A Review of Net-Zero Greenhouse Gas (GHG) Emission Non-Regulatory Environmental Building Standards and Frameworks

Abstract

Non-regulatory environmental building standards have been used in the built environment for more than thirty years and have had considerable influence over building development and policy. This paper identifies a trend, following the Paris Agreement, towards a new generation of non-regulatory building standards and frameworks based on defining net-zero greenhouse gas (GHG) emission performance. These standards and frameworks have been developed in response to the imperatives of the Paris Agreement and other contextual drivers. Post-Paris Agreement, net-zero GHG emission standards have the following characteristics: a threshold-based approach to achieving certification; the use of a small number of metrics (typically two: operational energy and embodied carbon); and compliance based on operational performance rather than predicted operational energy use with models used to replicate the building in use. This paper will discuss global non-regulatory, net-zero GHG emission standards comparing the relative requirements and highlighting commonalities and differences. The paper also compares the post-Paris Agreement, net-zero GHG emission standards with pre-Paris Agreement low carbon credit-based environmental building standards considering their role in the development of net-zero GHG building standards and the possible impact of performance-based standards on new buildings. This study is relevant for policy makers, designers, and building developers by identifying the developing global consensus around what constitutes a net-zero GHG building and theorises, in relation to their developmental context, the implications of widespread implementation of these standards.

1. Introduction

Non-regulatory environmental building standards have been part of the global building development landscape for more than thirty years, and more than seventy have been identified in use around the world [1,2,3]. BREEAM (Building Research Establishment’s Environmental Assessment Method) is regarded as the world’s first sustainability rating scheme for the built environment and was developed by the Buildings Research Establishment (BRE) in the UK and launched in 1990 [4]. This first environmental building standard (EBS) provided a template for the development of similar standards [5,6].

A diverse range of EBSs have been developed since the launch of BREEAM, including standards that have a regional focus, such as Minergie in Switzerland [7] and Greenstar in Australia [8], as well as others with a sectoral focus such as the Defence Related Environmental Assessment Methodology (DREAM) [9] in the UK for the Defence Sector. Other EBSs are global standards, used throughout the world in a variety of sectors. Examples of global standards include LEED (Leadership in Energy and Environmental Design), developed by the United States Green Building Council (USGBC) in the USA and launched in 1998 [5]; the Living Building Challenge (LBC), developed by the International Living Futures Institute in the USA (ILFI) and launched in 2006 [10]; and the DGNB (Deutsche Gesellschaft für Nachhaltiges Bauen) System, developed by the German Sustainable Building Council in Germany and launched in 2009 [11]. However, despite geographic and sectoral diversity, many EBSs share similar features (see

Table A1. An overview of pre-2015 environmental building standards.

Background Information			Accreditation Information
Standard Name	Developing Organisation and Country of Origin (in Brackets)	Launch Year	Certification Process (Verification Mechanism)	Certificate Renewal Period	Assessment Criteria (Scope)	Compliance Levels	Targets/Benchmarks and Minimum Requirements	Notes
BREEAM [4]	BRE (UK)	1990	An accredited assessor guides the certification process, ensures requirements are fulfilled, and undertakes a pre-assessment. Certification includes collating project information and submitting to the certification body.	One-off certificate achieved on completion of the project; BREEAM in-use provides for continual assessment.	Energy; Health and Well-being; Innovation; Land Use; Materials; Management; Pollution; Transport; Waste; Water.	Outstanding Excellent Very good Good Pass Acceptable	BREEAM uses six levels to describe points a project achieves: outstanding (above 85%), excellent (70–85%), very good (55–70%), good (45–55%), pass (30–45%), and acceptable (Under 30%).	BREEAM was the first certification system to assess, rate, and certify the sustainability of buildings. It is one of the most used systems in the world.
LEED [15]	U.S. Green Building Council	1998	Certification process has two phases—design and construction. For both phases, design documents are submitted and reviewed by the certification body. First review either approves or rejects the sustainable solutions proposed for the project.	One-off certificate achieved on completion of the project.	Location and Transportation; Sustainable Sites; Water Efficiency; Energy and Atmosphere; Materials and Resources; Indoor Environmental Quality; Innovation; Regional Priority.	Platinum Gold Silver Certified	The point system consists of 110 attainable total points. Projects with 40+ points achieve the Certified level, projects with 50+ achieve the Silver level, projects with 60+ achieve the Gold, and projects with 80+ achieve the Platinum level of certification.	LEED is one of the largest existing certification systems. It focuses both on the environmental and social aspects of building sustainability.
Greenstar [129]	Green Building Council of Australia	2003	After registration, the project’s sustainable attributes are documented with design and construction information. Documents are reviewed by the Council. Projects can choose to rate design-related credits before construction is completed.	One-off certificate achieved on completion of the project	Management Indoor Environmental Quality Energy Transport; Water; Materials; Land use and Ecology; Emissions; Innovation.	6 Star: International excellence 5 Star: Australian excellence 4 Star: Best practice	The Green Star rating system is based on a 1 to 6 Star framework with 1 Star as the lowest score and 6 Star as the highest. To achieve certification, a project must have 4 Stars or more. To achieve a 4 Star rating the project must score at least 45% of the available points, for a 5 Star rating 60% or more, and 75% or more for the highest 6 Star rating.	This standard allows certification of buildings and district scale development, and caters for design, delivery, and ongoing performance.
HQE [130,131]	CERTIVEA (non-domestic), CERQUAL (for housing) (France)	1995	Certification varies based on building type: new buildings, residential buildings, existing buildings in use, etc. Non-residential buildings have a three-step assessment process. When certifying residential buildings, the property developer or the building contractor which is certified.	One-off certificate—option for contractors and developers to have a licence that validates their experience (renewed every 3 years).	Energy; Environment; Health; Comfort.	Exceptional Excellent Very Good Good Pass	The five HQE certification levels are Exceptional, Excellent, Very Good, Good and Pass. These are determined by the level of achievement in 14 targets classified into four categories (eco-construction, eco-management, comfort, health)	This standard includes some continual assessment of the developer or contractor though a licencing scheme.
Living Buildings Challenge [10]	ILFI (USA)	2006	The certification process has three parts: (1) registration; (2) project documentation evaluated followed by a 12-month performance period, where data is recorded in relation to requirements; (3) audit of documentation and site inspection.	One-off certificate achieved on completion of the assessment period.	Place; Water; Energy; Health and Happiness; Materials; Equity; Beauty.	Living certified Petal certified	LBC has two certification degrees: Living and Petal. To obtain the full Living certification, all demands of the (principles) must be met. If the project can reach the standards of at least three out of the seven petals (with at least one being either Water, Energy or Health), it can receive a Petal Certification.	This standard is one that evaluates the design and the final building incorporating assessment a year after practical completion.
DGNB [11]	DGNB (Germany)	2007	Two types of DGNB certifications: a precertification and a final certification. Accredited assessor guides the certification process, ensures requirements are fulfilled—collates and submits project information.	One-off certificate achieved on completion of the project.	Environmental quality; Economic quality; Sociocultural and functional quality; Process quality; Technical quality.	Platinum Gold Silver Bronze	For platinum certification, the project must obtain at least 80% of the total points available. For gold, a minimum of 65% is required and for silver 50%. For the bronze (existing buildings only) a minimum of 35% of points must be achieved. A DGNB diamond certification, is available for high quality projects.
Passvihaus [47]	Passivhaus Institut (Germany)	1996	The certification covers the following phases: initial check; preliminary review—design phase; design stage review—before the start of the construction work; final review—after completion of the construction work.	One-off certificate achieved on completion of the project.	Energy; Thermal Comfort.	Passivhaus (Classic) Passivhaus Plus Passivhaus Premium	The heating demand of a Passive House should not exceed 15 kWh/(m2a). For Passivhaus Classic primary energy not more than 60 kWh/(m2a). A Passivhaus Plus should not consume more than 45 kWh/(m2a) of renewable primary energy and must generate 60 kWh/(m2a) of energy. For Passivhaus Premium, energy demand is 30 kWh/(m2a), with 120 kWh/(m2a) of energy generated by the building
Miljöbyggnad [132]	Sweden Green Building Council	2005	Application content is verified by professional verifiers. For new buildings, a pre-certification is awarded. After two years, the building is then verified, and if all requirements are fulfilled, the final certification is awarded.	The final certification must be checked every five years to maintain its validity.	Energy; Indoor climate; Materials.	Gold Silver Bronze	Miljöbyggnad levels relate to Swedish building regulations. Bronze certification complies with statutory requirements, Silver, well over the set values, and significantly better statutory requirements; Gold, is the highest certification requirements. In addition, to reach Gold, requires a survey of building users’ experience of the indoor environment.	This standard incorporates assessment of building performance in relation to indoor environment after practical completion.

