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).  

Community empowerment appears in the literature of participatory action research (Minkler, 2004), participatory planning (Jo & Nabatchi, 2018), and community development (Luttrell et al., 2009) as a key element of participatory practices, understanding it as a process that enables communities to take control of their lives and their environments (Rappaport, 2008; Zimmerman, 2000). Many argue that community participation becomes meaningless if it does not lead to, or pass through community empowerment. As the term is being used in diverse and ubiquitous ways, it runs the risk of ending up as an empty definition and a catch-all phrase (McLaughlin, 2015). It is therefore important to specify the perspective through which we will view the term and clarify the nuances.  Since its origins, empowerment has been used in two different ways. Firstly, top-down as the power that had been ‘granted’ by a higher authority, such as the state or a religious institution, and secondly, bottom-up, as a process by which groups or individuals come to develop the capacity to act and acquire power. Examples of the latter can be found in social groups such as feminists working in nongovernmental organizations throughout the global south in the 1970s, who found a way to address social issues and inequalities that enabled social transformation based on women’s self-organization (Biewener & Bacqué, 2015). The term was gradually appropriated by welfare, neoliberal, and social-neoliberal agendas whose priority was individual agency and choice. In neoliberal rationality, empowerment is related to efficiency, economic growth, business productivity, and individual rational choice to maximize profit in a competitive market economy. In social liberalism agendas, empowerment is understood as ‘effective agency’, where ‘agency’ is not an inherent attribute, but something that needs to be constructed through ‘consciousness-raising’ (McLaughlin, 2016). A broader definition sees empowerment as a social action process through which individuals, communities, and organizations take control of their lives in the context of changing the social and political environment to improve equity and quality of life (Rappaport, 2008; Zimmerman, 2000). Rowlands (1997), refers to four types of empowerment: power over, as the ability to influence and coerce; power to, to organize and change existing hierarchies; power with, as the power from the collective action and power within, as the power from the individual consciousness. Using this classification, Biewener & Bacqué (2015), adopting a feminist approach, understand empowerment as a multilevel construct with three interrelated dimensions: 1) an internal, psychological one, where ‘power within’ and ‘power to’ are developed, 2) an organizational, where ‘power with’ and ‘power over’ are strengthened and 3) a social or political level, where institutional and structural change is made possible through collective action. Thus, community empowerment links the individual level, which involves self-determination, growth of individual awareness, and self-esteem, to the collective level, relating critical consciousness and capacity building with the structural level, where collective engagement and transformative social action take place. This view of empowerment, which considers its goals and processes, has a social dimension that is lacking in other approaches that prioritize individual empowerment. Aside from the feminist movements, the philosophy and practices of community empowerment have been greatly influenced by the work of Paulo Freire, a Brazilian educator and an advocate on critical pedagogy. Freire proposed a dialogic problem-solving process based on equality and mutual respect between students and teachers; that engaged them in a process of iterative listening-discussing-acting. Through structured dialogue, group participants shared their experiences, discussed common problems, and looked for root causes and the connections among “problems behind the problems as symptoms” (Freire, 1970). The term conscientization, that Freire proposed, refers to the consciousness that arises through the involvement of people in the social analysis of conditions and their role in changing them. This awareness enables groups to be reflexive and open spaces, to enact change or to understand those limited situations that may deter change (Barndt, 1989). Empowerment can be understood as both a process and an outcome (Jo & Nabatchi, 2018). As a process, it refers to “the development and implementation of mechanisms to enable individuals or groups to gain control, develop skills and test knowledge”(Harrison & Waite, 2015) and it entails the creation of new subjects who have developed a critical consciousness and the formation of groups with a ‘collective agency’ ‚ or ‘social collective identity’ (Biewener & Bacqué, 2015). Empowerment as an outcome refers to “an affective state in which the individual or group feels that they have increased control, greater understanding and are involved and active” (Harrison & Waite, 2015). This can lead to a transformation of the social conditions by challenging the structures and institutionalized forms that reproduce inequalities. The values and the significance of community empowerment can be further applied in the participatory and community-based approaches of the housing sector. Examples of such approaches in the housing provision are the housing cooperatives, and self-developed and self-managed housing groups. Housing cooperatives aim at promoting co-creation to engage future residents, professionals, and non-profit organizations in all the stages of a housing project: problem-framing, designing, developing, cohabiting, managing, and maintaining. Such organisational models stress the importance and pave the way for community empowerment by uniting individuals with similar interests and ideals, enabling them to have housing that responds to their needs, preferences, and values. The participation of the residents aims to strengthen their sense of ownership of the process, the democratic decision-making and management, and the social collective identity, making community empowerment an integral characteristic of cooperative housing initiatives. With this social perspective, residents can gain individual and collective benefits while contributing to fairer and more sustainable urban development on a larger scale (Viskovic Rojs et al., 2020).

