Housing affordability pertains to the capacity of a given household to pay their rent or mortgage in relation to their financial means. Considering the criticism of the concept when viewed as a strict ratio rule between income and housing expenses (Hulchanski, 1995), it may be useful to focus on the relational nature of the concept and as a way to analyze the relationship between different processes. As Whitehead (2007, p. 30) contended, affordability is a composite of three main parameters: (1) housing cost, (2) household income and (3) direct state interventions (or third-actors) playing on the previous two factors, for instance by improving one’s capacity to pay through direct payments or by reducing housing costs through subsidized housing. Considering the current trend towards unaffordability in European cities (Dijkstra and Maseland, 2016, p. 96), the concept is particularly useful to understand the interplay of factors that both favour rising housing costs—through financialization (Aalbers, 2016), gentrification (Lees, Shin and López Morales, 2016), and entrepreneurial urban policies (Harvey, 1989)—with those that enable the stagnation of low- and middle-incomes, namely Neoliberal globalization (Jessop, 2002) the precarization of work and welfare policy reforms (Palier, 2010). The “hard reality” behind one’s home affordability can therefore be construed as the result of a complex interplay between large-scale processes such as those enumerated above, behind which lie the aggregated behaviours of a multitude of actors; from the small landlord to the large investment firm seeking to speculate in global real-estate markets, from the neighborhood association protecting tenants from evictions to national governments investing (or divesting) large sums of money into housing programs. The conceptual strength of affordability lies in its capacity to scrutinize a wide range of complexly interconnected phenomena, which ultimately affect greatly everyone’s quality of life.    

Environmental Retrofit Buildings are responsible for approximately 40% of energy consumption and 36% of carbon emissions in the EU (European Commission, 2021). Environmental retrofit, green retrofit or low carbon retrofits of existing homes ais to upgrade housing infrastructure, increase energy efficiency, reduce carbon emissions, tackle fuel poverty, and improve comfort, convenience and aesthetics (Karvonen, 2013). It is widely acknowledged that environmental retrofit should result in a reduction of carbon emissions by at least 60% in order to stabilise atmospheric carbon concentration and mitigate climate change (Fawcett, 2014; Johnston et al., 2005). Worldwide retrofit schemes such as RetrofitWorks, EnerPHit and the EU’s Renovation Wave, use varying metrics to define low carbon retrofit, but their universally adopted focus has been on end-point performance targets (Fawcett, 2014). This fabric-first approach to retrofit prioritises improvements to the building fabric through: increased thermal insulation and airtightness; improving the efficiency of systems such as heating, lighting and electrical appliances; and the installation of renewables such as photovoltaics (Institute for Sustainability & UCL Energy Institute, 2012). The whole-house systems approach to retrofit further considers the interaction between the occupant, the building site, climate, and other elements or components of a building (Institute for Sustainability & UCL Energy Institute, 2012). In this way, the building becomes an energy system with interdependent parts that strongly affect one another, and energy performance is considered a result of the whole system activity. Economic Retrofit From an economic perspective, retrofit costs are one-off expenses that negatively impact homeowners and landlords, but reduce energy costs for occupants over the long run. Investment in housing retrofit, ultimately a form of asset enhancing, produces an energy premium attached to the property. In the case of the rental market, retrofit expenses create a split incentive whereby the landlord incurs the costs but the energy savings are enjoyed by the tenant (Fuerst et al., 2020). The existence of energy premiums has been widely researched across various housing markets following Rosen’s hedonic pricing model. In the UK, the findings of Fuerst et al. (2015) showed the positive effect of energy efficiency over price among home-buyers, with a price increase of about 5% for dwellings rated A/B compared to those rated D. Cerin et al. (2014) offered similar results for Sweden. In the Netherlands, Brounen and Kok (2011), also identified a 3.7% premium for dwellings with A, B or C ratings using a similar technique. Property premiums offer landlords and owners the possibility to capitalise on their  retrofit investment through rent increases or the sale of the property. While property premiums are a way to reconcile          split incentives between landlord and renter, value increases pose questions about long-term affordability of retrofitted units, particularly, as real an expected energy savings post-retrofit have been challenging to reconcile (van den Brom et al., 2019). Social Retrofit A socio-technical approach to retrofit elaborates on the importance of the occupant. To meet the current needs of inhabitants, retrofit must be socially contextualized and comprehended as a result of cultural practices, collective evolution of know-how, regulations, institutionalized procedures, social norms, technologies and products (Bartiaux et al., 2014). This perspective argues that housing is not a technical construction that can be improved in an economically profitable manner without acknowledging that it’s an entity intertwined in people’s lives, in which social and personal meaning are embedded. Consequently, energy efficiency and carbon reduction cannot be seen as a merely technical issue. We should understand and consider the relationship that people have developed