).

This paper investigates how, since 2015, prompted by the Paris Agreement [12] and by greater awareness of Lifecycle Assessment (LCA) reframing the environmental impact of buildings [13,14], a new generation of EBS with the aim of defining and evaluating net-zero greenhouse gas (GHG) emission buildings has been developed (Figure 1). The key research questions here are (1) have the Paris Agreement and growing awareness of the climate emergency made the new generation of EBSs materially different from the first generation? and if so, (2) what are the unique characteristics and implications of the newly developed EBSs?

The next section of this paper (Section 2) outlines how, using a policy research framework, net-zero GHG building standards can be compared and analysed to identify contextual factors influencing their development. In Section 3, those contextual factors are described with reference to their place in the policy landscape. Section 4 gives a detailed overview of contextual factors that have influenced the development of the new generation of EBSs. Section 5 outlines the characteristics of Net-Zero Greenhouse Gas Emission Building Standards (NZGHGEBSs), often referred to as ‘Net Zero Carbon Standards’, with reference to international standards such as LEED Zero, developed by USGBC in the USA [15] and launched in 2018 [16]; the ILFI Zero Carbon Certification, developed by ILFI and launched in 2018 [17]; and DGNB Climate Positive, developed by the German Sustainable Building Council and launched in 2019 [18], and regional standards such as the Zero Carbon Building Standard, developed by the Canada Green Building Council [19].

Section 6 explains how, in contrast to the older (pre-2015) EBSs, which are predominantly based on design-based assessment with a broad range of assessment criteria, post-Paris Agreement NZGHGEBSs are characterised by performance-based assessment, a narrow range of assessment criteria, and a threshold-based approach to accreditation. This paper argues that NZGHGEBSs represent a new generation of EBSs, which share characteristics with each other but are distinct from earlier (pre-2015) standards. Also captured in this definition are net-zero GHG frameworks, which have the characteristics of NZGHGEBSs (i.e., a narrow range of assessment criteria, performance-based assessment, clearly defined thresholds for performance criteria, etc.) but which have neither formal checking and oversight provisions nor provide a route to certification. The discussion, in Section 7, postulates that the widespread adoption of NZGHGEBSs by developers, design teams, and regional administrations has the potential to have significant impacts on the process of designing and developing new buildings. The study highlights the role of NZGHGEBSs in filling the regulatory void left by insufficient national legislation. These standards, often developed by private institutions or professional coalitions, are increasingly adopted by developers, municipalities, and industry bodies seeking to align with climate targets. Their influence is likely to grow, particularly if regulatory frameworks continue to lag behind the ambitions of the construction and real estate sectors.

2. Methodology

Comparative policy analysis is a method for the systematic comparison of policymaking in different contexts to understand factors and processes underpinning similarities and contrasts in policy options [20]. It is used to compare the policy responses of different actors to a common problem and can be used to infer the determinants of variation as a basis for theory-building [21]. This approach is typically used to allow policymakers to draw lessons from the experiences of other jurisdictions for the development of parallel programmes [22,23]. Mayer et al.’s policy analysis model [24] identifies activities for this method of investigation, which include ‘research and analyse’, utilising the knowledge of research institutions and agencies; ‘clarify values and arguments’, attempting to understand the implicit normative questions and drivers behind the development of policy; and ‘mediation’, analysing contextual factors and the relations between the activity clusters to highlight the dominant discourses.

Comparative policy analysis is used in this paper to understand the response of expert organisations in different jurisdictions to the common problem of defining and evaluating net-zero GHG emission buildings. The responses of these organisations to this shared problem, the net-zero GHG standards and frameworks they publish, can be compared to identify common themes, an emerging consensus, and draw inferences about determinants of consensus where explicit data is not available. In addition, comparing NZGHGEBSs to their forerunners provides further opportunities to understand contextual factors influencing their development and, in relation to the impact of EBSs on the policy landscape, make predictions about their role in the development of net-zero GHG buildings and policy (see Figure 2). Policy analysis activities can be used in this regard to (1) understand how the knowledge of expert organisations and actors is being applied to defining net-zero GHG emission buildings in the built environment; (2) understand the drivers behind the development of their response; and (3) identify a dominant discourses or coalescing consensus and the relationship of these discourses to contextual factors.

In relation to the ‘research and analyse’ phase of policy analysis, a systematic desktop search was carried out of peer reviewed databases. Scopus was used for the initial research because of its broad journal coverage, and two searches were conducted using the database. The first was a search for “net zero” or zero GHG standards and frameworks, and the second was for “environmental standards”. These terms were searched with the key strings provided below. Identified papers were screened by first reading the abstract and second the introduction and methodology.

• TITLE-ABS-KEY (net AND zero OR zero AND GHG) AND (standards OR rating AND systems OR frameworks) AND (building OR building AND asset). With a year range limited from 2015 to 2022.
• TITLE-ABS-KEY (environmental OR sustainability) AND (standards OR rating AND systems OR frameworks) AND (building OR building AND asset). With a year range of 1999 to 2022.

The first search provided 24 search results (see Figure 3) of which, after a screening of the abstracts, 5 referred to the NZGHGEBSs, which were the focus of the research question (several referred to standards in sectors, which provide resources for the construction of buildings such as the cement or mining industries, and were therefore not relevant). Search two on broader environmental standards provided 1159 search results, of which 174 were relevant (see Figure 3). These results required further screening based on title and abstract and were used to identify key themes (such as LCA and the performance gap).

Further searches using Web of Science (WOS) were used to identify relevant journal articles on environmental performance of buildings and NZGHGEBSs. Keywords, including “LEED”, “BREEAM”, “LETI”, “Green Building Standard”, “Net Zero Standard”, and “Sustainable Building Standard”, were used under “Title” for WOS. Abstracts were read to filter out irrelevant papers to ensure that only papers focused on NZGHGEBSs or environmental rating systems were considered. These academic searches identified the limited scope of academic discourse on NZGHGEBSs, specifically, and the broader discourses on environmental building standards in general.

A second step was a review of the grey literature including industry websites and publications, with a particular focus on NZGHGEBSs. This search was undertaken using the internet search engines Microsoft Search and Google using keywords such as “Net Zero Carbon Standard” and “Net Zero GHG Standard”. Following the identification of a net-zero GHG emissions standard or framework, a necessary second step was to obtain detailed information on each of the standards. In cases where a standard or framework had little or no detailed information, perhaps due to the requirements still being under development, this standard or framework was excluded from the study. Where a standard was identified but the detailed information was in a language other than English, Google Translate was used to translate key documents. The coverage of the grey literature in this study was necessary to identify the origins and the structure of several environmental standards.

The first part of the investigation identified that there was a large body of criticism of EBSs in the academic literature. However, there was limited information on NZGHGEBSs, and it is noteworthy that the net-zero GHG emissions frameworks in the UK, such as LETI, were largely absent from the academic literature. The investigation of industry websites identified a central resource on NZGHGEBSs by the World Green Building Council (WGBC), which was developed as part of their Advancing Net-Zero programme [25]. The WGBC provided an interactive map on their website identifying NZGHGEBSs and their country of origin [26]. The absence of a similar database for other standards and frameworks outside of this programme means that the net-zero GHG emission standards and frameworks assessed were mostly part of the Advancing Net-Zero programme. In addition, it should be recognised that the use of English language searches for the second part of the investigation may have favoured the identification of English language NZGHGEBSs. Whilst this was a limitation of the study, key NZGHGEBSs originally developed in non-English speaking countries, such as Germany (DGNB Climate Positive), France (Energie Positive and Reduction Carbone), and Sweden (Miljöbyggnad), were covered in this study.