Affordability is defined as the state of being cheap enough for people to be able to buy (Combley, 2011). Applied to housing, affordability, housing unaffordability and the mounting housing affordability crisis, are concepts that have come to the fore, especially in the contexts of free-market economies and housing systems led by private initiatives, due to the spiralling house prices that residents of major urban agglomerations across the world have experienced in recent years (Galster & Ok Lee, 2021). Notwithstanding, the seeming simplicity of the concept, the definition of housing affordability can vary depending on the context and approach to the issue, rendering its applicability in practice difficult. Likewise, its measurement implies a multidimensional and multi-disciplinary lens (Haffner & Hulse, 2021). One definition widely referred to of housing affordability is the one provided by Maclennan and Williams (1990, p.9): “‘Affordability’ is concerned with securing some given standard of housing (or different standards) at a price or a rent which does not impose, in the eyes of some third party (usually government) an unreasonable burden on household incomes”. Hence, the maximum expenditure a household should pay for housing is no more than 30% of its income (Paris, 2006). Otherwise, housing is deemed unaffordable. This measure of affordability reduces a complex issue to a simple calculation of the rent-to-income ratio or house-price-to-income ratio. In reality, a plethora of variables can affect affordability and should be considered when assessing it holistically, especially when judging what is acceptable or not in the context of specific individual and societal norms (see Haffner & Hulse, 2021; Hancock, 1993). Other approaches to measure housing affordability consider how much ‘non-housing’ expenditures are unattended after paying for housing. Whether this residual income is not sufficient to adequately cover other household’s needs, then there is an affordability problem (Stone, 2006). These approaches also distinguish between “purchase affordability” (the ability to borrow funds to purchase a house) and “repayment affordability” (the ability to afford housing finance repayments) (Bieri, 2014). Furthermore, housing production and, ultimately affordability, rely upon demand and supply factors that affect both the developers and home buyers. On the supply side, aspects such as the cost of land, high construction costs, stiff land-use regulations, and zoning codes have a crucial role in determining the ultimate price of housing (Paris, 2006). Likewise, on the policy side, insufficient government subsidies and lengthy approval processes may deter smaller developers from embarking on new projects. On the other hand, the demand for affordable housing keeps increasing alongside the prices, which remain high, as a consequence of the, sometimes deliberate incapacity of the construction sector to meet the consumers' needs (Halligan, 2021). Similarly, the difficulty of decreasing household expenditures while increasing incomes exacerbates the unaffordability of housing (Anacker, 2019). In the end, as more recent scholarship has pointed out (see Haffner & Hulse, 2021; Mulliner & Maliene, 2014), the issue of housing affordability has complex implications that go beyond the purely economic or financial ones. The authors argue that it has a direct impact on the quality of life and well-being of the affected and their relationship with the city, and thus, it requires a multidimensional assessment. Urban and spatial inequalities in the access to city services and resources, gentrification, segregation, fuel and commuting poverty, and suburbanisation are amongst its most notorious consequences. Brysch and Czischke, for example, found through a comparative analysis of 16 collaborative housing projects in Europe that affordability was increased by “strategic design decisions and self-organised activities aiming to reduce building costs” (2021, p.18). This demonstrates that there is a great potential for design and urban planning tools and mechanisms to contribute to the generation of innovative solutions to enable housing affordability considering all the dimensions involved, i.e., spatial, urban, social and economic. Examples range from public-private partnerships, new materials and building techniques, alternative housing schemes and tenure models (e.g., cohousing, housing cooperatives, Community Land Trusts, ‘Baugruppen’), to efficient interior design, (e.g., flexible design, design by layers[1]). Considering affordability from a design point of view can activate different levers to catalyse and bring forward housing solutions for cities; and stakeholders such as socially engaged real estate developers, policymakers, and municipal authorities have a decisive stake in creating an adequate environment for fostering, producing and delivering sustainable and affordable housing.   [1] (see Brand, 1995; Schneider & Till, 2007)

Sustainability is primarily defined as 'the idea that goods and services should be produced in ways that do not use resources that cannot be replaced and that do not damage the environment' (Cambridge Advanced Learner’s Dictionary & Thesaurus, n.d.) and is often used interchangeably with the term “sustainable development”(Aras & Crowther, 2009). As defined by the UN, sustainable development is the effort to “meet the needs of the present without compromising the ability of future generations to meet their own needs” (United Nations, 1987) and is often interpreted as the strategies adopted towards sustainability with the latter being the overall goal/vision (Diesendorf, 2000). Both of these relatively general and often ambiguous terms have been a focal point for the past 20 years for researchers, policy makers, corporations as well as local communities, and activist groups, among others, (Purvis et al., 2019). The ambiguity and vagueness that characterise both of these terms have contributed to their leap into the global mainstream as well as the broad