Justice theory is as old as philosophical thought itself, but the contemporary debate often departs from the Rawlsian understanding of justice (Velasquez, Andre, Shanks, & Meyer, 1990). Rawls (1971) argued that societal harmony depends on the extent to which community members believe their political institutions treat them justly. His First Principle of ‘justice as fairness’ relates to equal provision of ‘basic liberties’ to the population. His Second Principle, later referred to as the ‘Difference Principle’, comprises unequal distribution of social and economic goods to the extent that it benefits “the least advantaged” (Rawls, 1971, p. 266).1[1] As this notion added an egalitarian perspective to Rawlsian justice theory, it turned out to be the most controversial element of his work (Estlund, 1996). The idea of a ‘just transition’ was built on these foundations by McCauley and Heffron (2018), who developed an integrated framework overarching the ‘environmental justice’, ‘climate justice’ and ‘energy justice’ scholarships. The term was first used by trade unions warning for mass redundancies in carbon-intensive industries due to climate policies (Hennebert & Bourque, 2011), but has acquired numerous interpretations since. This is because the major transition of the 21st century, the shift towards a low-carbon society, will be accompanied by large disturbances in the existing social order. In this context, a just transition would ensure equity and justice for those whose livelihoods are most affected (Newell & Mulvaney, 2013). A just transition implies that the ‘least advantaged’ in society are seen, heard, and compensated, which corresponds with three key dimensions conceptualised by Schlosberg (2004): distributive, recognitional, and procedural justice. Distributive justice corresponds with Rawls’ Difference Principle and comprehends the just allocation of burdens and benefits among stakeholders, ranging from money to risks to capabilities. Recognitional justice is both a condition of justice, as distributive injustice mainly emanates from lacking recognition of different starting positions, as well as a stand-alone component of justice, which includes culturally or symbolically rooted patterns of inequity in representation, interpretation, and communication (Young, 1990). Fraser (1997) stressed the distinction between three forms: cultural domination, nonrecognition (or ‘invisibility’), and disrespect (or ‘stereotyping’). Procedural justice emphasises the importance of engaging various stakeholders – especially the ‘least advantaged’ – in governance, as diversity of perspectives allows for equitable policymaking. Three elements are at the core of this procedural justice (Gillard, Snell, & Bevan, 2017): easily accessible processes, transparent decision-making with possibilities to contest and complete impartiality. A critique of the just transition discourse is that it preserves an underlying capitalist structure of power imbalance and inequality. Bouzarovski (2022) points to the extensive top- down nature of retrofit programmes such as the Green New Deal, and notes that this may collide with bottom-up forms of housing repair and material intervention. A consensus on the just transition mechanism without debate on its implementation could perpetuate the status quo, and thus neglect ‘diverse knowledges’, ‘plural pathways’ and the ‘inherently political nature of transformations’ (Scoones et al., 2020). However, as Healy and Barry (2017) note, understanding how just transition principles work in practice could benefit the act of ‘equality- proofing’ and ‘democracy-proofing’ decarbonisation decisions. Essentially, an ‘unjust transition’ in the context of affordable and sustainable housing would refer to low-income households in poorly insulated housing without the means or the autonomy to substantially improve energy efficiency. If fossil fuel prices – either by market forces or regulatory incentives – go up, it aggravates their already difficult financial situation and could even lead to severe health problems (Santamouris et al., 2014). At the same time, grants for renovations and home improvements are poorly targeted and often end up in the hands of higher income ‘free-riding’ households, having regressive distributional impacts across Europe (Schleich, 2019). But even when the strive towards a just transition is omnipresent, practice will come with dilemmas. Von Platten, Mangold, and Mjörnell (2020) argue for instance that while prioritising energy efficiency improvements among low-income households is a commendable policy objective, putting them on ‘the frontline’ of retrofit experiments may also burden them with start-up problems and economic risks. These challenges only accentuate that shaping a just transition is not an easy task. Therefore, both researchers and policymakers need to enhance their understanding of the social consequences that the transition towards low-carbon housing encompasses. Walker and Day (2012) applied Schlosberg’s dimensions to this context. They conclude that distributive injustice relates to inequality in terms of income, housing and pricing, recognitional justice to unidentified energy needs and vulnerabilities, and procedural injustice to inadequate access to policymaking. Ensuring that the European Renovation Wave is made into a just transition towards affordable and sustainable housing therefore requires an in-depth study into distributive, recognitional and procedural justice. Only then can those intertwining dimensions be addressed in policies.   [1] To illustrate his thesis, he introduces the ‘veil of ignorance’: what if we may redefine the social scheme, but without knowing our own place? Rawls believes that most people, whether from self-interest or not, would envision a society with political rights for all and limited economic and social inequality.  

