Towards net zero: sectoral ambitions and global trends in building decarbonisation

2.1 OVERVIEW

This paper focuses on the collection, analysis and assessment of DEs in the BRE sector worldwide between 2000 and 2024. The collection and analysis of DEs is conducted through an SLR. A global approach provides insight into the current state of research and policy, revealing trends and gaps in different regions and countries. The alignment of the literature with the goals of the Paris Agreement is assessed using a multi-criteria scoring and weighting framework.

2.2 LITERATURE SEARCH

The paper aims to answer the following research question:

• How have the DEs within the BRE sector been developed globally in the last two decades?

Three sub-questions were defined, from which four search strings for the SLR were derived (Figure 1). The sub-questions were as follows:

• When have DEs been published in research and policy for the BRE sector?

• How has the ambition of DEs changed over the years?

• How many DEs are aligned with the goals of the Paris Agreement?

Figure 1

The systematic screening process is illustrated in Figure 1 (for the full paper list, see the supplemental data online). The paper databases Scopus and Springer were chosen for their broad, complementary coverage of engineering, environmental sciences, policy and decarbonisation of the built environment. Backward and forward citation tracking along with the inclusion of relevant grey literature via snowballing were used to minimise database bias and ensure comprehensive coverage of key document types.

The search was conducted in June 2025, yielding 8616 relevant scientific articles. Then, 268 duplications were excluded using a Python script. A total of 5118 publications from research areas outside the SLR’s scope were filtered out (e.g. chemistry, medicine, physics). Afterward, the titles of the papers were manually screened, excluding 2914 papers that did not focus on the BRE sector (e.g. those focused on transport, industrial processes or infrastructure). Then, 87 papers were further filtered out based on their abstracts as they focused on economic or societal problems rather than environmental impact assessment. Afterwards, 63 documents were excluded after full-text review because they addressed technical and viability issues, leaving 167 articles. Through expert recommendations (IEA 2023b) and citation-tracking, 47 documents (including grey literature) were added during the snowballing phase, resulting in a final sample of 212 documents for data extraction. It is recognised that including the grey literature introduces variability in the quality of cited research; however, this is an unavoidable inherent limitation of capturing policy-relevant DEs at the global level.

2.3 DATA EXTRACTION

To answer the research questions, six key factors towards decarbonisation were analysed in the data-extraction phase (Table 1). These were inspired by the typology and conceptual framework proposed by Lützkendorf & Frischknecht (2020), which systematically distinguishes net zero approaches in the built environment by terminology and indicators. The Paris Agreement aims to mitigate climate change to well under 2°C, preferably 1.5°C. In the literature, DEs have focused primarily on these two temperature limits. Some papers consider only CO₂ emissions, while others expand their main indicator to include additional GHG emissions. These variations are categorised under the ‘main indicator’ factor. The ‘life-cycle scope’ factor indicates whether the documents focus on operational or embodied aspects, or on both (WLC approach). Three factors related to the decarbonisation goals were considered: the type of goal (reflecting ambition), the target year and the assessment scale (a key factor in assessing alignment with top-down goals). These variations are considerable across the literature, providing crucial insights into the temporal and geographical evolution of research and policy.

The documents were analysed and their properties categorised into these factors. To answer the research questions, geographical and temporal factors are needed. To this end, metadata useful for the analysis (such as year, location and document type) were also extracted. The document search was limited to publications in English, and although international experts were consulted in the snowballing phase, a potential language bias should be noted.