For the second part of the study, key criteria were identified that would allow a cross-comparison and provide an insight into the nature and evaluation processes of these standards and frameworks. These criteria would include the certification process; how compliance was reviewed on an ongoing basis; the scope and number of assessment measures (including key metrics); the number of compliance levels; and whether targets were based on accumulating credits to meet a performance level or specific thresholds relating to building performance. These criteria were chosen because they would explain the boundary conditions for the evaluation (temporal and spatial); identify whether a standard or framework was focused on a single issue (like GHG emissions) or multiple issues; outline the nature of compliance whether there were degrees of compliance or if it was pass or fail; and the point in time in relation to a project where an assessment would be considered complete (i.e., at the design stage, practical completion, or post-practical completion). Other criteria (of secondary importance), which would be compared, included the developing organisation (to understand the relationship of NZGHGEBSs to earlier EBSs developed by the same organisation); the year a standard was developed to understand the temporal relationship of one standard to another (to understand if it established a template for other similar standards or was developed concurrently with others); and the country of development (to understand the policy and environmental context under which the standard was developed).

3. Review of Non-Regulatory Building Standards and Policy Context

The focus of the standards examined in this study are non-regulatory standards. In describing non-regulatory EBSs, the first step is to identify their characteristics and explain how they differ from legislative standards, national regulations, and building energy codes. For this paper, a non-regulatory EBS is defined by the three following characteristics:

• Non-regulatory standards are developed by organisations fully or partially independent of government (see Figure 4). Examples of organisations developing EBSs include the Building Research Establishment (BRE) in the UK, the Passivhaus Institut in Germany, and the United States Green Building Council (USGBC) in the USA, all of whom are private institutions distinct from government bodies. In the case of the BRE, this organisation was founded as a government-funded research facility but has been independent of government since 1997 after being privatised [27]. Another example is DGNB, which was founded in 2007 by companies within the German construction and real-estate sectors with an aim to promote sustainable buildings [28].
• Organisations developing EBSs typically have a recognised level of expertise in their field. The bodies mentioned above (the BRE, DGNB, and USGBC) undertake independent research, provide training for professionals, produce white papers, and provide consultation for the government and industry in their respective countries [29,30,31]. Many of these organisations, such as the BRE, ILFI, USGBC, and DGNB, have developed several EBSs or produced several variations in EBSs (see Table A1). This definition can include organisations consisting of a coalition of experts and professionals assembled to drive changes in environmental development. One example of such a coalition is the Low Energy Transformation Initiative (LETI), which is a network of built environment professionals who assembled to define net-zero GHG emissions in the built environment in the UK [32] (see

  Table A2. Net-Zero GHG emissions building standards.

  Background Information			Accreditation Information
  Standard Name	Developing Institution and Country of Origin (in Brackets)	Launch Year	Certification Data Sources (Verification Mechanism)	Certificate Awarding Period	Assessment Criteria (Scope)	Compliance Levels	Targets/Benchmarks and Minimum Requirements	Offsetting Approach	Notes
  LEED Zero Carbon [15] (adjunct to LEED EBS)	USGBC (USA)	2018	Annually submitted performance data, metered energy, transport assessments and on-site and off-site renewable energy and offsets (proposed that in future it will incorporate carbon from water consumption, waste, and the embodied carbon).	LEED Zero certification is valid for three years.	Operational and Transport Energy	Pass or fail	Baseline performance requirements provided by mandatory LEED BD+C or O+M certification	Accredited offsets and off-site renewables permitted (Energy Attribute Certificates) by Green-e or equivalent	Assessment Based on Carbon Balance = Carbon Emitted (operational and transport energy) -Carbon Avoided LEED Zero Carbon
  Zero Carbon Certification [17]	ILFI (USA)	2018	Based on metered energy and utility bills 1 year after PC Metre data and on-site renewable energy production data. As-built material types and quantities	One-off certificate awarded at end of assessment period (1 year after PC).	Operational Energy and Upfront Embodied Carbon	Pass or fail	Benchmarks based on climatic region and asset type: New Buildings 25% reduction; Existing Buildings 30% reduction in EUI from a typical existing building of an equivalent type, size, and location. Embodied carbon not to exceed 500 kg CO2e/m2 (RICS A1-A5)	Off-site renewables for residual operational energy and Accredited Offsets permitted for residual embodied carbon
  Climate Active Carbon Neutral Certification [133]	NABERS National Administrator & Green Building Council of Australia (Australia)	2020	Annual metered operational energy subject to independent verification every three years. (Embodied energy of materials and processes may be considered in the future versions).	Certification is valid for three years.	Operational Energy, refrigerant-gas, and water	Pass or fail	4 Star or greater NABERS Energy rating; Or 4 Star or greater Green Star—Performance rating, (8 of 20 points base building or 9 out of 23 points (whole building) scored in the GHG credit	Accredited Offsets permitted either in arrears or Upfront (in advance)	Two pathways to standard one based on NABERS the other based on Greenstar Can be applied to the base build or the whole building
  DGNB Climate Positive [18]	DGNB (Germany)	2018	CO2 accounting according to the DGNB Framework and documentation of data in the DGNB-CO2 accounting tool. Evidence of key performance indicators self-generated fraction of consumed final energy	The award is granted when the DGNB system buildings in use is achieved. The building must have been in operation for one year.	CO2 reporting of the building in used based on metered energy their real consumption data.	Pass or fail	Evidence for a negative annual CO2 balance form measured data of one calendar year. Minimum requirements for the building envelope from DGNB System New Buildings.	Remote energy sources in the CO2 balance but must be disclosed. Off-site purchased energy must be compliant with minimum requirements.	Objectives for future energy saving (i.e., a climate Action plan) are required. The recording of CO2 emissions should verify the effectiveness of measures
  Noll CO2 [134,135]	[135] Sweden Green Building Council (Sweden)	2018	Metered energy 5 years after PC Verification of construction and of Report the amount of replaced and added materials/products/systems during renovations and conversions following PC.	Certification is valid for five years. Complete periodic reporting every five years to maintain the certification.	The whole-life carbon building service system is factored based on the component’s climate data (kg CO2e/kg) and respective quantity (kg).	Pass or fail	Benchmarks are based on minimum complementary certification levels: Miljöbyggnad level Silver; BREEAM-SE Very Good; LEED Gold. Operational energy 25–50% lower than code mandated energy performance. Embodied carbon benchmarks are based on a SGBC calculated baseline and a calculated value for stage A1-A3. The climate impact of A4-A5 not exceeding 55 kg CO2e/m2.	Compensation can be performed through one of three programmes: Verra, Gold Standard or Plan Vivo	Net-zero balance between the climate impact of the building’s whole-life carbon and the project’s climate actions (offsets).
  Energie Positive and Reduction Carbone [136]	Alliance HQE-GBC (France)	2016	Checks on documents and standardised thermal and environmental assessments including, models and results of performance calculations. Construction phase review of changes and updates and the calculation of their impact on the energy performance. Compliance review at the end of the construction phase.	One-off certificate awarded at the end of design and construction assessment period.	Operational Energy, Embodied Carbon, Thermal Comfort, and other environmental indicators.	4 Energy Levels: (1) (2) improvement on current requirements; (3) significant increase in energy efficiency; (4) zero (or negative) energy balance. 2 Carbon Levels: (1) construction methods and operations improvement; (2) best practice.	For operational energy there are four levels of performance with benchmarks for small scale domestic, large scale residential, offices and other building types. The reductions range from 5% and 10% for residential at Level 1 to 20% at Level 2 to 20% for Residential at Level 3 for Residential and 40% for Offices to achieving an energy. To carry out the analysis of the lifecycle of the building, taken as equal to 50 years for all buildings.	Carbon compensation is not part of the process.	Experimental voluntary standard. The energy balance of a building is defined by the difference, primary energy, and quantity of non-renewable or recovered energy consumed by the building.
  Zero Carbon Building Standard Performance and Design [137,138]	Canada Green Building Council (Canada)	2018	2 compliance routes: Design, measured or modelled carbon balance; and Performance, where certification is awarded based on one year of operating data evidencing a carbon balance.	Annual certification for existing buildings Design: One-time certification for new buildings and major renovations.	Operational Carbon and Embodied Carbon (including lifecycle carbon).	Pass or fail	Design standard operational energy 4 approaches: Flexible—Thermal Energy Demand I(TEDI) of 30–40 kWh/m2/yr and site energy use intensity 25% better than minimum requirements; passive design—(TEDI) of 20–30 kWh/m2/year; renewable energy (TEDI) of 30–40 kWh/m2/year; and zero carbon balance for operational carbon without offsets. LCA analysis demonstrating embodied carbon reduction for lifecycle stages A, B, and C. relative to baseline building Performance Standard: no benchmarks.	Embodied carbon offset by a single purchase or annually (up to five years). Offsets certified by Green-e or equivalent, or by high-quality international programmes. Green power products from renewable sources to offset grid electricity usage.	Lifecycle carbon (lifecycle stage D) does not require offsets.
  Net-Zero/Net Positive Certification Scheme [139]	Green Building Council South Africa (South Africa)	2019	Measured and modelled data	Certificate valid for 3 years	Carbon (Embodied and Operational) 0 kgCO2/m2/year Water Waste Ecology	Two certification levels: Net-Zero and Net Positive	For Net-Zero building Emissions services and occupants using a rating tool energy calculator value is 0 kgCO2/m2/year or equal or less than the on-site renewable energy carbon emissions reductions. For Net Positive Carbon: Tool value is 5% above zero. Requirements for water, waste, and ecology for Net-Zero: Water—consumption is 0 L/day/m2; waste—achieved when construction waste measured to be 0 kg/year to landfill; operational waste achieved when measured waste is 0 kg/year to landfill over 12 consecutive months.	Off-Site renewables permitted in country project is certified. Carbon offsets can be purchased from verified and permitted trading schemes.	Assessment is based on modelling, but GBCSA have reserved the right to remove modelled options for all or some certification types, or shorten the validity period.
  Net-Zero Energy Buildings Rating System [120]	Indian Green Building Council (India)	2018	Credit points with verification based on modelled and submission of documents. The measurement of Total Metered Energy Consumption (kWh) and Renewable Energy Generation based on a minimum of 80% occupancy.	One-off certificate awarded at end of assessment period; however, 80% occupancy is a requirement for assessment.	Mandatory credits for: (1) Energy Performance(2) Thermal Comfort. Energy Performance credits for Simulation; Energy Efficient Building Envelope, Services, and appliances; and Renewable Energy.	Net-Zero Energy (when all mandatory credits achieved) and Net-Zero Energy Platinum (mandatory credits and more than 80 credit points) or building to meet all energy requirements through renewable energy.	The project can demonstrate energy performance of the facility through (1) meeting the respective IGBC rating—minimum energy performance requirement; (2) the Energy Performance Index Ratio based on in-use less than or equal to the design energy performance index on annual basis; (3) demonstrating that the energy performance of major equipment is meeting Energy Conservation Building Code requirements.	Off-site renewable energy; Resources permitted and points are awarded based on the proportion of on-site to off-site generation.	Building rating: the project must satisfy all the mandatory requirements and can demonstrate that the net annual energy consumption as zero.
  UK Net-Zero Carbon Building Standard [85]	Coalition of organisations including BBP, BRE, Carbon Trust, CIBSE, IStructE, LETI, RICS, RIBA, and UKGBC, (UK)	2024	The total electricity generated on-site should be measured using metre readings, and the quantity used on-site should be separated from exported electricity. For embodied carbon, quantity information according to the sources listed for ‘post-completion phase—actual quantities’ should be used.	The minimum occupancy rate requirements for buildings intended to be occupied and at the post-completion stage.	Embodied Carbon; Operational Energy; Space Heating Demand GHG Refrigerant Gas.	Pass or fail	Embodied carbon limits for specific typologies based on kgCO2e/m2 GIA reducing on an annual basis derived from a top-down methodology. Operational energy limits for specific typologies based on kWh/m2 GIA/yr reducing on an annual basis derived from a top-down methodology. Limit on annual space heating delivered to the building, new buildings based on typology; GWP limit for refrigerant systems = 677 kg CO2e/kg.	For all building and works types, carbon emissions may be offset and reported. Carbon credits from programmes assessed as meeting the requirements, e.g.,: ICROA standards; ICVCM.	Development of limits based on the use of top-down and bottom-up methodologies.

