building: Resource conservation, Cost efficiency and Design for Human adaptation [25].

Sustainability can be explored for different types of construction, such as residential, commercial, industrial and infrastructures [26]. The work addresses, however, only the sustainability assessment of buildings.

Sustainability assessment systems are typically based on scientific data, but it is important to also consider national policies and the political context. It is known that sustainability plays an important role in government offices [27]. While local governments are involved in creating and promoting sustainable policies, the lack of indicators to track and assess said implementations exist in both the U.S. [28] and Europe [29]. These systems can help inform and improve current policies by providing governments with information on which measures to implement. As such, a close relationship must be kept between science and political forces.

Given the nature of their work, systems developed by scientists usually tend to undervalue the political dimension and give emphasis to knowledge creation. Gatekeeping also happens in the creation of these systems since only the opinions of people that are “experts” in that field will be considered. In order to increase the credibility of these systems, a new approach to creating sustainability indicators should be implemented that involves both scientists and policymakers. This approach should include open communication with society and the use of voting to determine certain parameters [30].

On the academic side, authors have proposed sustainability assessment systems using sustainability indicators with a confusing taxonomy. To this date, a consensus on a common taxonomy, namely the number of categories, levels of hierarchy and indicator weighting, has not been achieved. These assessment systems are still in their infancy when compared with the rating tools due to the lack of wide empirical field information.

Finally, with all of this in mind, a review of sustainability indicators proposed in the literature was done, as well as the exploration of existing certification tools.

2. Sustainability Indicators

Sustainability indicators can be either quantitative or qualitative. Quantitative indicators are based on variables that can be measured, such as the physical properties of a system. Qualitative indicators, on the other hand, are based on diffuse information, and quantification depends on the assessing entity or person. An example of a qualitative indicator is the level of happiness. Given the subjectivity of qualitative indicators, a preference for quantitative indicators is called for.

The sustainability hierarchy of indicators can be divided into four different levels [31]:

• Indicator: usually obtained as a measurement/process from primary data. An example of an indicator is the monthly energy consumption of a piece of equipment.
• Aggregated Indicator: a combination of components that are defined by the same units. An example of an aggregated indicator is the monthly energy consumption of an entire building.
• Composite Indicator: a combination of components that, when tied together, represent a complex concept into a single quantitative value. An example of a composite indicator is the ecological footprint.
• Index: usually a single number that encompasses all data analyzed for said assessment. An example of that is the BREEAM rating.

Most sustainability assessment systems produce a final index value that aims to summarize the whole sustainability analysis. The following section addresses different indicator lists and methods to determine the sustainability of a building. A thorough literature review was conducted to find the different indicators identified by different authors. The assessment systems developed by different authors often follow different methodologies, though based on the same macro-indicators; while some authors propose indicators under the three pillars of sustainability, others divide them into different categories.

In 2009, Ali et al. [32] used seven different sustainability indicator categories; in this work, Water and Energy Efficiency are the most important categories out of the seven. These weightings were determined by a combination of interviews and decision-making methodology implemented in a software application. This procedure is the most common approach found in the literature.

Bragança et al. [33] proposed sustainability indicators under the three aforementioned sustainability pillars-Environmental, Social and Economic. The authors then grouped the indicators under three levels of hierarchy, with the nomenclature going from top to bottom as categories, indicators and finally, parameters. The methodology developed used equal contribution (same weight) for all the parameters. These authors used, as a baseline for the environmental parameters and indicators, studies by the US Environmental Protection Agency’s Science Advisory Board and by Harvard University [34,35,36].

Heravi et al. [37] presented a literature review on sustainability indicators and selected the ones they found relevant for industrial buildings. After the sustainability indicators nomination, a survey among experts from the petrochemical industry in Iran was conducted to understand the relevance of each indicator in order to develop a holistic framework to evaluate the sustainability of industrial buildings in construction, operation and maintenance, and demolition phases.

Hassan et al. [38] also developed an integrated approach to assess the sustainability of buildings. A Technical category was added to the main three pillars of Sustainability, making them four-main indicators–Environmental, Social, Economic and Technical. The authors swapped the hierarchy order of indicators and criteria. Indicator means the highest level of the hierarchy, which before was named as a category; unfortunately, the lack of a uniform nomenclature leads easily to misunderstandings. Out of the 20 criteria proposed, 6 are subjective. A study case considering three different buildings was conducted using the proposed approach, and the final sustainable index of each building was calculated. This demonstration proved the usefulness of sustainability assessment systems and the potential improvement of the sustainable development of buildings.