2.4 MULTI-CRITERIA SCORING AND WEIGHTING FRAMEWORK

A simple multi-attribute rating technique was used, based on Siregar et al. (2017). This framework collects data on selected key factors and generates a rating classification based on each factor’s characteristics. The chosen factors were characterised based on the SLR’s findings, and their characteristics were assigned points (Table 1) according to their alignment with current decarbonisation needs, considering the typology of terms and definitions by Lützkendorf & Frischknecht (2020). Full alignment is defined as the decarbonisation of the whole BRE sector to limit global warming to 2°C at the latest by 2050 by reaching net zero GHG emissions during the WLC of buildings, as stated by the IPCC (2023), United Nations (2015) and World GBC (2019). Consistent with patterns observed across the reviewed literature and summarised in both ‘net zero carbon’ and ‘net zero emissions’ are frequently treated as Paris-aligned concepts; however, ‘net zero carbon’ is more often defined with a broader GHG-emission scope. The characteristics given 1 point describe the minimum requirements for alignment; characteristics beyond these requirements (e.g. sooner target years or lower temperature limits) are awarded higher points. For studies that considered more than one characteristic per factor, the points corresponding to the highest-rated characteristic were assigned. For non-aligned characteristics, the awarded points were based on their completeness and ambition. Zero points were awarded if a factor was not mentioned. The scoring framework reflects degrees of Paris alignment rather than a binary classification, allowing approaches that address necessary but incomplete dimensions of decarbonisation (e.g. energy performance without WLC coverage) to be distinguished from fully aligned pathways. Target-year scores reflect the relative ambition of stated goals at the time of publication, rather than their feasibility at the time of this review. Earlier target years, therefore, indicate higher ambition, even if they are no longer achievable at the time of analysis.

The reviewed literature spans a wide range of analytical scales, including individual buildings, building stocks and sector-wide assessments. The scale of assessment was therefore included as an explicit evaluation criterion. Studies focusing on individual buildings were assessed based on their potential contribution to scalable decarbonisation pathways, rather than being interpreted as sector-level solutions. For this reason, the attributed points reflect the scale and their linked uncertainty of representing sector-wide alignment.

3.1 DOCUMENT TYPE

The literature shows a clear temporal pattern in the emergence of different document types, with scientific research leading the development of DEs. Figure 2 shows the temporal distribution of document types found in the literature (books, conference papers, reports, policies, scientific papers). It can be seen that the publication of scientific papers precedes that of reports, which in turn precedes that of policies. Zimmermann et al. (2005) was the first scientific article found through this SLR. It was among the first to define permissible limit values for energy demands and pollutant loads during the construction, maintenance and operation of buildings. The present paper, like others predating the Paris Agreement, does not use terms such as ‘net’ or ‘near zero’ emissions, but rather aims to lower energy demand and emissions, in line with the publication of the Kyoto Protocol and the principles of the 2000 Watt Society. Since the Paris Agreement was established in 2015, the number of scientific papers on the decarbonisation of the BRE sector has increased significantly. The data indicate that the increase in the academic literature precedes the growth in reports and policies, suggesting a diffusion of concepts from academia to institutional or regulatory publications.

Figure 2

Focusing on operational energy demand, Pless & Torcellini (2010) published a technical report for the US Department of Commerce that defined net zero energy buildings. On the policy side, in 2011, a road map to reduce India’s energy demand was published as part of the United States Agency for International Development’s (USAID) programme (Kapoor et al. 2011). It was not until 2019 that (British) reports and policies adopted the term ‘net zero carbon buildings’ (CCC 2019; UKGBC 2019), while scientific publications had been using it and similar terms since 2011 (Xing et al. 2011). This temporal sequencing suggests a lag of approximately five years in the adoption of ambitious science-based goals into policies.

Overall, the temporal distribution of the documents shows that the publication of scientific research is followed by that of reports by organisations, which in turn is followed by the implementation into policies. The data show that translating scientific knowledge into climate policy can be delayed by up to a decade due to political, social and economic factors, a pattern observed internationally (Boykoff 2007; Colvin & Jotzo 2021; Roper et al. 2016; Shue 2023), which has such delays increasing future mitigation costs and reducing climate target feasibility (Luderer et al. 2013, 2016). At the same time, the literature shows a worrying trend: as the feasibility of the 1.5°C limit declines, recent DEs shift toward 2°C-based framing rather than increasing ambition. This reinforces the urgency of addressing the growing gap between scientific publications and policy adoption. As emphasised by Kuittinen et al. (2024), closer collaboration between researchers and policymakers is essential to shorten this gap between scientific evidence and effective policy implementation.