in their dwellings, through their everyday routines and habits and their long-term domestic activities (Tjørring & Gausset, 2018). Retrofit strategies and initiatives tend to adhere to a ‘rational choice’ consultation model that encourages individuals to reduce their energy consumption by focusing on the economic savings and environmental benefits through incentive programs, voluntary action and market mechanisms (Karvonen, 2013). This is often criticized as an insufficient and individualist approach, which fails to achieve more widespread systemic changes needed to address the environmental and social challenges of our times (Maller et al., 2012). However, it is important to acknowledge the housing stock as a cultural asset that is embedded in the fabric of everyday lifestyles, communities, and livelihoods (Ravetz, 2008). The rational choice perspective does not consider the different ways that occupants inhabit their homes, how they perceive their consumption, in what ways they interact with the built environment, for what reasons they want to retrofit their houses and which ways make more sense for them, concerning the local context. A community-based approach to domestic retrofit emphasizes the importance of a recursive learning process among experts and occupants to facilitate the co-evolution of the built environment and the communities (Karvonen, 2013). Involving the occupants in the retrofit process and understanding them as “carriers” of social norms, of established routines and know-how, new forms of intervention  can emerge that are experimental, flexible and customized to particular locales (Bartiaux et al., 2014). There is an understanding that reconfiguring socio-technical systems on a broad scale will require the participation of occupants to foment empowerment, ownership, and the collective control of the domestic retrofit (Moloney et al., 2010).

Buildings are responsible for approximately 40% of energy consumption and 36% of greenhouse gas emissions in the EU (European Commission, 2021). Energy retrofit is also referred to as building energy retrofit, low carbon retrofit, energy efficiency retrofit and energy renovation; all terms related to the upgrading of existing buildings energy performance to achieve high levels of energy efficiency. Energy retrofit significantly reduces energy use and energy demand (Femenías et al., 2018; Outcault et al., 2022), tackles fuel (energy) poverty, and lowers carbon emissions (Karvonen, 2013). It is widely acknowledged that building energy retrofit should result in a reduction of carbon emissions by at least 60% compared with pre-retrofit emissions, in order to stabilise atmospheric carbon concentration and mitigate climate change (Fawcett, 2014; Outcault et al., 2022). Energy retrofit can also improve comfort, convenience, and aesthetics (Karvonen, 2013). There are two main approaches to deep energy retrofit, fabric-first and whole-house systems. The fabric-first approach prioritises upgrades to the building envelope through four main technical improvements: increased airtightness; increased thermal insulation; improving the efficiency of systems such as heating, lighting, and electrical appliances; and installation of renewables such as photovoltaics (Institute for Sustainability & UCL Energy Institute, 2012). The whole-house systems approach to retrofit further considers the interaction between the climate, building site, occupant, and other components of a building (Institute for Sustainability & UCL Energy Institute, 2012). In this way, the building becomes an energy system with interdependent parts that strongly affect one another, and energy performance is considered a result of the whole system activity. Energy retrofit can be deep, over-time, or partial (Femenías et al., 2018). Deep energy retrofit is considered a onetime event that utilises all available energy saving technologies at that time to reduce energy consumption by 60% - 90% (Fawcett, 2014; Femenías et al., 2018). Over-time retrofit spreads the deep retrofit process out over a strategic period of time, allowing for the integration of future technologies (Femenías et al., 2018). Partial retrofit can also involve several interventions over time but is particularly appropriate to protect architectural works with a high cultural value, retrofitting with the least-invasive energy efficiency measures (Femenías et al., 2018). Energy retrofit of existing social housing tends to be driven by cost, use of eco-friendly products, and energy savings (Sojkova et al., 2019). Energy savings are particularly important in colder climates where households require greater energy loads for space heating and thermal comfort and are therefore at risk of fuel poverty (Sojkova et al., 2019; Zahiri & Elsharkawy, 2018). Similarly, extremely warm climates requiring high energy loads for air conditioning in the summer can contribute to fuel poverty and will benefit from energy retrofit (Tabata & Tsai, 2020). Femenías et al’s (2018) extensive literature review on property owners’ attitudes to energy efficiency argues that retrofit is typically motivated by other needs, referred to by Outcault et al (2022) as ‘non-energy impacts’ (NEIs). While lists of NEIs are inconsistent in the literature, categories related to “weatherization retrofit” refer to comfort, health, safety, and indoor air quality (Outcault et al., 2022). Worldwide retrofit schemes such as RetrofitWorks and EnerPHit use varying metrics to define low carbon retrofit, but their universally adopted focus has been on end-point performance targets, which do not include changes to energy using behaviour and practice (Fawcett, 2014). An example of an end-point performance target is Passivhaus’ refurbishment standard (EnerPHit), which requires a heating demand below 25 kWh/(m²a) in cool-temperate climate zones; zones are categorised according to the Passive House Planning Package (PHPP) (Passive House Institute, 2016).  