The three levels of hierarchy were used later by Hamzah et al. [39], published in 2016, though using different nomenclature. While the three pillars of sustainability were kept as the three main objectives, the bottom layer was known as sub-criteria instead of indicators. After conducting a survey with 24 worldwide experts and using fuzzy AHP (Analytic Hierarchy Process), weightings for all the criteria and sub-criteria were determined. The most important sub-criterion was “Design considerations towards safety,” which is a social sub-criterion. Interestingly enough, the most important environmental sub-criterion was “Environmental design”, which is number seven on Hamzah’s list, weighing less than half of the most important indicator [10]–in work by Hamzah et al. [39], the environmental impact was not yet valorized as it is presently.

Yadegarideh et al. [40] surveyed both academics and building industry workers. The authors proposed six different criteria, each with its sub-criteria. A total of 54 indicators were selected. The DEMATEL (Decision Making Trial and Evaluation Laboratory) method, introduced in 1972, was applied to determine the importance level of each criterion and sub-criteria [41].

The sustainability indicator approach was applied by Stanitsas et al. [42] to manage the construction of projects. After a thorough literature review, 127 potential indicators were identified, which were then validated and reduced to 82 via a survey by six construction management experts. The authors emphasize the need for more empirical studies on the sustainability of buildings due to the lack of a widely accepted strategy for achieving sustainability in construction projects.

Table 1. Comparison of different levels of hierarchy.

Author	Number of Levels of Hierarchy	Number of Main Categories	Number of Indicators
Ali et al. [32]	2	7	41
Bragança et al. [33]	3	3	31
Heravi et al. [37]	2	3	41
Hamzah et al. [39]	3	3	52
Hassan et al. [38]	2	4	20
Yadegarideh et al. [40]	3	6	54
Stanitsas et al. [42]	2	3	82
Zulkefli et al. [43]	2	3	87

indicates the relevant literature sustainability assessment methodologies, based on sustainability indicators, together with publication year and the number of hierarchy levels and main categories. Table 1 also displays the lack of agreement on the taxonomy proposed in the literature. A lack of consensus on the number of levels of hierarchy and main categories was verified.

It is known that regional climatic conditions affect the design of the building as well as their energy performance and lifetime [44]. Following that, Agol et al. [45] found that in developing countries, sustainability indicators tend to be overlooked or misinterpreted, as the socioeconomic panorama differs significantly from the ones where these methodologies were initially created. A sustainable assessment model should be able to adapt to the specific context of a project and should have flexible weightings to accommodate different scenarios. This is a common feature of many sustainable rating tools, as shown below.

2.1. Sustainability Certification Tools for Buildings

Parallel to academic research, government-owned/non-profit organizations onset the development of building certification tools. The first building certification tool was developed in the UK in 1990, and it was called BREEAM (Building Research Establishment’s Environmental Assessment Method) [46]. Some years later, France published a new tool, the HQE (High environmental quality), while in 1998, the USA launched the LEED tool (Leadership in Energy and Environmental Design). With the arrival of the new millennium, more certification systems were developed. In Portugal, the LiderA system was disclosed in 2000 and more recently, in 2017, the SBToolPT Urban, a branch of the SBTool, was reported by U. Minho [47,48].

The two best-known rating tools are BREEAM and LEED. BREEAM can be applied to several types of buildings, such as new constructions, infrastructures, in-use or refurbishment, while LEED has different guidelines for building design + construction, residential, operations + maintenance, among others. The present manuscript addresses the International New Construction Documentation by BREEAM and the Building Design and Construction guide by LEED [47,48]. BREEAM International New Construction 2016 has 10 different categories–9 environmental and 1 innovation category–and assessment issues, as shown in

Table 2. BREEAM International New Construction 2016 categories and assessment issues (Adapted from [49]).