3.2 LOCATION OF THE ASSESSMENT

Across regions, the scope of DEs has gradually expanded from operational energy use towards WLC perspectives (especially since 2020), although operational-only approaches remain prevalent. Figure 3 illustrates the temporal and geographical distribution of DEs by scope.

Figure 3

The first publications in Europe from the UK and Switzerland focused on reducing operational emissions through 2000 Watt Society-compatible energy-saving scenarios (Peacock & Newborough 2008; Schulz et al. 2008; Zimmermann et al. 2005). Recently (since 2021), nearly all European studies have shifted their focus to a WLC approach.

The aforementioned report by Pless & Torcellini (2010) was among the earliest contributions originating from North America. While all identified North American studies published since 2022 adopt a WLC scope, the number of publications declines after 2017. This trend may be partly associated with shifts in US climate policy following its withdrawal from the Paris Agreement in 2017 (and again in 2025); however, broader socio-economic factors are outside the scope of this SLR.

For Asia, the data do not indicate a clear transition to a WLC scope. In several Asian countries, including China, DEs remain strongly operationally focused, often overlooking the embodied impacts of construction materials (Cui et al. 2019; Du et al. 2024; Hu et al. 2022; Huo et al. 2021; Kang et al. 2020; Li et al. 2022; Liu et al. 2019a, 2019b; Yang et al. 2021; Zou et al. 2023). While operational emissions account for a substantial share of China’s total emissions (Liu et al. 2019b), excluding embodied emissions risks significantly underestimating the climate impacts of refurbishments and renovation (Röck et al. 2020).

In Oceania, the first publication picked up in the SLR search was by Ximenes & Grant (2013) on the embodied impacts of timber maximisation in two popular house designs in Sydney, Australia. They considered temporary carbon storage within buildings and different end-of-life parameters for landfill decomposition, which significantly influence GHG outcomes. Under these assumptions, they present timber use in construction, combined with timber landfilling, as a potential CO₂ sink, thereby potentially contributing to the decarbonisation of the BRE sector. Nonetheless, no carbon opportunity (i.e. unrealised carbon storage potential in forests) was considered in this paper (Maierhofer et al. 2024). Since 2018, there has been a shift toward WLC, as exemplified by Chandrakumar et al. (2019), who defined 1.5 and 2°C-compatible carbon budgets for New Zealand. Compared with other regions, Oceania was among the first to adopt a WLC approach.

An unequal geographical distribution of publications is very evident. South America and Africa are underrepresented in the literature, with only one (Besser & Vogdt 2017) and two (Fan & Xia 2017; Ohene et al. 2023) studies identified, respectively. These publications predominantly adopt an operational focus and are largely authored by institutions based outside of the studied regions, a pattern also noted in previous research (Ala-Mantila et al. 2023; Furini 2019; Perissi et al. 2018). While countries in these regions may face other development and funding priorities (Mata et al. 2020), the projected growth of their building stocks makes early integration of DEs critical. Without such integration, future emissions from their BRE sectors risk overshooting climate goals (Caballero-Güereca et al. 2023).

3.3 DECARBONISATION TARGETS AND GOALS

Across the analysed timeframe, the terminology used to define decarbonisation goals has changed noticeably. Table 2 presents a typology of these goals, as defined in the literature, including terms no longer used in current standards. For example, some recent standards have updated their treatment of operational energy offsets in the net zero energy concept to better reflect climate science. Because exporting renewable energy produced in situ does not constitute a negative emission (i.e. no CO₂ is removed from the atmosphere), the latest draft of the European Standard for building life-cycle assessment, FprEN 15978 (CEN 2025), does not allow grid electricity demand to be offset by exported electricity; instead, grid demand and exports must be reported separately.