political consensus regarding their value and significance (Mebratu, 1998; Purvis et al., 2019), rendering them one of the dominant discourses in environmental, socio-political and economic issues (Tulloch, 2013). It is, however, highly contested whether their institutionalisation is a positive development. Tulloch, and Tulloch & Nielson (2013; 2014) argue that these terms -as they are currently understood- are the outcome of the “[colonisation of] environmentalist thought and action” which, during the 1960s and 1970s, argued that economic growth and ecological sustainability within the capitalist system were contradictory pursuits. This “colonisation” resulted in the disempowerment of such discourses and their subsequent “[subordination] to neoliberal hegemony” (Tulloch & Neilson, 2014, p. 26). Thus, sustainability and sustainable development, when articulated within neoliberalism, not only reinforce such disempowerment, through practices such as greenwashing, but also fail to address the intrinsic issues of a system that operates on, safeguards, and prioritises economic profit over social and ecological well-being (Jakobsen, 2022). Murray Bookchin (1982), in “The Ecology of Freedom” contends that social and environmental issues are profoundly entangled, and their origin can be traced to the notions of hierarchy and domination. Bookchin perceives the exploitative relationship with nature as a direct outcome of the development of hierarchies within early human societies and their proliferation ever since. In order to re-radicalise sustainability, we need to undertake the utopian task of revisiting our intra-relating, breaking down these hierarchical relations, and re-stitching our social fabric. The intra-relating between and within the molecules of a society (i.e. the different communities it consists of) determines how sustainability is understood and practised (or performed), both within these communities and within the society they form. In other words, a reconfigured, non-hierarchical, non-dominating intra-relationship is the element that can allow for an equitable, long-term setting for human activity in symbiosis with nature (Dempsey et al., 2011, p. 290). By encouraging, striving for, and providing the necessary space for all voices to be heard, for friction and empathy to occur, the aforementioned long-term setting for human activity based on a non-hierarchical, non-dominating intra-relating is strengthened, which augments the need for various forms of community participation in decision-making, from consulting to controlling. From the standpoint of spatial design and architecture, community participation is already acknowledged as being of inherent value in empowering communities (Jenkins & Forsyth, 2009), while inclusion in all facets of creation, and community control in management and maintenance can improve well-being and social reproduction (Newton & Rocco, 2022; Turner, 1982). However, much like sustainability, community participation has been co-opted by the neoliberal hegemony; often used as a “front” for legitimising political agendas or as panacea to all design problems, community participation has been heavily losing its significance as a force of social change (Smith & Iversen, 2018), thus becoming a depoliticised, romanticised prop. Marcus Miessen (2011) has developed a critical standpoint towards what is being labelled as participation; instead of a systematic effort to find common ground and/or reach consensus, participation through a cross-benching approach could be a way to create enclaves of disruption, i.e. processes where hierarchy and power relations are questioned, design becomes post-consensual spatial agency and participation turns into a fertile ground for internal struggle and contestation. Through this cross-benching premise, community participation is transformed into a re-politicised spatial force. In this context, design serves as a tool of expressing new imaginaries that stand against the reproduction of the neoliberal spatial discourse. Thus, sustainability through community participation could be defined as the politicised effort to question, deconstruct and dismantle the concept of dominance by reconfiguring the process of intra-relating between humans and non-humans alike.

Sustainability of the built environment The emergence of the contemporary environmental movement between the 1960s and 1970s and its proposals to remedy the consequences of pollution can be seen as one of the first steps in addressing environmental problems (Scoones, 2007). However, the term “sustainable” only gained wider currency when it was introduced into political discourse by the Club of Rome with its 1972 report “The Limits to Growth”, in which the proposal to change growth trends to be sustainable in the far future was put forward (Grober, 2007; Kopnina & Shoreman-Ouimet, 2015a; Meadows et al., 1972). Since then, the use of the term has grown rapidly, especially after the publication of the 1978 report “Our Common Future”, which became a cornerstone of debates on sustainability and sustainable development (Brundtland et al., 1987; Kopnina & Shoreman-Ouimet, 2015a). Although the two terms are often used indistinctively, the former refers to managing resources without depleting them for future generations, while the latter aims to improve long-term economic well-being and quality of life without compromising the ability of future generations to meet their needs (Kopnina & Shoreman-Ouimet, 2015b; UNESCO, 2015). The Brundtland Report paved the way for the 1992 Earth Summit, which concluded that an effective balance must be found between consumption and conservation of natural resources (Scoones, 2007). In 2000, the United Nations General Assembly published the 8 Millennium Development Goals (UN, 2000), which led to the 17 Sustainable Development Goals (SDGs) published in 2016 (UN, 2016). The 17 SDGs call on all countries to mobilise their efforts to end all forms of poverty, tackle inequalities and combat climate change (UN, 2020; UNDP, 2018). Despite