Management	Health and Wellbeing
Project brief and design	Visual comfort
Life cycle cost and service life planning	Indoor air quality
Responsible construction practices	Safe containment in laboratories
Commissioning and handover	Thermal comfort
Aftercare	Acoustic performance
	Accessibility
	Hazards
	Private space
	Water quality
Energy	Transport
Reduction of energy use and carbon emissions	Public transport accessibility
Energy monitoring	Proximity to amenities
External lighting	Alternative modes of transport
Low carbon design	Maximum car parking capacity
Energy-efficient cold storage	Travel plan
Energy-efficient transport systems
Energy-efficient laboratory systems
Energy-efficient equipment
Drying space
Water	Materials
Water consumption	Life cycle impacts
Water monitoring	Hard landscaping and boundary protection
Water leak detection	Responsible sourcing of materials
Water efficient equipment	Insulation
	Designing for durability and resilience
	Material efficiency
Waste	Land use and ecology
Construction waste management	Site selection
Recycled aggregates	Ecological value of site and protection of ecological features
Operational waste	Minimizing impact on existing site ecology
Speculative floor and ceiling finishes	Enhancing site ecology
Adaptation to climate change	Long-term impact on biodiversity
Functional adaptability
Pollution	Innovation
Impact of refrigerants	Innovation
NOx emissions
Surface water run-off
Reduction of nighttime light pollution
Reduction of noise pollution

.

There are minimum BREEAM’s standards for key categories to ensure that the performance of all fundamental environmental is not overlooked; these key categories are namely Energy, Water, Waste, Management, Health, and Wellbeing. Depending on the type of building and location–according to Köppen-Geiger climate classification, different categories will receive different weightings.

Each category has several credits. During the building assessment, the total number of credits achieved is determined. For each category, the fraction of credits obtained (ratio between the number of credits obtained and the maximum number of credits for this category) is multiplied by the category weighting, giving out the category score (in %). Adding the 10 category scores, the final BREEM score is obtained. The final score is then categorized into one of the final six BREEAM ratings, as shown in

Table 3. BREEAM rating benchmarks.

BREEAM Rating	% Score
Outstanding	≥85
Excellent	≥70
Very Good	≥55
Good	≥45
Pass	≥30
Unclassified	<30

.

In order to achieve a given BREEAM rating, the minimum overall score must be met, as well as the minimum standards established for said rating. The LEED certification tool–v4.1 Building Design and Construction–has some similarities to the BREEAM rating tool. Instead of minimum standards, the LEED certification tool has prerequisites and credits for the different categories. The distribution is shown in

Table 4. LEED v4.1 Building Design + Construction Scorecard (prerequisites start with an asterisk *) (Adapted from [50]).

Indoor Environmental Quality	Location and Transportation	Sustainable Sites
* Minimum indoor air quality performance	LEED for neighborhood development location	* Construction activity pollution prevention
* Environmental tobacco smoke control	Sensitive land protection	* Environmental site assessment
* Minimum acoustic performance	High-priority site and equitable development	Site assessment
Enhanced indoor air quality strategies	Surrounding density and diverse uses	Protect or restore habitat
Low-emitting materials	Access to quality transit	Open space
Construction indoor air quality management plan	Bicycle facilities	Rainwater management
Indoor air quality assessment	Reduced parking footprint	Great island reduction
Thermal comfort	Electric vehicles	Light pollution reduction
Interior lighting		Site master plan
Daylight		Tenant design and construction guidelines
Quality views		Places of respite
Acoustic performance		Direct exterior access
		Joint use of facilities
Water Efficiency	Energy and Atmosphere	Materials and Resources
* Outdoor water use reduction	* Fundamental commissioning and verification	* Storage and collection of recyclables construction and demolition
* Indoor water use reduction	* Minimum energy performance	* Waste management planning
* Building-level water metering	* Building-level energy metering	* PBT source reduction-Mercury
Outdoor water use reduction	* Fundamental refrigerant management	Building lifecycle impact reduction
Indoor water use reduction	Enhanced commissioning	Building product disclosure and optimization-EDP
Optimize process water use	Optimize energy performance	Building product disclosure and optimization-Sourcing of raw materials
Water metering	Advanced energy metering	Building product disclosure and optimization-Material ingredients
	Grid harmonization	PBT source reduction-Mercury
	Renewable energy	PBT source reduction-Lead, cadmium, and copper
	Enhanced refrigerant management	Furniture and medical furnishings
		Design for flexibility
		Construction and demolition waste management
Integrative Process	Innovation	Regional Priority
* Integrative project planning and design	Innovation	Regional priority
Integrative Process	LEED accredited professional

, where prerequisites start with an asterisk (*).