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.

Social value (SV) is a wide-ranging concept that encompasses the wider economic, social and environmental well-being impacts of a specific activity. Given its applicability across various sectors, diverse interpretations and definitions exist, often leading to its interchangeable use with other terms, such as social impact. This interchangeability makes it difficult to establish a universally accepted definition that satisfies all stakeholders, contributing to the term’s adaptability and to a variety of methods for identification, monitoring, measurement and demonstration. Nevertheless, common themes emerge from literature definitions. First, SV involves maximizing benefits for communities and society beyond an organisation's primary goals, which requires innovation and a focus that goes beyond financial values. It is often referred to as the added value of an intervention. Second, the short-, medium- and long-term effects of activities, as well as their broader community reach, need to be assessed in terms of a life-cycle project perspective. Thirdly, SV aligns with the triple bottom line of sustainability, which underlines social, environmental and economic considerations in well-being. In the UK, SV gained prominence with the introduction of the Public Services (Social Value) Act 2012. This legislation mandates organisations commissioning public services to consider and account for the wider impacts of their operations (UK Government 2012; UKGBC, 2020, 2021). The Act has provided incentives to quantitatively measure the impact of projects on communities and standardise approaches in the built environment, a sector that has been significantly influenced by this regulatory framework. Organisations such as the UK Green Building Council (UKGBC) have played a crucial role in shaping a common agenda through reports such as Delivering Social Value: Measurement (2020) and Framework for Defining Social Value (2021), which set out the steps needed to determine social value. Recognising that SV is strongly influenced by contextual factors, these publications emphasize the challenge for formulating an all-encompassing definition. Instead, they advocate for focusing efforts on developing context-specific steps and methods for measurement.     However, the existing literature is mainly concerned with SV during the procurement and construction phases, overlooking the SV of buildings during the use phase and the potential opportunities and benefits they offer to users. This bias is due to the construction sector's rapid response to the Act and its easier access to certain types of information. This influences the prominence of certain data in project’s impact assessments and SV reports, such as employment opportunities, training, placements, and support of local supply chains through procurement. More intangible outcomes such as community cohesion, quality of life improvements, enhanced social capital, cultural preservation, empowerment and long-term social benefits are rarely featured as they are deemed more challenging to quantify due to their subjective or qualitative nature. Similarly, there remains a lack of clarity and consensus regarding a standardised approach to assessing the added value created. The challenge stems from diverse interpretations of value among stakeholders, influenced by their unique interests and activities. Communicating something inherently subjective becomes particularly daunting due to these varying perspectives. Additionally, translating all outcomes into financial metrics is also problematic. This is primarily due to the unique circumstances that characterise each development and community, making it impractical to hastily establish targets and universal benchmarks for their assessment. (Raiden et al., 2018; Raiden & King, 2021a, 2023). This complexity is recognised by Social Value UK (2023: n.p.), stating: “Social value is a broader understanding of value. It moves beyond using money as the main indicator of value, instead putting the emphasis on engaging people to understand the impact of decisions on their lives.” Moreover, the growing significance and momentum that SV is gaining are evident in the emergence of analogous legislations that have appeared in recent years and that have a direct influence on shaping how the built environment sector operates in their respective countries. Noteworthy examples of social value-related regulations include the Well-being of Future Generations Act 2015 in Wales; the Procurement Reform Act 2014 in Scotland; the social procurement frameworks in Australia; the Community Benefit Agreements in Canada; the Government Procurement Rules in New Zealand; and the Environmental, Social, and Governance (ESG) criteria considered in various countries around the world, among others.   Identifying and measuring social value SV should be an integral aspect of project development and, therefore, must be considered from the early stages of its conception, taking into account the entire lifecycle. The literature highlights a three-step process for this: 1) identifying stakeholders, 2) understanding their interests, and 3) agreeing on intended outcomes (UKGBC 2020, 2021). More recently, Raiden & King (2021b) linked the creation of SV to the achievement of the United Nations Sustainable Development Goals (SDGs). In the context of the built environment, SV can contribute to reporting on the SDGs, elevating the value the sector creates to society onto the international agenda (Caprotti et al., 2017; United Nations, 2017). While SDG 11 “Make cities and human settlements inclusive, safe, resilient and sustainable”, is often placed within the remit of the built environment, SV programmes developed by social housing providers, for example, extend the sector’s impact beyond SDG 