  ).
• Because non-regulatory standards are developed by private institutions, their implementation is discretionary rather mandatory. This is significant because mandatory national regulations (see Figure 4 below) typically establish minimum standards for a country. An example of legislative standards is the building regulations in the UK [33], which has specific requirements for operational energy reduction in buildings defined in the Approved Document Part L (conservation of fuel and power) [33].

The literature review identified that EBSs are a subject of increasing academic interest, and Doan et al. [34] and Li et al. [35] identified that the number of green rating-related papers has risen significantly between 1998 and 2017. Several papers on EBSs have examined their evaluation criteria [36], hierarchy scoring system, and evaluation categories. Other papers have used the certification of buildings to EBS to investigate the issues affecting green buildings. Zuo and Zhao [37] identified that these studies can be classified into three categories, namely, the definition and scope of green buildings; benefits and costs of green buildings; and ways to achieve green buildings. The literature review identified how most EBS were focused on various aspects of sustainable building design including energy consumption, water efficiency, and greenhouse gas emission, along with the technical solutions [38].

Doan et al. [34] identified how the number of credits and categories of EBSs had increased over time and highlighted how, for example, the mandatory credits for LEED had doubled between Version 2 and Version 4. The literature identified that EBSs have evolved through updates in response to technological advances, such as BIM [39], and emergent issues affecting the built environment [40] such as climate resilience [41]. Another major driver for change was the increased recognition of embodied carbon in global carbon emissions [14]. The response of EBSs to the role of embodied carbon and the approach of using LCA to assess buildings was highlighted by Trigaux et al. [42], who identified that increased recognition of this approach was required to ensure EBSs were in line with long-term policy targets. Shan and Hwang [43] examined how LCA was among the new features being added to newly released EBS versions. Another significant theme was an increasing focus on building users, especially in relation to health and building performance. Khoshbakht et al. [44] and Shan and Hwang [43] identified that post-occupancy evaluation (POE) would be required to validate building performance and the effectiveness of EBSs. These papers identified changes in EBSs in response to changes in contextual conditions.

With more than seventy EBSs identified globally, some generalisations are necessary in reviewing them [1,2,3]. Nevertheless, there is enough replication of themes and approaches in EBSs for their characteristics to be identified (see Table A1). Many of these characteristics arise from a template initially established by BREEAM and are described below:

• Many EBSs use a credit-based scoring matrix, whereby a broad range of criteria are identified, weighted, and scored (see Table A1, below). Criteria and credits are frequently grouped into themes based on key sustainability principles. For example, LEED has nine main categories based on the economic impact; demographic needs and priorities; flood risk assessment; noise pollution; energy strategy; existing buildings and infrastructure; water strategy; ecological strategy; land use and transport. BREEAM has nine categories, which include energy; land use and ecology; water; health and wellbeing; pollution; transport; materials; waste; and management (see Table A1).
• Performance tiers are another feature of EBSs. For example, LEED has Certified, Silver, Gold, and Platinum levels of compliance and BREEAM has Pass, Good, Very Good, Excellent, and Outstanding (see Table A1). These ratings are achieved based on the number of credits achieved.
• These standards typically have an accredited assessor, who will act as an intermediary between the certifying organisation, which is tasked with acquiring and auditing the data required for certification, and the design team.
• Typically, compliance with these standards is based on the building as designed rather than the building in use. Therefore, data will be submitted in advance of building completion to achieve certification. In-use performance standards have been introduced such as BREEAM In-use [45] and LEED Zero [16], which will be discussed in more detail later in this paper. However, even in these cases, the core assessments are based on a design rather than an occupied building (see Table A1).

This credit-based system is the template for many EBSs. However, there are notable exceptions. One exception is the Passivhaus standard, which is a global standard developed in Germany in the 1990s. The Passivhaus standard has a narrow focus on reductions in energy demand and occupant comfort [46]. The standard has five key criteria (for a building in the UK), which are as follows: energy demand not to exceed 15 kWh/m²; primary energy demand not to exceed 60 kWh/m²/yr; a maximum airtightness of 0.6 air changes per hour at 50 Pascals pressure gradient; and living areas should not have more than 10% of the hours each year over 25 °C [47]. Another notable exception is NABERS (National Australian Built Environment Rating System), launched in Australia in 1999 as an Australian government initiative to measure and compare the energy performance of buildings. NABERS provides a rating from one to six Stars for buildings [48]. NABERS differs from BREEAM and its equivalent in Australia, Greenstar, by having a narrow focus on energy (and water) use, with accreditation based on in-use performance and ratings renewed on an annual basis.