Unlike BREEAM, not all prerequisites and credits are assessed for a given building type. The full scorecard shows which categories need to be assessed, and the maximum number of points for categories of LEED scores goes up to 110 possible points. The building also needs to meet the three LEED Minimum Program Requirements:

• ▪ The building must be in a permanent location on existing land.
• ▪ The building must use reasonable LEED boundaries.
• ▪ The building must comply with project size requirements.

A minimum of 40 points are required to obtain a positive certification. The four levels of certifications are displayed in

Table 5. LEED certification levels.

LEED Certification	Total Points
Platinum	80+
Gold	60–79
Silver	50–59
Certified	40–49

.

The developed sustainability assessment tools assigned different names to similar categories. While BREEAM and LEED sustainability assessment tools share common names such as “Energy”, “Water”, and “Materials”, there are some categories that are only found in some of these two tools (for example, LEED has the “Sustainable Sites” category, while BREEAM has the “Management”). Zulkefli et al. [43] compared the indicators of different rating tools and organized them into the primary themes of sustainability (Environment, Social and Economic Indicators). A total of 87 indicators were proposed to assess the sustainability of buildings.

In 2015, the European Commission started the development of a common European approach to assessing the environmental performance of buildings. The proposed tool, which is still under development, is known as Level(s), which is a framework that has core indicators of sustainability for buildings [50]. The tool has been developed with six macro-objectives in mind, as depicted in

Table 6. Level(s) macro-objectives and their definition (Adapted from [51]).

Level(s) Macro-Objectives	Definition
1- Greenhouse gas and air pollutant emissions along a building life cycle	Minimize the total greenhouse gas emissions along a building’s life cycle, from the cradle to the grave, with a focus on emissions from building operational energy use and embodied energy.
2- Resource-efficient and circular material life cycles	Optimize the building design, engineering and form in order to support lean and circular flows, extend the long-term material utility and reduce significant environmental impacts.
3- Efficient use of water resources	Make efficient use of water resources, particularly in areas of identified long-term or projected water stress.
4- Healthy and comfortable spaces	Create buildings that are comfortable, attractive and productive to live and work in and which protect human health.
5- Adaptation and resilience to climate change	Futureproof building performance against projected future changes in the climate in order to protect occupier health and comfort and to minimize long-term risks to property values and investments.
6- Optimized lifecycle cost and value	Optimize the life cycle cost and value of buildings to reflect the potential for long- term performance improvement, inclusive of acquisition, operation, maintenance, refurbishment, disposal and end of life.

.

Out of the 16 core indicators presented in

Table 7. Level(s) macro-objectives and their corresponding indicators (Adapted from [51]).

Greenhouse gas and air pollutant emissions along a building’s life cycle	Use stage energy performance
	Lifecycle Global Warming Potential
Resource-efficient and circular material life cycles	Bill of quantities, materials and lifespans
	Construction & demolition waste and materials
	Design for adaptability and renovation
	Design for deconstruction, reuse and recycling
Efficient use of water resources	Use stage water consumption
Healthy and comfortable spaces	Indoor air quality
	Time outside of thermal comfort range
	Lighting and visual comfort
	Acoustics and protection against noise
Adaptation and resilience to climate change	Protection of occupier health and thermal comfort
	Increased risk of extreme weather events
	Increased risk of flood events
Optimized life cycle cost and value	Life cycle costs
	Value creation and risk exposure

, 3 of them are composite indicators (Life cycle Global Warming Potential, Construction and demolition waste and materials and Indoor air quality), five of them are qualitative (Lighting and visual comfort, Acoustics and protection against noise, Increased risk of extreme weather events, Increased risk of flood events and Value creation and risk exposure) and one (Bill of quantities, materials and lifespans) is reported as information reporting.

The Level (s) framework is divided into three levels. The first level regards the conceptual design for the building project. It is the simplest level, in which early-stage qualitative assessments are applied to the conceptual design or concepts of the building. The second level covers the detailed design and construction performance of the building. This intermediate level entails quantitative assessments of the designed performance and monitoring of the building. The third and final level encompasses the as-built and in-use performance of the building after completion. It is the most advanced level, and it entails the monitoring and surveying of activity on the construction site and the building, as well as its occupants. The higher the level, the more accurate and reliable the report will be, but the framework is built so that one can choose which level/combination of levels to work at [52].