11, covering a broader range of areas  (Clarion Housing Group, 2023; Peabody, 2023). This aspect is also echoed in the Royal Institute of British Architects (RIBA) Sustainable Outcomes Guide, which links the SDGs to specific outcomes, including the creation of SV (Clark & HOK, 2019). Over the past decade, various methodologies have been proposed to undertake the intricate task of assessing value beyond financial metrics, drawing inspiration from the work of social enterprises. Among the most prominent and widely adopted by diverse stakeholders in the sector are the Social Return on Investment (SROI), Cost-Benefit Analysis (CBA) — sometimes referred to as SCBA when given the social epithet—, and the well-being valuation approach. (Fujiwara & Campbell, 2011; Trotter et al., 2014; Watson et al., 2016; Watson & Whitley, 2017). The widespread implementation of these approaches can be explained by the development of tools such as the UK Social Value Bank, linked to the well-being valuation method. This tool, used to monetise ‘social impacts’, is endorsed by influential stakeholders in the UK’s housing sector, including HACT (2023), or the Social Value Portal and National TOMs (Themes, Outcomes and Measures) (Social Value Portal 2023). In the measuring of SV, these methodologies unanimously emphasize the importance of avoiding overclaiming or double-counting outcomes and discounting the so-called deadweight, which refers to the value that would have been created anyway if the intervention had not taken place, either through inertia or the actions of other actors. While the development of these approaches to measuring SV is pivotal for advancing the social value agenda, some critics contend that there is an imbalance in presenting easily quantifiable outcomes, such as the number of apprenticeships and jobs created, compared to the long-term impact on the lives of residents and communities affected by projects. This discrepancy arises because these easily quantifiable metrics are relatively simpler to convert into financial estimates. Steve Taylor (2021), in an article for The Developer, pointed out that the methods employed to measure social value, coupled with the excessive attention given to monetisation and assigning financial proxy values to everything, may come at the expense of playing down the bearing of hard-to-measure well-being outcomes: “As long as measurement of social value is forced into the economist’s straightjacket of cost-benefit analysis, such disconnects will persist. The alternative is to ask what outcomes people and communities actually want to see, to incorporate their own experiences and perspectives, increase the weighting of qualitative outcomes and wrap up data in narratives that show, holistically, how the pieces fit together. We loosen the constraints of monetisation by mitigating the fixed sense of value as a noun; switching focus to its role as an active verb – to ‘value’ – measuring what people impacted by changes to their built environment consider important or beneficial.” The process of comprehensively measuring and reporting on SV can be challenging, time-consuming and resource-intensive. It is therefore important that stakeholders truly understand the importance of this endeavour and appreciate the responsibilities it entails. Recently, Raiden and King (2021a, 2023) have highlighted the use of a mixed-methods approach for assessing SV, proposing it as a strategy that can offer a more thorough understanding of the contributions of actors in the field. They argue that an assessment incorporating qualitative methods alongside the already utilized quantitative methods can provide a better picture of the added value created by the sector. These advancements contribute to the overarching goal of showcasing value and tracking the effects of investments and initiatives on people's well-being. Nevertheless, a lingering question persists regarding the feasibility of converting all outcomes into monetary values. Social value in architecture and housing design In the field of architecture, the RIBA, in collaboration with the University of Reading, took a significant step by publishing the Social Value Toolkit for Architecture (Samuel, 2020). This document provides a set of recommendations and examples, emphasizing why architects should consider the SV they create and providing guidance on how to identify and evaluate projects, incorporating techniques such as Post-Occupancy Evaluation. This is a remarkable first step in involving architects in the SV debate and drawing attention to the importance of design and the role of architecture in creating value (Samuel, 2018). More recently, Samuel (2022:76) proposed a definition of SV in housing that places the well-being of residents at the centre of the discussion. Accordingly, SV lies in “fostering positive emotions, whether through connections with nature or offering opportunities for an active lifestyle, connecting people and the environment in appropriate ways, and providing freedom and flexibility to pursue different lifestyles (autonomy).” In this context, it is also relevant to highlight the work of the Quality of Life Foundation (QoLF) & URBED, who published The Quality of Life Framework (URBED, 2021). This evidence-based framework identifies six themes in the built environment crucial for assessing relationships between places and people:  control, health, nature, wonder, movement, and community. More recently, Dissart & Ricaurte (2023) have proposed the capability approach as a more comprehensive conceptual basis for the SV of housing. This approach expands the work of the QoLF, focusing the discussion on the effective freedoms and opportunities that the built environment, specifically housing, offers its inhabitants. It serves as a means to gauge the effectiveness of housing solutions and construe SV.