the rapidly growing literature on sustainability, the term remains ambiguous and lacks a clear conceptual foundation (Grober, 2007; Purvis et al., 2019). Murphy (2012) suggests that when defining sustainability, the question should be: Sustainability, of what? However, one of the most prominent interpretations of sustainability is the three pillars concept, which describes the interaction between the social, economic and environmental components of society (Purvis et al., 2019). The environmental pillar aims to improve human well-being by protecting natural capital -e.g. land, air and water- (Morelli, 2011). The economic sustainability pillar focuses on maintaining stable economic growth without damaging natural resources (Dunphy et al., 2000). Social sustainability, on the other hand, aims to preserve social capital and create a practical social framework that provides a comprehensive view of people's needs, communities and culture (Diesendorf, 2000). This latter pillar paved the way for the creation of a fourth pillar that includes human and culture as a focal point in sustainability objectives (RMIT, 2017). Jabareen (2006) describes environmental sustainability as a dynamic, inclusive and multidisciplinary concept that overlaps with other concepts such as resilience, durability and renewability. Morelli (2011) adds that it can be applied at different levels and includes tangible and intangible issues. Portney (2015) takes Morelli's explanation further and advocates that environmental sustainability should also promote industrial efficiency without compromising society's ability to develop (Morelli, 2011; Portney, 2015). Measuring the built environment sustainability level is a complex process that deploys quantitative methods, including (1) indexes (e.g. energy efficiency rate), (2) indicators (e.g. carbon emissions and carbon footprint), (3) benchmarks (e.g. water consumption per capita) and (4) audits (e.g. building management system efficiency) (Arjen, 2015; Berardi, 2012; James, 2014; Kubba, 2012). In recent years, several rating or certification systems and practical guides have been created and developed to measure sustainability, most notably the Building Research Establishment Environmental Assessment Method (BREEAM) introduced in the UK in 1990 (BRE, 2016) and the Leadership in Energy and Environmental Design (LEED) established in the US in 2000 (USGBC, 2018). In addition, other overlapping methodologies and certification frameworks have emerged, such as the European Performance of Buildings Directive (EPBD) in 2002 (EPB, 2003) and the European Framework for Sustainable Buildings, also known as Level(s) in 2020 (EU, 2020), amongst others. The sustainability of the built environment aims to reduce human consumption of natural resources and the production of waste while improving the health and comfort of inhabitants and thus the performance of the built environment elements such as buildings and spaces, and the infrastructure that supports human activities (Berardi, 2012; McLennan, 2004). This aim requires an effective theoretical and practical framework that encompasses at least six domains, including land, water, energy, indoor and outdoor environments, and economic and cultural preservation (Ferwati et al., 2019). More recently, other domains have been added, such as health and comfort, resource use, environmental performance, and cost-benefit and risk (EU, 2020). Sustainability of the built environment also requires comprehensive coordination between the architectural, structural, mechanical, electrical and environmental systems of buildings in the design, construction and operation phases to improve performance and avoid unnecessary resource consumption (Yates & Castro-Lacouture, 2018).

Transdisciplinarity is a research methodology crossing several disciplinary boundaries, creating a holistic approach to solve complex problems. A transdisciplinary approach fosters bottom-up collaboration, provides an environment for mutual learning, and enhances the knowledge of all participants (Klein et al., 2001, Summary and Synthesis). Transdisciplinarity is a relatively young term, first used just over fifty years ago at the Organisation for Economic Co-operation and Development (OECD) congress by Jean Piaget, who described it in a broader sense as “a higher stage succeeding interdisciplinary relationships…without any firm boundaries between disciplines” (Piaget, 1972, p.135). Transdisciplinarity goes beyond interdisciplinarity through a fusion of academic and non- academic knowledge, theory and practice, discipline and profession (Doucet & Janssens, 2011). Stokols (2006) asserts transdisciplinarity is inextricability linked to action research; a term coined by Lewin (1946) as comparative research leading to social action. Lewin sought to empower and enhance the self-esteem of participants, which included residents of minority communities, through horizontal and democratic exchange between the researcher and participants. Familiar devices rooted in action research, such as surveys, questionnaires, and interviews are common in transdisciplinary research (Klein et al., 2001). A transdisciplinarity approach has been used to address complex global concerns in recent decades, beginning with climate change and extending into many areas including socio-political problems (Bernstein, 2015). Lawrence et al. (2010) stress that in addressing community related issues such as housing, it is crucial a transdisciplinary approach is adopted not only to integrate various expert opinions but to ensure the inclusion of affected communities such as the residents themselves. Housing is a complex social issue, therefore requiring such an approach to foster participation of non-academics to provide socially relevant solutions. Salama (2011) advocates for the use of transdisciplinarity in the creation of affordable and sustainable housing, which is often restricted by stakeholders working in silos, the oversimplification of housing-related issues, and a disconnect from local communities.