The terminology used to express decarbonisation goals has evolved over time, reflecting a gradual increase in ambition and a shift towards different offsetting approaches (i.e. net zero). Figure 4 illustrates the temporal evolution of terms used to express decarbonisation goals, revealing a stepwise increase in ambition over time. This trend reflects growing urgency to meet climate targets as action remains insufficient, leading to stricter policies, steeper decarbonisation pathways and swifter lifestyle changes to remain within shrinking carbon budgets (Global ABC 2024). Energy-focused goals (e.g. low energy, 2000 Watt Society, near zero energy, net zero energy and zero energy) dominated the literature between 2010 and 2020, whereas more recent literature increasingly emphasises carbon neutrality. This shift towards net zero emission goals aligns with the academic literature (Roberts et al. 2020), and also with the grey literature (predominantly published in Europe), where reports and policies from 2019 onwards have had an overwhelming focus on reaching net zero carbon (CCC 2019; European Commission 2024; Global ABC 2024; Hill et al. 2019; IEA 2023a; IGBC 2022a; LETI 2020; O’Dwyer et al. 2023; Passivhaus Trust 2019; Toth et al. 2022; UKGBC 2019; World GBC 2019).

Figure 4

In the literature on DEs for the BRE sector, climate neutrality and carbon neutrality are often treated as synonymous. As they are not differentiated in the analysed literature, they are therefore considered here under a single term. Nonetheless, the recent literature has clarified important differences between these concepts, which are particularly relevant for methane (CH₄)-intensive sectors such as agriculture. Carbon neutrality is commonly associated with net zero CO₂ emissions, typically achieved by balancing emissions and removals (Chen et al. 2022; Wang et al. 2022). Climate neutrality, by contrast, has a broader scope, encompassing all GHG emissions and accounting for their differing global warming potentials (Borning et al. 2020). Whether mitigation efforts address only CO₂ or all GHG emissions has important policy implications, as carbon-neutral strategies may overlook non-CO₂ emissions that are critical for achieving Paris-aligned climate outcomes. For this reason, this distinction on the main indicator was explicitly included as an additional assessed key factor. Although the need for harmonised definitions and transparent system boundaries has been explicitly highlighted in IEA EBC Annex 72 (Frischknecht et al. 2023), the current scientific literature remains methodologically and terminologically ambiguous and unaligned with the principles of the Paris Agreement.

3.4 SCALE OF THE ASSESSMENT

Across all scales, an increase in publications is observed after 2016, reflecting the influence of the Paris Agreement. Figure 5 presents the three assessment scales identified in the literature: individual buildings, building stocks and the BRE sector. A stepwise progression is evident, with building-level analyses appearing first, followed by building stock assessments and, more recently, sector-wide studies. While individual building studies cannot ensure sector-level compliance with the Paris Agreement, they can inform typology-specific, bottom-up approaches to benchmarking and building stock modelling to explore decarbonisation trajectories across different policy settings and frameworks (Alaux et al. 2025; Chan et al. 2024; Foliente & Seo 2012).

Figure 5

Specific examples of the early literature predominantly focusing on the individual building scale include Zimmermann et al. (2005), who defined energy demand benchmarks per floor area for residential and office typologies, and Peacock & Newborough (2008), who addressed heat-saving measures across UK residential buildings. These approaches enable comparability, but are inherently limited in their ability to assess system-wide alignment with climate targets.

From 2011 onward, building stock-based approaches emerged, allowing DEs to account for aggregate effects, geographical and temporal dynamics. For example, a strategy net zero energy road map for India applied a stock-level perspective across commercial and residential buildings. Heeren et al. (2012) modelled different structural changes, retrofit rates and thermal insulation factors to align the Swiss residential building stock with the 2000 Watt Society’s goals. Since 2016, particularly after 2020, stock-level analyses have become more prevalent, reflecting a growing recognition of the need to capture cumulative impacts and the mid- to long-term effects of DEs.

In the case of sector-wide BRE analyses explicitly addressing material flows, technology scenarios and policy levers, Xing et al. (2011) adopted an operational approach in the UK to phase out fossil fuels, including scenarios for thermal insulation, lighting, heating and ventilation technologies. From 2015 onward, the publication of sectoral-level studies became mainstream, particularly in the UK (Chaudry et al. 2015; Hannon 2015; UKGBC 2014). These studies coincided with the UK’s commitment to reducing its GHG emissions by 80% by 2050, announced in 2015, and illustrate how sector-level framing enables the integration of operational, embodied and policy dimensions that cannot be captured at smaller scales.