Financial wellbeing is an emerging concept with valyrious definitions, many of which focus on the financial capabilities of individuals. A household's financial wellbeing encompasses its capacity to comfortably meet current and ongoing financial responsibilities, fostering a sense of security about future obligations while enjoying the ability to make life choices (Aubrey et al., 2022). Riitsalu et al. (2023) describe it as "feeling good about one's personal financial situation and being able to afford a desirable lifestyle both now and in the future" (p.2). Brüggen et al. (2017:229) frame it as "the perception of being able to sustain current and anticipated desired living standards and financial freedom." This perception highlights the robust link of financial wellbeing influencing human wellbeing, which is a combination of "feeling good and functioning well" (Ruggeri et al., 2020:1). Other terminologies are used interchangeably to describe financial wellbeing, including financial health, financial resilience, and financial freedom (Riitsalu et al., 2023).     In the UK, the public health sector cares to raise awareness of financial wellbeing due to its impact on households' health and populations' productivity. On their official website page on Financial Wellbeing, they used the definition by The Money and Pension Service (Gov.UK, 2022: online) as follows:   "Feeling secure and in control of your finances, both now and in the future. It's knowing that you can pay the bills today, can deal with the unexpected, and are on track for a healthy financial future."   These explanations and the terminology used, including "afford" and "sustain," underscore the interconnections between financial wellbeing and the vital components of household life. These components encompass mental health, productivity, and pursuing economic sustainability in the present and future. Therefore, a household's financial wellbeing is pressured by various housing-related factors, including the costs of renting or buying and non-housing costs like utility bills and repairs, all of which can affect the household's income.   The issue of rising housing costs directly undermines financial wellbeing. This trend can be attributed to several factors, including increased construction costs, labour shortages, and rising material prices (Brysch & Czischke, 2021). Furthermore, there is a notable shortage in affordable and social housing supply (Emekci, 2021; Gov.UK, 2022). This scarcity is partly due to decreased public investment in new dwellings (Housing Europe, 2021; OECD, 2020). This issue further burdens low-income households who face high private rental costs and a gradual reduction in housing benefits (Tinson & Clair, 2020).   This issue also leads many households to cut back on essential needs. For instance, interviews with social housing residents in Scotland with low to modest incomes revealed a tendency to prioritize rent payments over other necessities, such as food and heating (Garnham et al., 2022). Similarly, Adabre and Chan (2019), , citing Salvi del Pero et al. (2016), warned that:   "Households who are overburdened by housing cost may cut back on other important needs such as health care and diet. Besides, in the medium term, households may trade-off costs for lower quality housing such as smaller size of rooms and housing in poorer locations which lack better access to education and other social amenities. The latter has often been cited as the cause of residential segregation."   Another financial burden is non-housing costs involving energy costs for heating (AHC, 2019; Stone et al., 2011). According to Lee et al. (2022), this issue persists, contributing to financial strain and even excess winter deaths in the UK. Poor housing quality raises energy bills (AHC, 2019; Lameira et al., 2022). It presents the risk of considering dwellings as affordable due to local authority support focusing on housing costs alone (Granath Hansson & Lundgren, 2019), regardless of its quality impacting energy bills (OECD, 2020). Social housing residents, particularly the ageing population and those living in poverty are at increased risk of fuel poverty (Tu et al., 2022). Fuel poverty occurs when more than 10% of a household's income goes towards energy consumption for heating (Howden-Chapman et al., 2012).   Looking forward, two factors could continue burdening households’ financial wellbeing. One factor is the fluctuating energy prices that are often increasing, such as the case in the UK (Bolton, 2024). Another factor is the impact of climate change, leading to colder winters and the potential for overheating, increasing energy demand during extreme weather conditions, as warned by the Committee of Climate Change in the UK (Holmes et al., 2019).   Non-housing costs associated with extensive housing repairs can also impact household financial wellbeing, which may arise from several factors. For instance, selecting low-quality construction materials, workforce or equipment to reduce construction costs might lead to increased repair costs over time (Emekci, 2021). Hopkin et al. (2017) highlighted a related issue in England, where new housing defects were believed to be partly attributed to the building industry's prioritization of profitability over customer satisfaction. Another factor could be improper periodic maintenance, potentially accelerating the physical deterioration of the dwelling (Kwon et al., 2020). Additionally, dwellings may fall into disrepair due to unresponsive maintenance services from housing providers, and residents may lack the financial means to cover repair costs themselves (Garnham et al., 2022).     