Non-regulatory standards are not stand-alone methodologies and are linked to a regulatory ecosystem utilising recognised calculation methods, local and international standards (such as ISO and British Standards), or approved software developed by other organisations to inform their assessments (see Figure 3). For example, the Royal Institution of Chartered Surveyors (RICS) methodology for lifecycle assessment is based on British Standard BS EN 15978:2011 [49], which is in turn used as a framework by several NZGHGEBSs. In addition, approved software for lifecycle analysis, such as One Click LCA, or thermal modelling software, such as IES VE and DesignBuilder, means that these standards are dependent on other private companies to provide tools for assessment [50]. The Passivhaus standard has its own energy evaluation tool, the Passivhaus Planning Package, which is used for assessment and accreditation. However, this tool is informed by the German national DIN standards [51]. The complexity of the regulatory ecosystem in which environmental standards are developed is highlighted by a diagram prepared by the developers of the UK Net Zero Carbon Buildings Standard [52] (see Figure 5), which highlights more than twenty British and international standards that were considered in its development.

Whilst EBSs are not mandatory, they can still have considerable influence over the built environment and built environment policy for the following reasons:

• Non-regulatory EBSs are used by private and public organisations to set environmental targets for buildings beyond the mandatory minimum requirements of national regulations. One reason for the widespread use of EBSs is that accreditation provides a means for private organisations, state agencies, and regional authorities to identify and validate the environmental credentials of their buildings. For example, the BRE literature explains that, since 1998, over 16,000 projects have been BREEAM certified, equating to over 250,000 buildings [53].
• Whilst EBSs are not mandated by national governments, these standards can be adopted by municipal authorities and city administrations keen to enact more challenging environmental targets than national governments [54]. These standards can be enacted directly through local legislation or indirectly by making their use compulsory funding requirements for municipal authorities and national agencies [40] (see Figure 2). For example, in the UK, regional municipal authorities such as the Welsh and Scottish governments have made achieving BREEAM Very Good or Excellent a compulsory requirement for all new buildings fully or partially funded by them [55,56]. In addition, again in the UK, government agencies such as the Defence Estates and the Department of Health, with extensive property portfolios, have similarly made BREEAM and DREAM compulsory requirements for new buildings [57,58]. Similarly, LEED is a requirement for buildings for state-funded buildings in the USA [59], and Passivhaus is a requirement for public buildings in several municipal authorities in Europe, such as Voralburg in Austria [60].
• Finally, non-regulatory building standards can influence national building regulations. For example, in the UK, NABERS is cited as an EBS that informs the development of a performance-based policy framework for large commercial and industrial buildings in England and Wales [61].

4. The Development Context for Net-Zero GHG Emission Building Standards

In this section, an overview of the contextual factors identified in the review of the literature, which inform an understanding of the development of NZGHGEBSs, is presented.

4.1. Zero GHG Emission Building Standards Before the Paris Agreement

Whilst the Paris Agreement 2015 [12] has been seminal as a catalyst for the development of net-zero GHG emissions standards [62,63], this agreement was one of a series of steps towards the development of NZGHGEBSs and earlier efforts to define that net-zero should be recognised. The European Energy Performance of Buildings Directive (EPBD) in 2010 [64] required all new building built after 2020 to be ‘nearly zero-energy’, meaning they must have a high energy performance and very low energy demand covered largely by on-site renewable energy sources. This directive required Member States to define ‘nearly zero-energy’ in their national building regulations and to facilitate a transition to nearly zero-energy buildings. In the period leading up to 2020, the EPBD asked that Member States identify national benchmarks and investigate barriers to the application of ‘nearly zero-energy buildings’ [64].

This EU target was adopted by the UK government [65], which supported a 2007 commitment for zero GHG emissions homes by 2016. To support these commitments, the UK Government established the Zero Carbon Hub, a non-profit organisation, in 2008, which was given responsibility for achieving the government’s target of delivering zero GHG emissions homes [66]. The Zero Carbon Hub undertook work identifying zero carbon definitions [67] and barriers to the implementation of zero carbon standards such as the performance gap [68] but was closed in 2016.

Internationally, the International Energy Agency Solar Heating and Cooling Programme Task 40 [69] undertook a study on net-zero and very low energy buildings to harmonise international definitions and develop tools and industry guidelines. This joint international research aimed to address issues around the comparability of performance for buildings and communities in different climates and produced a net-zero evaluation tool and several publications [70].

Whether these definitions have informed the development of current NZGHGEBSs is unclear. However, it is notable that embodied carbon of buildings, detailed lifecycle assessment, and monitoring of in-use building performance as approaches to defining net-zero GHG emissions development (as shown in Table A2) were not features of most of these definitions. Indeed, by the standards described in Table A2, these definitions would be regarded ‘zero energy’ or ‘operationally zero carbon’ rather ‘net zero carbon’.

4.2. Drivers for the Development of Net-Zero GHG Emission Standards

The literature identified various contextual factors, which have informed the development of NZGHGEBSs. These factors help to inform understanding of the distinctness of NZGHGEBSs from earlier EBSs. Key factors identified are as follows:

• Recognition that more significant action was required to address the issue of global warming;
• Identification of issues around building performance and the performance gap;
• Increased awareness of embodied energy and carbon as a contributor of GHG emissions from the construction sector;
• Perceived flaws with current EBS frameworks.

It is of note that in response to perceived failings in building codes, standards, and regulations, Rosenberg et al. [71] predicted, in 2017, that future energy codes would be performance-based and would pivot from an emphasis on prescriptive design requirements to ‘meeting requirements for energy performance’, as indicated by operational energy use; that realistic energy benchmarking would be a feature of future codes; and that building energy codes would address the broader energy impacts of buildings and include ‘consideration of embodied energy in construction materials’ and a need to minimise ‘fossil fuel-based transportation systems’. Although Rosenberg et al. referred to codes (US regulations) rather than standards, this was nevertheless an accurate prediction of an NZGHGEBS consensus.

4.2.1. Global Warming and the Paris Agreement

Global warming and other environmental crises have been on the public agenda for decades and have informed the development of environmental standards in the built environment [6,72]. However, a growing awareness of the need to limit global warming to 1.5 °C in line with Paris Agreement targets brought renewed national commitments, such as the Climate Change Amendment Act in the UK [73], and a need for the built environment to respond to this challenge. With a 1.5 °C commitment in the Paris Agreement, the concept of climate neutrality and net-zero became more fully embedded in global and national discourse [74]. Reports and legislation highlight that for the developed world to achieve 1.5 °C by 2050 climate neutrality would be required for all buildings, and this would affect GHG emissions emitted throughout the lifecycle of a building [62].

Translating the concept of climate neutrality in the built environment into a set of requirements proved to be challenging, in part, because of the many ways the built environment contributes to climate emissions, which include embodied energy from extraction and productions of material used to construct a building; emissions from the energy used to construct a building and transport materials to a site; the operational energy required to provide a suitable internal environment; the release of carbon in demolition; and the relationship of a building to other carbon emitting systems such as transport and energy grids [75,76,77]. Questions around the temporal and spatial relationship of a building to emission sources further complicate definitions [62] and help to explain some of the diverging metrics shown in Table A1 and Table A2.

Attempts to define net-zero in the UK have taken place at different levels and include voluntary professional level responses such as the LETI framework [32]; professional body responses such as the Royal Institute of British Architects (RIBA) 2030 Climate Challenge [78]; industry sponsored responses such as the United Kingdom Green Building Council [79]; and revisions to national regulations enacted though the Future Homes Standard [80] and the Future Buildings Standard [81], introduced in response to national legislative commitments [73].

For some NZGHGEBSs, the commitments of the Paris Agreement provide a conceptual framework, whilst others use national commitments to directly inform target sets. In broad terms, two approaches to setting net-zero GHG emissions targets have been identified (Figure 6). One approach is ‘bottom up’, where the perceived capacity of the construction industry to deliver carbon reductions is the driver for the development of targets for a standard. Examples of this approach included the UKGBC Paris Proof method, which was the product of industry consultation [82], and the RIBA 2030 Climate Challenge (see Table A2). Another approach is top-down, where national and sectoral commitments derived from the Paris Agreement are converted into targets for individual buildings [83]. An example of this approach is the CRREM downscaling methodology [84], used to establish carbon budgets for buildings in the real estate sector. One standard, the UK Net-Zero Carbon Buildings Standard, launched in 2024 [52], has combined the top-down and bottom-up approaches to develop performance targets [85]. Bullen [86], Habert et al. [87], and Hoxha et al. [88] highlighted how the ‘top down’ and ‘bottom-up’ approaches can result in different spatio-temporal perspectives and interpretations of net-zero and highlighted the sensitivity of the top-down approach to the selected methodological approach, which can significantly affect the available carbon budget and carbon footprint of a building.