Improving indoor thermal comfort is a widely agreed motivate for housing retrofit (Femenías et al., 2018; Outcault et al., 2022; Sojkova et al., 2019; Zahiri & Elsharkawy, 2018). Low carbon retrofit of existing social housing tends to be driven by cost, the use of eco-friendly products, and energy savings (Sojkova et al., 2019). Energy savings are particularly important in colder climates where households require larger energy loads for space heating and thermal comfort and are therefore at greater risk of fuel (energy) poverty (Sojkova et al., 2019; Zahiri & Elsharkawy, 2018). Femenías et al.’s (2018) extensive literature review on property owners’ attitudes to energy efficiency argues that renovations are typically motivated by other needs, referred to by Outcault et al (2022) as ‘non-energy impacts’ (NEIs). While lists of NEIs are inconsistent in the literature, categories related to “weatherization retrofit” (Outcault et al., 2022, p.3) refer to comfort, modernity, health, safety, education, and better indoor air quality (Amann, 2006; Bergman & Foxon, 2020; Broers et al., 2022; Outcault et al., 2022). In poorly maintained social housing, however, the desire to improve indoor air quality and thermal comfort will have an impact on energy consumption. Occupants will, for example, use extra heating to feel comfortable in a damp, mouldy, or cold home. (Zahiri & Elsharkawy, 2018).   There are three main technical improvements to low carbon retrofit: (1) enhancing the building fabrics thermal properties; (2) improving systems efficiency; and (3) renewable energy integration (Institute for Sustainability & UCL Energy Institute, 2012). In order for the Passivehaus Institut’s EnerPHit Retrofit Plan to meet Passivhaus standards for indoor air quality, homes must achieve high levels of air tightness complemented by a mechanical ventilation system including heat recovery (MVHR). Specifically, “airtightness of a building must achieve an air change per hour rate of less than 0.6 at 50 Pa of pressure (n50), and have ventilation provided by either a balanced mechanical heat recovery ventilation or demand-controlled ventilation systems” (McCarron et al., 2019, p.297). This airtightness concept is revered for saving energy, avoiding structural damage, and contributing to thermal comfort (Bastian et al., 2022) while requiring no natural ventilation such as open windows. Mechanical HVAC units alter indoor air temperature, air movement, ventilation, noise levels, and humidity (Outcault et al., 2022). But despite known benefits to physical health and clean air, this may not lead to optimum user-comfort. This is because social housing residents have unique housing needs that differ from homeowners (Sunikka-Blank et al., 2018) and cannot be predicted without resident engagement, as residents are experts in the way they live and use their homes (Boess, 2022; Gianfrate et al., 2017; Walker et al., 2014).   Post Occupancy Evaluation after retrofit has found that social housing residents are often unfamiliar with mechanical systems and their sustainable benefits, especially when retrofit occurs without resident input (Garnier et al., 2020). This can lead to misuse, overheating, the prebound effect, and the rebound effect where affordable energy bills lead to excessive heating—at times 25-26°C (Zoonnekindt, 2019)—contributing to performance gaps as high as five times the predicted energy consumption (Traynor, 2019). Other households considered mechanical systems to be bulky, ugly, and noisy, prompting removal, lack of use, and at times emotional distress (Lowe et al., 2018). DREEAM’s Berlin pilot site found one household blocking mechanical ventilation with tissue paper because they considered the air too cold and residents “haven’t been informed about the positive impact of a well working ventilation on their health and on the energy efficiency of the heating in their apartment” (Zoonnekindt, 2019). DREEAM continued the project with Green Neighbours (Zoonnekindt, 2019), an innovative engagement program co-designed with and for residents to better inform mechanical systems usage. However, literature shows (Boess, 2022; Gianfrate et al., 2017; Walker et al., 2014) that informing residents on how to use mechanical systems is unlikely to change use-habits or adequately combat performance gaps. In order to change residents’ energy behaviours, resident stakeholders should be integrated in retrofit decision-making.