Mass customisation (MC) is a process by which a company approaches its production in a customer-centric manner, developing products and services according to the needs and requirements of each individual customer, while keeping costs near to mass production (Piller, 2004). MC establishes a new relationship between producers and customers which becomes crucial in product development  (Khalili-Araghi & Kolarevic, 2016). Alvin Toffler (1970, 1980) was the first to refer to the MC concept in his books “Future shock”  and “The third wave”. Stanley Davis (1987) later cemented the term in his book “Future Perfect”. But it was not until 1993, when Joseph Pine  developed its practical application to business, that the concept started gaining greater importance in research and practice (Pine, 1993; Brandão et al., 2017; Piller et al., 2005). Nowadays, MC is understood as a multidimensional process embracing a combination of mass production, user-driven technologies, big data, e-commerce and e-business, digital design, and manufacturing technologies (Brandão et al., 2017). In the last twenty years, almost every sector of the economy, from industrial production to consumer products and services, has been influenced by mass customisation. The difference between mass customisation and massive customisation is the ability to relate the contextual features to the product features. This means that a random generation of design alternatives would not be sufficient; these alternatives should be derived from the cultural, technological, environmental and social context, as well as from the individual context of the user (Kolarevic & Duarte, 2019). As a business paradigm,  MC provides an attractive added value by addressing customer needs while using resources efficiently and avoiding an increase in operational costs (Piller & Tseng, 2009). It seeks to incorporate customer co-design processes into the innovation and strategic planning of the business, approaching economies of integration (Piller et al., 2005). As a result, the profitability of MC is achieved through product variety in volume-related economies (Baranauskas et al., 2020; Duray et al., 2000). The space in which it is possible to meet a variety of needs through a mass customisation offering is finite (Piller, 2004). This solution space represents the variety of different customisation units and encompasses the rules to combine them, limiting the set of possibilities in the search of a balance between productivity and flexibility (Salvador et al., 2009). The designer’s responsibility would be to meet the heterogeneities of the users in an efficient way, by setting a solution space and defining the degrees of freedom for the customer within a manufacturer’s production system (Hippel, 2001). Therefore, an important challenge for a company that aims at becoming a mass customizer is to find the right balance between what is determined by the designer and what is left for the user to decide (Kolarevic & Duarte, 2019). Value creation within a stable solution space is one of the major differences between traditional customisation. While a traditional customizer produces unique products and processes, a mass customizer uses stable processes to provide a high range of variety among their products and services (Pine, 1993). This would enable a mass customizer to achieve “near mass production efficiency” but would also mean that the customisation alternatives are limited to certain product features (Pine, 1995). As opposed to the industrial output of mass production, in which the customer selects from options produced by the industry, MC facilitates cultural production, the personalisation of mass products in accordance with individual beliefs. This means that the customer contributes to defining the processes, components, and features that will be involved in the flow of the design and manufacturing process (Kieran & Timberlake, 2004). Products or services that are co-designed by the customer may provide social benefits, resulting in tailor-made, fitting, and resilient outcomes (Piller et al., 2005). Thanks to parametric design and digital fabrication it is now viable to mass-produce non-standard, custom-made products, from tableware and shoes to furniture and building components. These are often customizable through interactive websites (Kolarevic & Duarte, 2019). The incorporation of MC into the housebuilding industry, through supporting, guiding, and informing the user via interactive interfaces (Madrazo et al., 2010), can contribute to a democratisation of housing design, allowing for an empowering, social, and cultural enrichment of our built environment. Our current housing stock is largely homogeneous, while customer demands are increasingly heterogeneous. Implementing MC in the housing industry could address the diverse consumer needs in an affordable and effective way, by creating stable solution spaces that could make good quality housing accessible to more dwellers. Stability and responsiveness are key in the production of highly customised housing. Stability can be achieved through product modularity, defining and producing a set of components that can be combined in the maximum possible ways, attaining responsiveness to different requests while reducing the complexity of product variation. This creates customisation alternatives within the solution space which require a smooth flow of information and effective collaboration between customers, designers, and manufacturers (Khalili-Araghi & Kolarevic, 2018). ICT technologies can help to effectively materialise this multidimensional and interdisciplinary challenge in the Architecture, Engineering and Construction (AEC) industry, as showcased in the Sato PlusHome multifamily block in Finland[1]. Nowadays, there