Financial wellbeing is closely tied to household income. Low-income households are particularly vulnerable to being burdened by rising housing costs (Housing Europe, 2021; OECD, 2020), leading to financial insecurity (Hick et al., 2022). In addition, they might suffer housing deprivation due to the increasing housing and non-housing expenses coupled with their declining incomes (Emekci, 2021; Wilson & Barton, 2018). The financial pressure due to low income is further exacerbated if a household member has a disability or severe illness, potentially consuming up to 35% of their income (AHC, 2019). Recently, the COVID-19 pandemic period highlighted households' financial wellbeing vulnerability to housing-related financial challenges (Brandily et al., 2020; Hick et al., 2022; National Housing Federation, 2020). During this period, job losses led to difficulties covering housing and non-housing costs, with a third of low-income social housing residents burdened by housing costs (OECD, 2020).   The issues discussed above on dwellings being of poor quality or unaffordable harm financial wellbeing, leading to residential segregation (Adabre & Chan, 2019; Salvi del Pero et al., 2016) as well as intensifying gaps of social injustice, health injustice, poverty, and fuel poverty (Barker, 2020; Garnham et al., 2022). Without addressing those housing-related issues, many households' financial wellbeing would remain vulnerable to economic insecurity even if they live in housing considered to be "affordable" in terms of rent-to-income ratio.

Techno-optimism refers to the belief that advances in technology will improve humanity, enhance quality of life, and solve critical problems including climate change, health issues and social inequality (Danaher, 2022). According to Danaher (2022), techno-optimism assumes technology will ensure “the good does or will prevail over the bad” (p.54). Techno-optimists believe that technological innovation is a key driver for economic growth and can provide solutions to many of the pressing challenges faced by contemporary society (Wilson, 2017). Keary (2016) links faith in technological optimism to an unshakable commitment to economic growth. Technological change modelling (TCM), he argues, has shifted the terms of environmental debate, pulling efforts away from ‘green’ ecologism (associated with degrowth movements), and toward techno-optimism; a belief that mitigation pathways should rely on technological advancements. Techno-optimism emerges from enlightenment ideals, whereby reason and scientific progress are seen as pathways to improving human conditions and capabilities by overcoming “existential risk” (Bostrom, 2002) through technological advancements (Wilson, 2017). Hornborg (2024) criticises techno-optimism for its failure to address ecological and social inequalities exacerbated by technology. Further, technological solutions often address symptoms rather than root causes, leading to a superficial treatment of complex problems (Wilson, 2017).  Hornborg, using Marx’s commodity fetishism and World Systems Theory as his guide (Marx, 1990), seeks to unmask modern assumptions about what technology is. Both capitalists and certain left-wing thinkers exalt technology, viewing it as embodying human progress — a promethean mode of thinking. This overlooks, however, the social relations and material, energetic, and metabolic flows needed to maintain technological systems. Technology needs a “sociometabolic reconceptualization” (Hornborg, 2024, p. 28). Historically, technological progress in the world’s industrial core, was dependent on unequal social relations and colonial patterns of extraction from non-industrial peripheries. Shifting to green technologies, in Horrnborg’s view, will involve repeating these inequities: sugar-ethanol, or electric powered cars, for instance, will rely on exploited land in Brazil and the cobalt-rich Congo. “High tech cores versus their exploited peripheries” (Hornborg, 2024, p. 38), recasts the colonial industrial core-periphery dynamic (Wolf et al., 2010), exacerbating ecological and social inequalities. By attributing too much power to technology itself, techno-optimists may neglect the need for conscious and deliberate governance of technological change (Bostrom, 2002, p. 11). Further, it is crucial to maintain a balanced perspective that recognises both the opportunities and the limitations of technological advancements (Wilson, 2017). Social, political, and cultural contexts must shape technological outcomes. Danaher (2022) argues through collective effort, it is possible to create the right institutions and frameworks to guide technological development towards beneficial ends. Technological innovation plays a key role in deep energy retrofit (DER), which relies on three main technical improvements to reach end point performance targets, measured in kWh/m2/year: increased thermal insulation and airtightness; 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). Techno-optimism in DER has led to the widespread adoption of ground source and air source heat pumps, such as mechanical heat and ventilation systems (MVHR) (Traynor, 2019), to mechanically stabalise indoor air temperatures (Outcault et al., 2022), LED lighting smart systems (Bastian et al., 2022), and upgraded systems for heating and hot water (Roberts, 2008). There are many concerns with techno-optimism in DER: (1) the gap between predicted and actual energy performance can reach as high as five times the prediction (Traynor, 2019), (2) the adoption of techno-optimism does not consider the certainty of technological obsolescence, (3) inoperable windows due to mechanical heating and ventilation increases the risk of future overheating, and cooling costs, and (4) DER disregards architectural vernacular and passive energy strategies, including cross ventilation, thermal mass, and solar gains. In social housing retrofit, non-energy benefits including comfort, modernity, health, and safety, (Amann, 2006; Bergman & Foxon, 2020; Broers et al., 2022)—negated in techno-optimism—are often more important to social housing residents than energy-related benefits. Further, technological innovation in retrofit is often tested on social housing (Morgan et al., 2024), despite housing tenants from marginalised groups, to convince private markets to adopt technologies.