Window guidance is a credit policy allowing central banks to steer bank lending toward certain economic activities. In the post-war period, it was common for both developed and emerging economies to employ various forms of credit control and allocation. However, these policies were virtually discontinued by the 1980s and the mandate of the central banks was reduced to controlling inflation through interest rates. Housing affordability and sustainability are strongly interlinked with monetary policies, particularly because housing prices and supply rely on debt for financing (Muellbauer, 2018). This link is embodied in inflation-adapted interest rates, which are used by central banks to “cool down” the economy and control prices. Currently, high inflation has pushed central banks all over the world to increase interest rates. Increases in interest rates impact the interbank lending rates such as the Euribor or the Libor and ultimately affect the price of credit in an economy. This then influences in particular capital-intensive industries such as housing development and renovation. Social housing organisations (SHOs) which provide social -thus affordable- rental housing, particularly in North-Western Europe, are dependent on credit to finance not only the provision of housing, but also the energy-efficient renovation of their stock. The rise in interest rates resulting from central banks’ monetary policy aimed at curbing inflation puts the financial viability of renovation and new construction in jeopardy. This insight is not new, as the dependence on credit for renovation and maintenance was already foreseen as an issue in the late 90s by the British housing economist Christine Whitehead (1999). Traditionally, governments support social housing providers through grants, subsidies and through the guaranteeing of their debt (Lawson, 2013). For example, publicly owned social housing providers in Germany have their debt rated equally to that of their main owners: municipalities and regions. As a result, their financing costs also benefit from a high rating implying low-interest rates for their debt. This is also the case in France and the Netherlands where ultimately it is public institutions that guarantee SHO debt. For instance, a Dutch social housing provider raises debt at a triple AAA rating, that of the Dutch state. This lowers their interest costs in comparison to that of other companies which may be rated lower, hence have a higher risk premium and pay more for their debt (Fernández et al., forthcoming). In an inflationary environment, where interest rates rise across the board, this means higher financing costs for SHOs despite their risk premium remaining constant. Window guidance is relevant in this context because it would allow central banks to set a lower interest rate for lending to certain activities, thus creating a window. During the period between 1945-1980, advanced and emerging economies alike implemented interventions on credit and capital markets. Central banks would align lending with industries, exports and manufacturing while increasing interest rates for less desirable sectors (Bezemer et al., 2023; Hodgman, 1973). According to Bezemer et al., (2023) based on Hodgman (1973) and Goodhart (1989 pp. 156–158), ‘credit guidance’, ‘credit controls’, ‘credit ceilings’, ‘directed credit’, and ‘moral suasion’ are also common names for these types of policy. More recently, organisations such as Positive Money have been advocating for a sovereign money proposal where banks would obtain funds from their national central bank with limitations on their usage (Youel, 2022). This enhanced control over bank lending opens up the possibility of earmarking private capital for investment in decarbonisation activities. For example, lending for speculative purposes or for highly polluting activities could be curtailed while the financial viability of environmentally friendly activities could be expanded. Ultimately, credit controls offer the possibility to guide credit toward the provision of affordable and sustainable housing and away from sectors such as fossil fuels or speculative bubbles.  