3.5 ALIGNMENT WITH THE PARIS AGREEMENT GOALS

Across the analysed literature, significant methodological discrepancies are observed, even where identical terminology is used. These differences appear across key factors such as the temperature limit, the accounting of CO₂ or GHG emissions, the life-cycle scope considered, the scale of assessment, the target year and the set goal. As outlined in the methods section, not all characteristics are consistent with the principles of the Paris Agreement. These criteria are systematically assessed to assign an alignment rating to the DEs identified in the literature, reflecting their degree of alignment with the goals of the Paris Agreement. Although emission mitigation strategies in the BRE sector predated the Paris Agreement, the Agreement marked a turning point by clearly defining long-term temperature limits and net-zero objectives. Prior to 2015, most of the literature did not link DEs to explicit temperature thresholds or sector-specific net zero commitments.

Before the adoption of the Paris Agreement (United Nations 2015), explicit temperature limits for global warming were rarely mentioned, with only 5% of documents prior to 2015 mentioning a 1.5°C threshold. Between 2015 and 2017, this share increased rapidly, with approximately half of the studies adopting a 1.5°C limit. Since 2018, however, an increasing number of DEs have incorporated both 1.5 and 2°C in pathways for 2050 and beyond. This finding provides evidence that reflects the growing difficulty of limiting global warming to 1.5°C under current trajectories, as highlighted in the recent literature (Alaux et al. 2025; IEA 2023a; Kuramochi et al. 2018) and by Intergovernmental Panel on Climate Change (IPCC) climate scientists (Carrington 2024).

The indicator used to quantify global warming potential has also evolved unevenly. While early benchmarks already accounted for multiple GHG emissions from buildings (Zimmermann et al. 2005), a substantial share of recent DEs has focused exclusively on CO₂ emissions. Overall, around 25% of the assessed documents quantify CO₂ emissions only. Even though CO₂ emissions account for the greatest share of GHGs emitted by the BRE sector (Nejat et al. 2015), disregarding other GHGs increases the risk of overshooting temperature limits when defining DEs. Additionally, the lack of transparency and confusion about the BRE’s contribution to global GHG emissions (21% according to IPCC 2023) and global CO₂ emissions (37% according to UNEP 2024) can lead to incompatible national pathways, increasing the risk of overshoot.

Based on the Paris Agreement goals, this study defines full alignment as (1) limiting global warming to at most 2°C, relative to preindustrial levels; (2) achieving net zero emissions in the entire BRE sector by 2050 at the latest; and (3) accounting for all GHG emissions over the WLC of buildings. Using these criteria, a non-binary multi-attribute rating framework was applied to assess the degree of alignment across the reviewed literature.

In the rating, high scores are consistently associated with ambitious temperature targets, WLC scopes, sector-level assessments and explicit net zero carbon goals. Figure 6 illustrates how the combinations of analytical factors considered in the literature relate to overall alignment scores. In contrast, documents with limited scope, narrow scale or less ambitious targets have lower alignment levels. Figure 6 highlights the small subset of documents that fully meet all alignment criteria, underscoring the fragmented nature of current DEs. Notably, most of the analysed literature reflects only partial integration of Paris-compatible criteria, such as ambitious net zero goals with an incomplete scope, or aligned temperature limits with a single-building approach.

Figure 6

Only four documents fully align with the Paris Agreement’s compatibility criteria defined in this study. Despite different scopes and formats (i.e. scientific papers versus policy-oriented reports), these documents share a combination of key characteristics in which they frame their DEs in alignment with the Paris Agreement by explicitly addressing a 1.5°C limit, WLC coverage of GHG emissions, sectoral-level perspectives and clearly defined net zero carbon end goals within mid-century timeframes. These four studies will be described below.

A central reference was the study by Lützkendorf & Frischknecht (2020), which defines and characterises the different balancing mechanisms of net zero. Their typology on terms and definitions informed the construction of the multi-criteria scoring framework applied in the present study. By explicitly defining net balance, offsetting and technical net zero pathways, their work enables the comparability across studies and avoids the ambiguity that characterises much of the earlier literature.