Increasing the thermal properties of the building envelope is a passive strategy to reduce energy loss and ensure significant reductions in energy demand (Grecchi, 2022). Van den Brom et al (2019) define thermal renovation as “renovation measures that are taken to reduce energy consumption used for thermal comfort”, and group thermal insulation, airtightness and efficient electrical system into a single category. Accordingly, deep ‘thermal’ renovation occurs when significant improvement in at least three building components bring thermal performance to a level equal to or higher than the current building regulation standards (van den Brom et al., 2019). These building components include roof insulation, floor insulation, façade insulation, window improvements, heating system, domestic hot water system, and ventilation system (van den Brom et al., 2019). Other authors (Institute for Sustainability & UCL Energy Institute, 2012; Sojkova et al., 2019; Traynor, 2019) divide electrical systems into a further category for clearer practical application. The concept of airtightness is revered for saving energy, avoiding structural damage, contributing to thermal comfort (Bastian et al., 2022), and is key to reducing heat loss through ventilation (Roberts, 2008). Draught proofing involves draught-stripping, replacing leaky windows and closing off unused chimneys (Roberts, 2008). The location of an airtight layer should be identified, and all penetrations through it minimised, sealed, and recorded (Traynor, 2019). This airtight layer can be airtight board, a plastered wall, or a membrane with appropriate tape at all junctions such as window openings (Traynor, 2019). Triple-glazed windows in combination with any frame material are the most efficient glazing system at reducing primary energy cost and CO₂ emissions (Sojkova et al., 2019). All air pockets should be sealed to prevent draughts and thermal bridging. Thermal bridging should be eliminated wherever possible, although a comprehensive thermal reduction with low internal surface temperatures can prevent physical problems such as moisture and mould (Bastian et al., 2022). There are many forms of insulation to consider during retrofit that considerably contribute to a reduction in heat loss. Filling external cavity walls with insulation can reduce heat loss through walls by up to 40% (Roberts, 2008). Ground floor insulation and roof insulation are also necessary steps in DER (Grecchi, 2022; Roberts, 2008; Traynor, 2019). Ground floor insulation can occur in suspended timber floors between joists or above solid concrete floors (Traynor, 2019). Roof insulation can be added between structural elements, or using a ‘cold’ roof solution, with insulation laid or sprayed over the existing ceiling (Traynor, 2019). Alternatively, green roofs can reduce the amount of heat penetration through roofs, playing a similar role to roof insulation. This is done by absorbing heat into their thermal mass alongside the evaporation of moisture but will require structural upgrades to manage the new load (Roberts, 2008). External wall insulation (EWI) protects the building fabric, improves airtightness and is relatively quick and easy to install (Roberts, 2008). EWI can also help mitigate overheating by absorbing less heat than the original material, while allowing existing thermal mass from solid masonry walls and concrete to be retained within the insulated envelope (Bastian et al., 2022). The two main external insulation systems are ventilated rainscreen systems and rendered insulation systems (Roberts, 2008). EWI is inappropriate for historical building use because it will cover the historical architectural character. Gupta & Gregg’s (2015) preserved the original exterior façade by using internal wall insulation inside the front façade and EWI on all other façades. However, drawbacks to this solution can include the loss of internal floor area, and reduced energy efficiency as notable heat loss can occur where the internal insulated wall meets the external insulated wall (Gupta & Gregg, 2015).