Finally, Level(s) has four briefings on the key concepts of the framework, as follows:

• ▪ Whole life cycle and circular thinking;
• ▪ Closing the gap between design and actual building performance;
• ▪ Achieving a sustainable renovation;
• ▪ Sustainability has a positive influence on the market value of a property.

2.2. Compilation of Sustainability Indicators

After a thorough literature review, sustainability indicators proposed by the present work were compiled into a single list. They were divided into five levels of weighting, where a higher weight was assigned to the indicators shared by an increased number of reviewed rating systems of sustainability. The indicators with higher weights are shown in

Table 8. Compiled sustainability indicators of the reviewed ratings systems. Higher weighting is related to a higher number of sustainability rating systems that use them.

Weight	Environment	Social	Economic
5	Renewable energy	Design considerations toward safety	Innovation management/new product development
	Thermal comfort	Acoustic and noise control
	Site selection
4	Recycled/reused materials	Public transportation access & transportation plan	Use of regional resources
	Indoor air quality performance	Thermal comfort
		Daylight
3	Climate Change	Visual quality	Cost of construction
	Noise Pollution	Employment (social aspects)
	Energy Efficiency	Infrastructure improvement
	Indoor air quality	Community relationships and involvement	Cost of operation and maintenance
		Public acceptance of the project
	Visual comfort	Stakeholder engagement/management
		Sustainable development supported by local laws
2	Climate change adaptation/disaster risk management	Public Comfort	Regional workers and personnel
		Cultural heritage	Supply and demand sides
	Recycled water	Natural heritage	Marketing price
	Destruction of the stratospheric ozone layer	Workers and personnel comfort	Return on Investment
			Durability of building
	Efficient lighting	Post-occupancy user satisfaction survey (to assess end-user comfort)	Direct job opportunities
	Sensitive land protection		Indirect job opportunities
	Public health and safety		Economic and political stability

, and the others with the lowest weights are shown in

Table 9. Compiled sustainability indicators with the lowest weights (weight equal to 1).

Environment	Social	Economic
Workers’ and personnel’s health and safety	Migration effects	Effects on national economy
Loss of habitats, agricultural farms and trees	Social responsibility	Use of national resources
Construction water quality impact	Social action funding/Concepts of social justice	Enhancement in the capacity of infrastructure
Considering the life cycle of products and services to reduce environmental impacts	Corporate sustainability and organizational culture	Effects on trade balance (national/regional)
Project biodiversity	Labor practices	Financing (loan interests)
Environmental impact assessment project report	Needs assessment of society/people	Opportunity-cost
Environmental tobacco smoke (ETS) control	Human rights	Cost of equipment and their installation
Carbon dioxide monitoring and control	Employee commitment/commitment in the workplace	Distributed income innovation and technological advance
Minimum IAQ performance	Project independence of political factors
Envelope Insulation	Social impact reports	Stakeholder involvement/participation
Use of environmentally friendly refrigerants and cleaning materials, effective and low-carbon cleaning equipment and machinery	Transparent and competitive procurement processes	Target marketing and benefits
Renewable raw materials	Absence of bureaucracy in the workplace	Effective project control
Hazardous degradable wastes	Contractor–supplier relationship	Best practice strategy
Hazardous non-degradable wastes	Commitment to the stakeholders’ needs	Customer-relationship management/Access to a range of customers
Environmental management systems/policy implications	Well-defined project scope and project limitations
Flood risk assessment strategy to prevent flooding	Holistic view of benefits	Scope control through managing changes
Air Pollution	Product–service systems	Business ethics
Violation of animal’s territory	Emphasis on high-quality workmanship	Facility management Technologies/general improvements
Durable materials	Encourage competition
Non-renewable energy	Implementing a quality management system	Supply chain collaboration
Reuse of processed water	First mover advantage	Effective strategic planning
Non-hazardous recyclable wastes	Culture of accountability	Organizational culture
Non-hazardous non-recyclable wastes	Comprehensive contract documentation	Project outputs emphasis
Environmental management plan for impacts by the Project Management Team (PMT)	Diversification	Ability to pay and affordability
Sustainable project delivery through project stakeholder management	Competitive tendering/comprehensive pre-tender investigation of the project	Environmental/economics accounting
Environmental education and training	Adaptability in project environment
Eco-efficiency	Intangible asset management	Developing an efficient risk management plan by the PMT
Consistent and predictable load	Multidisciplinary/competent Project Management Team (PMT)
Up-to-date environmental construction technologies and methods	The role of trust within the PMT	Implementing an effective change management strategy
Environmental responsibility/justice	Following project management phases/processes
Identify and address choke points	Project manager’s leadership style	Efficient data processing for decision-making practices
Appropriate and flexible environmental design details and specifications	Employing operational decision-making techniques by the PMT
Mold Prevention	Project monitoring and evaluation by the PMT, though previous experiences in projects	Bureaucratic streamlining
Sustainable maintenance	Managing knowledge and awareness to promote sustainable project delivery (PMT)	Internationalization
Acidification potential	Management considerations toward safety	Cargo delivery route & proximity
Establish environmental policy and end-user guide, and manual	Affordability
	Neighborhood accessibility and amenities	Expenditure on R&D
Low-carbon design	Maximum car parking capacity	Lifecycle costs
Grid harmonization	Places of respite	Reserve funds