are companies that have integrated a systematic methodology to produce mass customised single-family homes using prefabrication methods, such as Modern Modular[2]. On the other hand, platforms such as BIM that act as collaborative environments for all stakeholders have demonstrated that building performance can be increased and precision improved while reducing construction time. These digital twins offer a basis for fabricated components and enable early cooperation between different disciplines. Parametric tools have the potential to help customisation comply with the manufacturing rules and regulations, and increase the ability to sustainably meet customer requirements, using fewer resources and shorter lead times (Piroozfar et al., 2019). In summary, a mass customisable housing industry could be achieved if the products and services are parametrically defined (i.e., specifying the dimensions, constraints, and relationships between the various components), interactively designed (via a website or an app), digitally fabricated, visualised and evaluated to automatically generate production and assembly data (Kolarevic, 2015). However, for MC to be integrated effectively in the AEC industry, several challenges remain that range from cultural, behavioural and management changes, to technological such as the use of ICTs or those directly applied to the manufacturing process, as for example automating the production and assembly methods, the use of product configurators or managing the variety through the product supply chain (Piroozfar et al., 2019).   [1] Sato PlusHome. ArkOpen / Esko Kahri, Petri Viita and Juhani Väisänen (http://www.open-building.org/conference2011/Project_PlusHome.pdf) [2] The Modern Modular. Resolution: 4 Architecture (https://www.re4a.com/the-modern-modular)

Building Information Modelling (BIM) is the process of creating a set of digital representations which consists of both graphical and non-graphical data for the entire building cycle  (Eastman et al., 2011). This process involves documenting, gathering, organising, and updating this information throughout the whole life cycle of a building from conception to demolition (Eschenbruch & Bodden, 2018). Beyond the demolition stage BIM can also support circular principles; managing the re-use, recovery, and recycling-potential of a building (Akbarieh et al., 2020; Xue et al., 2021). Whilst the concept of BIM as a process is supported by the International Organisation for Standardisation in ISO 19650-1:2018 (ISO, 2018), the National BIM Standard describes BIM as a digital technology (NBIMS-US, 2015). Despite the origins of BIM dating back to the 1970s, it did not become widely adopted by the Architecture, Engineering and Construction (AEC) industry as a computer design tool until the 2000s (Costa, 2017). The digital building information model uses intelligent objects to store information in the form of three-dimensional geometric components along with its functional characteristics such as type, materials, technical properties, or costs (Eschenbruch & Bodden, 2018). This model forms the basis of a shared knowledge resource to support the various digital workflows of multidisciplinary stakeholders (Chong, Lee and Wang, 2017; Barile et al., 2018). Moreover, it serves the purpose of visualisation, clash detection between different building components, code criteria checking, environmental analysis, and cost estimation to name a few (Kamel & Memari, 2019; Krygiel & Nies, 2008). Therefore, utilising BIM can improve construction accuracy and enhance the built asset’s performance (Kubba, 2017; Love et al., 2013). The building information model facilitates the knowledge transfer between experts and project participants to satisfy end-user needs and support early-stage decision-making (Chong et al., 2017; Lu et al., 2017). Therefore, BIM can be considered a transdisciplinary practice as it communicates AEC, computation, and science (Correia et al., 2017). In the AEC industry implementing BIM involves several stages, which are known as BIM maturity models. The maturity here means the extent of the user’s ability to produce and exchange information. These stages are the milestones, or levels, of collaboration and sharing of information that teams, and organisations aspire to. Defining these milestones is the main purpose of the different BIM maturity models that exist nowadays (Succar et al., 2012). The European Commission (EC) encourages step-by-step maturity models starting from BIM level 0 up to 4, to move the industry from a traditional modelling approach towards an open BIM approach. According to the EC, to reach BIM level 4 “all project, operational documentation and history are linked to objects in the model” (European Commission, 2017). Due to growing concerns over the environmental, economic, and social impacts of the built environment, BIM is increasingly used to facilitate various sustainability analyses. In this regard, the concept of Green BIM initiated as the systematic digitalisation of building life cycles to accomplish established sustainability goals (Barile et al., 2018; Wong & Zhou, 2015). As such BIM has been integrated with Life Cycle Analysis (LCA), Life Cycle Costing Analysis (LCCA), and recently with Social Life Cycle Analysis (S-LCA) (Llatas et al., 2020). Today several BIM applications perform sustainability analysis in conjunction with Green Building Rating Systems (Sartori et al., 2021). In relation to housing BIM plays a crucial role in addressing affordability and sustainability issues from creation to maintenance, as well as the beyond end-of-life phases. However, many challenges remain for it to be fully and inclusively integrated within the AEC practice and for the full potential of BIM to be realised.