The performance gap in retrofit refers to the disparity between the predicted and actual energy consumption after a retrofit project, measured in kWh/m2/year. This discrepancy can be substantial, occasionally reaching up to five times the projected energy usage (Traynor, 2019). Sunikka-Blank & Galvin (2012) identify four key factors as contributing to the performance gap: (1) the rebound effect, (2) the prebound effect, (3) interactions of occupants with building components, and (4) the uncertainty of building performance simulation outcomes. Gupta & Gregg (2015) additionally identify elevated building air-permeability rates as a factor leading to imbalanced and insufficient extract flowrates, exacerbating the performance gap. While post occupancy evaluation of EnerPhit—the Passivhaus Institut certification for retrofit—has shown far better building performance in line with predictions, the human impact of building users operating the building inefficiently will always lead to some sort of performance gap (Traynor, 2019, p. 34). Deeper understanding of the prebound effect and the rebound effect can improve energy predictions and aid in policy-making (Galvin & Sunikka-Blank, 2016). Therefore, the ‘prebound effect’ and the ‘rebound effect’, outlined below, are the most widely researched contributors to the energy performance gaps in deep energy retrofit.   Prebound Effect The prebound effect manifests when the actual energy consumption of a dwelling falls below the levels predicted from energy rating certifications such as energy performance certificates (EPC) or energy performance ratings (EPR). According to Beagon et al. (2018, p.244), the prebound effect typically stems from “occupant self-rationing of energy and increases in homes of inferior energy ratings—the type of homes more likely to be rented.” Studies show that the prebound effect can result in significantly lower energy savings post-retrofit than predicted and designed to achieve (Beagon et al., 2018; Gupta & Gregg, 2015; Sunikka-Blank & Galvin, 2012). Sunikka-Blank & Galvin’s (2012) study compared the calculated space and water heating energy consumption (EPR) with the actual measured consumption of 3,400 German dwellings and corroborated similar findings of the prebound effect in the Netherlands, Belgium, France, and the UK. Noteworthy observations from this research include: (1) substantial variation in space heating energy consumption among dwellings with identical EPR values; (2) measured consumption averaging around 30% lower than EPR predictions; (3) a growing disparity between actual and predicted performance as EPR values rise, reaching approximately 17% for dwellings with an EPR of 150 kWh/m²a to about 60% for those with an EPR of 500 kWh/m²a (Sunikka-Blank & Galvin, 2012); and (4) a reverse trend occurring for dwellings with an EPR below 100 kWh/m²a, where occupants consume more energy than initially calculated in the EPR, referred to as the rebound effect. Galvin & Sunikka-Blank (2016) identify that a combination of high prebound effect and low income is a clear indicator of fuel poverty, and suggest this metric be utilised to target retrofit policy initiatives.   Rebound Effect The rebound effect materializes when energy-efficient buildings consume more energy than predicted. Occupants perceive less guilt associated with their energy consumption and use electrical equipment and heating systems more liberally post-retrofit, thereby diminishing the anticipated energy savings (Zoonnekindt, 2019). Santangelo & Tondelli (2017) affirm that the rebound effect arises from occupants’ reduced vigilance towards energy-related behaviours, under the presumption that enhanced energy efficiency in buildings automatically decreases consumption, regardless of usage levels and individual behaviours. Galvin (2014) further speculates several factors contributing to the rebound effect, including post-retrofit shifts in user behaviour, difficulties in operating heating controls, inadequacies in retrofit technology, or flawed mathematical models for estimating pre- and post-retrofit theoretical consumption demand. The DREEAM project, funded by the European Union, discovered instances of electrical system misuse in retrofitted homes upon evaluation (Zoonnekindt, 2019). A comprehensive comprehension of the underlying causes of the rebound effect is imperative for effective communication with all retrofit stakeholders and for addressing these issues during the early design stages.   Engaging residents in the retrofit process from the outset can serve as a powerful strategy to mitigate performance gaps. Design-thinking (Boess, 2022), design-driven approaches (Lucchi & Delera, 2020), and user-centred design (Awwal et al., 2022; van Hoof & Boerenfijn, 2018) foster socially inclusive retrofit that considers Equality, Diversity, and Inclusion (EDI). These inclusive approaches can increase usability of technical systems, empower residents to engage with retrofit and interact with energy-saving technology, and enhance residents’ energy use, cultivating sustainable energy practices as habitual behaviours. Consequently, this concerted effort not only narrows the performance gap but simultaneously enhances overall wellbeing and fortifies social sustainability within forging communities.