4.2.2. The Performance Gap

In addition to increased awareness of more stringent GHG reduction targets in the built environment, there is a growing recognition within the construction industry that existing low carbon buildings are not performing to the level to which they were designed. This disparity between design performance and built operational reality is referred to as the performance gap [68]. Various studies identify the performance gap as a product of deficiencies throughout the building lifecycle, which includes a lack of clear energy performance targets; early design decisions; poor specification; uncertainty in building energy modelling; site issues including on-site workmanship [89]; changes after design; poor commissioning; poor operational practice; and occupant behaviour [90].

The broad scope of deficiencies in the delivery of energy reductions in buildings means that failures to achieve anticipated energy reduction targets cannot be directly attributed to EBSs. However, the performance gap highlights the inadequacies of many EBSs in addressing this phenomenon. One aspect of the performance gap, which relates to EBSs, is that their assessment of energy performance and compliance with operational energy target are generally based on predictive energy models rather than the metered energy of the building in use. Methodologies such as the International Performance Measurement and Verification Protocol (IPMVP) Option C and Option D highlight how energy consumption baselines can be adjusted despite variable weather and occupancy conditions to facilitate comparisons of building performance [91]. Studies have highlighted a weak correlation between EBS accreditation level and in-use energy performance. Newsham et al. [92] identified that whilst LEED buildings in the research sample use 18–39% less energy per floor area than conventional counterparts, 28–35% of LEED buildings used more energy and that ‘measured energy performance of LEED buildings had little correlation with certification level’ of a building. Similarly, De Wilde [93] identified that measured GHG emissions of BREEAM accredited buildings in the UK two years after completion were three times higher than the design estimates, highlighting a disconnect between certification and energy savings.

Measures and processes have been identified in the literature to reduce the performance gap which include reference to energy in use for certification or accreditation; the use of more detailed and sophisticated predictive modelling reflecting the building as it is likely to be used as opposed to default values at design stages [94]; additional commitments to energy data that is gathered and evaluation after post completion; ensuring that measured performance is the benchmark; and providing a capacity for monitoring and data analysis of operational building performance.

4.2.3. Embodied Carbon and Lifecycle Assessment

There is growing recognition of the contribution of embodied energy to global carbon emissions and that, to achieve net-zero GHG emissions, the impact of lifecycle of buildings will need to be addressed alongside operational emissions. The environmental impact of buildings is the result of processes that occur throughout their lifecycle such as construction, usage, and demolition. The World Building Council attributes around 11% of all global carbon emissions to the manufacturing, transportation, construction, and end-of-life phases of built assets [95], while the UN Global Status Report attributes 10% to the construction of the buildings industry [96]. The United Nations Framework Convention on Climate Change’s Marrakech Partnership for Global Climate Action Human Settlements Pathway identified that, by 2030, the built environment embodied carbon must be reduced by at least 40 per cent [96,97].

However, there are uncertainties associated with the challenge of mapping activity and resource flows at a global sector level due to the number and complexity of interactions [98], inconsistencies in calculation boundaries, and the challenge of mapping system input-output environmental flows [99].

At an individual building level, LETI attribute up to 34% of carbon emissions to embodied carbon and lifecycle carbon based on current UK building regulations, with this proportion rising to as much as 50% for low energy buildings [100]. However, again, there can be uncertainties due to the temporal nature of LCA emissions, as highlighted by Lausselet et al. [101], who identified that 48% of embodied carbon emissions could be due to material replacements over a 45-year span for some buildings. Röck et al. [102] argue that embodied carbon is a significant proportion of a building’s lifecycle GHG emissions and provide evidence that GHG emissions associated with embodied carbon might exceed 90% in some cases. It is argued by Pomponi et al. [103] that a dichotomy between operational energy and embodied carbon results in increased construction carbon emissions and, in some cases, the shifting of the environmental burdens to the occupancy stage.

At the time of writing, in 2025, UK policy and legislation are focused on targeting operational CO₂ emissions (emissions that occur because of heating/cooling and electricity use), and there are no regulations around whole-life and embodied carbon. Measures to address this oversight in addressing carbon emissions include the Buildings Bill [104] and an industry led Part Z campaign [105], both of which propose introducing whole-life carbon assessment into the national building regulations. Whilst embodied carbon is not currently being addressed by national legislation and regulations, in the UK, there is substantial efforts from the industry to highlight this issue, from organisations including LETI [100]; RICS, [106]; UKGBC, [107]; and CLR [108].

Many EBSs include lifecycle carbon in their assessment framework. However, this is often a small component and unrelated to the scale of impact identified in the studies mentioned earlier. Amiri et al. [109] argue that ‘embodied emissions of buildings [is] A forgotten factor in green building certificates’ and explain that, in total, 14 points (13%) of the total LEED points are directly related to material selection, of which 5 points (5%) need substantial changes (e.g., LCA). For BREEAM, 12 points (8%) are directly related to material selection, i.e., less than in LEED, and of these, 5 (3%) points are based on LCA. Similarly, Sartori et al. [110] highlight that LEED for new building design and construction gives five points for reducing the building’s lifecycle impacts, which represents just 4.5% of all credits available. The international version of BREEAM for new non-residential buildings provides six points for performing a whole-building LCA, which represents 5.9% of credits available.

4.2.4. Criticisms of Existing EBS

Alongside awareness of the performance gap and acknowledgment of the role of embodied carbon in global carbon emissions, there have been general criticisms of the structure of evaluation mechanisms of EBSs. It is argued that the use of credit-based systems allows points to be chosen by a developer, with easier or cheaper credits often prioritised over credits that might have greater environmental benefits [111]. O’Malley et al. [112] made similar observations that adopting a checklist approach can result in a system that designs around the checklist rather than constructing the most sustainable building. Regarding the effect of the adoption of EBSs on clients and construction professionals, Schweber [113] noted, specifically regarding BREEAM, that ‘the multiplicity of regimes at play in any given assessment process’ and the limitations of the methods used have the effect of hindering variation and wider systemic change.

Another criticism is that many EBSs rely on design stage calculations to identify compliance. Pritchard and Kelly [114] described, with reference to a case study, how BREEAM energy credits awarded at the design stage were finalised three months prior to occupancy and nine months prior to official opening of the building to highlight that certification was entirely based on design ambitions rather than building performance. Furthermore, they explain that no follow-up post-occupancy evaluation occurred to check that credit points awarded, including those related to the building energy performance, had been implemented. Another criticism is that these standards fail to provide enough weight to significant metrics. Pritchard and Kelly [114] argue that whilst energy is the largest single category in BREEAM International with 19% of total available points, the category is underweighted in relation to environmental impact.

5. Critical Review of Net-Zero GHG Emissions Building Standards

Table A2 provides an overview of NZGHGEBSs and outlines their characteristics. It describes the certification process undertaken by the organisation developing the standard, which in most cases is completed after practical completion. Table A2 also indicates that NZGHGEBSs have significantly less assessment criteria than earlier EBSs, along with a threshold-based approach to compliance based on performance in use, with energy use intensity and embodied carbon as common metrics across the standards.

The ILFI Zero Carbon Certification describes itself as the ‘first worldwide Zero Carbon third-party certified standard’ and was launched in 2018 [17]. The extent to which this standard has served as a template for other NZGHGEBSs in the same way BREEAM did in the 1990s is not clear. Based on the launch date of the other zero standards, it appears that several NZGHGEBSs were developed at the same time as the ILFI Zero Carbon Certification, including LEED Zero, which was launched in the same year, and the Canada Green Building Council Zero Carbon Building Standard, which was launched in 2017 [115].