Housing can be perceived as consisting of two inseparable components: the product and the process. The product refers to the building as a physical artefact, and the process encompasses the activities required to create and manage this artefact in the long term (Turner, 1972), as cited in (Brysch & Czischke, 2021). Affordability is understood as the capability to purchase and maintain something long-term while remaining convenient for the beneficiary's resources and needs (Bogdon & Can, 1997). Housing Affordability is commonly explained as the ratio between rent and household income (Hulchanski, 1995). However, Stone (2006, p.2) proposed a broader definition of housing affordability to associate it with households' social experience and financial stability as: "An expression of the social and material experiences of people, constituted as households, in relation to their individual housing situations", ….. "Affordability expresses the challenge each household faces in balancing the cost of its actual or potential housing, on the one hand, and its non-housing expenditures, on the other, within the constraints of its income." Housing costs signify initial and periodic payments such as rent or mortgages in the case of  homeowners, housing insurance, housing taxes, and so on. On the other hand, non-housing costs include utility charges resulting from household usage, such as energy and water, as well as schools, health, and transportation (AHC, 2019; Ezennia & Hoskara, 2019). Therefore, housing affordability needs to reflect the household's capability to balance current and future costs to afford a house while maintaining other basic expenses without experiencing any financial hardship (Ezennia & Hoskara, 2019). Two close terminologies to housing affordability are  “affordable housing” and “affordability of housing”. Affordable housing is frequently mentioned in government support schemes to refer to the housing crisis and associated financial hardship. In England, affordable housing is still concerned with its financial attainability, as stated in the UK Government's official glossaries: "Housing for sale or rent, for those whose needs are not met by the market (including housing that provides a subsidised route to home ownership and/or is for essential local workers)", while also complying with other themes that maintain the affordability of housing prices in terms of rent or homeownership (Department for Levelling Up Housing and Communities, 2019). The affordability of housing, on the other hand, refers to a broader focus on the affordability of the entire housing market, whereas housing affordability specifically refers to the ability of individuals or households to afford housing. In the literature, however, the term “affordability of housing” is frequently used interchangeably with “housing affordability,” despite their differences (Robinson et al., 2006). The "affordability of housing" concerns housing as a sector in a particular region, market or residential area. It can correlate affordability with population satisfaction, accommodation types and household compositions to alert local authorities of issues such as homelessness (Kneebone & Wilkins, 2016; Emma Mulliner et al., 2013; OECD, 2021). That is why the OECD defined it as "the capacity of a country to deliver good quality housing at an accessible price for all" (OECD, n.d.). Short-term and long-term affordability are two concepts for policymakers to perceive housing affordability holistically. Short-term affordability is "concerned with financial access to a dwelling based on out-of-pocket expenses", and long-term affordability is " about the costs attributed to housing consumption" (Haffner & Heylen, 2011, p.607). The costs of housing consumption, also known as user costs, do not pertain to the monthly utility bills paid by users, but rather to the cost associated with consuming the dwelling as a housing service  (Haffner & Heylen, 2011). “Housing quality” and “housing sustainability” are crucial aspects of housing affordability, broadening its scope beyond the narrow economic perspective within the housing sector. Housing affordability needs to consider "a standard for housing quality" and "a standard of reasonableness for the price of housing consumption in relation to income" (p. 609) (Haffner & Heylen, 2011). In addition, housing affordability requires an inclusive aggregation and a transdisciplinary perspective of sustainability concerning its economic, social, and environmental facets (Ezennia & Hoskara, 2019; Perera, 2017; Salama, 2011). Shared concerns extend across the domains of housing quality, sustainability, and affordability, exhibiting intricate interrelations among them that require examination. For instance, housing quality encompasses three levels of consideration: (1) the dwelling itself as a physically built environment, (2) the household attitudes and behaviours, and (3) the surroundings, encompassing the community, neighbourhood, region, nation, and extending to global circumstances (Keall et al., 2010). On the other hand, housing sustainability embraces the triad of economic, social, and environmental aspects. The shared problems among the three domains encompass critical aspects such as health and wellbeing, fuel poverty and costly long-term maintenance  proximity to workplaces and amenities, as well as the impact of climate. Health and wellbeing Inequalities in health and wellbeing pose a significant risk to social sustainability, mainly in conditions where affordable dwellings are of poor quality. In contrast, such conditions extend the affordability problem posing increased risks to poor households harming their health, wellbeing and productivity (Garnham et al., 2022; Hick et al., 2022; Leviten-Reid et al., 2020). An illustrative example emerged during the COVID-19 pandemic, where individuals residing in unsafe and poor-quality houses faced higher rates of virus transmission and mortality (Housing Europe, 2021; OECD, 2020). Hence, addressing housing affordability necessitates recognising it as a mutually dependent relationship between housing quality and individuals (Stone, 2006). Fuel poverty and costly long-term maintenance Affordable houses of poor quality pose risks of fuel poverty and costly long-term maintenance. This risk makes them economically unsustainable. For example, good quality entails the home being energy efficient to mitigate fuel poverty. However, it might become unaffordable to heat the dwelling after paying housing costs because of its poor quality (Stone et al., 2011). Thus, affordability