The in-depth study of energy poverty as a social phenomenon commenced in the late 19th century through the works of British social researchers Booth and Rowntree (O’Connor, 2016). This era was characterised by significant social and economic transformation, and these scholars were troubled by the living conditions and welfare of impoverished urban populations, who were residing in congested and unsanitary environments. Throughout the 20th century, poverty in policy contexts became quite narrowly defined as a lack of income. However, it was another social concern in the UK that led to the development of concepts like ‘fuel poverty’ or ‘energy poverty’ a century after Booth and Rowntree.[i] Following the 1973 oil crisis, the Child Poverty Action Group took the initiative to address how increasing energy costs were affecting low-income households in the UK (Johnson & Rowland, 1976). As essentials like heating, electricity, and fuels became necessary for maintaining a decent standard of living in modern British society, this advocacy group pushed for government financial support. Later, Bradshaw and Hutton (1983) introduced a narrower definition of energy poverty: “the inability to afford adequate heat in the home”. Since then, studies on energy poverty have typically excluded motor fuels, as they fall under transport poverty, a related but separate area of study (Mattioli et al., 2017). Energy poverty, as defined by Bouzarovski and Petrova (2015, p. 33), refers to "the inability to secure or afford sufficient domestic energy services that allow for participation in society." Although the precise boundaries of relevant domestic energy usage are still debated, this definition expands beyond mere heating as it encompasses energy used for cooling, which is particularly relevant in warmer climates (Thomson et al., 2019). Moreover, it enables a socially and culturally dependent understanding of what it means to participate in society (Middlemiss et al., 2019). On 13 September 2023, the European Union (2023) officially defined energy poverty as “a household’s lack of access to essential energy services, where such services provide basic levels and decent standards of living and health, including adequate heating, hot water, cooling, lighting, and energy to power appliances, in the relevant national context, existing national social policy and other relevant national policies, caused by a combination of factors, including at least non-affordability, insufficient disposable income, high energy expenditure and poor energy efficiency of homes”. The doctoral thesis and subsequent book by Brenda Boardman, Fuel Poverty: From Cold Homes to Affordable Warmth (1991), marked a significant breakthrough in energy poverty research. She emphasised the detrimental impact of energy-inefficient housing on health and quality of life. In the decades that followed, substantial literature confirmed her qualitative findings (Thomson et al., 2017). Notably, studies have demonstrated the adverse effects of living in energy poverty on physical health (Liddell & Morris, 2010), mental health (Liddell & Guiney, 2015), stress levels (Longhurst & Hargreaves, 2019), social isolation (Harrington et al., 2005), and absenteeism (Howden-Chapman et al., 2007). Boardman’s work introduced an indicator that has remained influential to this date, although it was not the first attempt to operationalise the concept of fuel poverty (Isherwood & Hancock, 1979). Her ‘2M’ indicator categorises a household as energy poor if it needs to allocate twice the median share of its budget for energy expenses to heat its home adequately. Boardman calculated this threshold to be 10% at that time. Due to its simplicity and ease of comprehension, many governments directly adopted this 10% threshold without considering specific contextual circumstances. Since the early nineties, numerous attempts have been made to develop alternative indicators. Highly influential ones include ‘Low Income High Cost’ (LIHC) by John Hills (2012), ‘Low Income Low Energy Efficiency’ (LILEE) that subsequently became the official British indicator (BEIS, 2022), and a 'hidden' energy poverty indicator by (Meyer et al., 2018). Critiques of these indicators focus, amongst other things, on their simplicity and perceived 'technocratic' approach (Croon et al., 2023; Middlemiss, 2017). This marked the beginning of significant government commitment, initially in the UK and later in other countries to address energy poverty. Although certain forms of cold weather payments had already been introduced by the UK's Conservative administrations, it was under the successive governments of Blair and Brown, following the publication of Boardman's work, that programmes such as the Winter Fuel Payment and Warm Home Discount were implemented (Koh et al., 2012). The UK examples highlight bipartisan support for addressing energy poverty, with both the Conservatives and Labour backing these efforts. This policy objective has also gained momentum in various legislative contexts, leading the EU to incorporate energy poverty alleviation as a fundamental pillar of the European Green Deal and a specific goal of its landmark Social Climate Fund (European Commission, 2021). Over the last three decades, public interest in energy poverty as a 'wicked' problem has surged, particularly during the recent energy crisis. This crisis began in 2021 when energy markets tightened due to a post-pandemic economic rebound, and it worsened dramatically after Russia's invasion of Ukraine in February 2022 (IEA, 2023). Extensive research on the impact of this price surge on energy poverty levels has been carried out throughout Europe and globally (Guan et al., 2023; Simshauser, 2023). Consequently, energy poverty has become a significant focal point in discussions related to the 'just transition,' especially within the realm of energy justice, as it serves as a valuable concept for targeting policies towards a specific vulnerable group in this context (Carrosio & De Vidovich, 2023).     [i] ‘Fuel poverty' and 'energy poverty' are used interchangeably, with the former being more common in the UK and the latter in mainland Europe (Bouzarovski & Petrova, 2015). Previously, scholars in the UK used 'energy poverty' to denote a lack of access to energy and 'fuel poverty' when affordability was the concern (Li et al., 2014). However, this distinction is no longer maintained.