Another fully aligned paper was that of Steininger et al. (2020), which operationalises Paris-aligned climate goals through a top-down carbon budget allocation framework that translates global temperature limits into sectoral and national carbon constraints for the built environment. Their approach explicitly confronts the inconsistencies between sectoral pathways and carbon budgets, revealing systematic overshoots when sectoral ambitions are assessed in isolation. This contribution is particularly important because it highlights the uncertainties related to the scale of assessment and alignment with global targets, which were also considered in the rating framework of the present paper.

Where Steininger et al. (2020) provide a budgetary boundary, Allen et al. (2022) demonstrate feasibility and coherence through dynamic national pathway modelling. Allen et al. also consider a WLC perspective in a single system framework and test whether net zero WLC outcomes are achievable by 2050 under varying ambition levels. Their results show that deep operational decarbonisation alone is insufficient, since embodied residuals become prevalent, reinforcing the need for low-emission materials, biogenic carbon storage and end-of-life management. The present paper aligns with the balancing principles defined by Lützkendorf & Frischknecht (2020) and complements the global budgetary constraints as highlighted by Steininger et al. (2020).

The only policy document that fully aligns with the principles of the Paris Agreement is the Buildings Performance Institute Europe’s (BPIE) life-cycle road map for Germany (BPIE 2023b). It translates prior scientific DEs into an actor-specific, time-bound implementation framework, bridging the gap between science and policy (albeit with a relevant delay, as mentioned previously). Unlike other national strategies that adopt terminologies without transparency, this road map explicitly embeds WLC, sector-wide coverage and step-wise milestones (2025–45). Its alignment is further strengthened by its assessment of its consistency with national carbon-budget discussions in Germany. Furthermore, it explicitly recognises the governance responsibilities across multiple stakeholder groups, exemplifying how Paris-aligned scientific principles can be translated into actionable DEs.

Although they do not directly reference one another, these four documents illustrate the progression of the Paris Agreement-aligned literature over time. Ideally, the broader literature should be able to follow a similar trajectory: from conceptual clarity in terminology and definitions (Lützkendorf & Frischknecht 2020), to budgetary consistency (Steininger et al. 2020), to feasibility assessments (Allen et al. 2022), and finally to policy adoption (BPIE 2023b). Their publication dates indicate a maturation phase in the literature following the Paris Agreement, alongside a growing recognition of embodied emissions within WLC scopes, the development of sectoral carbon budgets and increasing urgency to reach net zero GHG emissions. Earlier studies typically meet one or two of these criteria, but fail to integrate them simultaneously, resulting in lower alignment scores. Notably, a small subset of studies (Koo et al. 2015; Liu et al. 2019b; Pless & Torcellini 2010; Soares et al. 2017) mentions highly ambitious target years (i.e. 2020–25), yet remains operationally focused on or limited to individual buildings; despite their apparent ambition, such approaches do not meet Paris Agreement compatibility due to incomplete life-cycle scope and insufficient scaling, and an assessment of their feasibility lies outside the scope of this paper.

Despite these aligned examples, the majority of reviewed documents fall short of full Paris compatibility due to ambiguous treatment of temperature-based limits or emission indicators, incomplete life-cycle scopes, limited scales beyond individual buildings, unambitious target years, or outdated decarbonisation goals. While the results indicate meaningful progress since the adoption of the Paris Agreement, they also reveal persistent disparities, delays in policy uptake, and cross-country misalignments that remain highly relevant for implementation and may risk undermining collective progress toward the Agreement’s goals. This is particularly important given the temporal gap between academic publications and their adoption into policy frameworks. The limited number of fully aligned studies underscores a critical gap: although the goals of the Agreement are conceptually defined, DEs in the BRE sector are rarely articulated in a comprehensive, coherent and policy-relevant way. Addressing this gap requires urgent alignment of research with the implementation of science-based principles into policy, while integrating sector-wide pathways and action plans within coherently defined carbon budgets. For a complete list of documents and their alignment rating, see the supplemental data online.