Nevertheless, ILFI Zero Carbon Certification standard is significant because it has many features typical of the other zero GHG emissions standards. The features include certification awarded after practical completion (one year in this case) and based on performance data including metered data and records of built material types and quantities [116]. In addition, embodied energy is a key metric, and a target of 500 kg Co₂e/m² is set for the carbon emission associated with the construction of a building, sometimes referred to as the upfront carbon (cradle to gate or RICS A1-A5). Targets for operational energy are based on climatic zones as follows: for the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) climate zones 0, 1, 2A, 2B, 5A, 5B, 7, or 8, a target of 101 kwh/m² per annum; and for all other ASHRAE climate zones, the target is 88 kwh/m² per annum. The use of carbon offsets is recognised, and the standard allows the purchase of off-site renewables to compensate for operational energy use and accredited offsetting for the residual component of the embodied carbon element of a new building.

The ILFI Zero Carbon Certification web page [17] provides some of the research sources used in the development of the standard, and these sources were further confirmed as data sources for the development of the standard through correspondence with the ILFI by the lead author. These sources identify embodied carbon targets derived from industry benchmarking research undertaken by the Carbon Leadership Forum [108] of mainly north American buildings, indicating that the targets are bottom-up, based on industry capability to deliver emissions reductions, rather national or sectoral Paris Agreement commitments. The use of north American benchmarks for a global standard raises questions about the universality of this standard.

LEED Zero is another global NZGHGEBSs launched in the same year as the ILFI Zero Carbon Certification. However, unlike ILFI Zero Carbon Certification, it is an adjunct to existing LEED standards rather than a stand-alone standard, and full LEED certification is required before this standard can be applied [15]. LEED Zero is one of a few instances where a NZGHGEBS has been attached to an EBS, and this is interesting for two reasons: firstly, other global organisations with EBS, such as ILFI, have launched new NZGHGEBSs rather than attach new requirements to existing standards; and secondly, other organisations, notably the BRE, whilst advocating Net-Zero [117], have decided not to produce a similar addendum to their own standards.

LEED Zero is described as an operational verification system to ensure that buildings are meeting net-zero goals. The verification approach is based on achieving a balance between sources (building and transport emissions) and mitigation measures (permitted carbon offsets). Certification is awarded one year after completion and renewed on an annual basis. LEED Zero in its current form does not account for embodied energy. However, the programme guide [15] explains that it ‘will expand in the future to incorporate carbon caused from water consumption, waste generation, and the embodied carbon of materials’. Uniquely, among NZGHGEBSs, the energy from transport of building users is one of the key metrics for assessing carbon neutrality, and a transport survey of users is a key component of the assessment methodology.

Similarly to LEED Zero, NABERS Carbon Neutral Building Certification is an adjunct to an existing EBS [118]. To achieve certification, a NABERS Energy rating of four Stars or above is required, at which point approved carbon offsets can be used to cancel the building’s operational emissions. NABERS is one of the few EBSs that assess in-use operational performance and has a narrow focus (i.e., on in-use energy). NABERS provides a precedent for NZGHGEBS and has already influenced the UK government proposals for future regulations.

The DGNB Climate Positive is a German Building Standard developed by DGNB [18]. The DGNB Climate Positive award works on a building-specific CO₂ balance, where the GHG emissions from energy consumption of a building are compared with the emissions that are avoided by the building’s own energy production at the site. Like LEED Zero, the award is based on operational performance for the year of assessment [119]. With the Climate Positive award, embodied energy from construction is compensated by renewables over the life of the building, and as a result, buildings are likely to be energy positive on an annual basis. A key component of this standard is a Climate Action Plan outlining the process of decarbonisation and setting building specific targets and annual carbon accounting. The purchase of carbon credits is not permitted, and it is a post-occupancy standard. Certification is awarded one year after completion and renewed on an ongoing yearly basis.

6. Net-Zero GHG Emissions Building Standard Distinguishing Features

Table A2 identifies the NZGHGEBS benchmarks and methodologies. Viewed collectively, the shared characteristics of NZGHGEBSs can be identified, along with the characteristics that separate them from earlier EBSs. Identifying these shared characteristics can inform current understandings of how net-zero GHG emission buildings should be defined. Whilst there were considerable differences between NZGHGEBSs and earlier EBSs, there were also areas of overlap and significant contextual clusters around dominant discourses, as shown in Figure 7. The key characteristics of NZGHGEBSs as identified from Table A2 are as follows:

• A key feature of NZGHGEBSs is that compliance should be based on post-occupancy or as-built performance, rather than on design or predicted performance. This is a significant departure from most EBSs, and it can be postulated, based on critiques in the literature, that this is a response to the problem of the performance gap. While most NZGHGEBSs require post occupancy evaluation of performance to ensure compliance, the assessment period varies considerably. The point at which an asset can be considered a net-zero GHG emission building can be one year after practical completion, as is the case with ILFI Zero Carbon Certification, to five years for Noll CO₂, to ongoing on an annual basis until the end of a building’s life, as is the case with LEED ZERO. This variance highlights some discord around the temporal boundaries of net-zero GHG emission definitions but is also a reflection of the practicalities of applying a standard.
• Another feature is the use of a limited set of assessment criteria. In some cases, such as ILFI Zero Carbon Certification and LEED ZERO, only two principal metrics are evaluated. The use of a limited set of evaluation criteria has more in common with the Passivhaus standard than with EBSs that have numerous criteria across a range of themes. However, it is notable that the Passivhaus standard has criteria relating to user comfort, something which is a notable absence in many NZGHGEBSs. Whilst comfort criteria are absent in most standards, it is notable that the Indian Green Building Council Net-Zero Energy Buildings Rating System [120] is one of the exceptions. The Indian Green Building Council Net-Zero Energy Buildings Rating System provides scope for comfort conditions to be compromised to meet carbon reduction requirements, and there is some evidence to indicate that this is already happening where in-use performance standards have been applied, such as in some cases where NABERS has been implemented on projects [121].
• The use of benchmarking based on assessment of building performance and the widespread identification of best practice as the basis of performance targets (i.e., a bottom-up methodology) is another feature of these standards. Again, this is not universal, and there were gaps in the data, with few developing organisations providing details of the data sets that had informed the benchmarks. However, it appeared that a common response of the challenge of defining a net-zero GHG building was to examine best practice in the current building stock and use this data as the basis for performance targets.
• The use of a binary pass/fail or threshold-based approach based on in-use metrics as opposed to levels of compliance is another common feature of the net-zero EBSs. Whilst not stated explicitly, this could be a response to some of the criticisms levelled at some EBSs, where levels of compliance fail to represent building performance.
• Regarding one of the more controversial aspects of the net-zero GHG compliance, carbon offsetting, there is agreement among the NZGHGEBSs that operational carbon emitted should be compensated (or surpassed) on an annual basis, with almost all standards providing this capacity in the assessment method. However, there is disagreement about what is included in the calculation methods. All the standards allow the use of off-site renewables; however, there is no consensus on the use of carbon offsetting for embodied carbon. Carbon offsetting can be interpreted as a response to the use of a bottom-up methodology, which identifies best practice but leaves residual GHG emissions that needed to be addressed. However, there are several potential issues that could compromise the role of carbon offsets in reducing emissions and achieving net-zero greenhouse gas emissions. For example, verifying the additionality of a carbon offsetting project, which means that any reduction in emissions is only caused by the offset project taking place, is challenging. There are also risks associated with carbon leakages and reversals [122]. Therefore, priority should always be given to reducing or eliminating emissions at source. For example, on-site renewables and sequestration of carbon on-site (using measures as structural timber) should be prioritised over carbon offsets and biogenic sequestration off-site. Offsetting is generally regarded as a final step to be applied when benchmarks are met and should follow rigorous verification methods such as the guidelines provided in the latest edition of the Oxford Offsetting Principles [123].

One of the widely considered perceived barriers to the implementation of net-zero GHG emissions in the built environment has been the lack of a clear definition or differences in definition [124]. However, this study identifies that, whilst the precise targets and specifics vary, partly as a reflection of national benchmarks, there is a consensus around many of the principles for identifying and evaluating net-zero buildings. These standards confirm that there is consensus that the ability of a building to claim net-zero GHG emissions status should be connected to its in-use performance rather than design predictions. In addition, it is generally recognised that there should not be degrees of ‘net-zeroness’ and that a building will either fulfil this requirement or not. There is also a degree of consensus the embodied carbon should be considered within the evaluation framework of net-zero GHG emissions. However, whether that is embodied carbon from the initial construction of the building or whole-life carbon, representing emissions over the life of an asset, remains an area of contention. Finally, carbon offsets are probably one of the more contentious aspects of net-zero. However, by virtue of their inclusion in all but one standard, there is acceptance that they are necessary under current development frameworks, but that their use should be minimised through the application of challenging but appropriate benchmarks.