Decarbonisation, a term which echoes through the corridors of academia, politics, practical applications, and stands at the forefront of contemporary discussions on sustainability. Intricately intertwined with concepts such as net-zero and climate neutrality, it represents a pivotal shift in our approach to environmental sustainability. In its essence, decarbonisation signifies the systematic reduction of carbon dioxide intensity, a crucial endeavour in the battle against climate change (Zachmann et al., 2021). This overview delves into the multifaceted concept of decarbonisation within the context of the European Union. Beginning with a broad perspective, we examine its implications at the macro level before homing in on the complexities of decarbonisation within the realm of building structures. Finally, we explore the literature insights, presenting key strategies that pave the way toward achieving a decarbonised building sector. From a broad perspective, decarbonisation is an overarching concept that aims to achieve climate neutrality (Zachmann et al., 2021, p.13). Climate neutrality means achieving a state of equilibrium between greenhouse gas emissions and their removal from the atmosphere, preventing any net increase in atmospheric CO2 concentration (IEA, 2022). From an energy decarbonisation perspective, however, in a document provided by the Economic, Scientific and Quality of Life Policy Department at the request of the Industry, Research and Energy (ITRE) Committee, Zachmann et al. (2021) explain that energy systems require a fundamental shift in the way societies provide, transport and consume energy (Zachmann et al., 2021). In the construct of decarbonisation, as outlined by the Intergovernmental Panel on Climate Change (IPCC), the focus lies on strategic directives aimed at reducing the carbon content of energy sources, fuels, products and services (Arvizu et al., 2011; Edenhofer et al., 2011). This complex process involves the transition from carbon-intensive behaviours, such as fossil fuel use, to low-carbon or carbon-neutral alternatives. The main goal of decarbonisation, therefore, is to reduce emissions of greenhouse gases such as CO2 and methane, which are closely linked to the growing threats of climate change (Edenhofer et al., 2011). Hoeller et al. (2023) explain that decarbonisation efforts within the Organisation for Economic Co-operation and Development (OECD) focus on harmonising economic growth, energy production and consumption with climate objectives to mitigate the adverse effects of climate change while promoting sustainable development (Hoeller et al., 2023). From a pragmatic perspective, however, according to the OECD Policy Paper 31: A framework to decarbonise the economy, published in 2022,  progress on economic decarbonisation remains suboptimal. This raises the urgent need for a multi-dimensional framework that is not only cost-effective but also inclusive and comprehensive in its strategy for decarbonisation (D’Arcangelo et al., 2022). D’Arcangelo et al. (2023) add that such framework should include several steps such as setting clear climate targets, measuring progress and identifying areas for action, delineating policy frameworks, mapping existing policies, creating enabling conditions, facilitating a smooth transition for individuals, and actively engaging the public. From an academic perspective, Weller and Tierney (2018) provide an explanation of decarbonisation, defining it as a twofold concept. Firstly, it involves reducing the intensity of fossil fuel use for energy production. Secondly, it emphasises the role of policy in mitigating the negative externalities associated with such use. They argue that decarbonisation is a politically charged policy area that needs to be 'just', while also serving a means to revitalise local economies (Weller & Tierney, 2018). Kyriacou and Burke (2020) expand on this definition, highlighting decarbonisation as the transition from a high-carbon to a low-carbon energy system. This transition is driven by the need to mitigate climate change without compromising energy security. Boute (2021), on the other hand, emphasises the long-term structural reduction of CO2 emissions as the core strategy of decarbonisation. Boute adds that the effectiveness of decarbonisation must be measured in terms of a unit of energy consumed across all activities. In the economic context, the Oxford Institute for Energy Studies concludes that decarbonisation aims to reduce the carbon intensity of an economy. This reduction is quantified as the ratio of CO2 emissions to gross domestic product (Henderson & Sen, 2021). Addressing methodological concerns, Buettner (2022) added that