.

As shown in Table 8, the most prevalent indicators in the Environment pillar are “Renewable energy”, “Thermal comfort”, and “Site selection”. In the Social Pillar, the most used indicators are “Design considerations towards safety” and “Acoustic and noise control”. Finally, in the Economic Pillar, the most mentioned indicator is “Innovation management/new product development”.

A total of 153 indicators were identified. The Social Pillar has the highest number of indicators at 56. It is followed by the Environmental Pillar with 54 indicators, and lastly, by the Economic Pillar with 43 indicators.

3. Discussion

Different taxonomies of the sustainability assessment systems proposed by the reviewed authors are one of the hurdles of this research area. The use of different nomenclatures, namely the use of different names for distinct levels of hierarchy (e.g., Hassan et al. [38] vs. Hamzah et al. [39]), can make the study of this research area very complex. These two authors actually use the same names (that is, criteria and indicators) for labeling reversed levels of hierarchy. It is necessary to standardize the names of the different hierarchy levels as well as of the name and number of the main categories, though, leaving room for new categories. These new categories, however, should obey established rules for avoiding over-resolved notation systems.

There are subjective sustainability indicators, especially in the social sector, which makes bias-free analysis difficult. Furthermore, most of the indicators and their weights were validated by small groups of experts, often geographically close to the authors; this can produce biased weightings. Conducting a worldwide survey would be an effective method for making a robust and trustable sustainability assessment tool. On the other hand, an assessment should be flexible and take into account the context and location of the project, making it difficult to create a “one size fits all” model.

As for the sustainability rating tools of buildings, these predate the sustainability assessment systems proposed in the literature. The most popular tools, like LEED and BREEAM, are robust systems that are being updated frequently. In fact, over a hundred thousand buildings have been certified using these tools. However, these tools display a quite complex utilization, namely requiring specially trained personnel.

Having a sustainability certification can add economic value to the building, both through lower operating costs and higher market value. Governments also offer tax benefits and funding opportunities to create sustainable buildings. Certification has a cost that varies depending on the size, type, and location of the building.

4. Conclusions

The 1990s witnessed the onset of a drive for higher sustainability in the construction industry. The first rating tools developed for sustainability assessment, such as BREEAM and LEED, have been used in building certification for more than two decades. Moreover, these tools have been continuously reviewed, making them more useful choices. The benefits of certification include tax incentives, visibility of commitment, an increase in sales, lease rates, and improved indoor air quality. However, the added cost and complexity of the auditory makes it harder to convince constructors and establish them as industry standards.

An extensive review of the literature was conducted to identify the different sustainability assessment systems proposed by each author. The lack of a generally accepted taxonomy of indicators makes the comparison of different systems a difficult task. Adding to this, the scarcity of empirical studies using said systems make them harder to implement when compared to more established certification rating tools.”

A compilation of sustainability indicators was carried out. They were grouped under the three main pillars of Sustainability-Environment, Social and Economic-and weighted according to their frequency in the systems found in the literature review. Interviews with field experts should be analyzed, using decision-making methods for identifying and sorting the most relevant indicators.