7. Discussion

Using the methodology described in Section 2, it is possible to identify contextual clusters and areas of consensus and discord in the development of NZGHGEBSs. However, the opaque nature of many standards, with few disclosing the data which established their benchmarks and even less subjecting their methodology to peer-review through academic review or by similar institutions, means that it is difficult to interpret the basis of targets and underlying approach. In addition, the widespread use of a bottom-up approach means that the relationship of the standards to national carbon reduction targets is not clear. The literature suggests that the use of in-use performance for verification of a certificate represents a positive step to address the operational energy performance gap and other issues with EBSs. However, incorporating embodied carbon into assessment provides new opportunities for a performance gap to emerge around the measurement and evaluation of lifecycle carbon and emissions not typically measured such as fugitive-gas emissions (e.g., refrigerant leakage from air conditioning systems). It is anticipated that, as these issues become more clearly defined, it is likely that we will see the revision of these standards to address these issues more effectively.

The use of a performance-based assessment has the potential to be an important development in the delivery of net-zero GHG emission accredited buildings, as it suggests that the burden of compliance will be shared between the design team and building operators. In the case of the buildings with tenants, whether they are residential or commercial, this suggests that closer collaboration will be required for the targets to be met. This is because the conditions that will facilitate compliance will be established by the design and delivery team. However, ensuring compliance will be the responsibility of facility managers and/or building operators. In some cases, legal instruments, such as green leases, are likely to be used to support tenant compliance with operational energy targets. Performance contracts, on the other hand, can be used to ensure sufficient and proactive aftercare from the construction teams to achieve performance targets. Whilst this shared responsibility creates uncertainty, it is arguably a more accurate reflection of the roles of the various parties (i.e., designers, builders, and users) in delivering building performance. In addition, the literature on the psychology of goal and target setting highlights the benefit of having a small number of targets, which require a collective effort, as characterised by NZGHGEBSs, for achieving behaviour change [125]. However, it should be noted that these changes will not happen without a robust business case that aligns environmental outcomes with financial return for stakeholders. Owner-occupiers have a strong incentive to achieve performance targets in practice and will benefit from lower utility bills and operational costs. However, developers may not necessarily see the value of opting for stricter requirements, unless they can achieve price premiums for their higher-rated buildings or can benefit from the social and reputational value of following the best practice.

This paper explains how the Paris Agreement and perceived failing in current standards and regulations have prompted a response to develop NZGHGEBSs by various organisations around the world. It is the gap between regulatory codes and aspirations by sections of the construction industry, property owners, and investors that has created a space for private organisations and coalitions of actors to develop frameworks, standards, and methodologies for identifying zero GHG buildings. These standards exist in a space created by a lack of government legislation, and, indeed, these standards might become obsolete if robust regulations were introduced in many countries. They can, however, inform the development of such regulations. Regional and contextual factors, including political dynamics, play a major role in how these frameworks and standards are developed. These sometimes serve as precursors to future mandatory environmental regulations, as demonstrated by the Energie Positive and Réduction Carbone (E+C−) framework in France. Conversely, in contexts where political support is insufficient—at least in the short term—to implement compulsory performance targets, an initial net-zero framework may instead guide the development of a broader voluntary industry standard. The LETI framework, for example, illustrates how a grassroots initiative led by practitioners mobilised multiple professional bodies and private-sector organisations to produce the first Net-Zero Carbon Buildings standard in the UK.

These criticisms of regulations can be seen alongside criticisms of existing EBSs, which, it can be argued, fail to (1) set actual energy performance targets for buildings; (2) ensure new buildings are really on track for net-zero GHG emissions, with low energy demand and no fossil fuels; (3) assess building performance to close the performance gap; and (4) regulate the embodied carbon of buildings. Should regulations continue to be perceived as insufficient to address the climate emergency or meet the commitments of the Paris Agreement, it is likely that there will be a widespread adoption of NZGHGEBSs by companies, municipal authorities, and national agencies as a tool to address these deficiencies. This would repeat a pattern seen in the adoption of earlier EBSs by similar agencies.

The introduction of the NABERS UK scheme, following the success of the original Australian scheme, is an example of how the new wave of EBSs are being used in the construction industry as a voluntary measure to demonstrate buildings’ sustainability credentials. There are several examples of NABERS 5-6 Star–rated buildings in Australia achieving energy use intensities close to 30 kWh/m² per annum in the commercial office sector [126]. The highest UK NABERS rating for the base-building of commercial offices (the space and services managed by the Landlord), at the time of writing this article, is 5-Star according to CIBSE, the respective accreditation body [127]. This is commensurate with the RIBA 2030 Climate Challenge interim target set out for 2025.

It should, however, be noted that most NZGHGEBSs are recently developed, and there is still a lack of strong empirical evidence to demonstrate whether these standards are succeeding to deliver net-zero carbon emissions in practice at scale. Studies carried out on early examples of the implementation of these standards suggest that while net-zero-designed buildings perform better than the rest of the building stock, they still suffer from the problem of the performance gap. This reinforces the necessity of a shift towards an outcome-focused design and procurement approach [128]. Scarcity of peer-reviewed research covering robust and verifiable empirical data in the context of new NZGHGEBSs is a limitation of this study. It is recommended that future review studies in this field address this limitation as and when more operational data is collated from new buildings designed and procured following these new standards. It will also be important to investigate potential cost trade-offs and rebound effects in implementation of these standards in practice. At the time of writing, several pilot projects have submitted their performance data to the newly developed Net-Zero Carbon Buildings Standard in the UK [52], which could be analysed and used to evaluate the effectiveness of the standard and identify improvement opportunities.

8. Conclusions

This paper examined the evolution and current landscape of non-regulatory environmental building standards, with a particular focus on the emergence of Net-Zero Greenhouse Gas Emission Building Standards (NZGHGEBSs) in the post-Paris Agreement era. Through comparative policy analysis, it has been demonstrated that NZGHGEBSs represent a significant departure from earlier environmental building standards (EBSs), shifting from credit-based, design-stage assessments to performance-based, post-occupancy evaluations. This transition reflects a growing recognition of the limitations of traditional EBSs in addressing the performance gap, embodied carbon, and the broader climate impact of buildings.

The analysis reveals a developing global consensus around the core principles of NZGHGEBSs, including the use of a limited set of key metrics (primarily operational energy and embodied carbon), threshold-based compliance mechanisms, and the prioritisation of in-use performance data over predictive modelling. While there is variation in the specific benchmarks and methodologies employed, the convergence on these principles suggests a maturing understanding of what constitutes a net-zero GHG building. Furthermore, the inclusion of carbon offsetting, though contentious, is widely adopted.

The study also highlights the role of NZGHGEBSs in filling the regulatory void left by insufficient national legislation. However, challenges remain. The lack of transparency in benchmark development, inconsistencies in offsetting practices including the risk of carbon leakage and reversal or not meeting the additionality requirement in practice, and the potential for new performance gaps, particularly in embodied carbon, highlight the need for ongoing refinement and standardisation. The review presented in this paper points to the following key requirements that can help maximise the benefits of the new generation of environmental building standards:

• Improved transparency in how the benchmarks and targets are derived, reconciling the bottom-up (best-practice building performance) approach with the top-down (GHG-based budget) approach (see Figure 6);
• Contractual arrangements to facilitate building fine tuning after completion and post-occupancy evaluations (including post-construction LCA audits to cover both operational and embodied carbon);
• Robust measurement and verification protocols to demonstrate the effectiveness of these standards in practice, using third party independent verification;
• Address interoperability or equivalence agreements between regional standards to prevent market fragmentation, especially for international real estate portfolios.

In conclusion, NZGHGEBSs represent a critical step forward in aligning the built environment with global decarbonisation goals. By emphasising actual performance, narrowing assessment criteria, and fostering accountability across the building lifecycle, these standards offer a more robust framework for achieving meaningful emission reductions. Their continued development and adoption will be instrumental in transforming building practices and supporting the transition to a low carbon future.