decarbonisation is often misused as a generic term. Moreover, Buettner highlights the diverse levels at which decarbonisation occurs, ranging from carbon neutrality (focused on reducing CO2 emissions), to climate neutrality (aiming to reduce CO2, non-fluorinated greenhouse gases, and fluorinated greenhouse gases) and, finally, to environmental neutrality (which reduces all substances negatively impacting the environment and health) (Buettner, 2022). The debate on the decarbonisation of the construction sector revolves around similar issues. The report on Decarbonising Buildings in Cities and Regions, published by the OECD in 2022, defines the concept as reducing energy consumption by improving envelope insulation, installing high performance equipment, and scaling up the use of renewable sources to meet the energy demands (OECD, P24). Another definition comes from a working paper by the OECD Economics Department, Hoeller et al. (2023) contend, it is necessary to consider direct emissions from household fossil fuel combustion and indirect emissions from the generation of electricity and district heating used by households (Hoeller et al., 2023). The comprehensive study “Decarbonising Buildings” published by the Climate Action Tracker (CAT) in 2022, defines the term as transforming the building sector to achieve net zero emissions by 2050. Achieving this goal requires various technological solutions and behavioural changes to decarbonise heating and cooling, such as energy-efficient building envelopes, heat pumps and on-site renewables (CAT, 2022). Gratiot et al. (2023) consider decarbonisation as the process of reducing or eliminating CO2 emissions that contribute to climate change from a building’s energy sources. This involves systematically shifting buildings from carbon-intensive energy sources (e.g., gas, oil and coal) to low-carbon or carbon-neutral alternatives (e.g., solar, wind and geothermal). This process includes improving the energy efficiency of buildings through better insulation, lighting and appliances (Gratiot et al., 2023). Blanco et al. (2021) consider the decarbonisation of buildings and operation of buildings. This includes enhancing the energy efficiency of buildings and minimizing embodied carbon from building materials and construction activities of greenhouse gas emissions from the construction and operation of buildings. Achieving a decarbonised building sector is a multifaceted endeavour that demands extensive efforts in several key areas, such as energy sources, building envelope, building policy and transformation funds. The objective of the energy transition is to shift from reliance on fossil fuels to clean or renewable energy sources, primarily used for heating and cooling, such as heat pumps, district heating, hydrogen (Jones, 2021). Decarbonising the building envelope, on the other hand, involves improving the energy efficiency of buildings through better insulation, lighting and appliances. It also necessitates minimising embodied carbon from building materials and construction activities (CAT, 2022; D’Arcangelo et al., 2022). Incorporating effective policies into building construction is crucial. This includes adopting of performance standards and building codes that regulate the energy use and emissions of both new and existing buildings. These regulations directly impact the extent and pace of decarbonisation (CAT, 2022; Jones, 2021). Additionally, it is essential to establish a clear vision and climate targets for the buildings sector and operationalise them with a comprehensive policy mix that encompass emissions pricing, standards, regulations and complementary measures (Jones, 2021). The most significant challenge lies in financing the transition to a decarbonised sector. Therefore, it is imperative to mobilise finance on a large scale and collaborate with industry stakeholders. This collaboration is vital to facilitate the transition, overcome barriers, and manage the costs associated with deploying low- or zero-carbon technologies (D’Arcangelo et al., 2022). In summary, the overarching concept of decarbonisation primarily targets the reduction of carbon dioxide in economic and industrial activities, with a focus on energy production and distribution systems. At the building level, the emphasis lies in integrating low-carbon or carbon-neutral systems to minimise both direct and indirect emissions. Nevertheless, the literature examined indicates that other societal aspects, including social and behavioural factors, have not been thoroughly researched. This gap in knowledge could challenge the realisation of the goal of carbon neutrality by 2050 and underscores the need for further studies in these areas.