needs to consider potential fluctuations in non-housing prices, such as energy bills (AHC, 2019; Smith, 2007). Poor quality also can emerge from decisions made during the design and construction stages. For example, housing providers may prioritise reducing construction costs by using low-quality and less expensive materials or equipment that may lead to costly recurring maintenance and running costs over time (Emekci, 2021). Proximity to work and amenities The proximity to workplaces and amenities influences housing quality and has an impact on economic and environmental sustainability. From a financial perspective, Disney (2006) defines affordable housing as "an adequate basic standard that provides reasonable access to work opportunities and community services, and that is available at a cost which does not cause substantial hardship to the occupants". Relocating to deprived areas far from work opportunities, essential amenities, and community services will not make housing affordable (Leviten-Reid et al., 2020). Commuting to a distant workplace also incurs environmental costs. Research shows that reduced commuting significantly decreases gas emissions (Sutton-Parker, 2021). Therefore, ensuring involves careful planning when selecting housing locations, considering their impact on economic and environmental sustainability (EK Mulliner & Maliene, 2012). Moreover, design practices can contribute by providing adaptability and flexibility, enabling dwellers to work from home and generate income (Shehayeb & Kellett, 2011). Climate change's mutual impact Climate change can pose risks to housing affordability and, conversely, housing affordability can impact climate change. A house cannot be considered "affordable" if its construction and operation result in adverse environmental impacts contributing to increased CO2 emissions or climate change (Haidar & Bahammam, 2021; Salama, 2011). For a house to be environmentally sustainable, it must be low-carbon, energy-efficient, water-efficient, and climate-resilient (Holmes et al., 2019). This entails adopting strategies such as incorporating eco-friendly materials, utilizing renewable energy sources, improving energy efficiency, and implementing sustainable water management systems (Petrović et al., 2021). However, implementing these measures requires funding initiatives to support the upfront costs, leading to long-term household savings (Holmes et al., 2019). Principio del formulario Furthermore,  when houses lack quality and climate resilience, they become unaffordable. Households bear high energy costs, especially during extreme weather conditions such as heatwaves or cold spells (Holmes et al., 2019). Issues like cold homes and fuel poverty in the UK contribute to excess winter deaths (Lee et al., 2022). In this context, climate change can adversely affect families, impacting their financial well-being and health, thereby exacerbating housing affordability challenges beyond mere rent-to-income ratios.    

Measuring housing affordability refers to assessing the extent to which households can secure suitable housing in relation to their financial resources and other relevant factors. To date there is no global agreement on measuring housing affordability, nor is there a single metric which comprehensively encompasses all the considerations regarding households' ability to access suitable housing in a convenient location at an affordable cost (Ezennia & Hoskara, 2019; OECD, 2021b). Several approaches exist to measure housing affordability, with two popular approaches, namely the Income Ratio Method (IRM), and the Residual Income Method (RIM) (Ezennia & Hoskara, 2019; Stone et al., 2011). Both are recommended to be accompanied by housing quality standards to evaluate what a household is paying for and a measure of housing satisfaction (Haffner & Heylen, 2011; OECD, 2021b). However, the perception of what constitutes satisfactory, quality, or affordable housing is subjective. This perception can be influenced by economic and social circumstances that policymakers may not perceive as directly relevant to housing policy (OECD, 2021b). The Income Ratio Method (IRM) is the most commonly used in policy and housing market-relevant statistics, as it is easy to measure and compare among different countries. It is based on the housing costs to income ratio defined by national authorities not to exceed a certain proportion (Haidar & Bahammam, 2021; Smith, 2007; Stone, 2006). The official EU indicator for IRM is the "Housing Cost Overburden" index. It considers households suffering from affordability issues if more than 40% of their net income is spent on housing costs (AHC, 2019; Hick et al., 2022; OECD, 2020). However, IRM has been widely criticised as it does not reflect if the household could afford non-housing costs and for how long. The focus on housing costs neglects non-housing costs of utility bills, schools, health, transportation, and so on (AHC, 2019). In this sense, Ezennia & Hoskara, (2019) investigation of the weaknesses of measuring housing affordability emphasised the need to reflect a household's capability to balance current and future costs to attain a house – "access to a house at a certain period" while maintaining other basic expenses without experiencing any financial hardship. The Residual Income Method (RIM) is the second dominant approach. It recognises that after paying the housing costs, a household might be unable to satisfy its non-housing requirements. Thus, the RIM is the remaining income after subtracting housing costs, based on the idea that Housing Affordability is the households' ability to cover their housing costs while still being able to pay their non-housing expenditures (Stone et al., 2011; Stone, 2006). The residual income method took a step closer to resonating with non-housing costs. However, both Haffner & Heylen (2011) and Bramley (2012) advised that the IRM and RIM approaches "are not interchangeable" and need to be combined to provide a comprehensive perception of housing affordability. This combination becomes apparent when comparing both for different household compositions, health, or work conditions. For instance, a house might be affordable when measured using the IRM from the housing costs standpoint, but it might not be affordable utilising the RIM, which is connected with non-housing costs. This combination is referred to as the Composite Method from which several advanced economic modelling approaches to measure housing affordability were developed (Ezennia & Hoskara, 2019). However, relying solely on economic criteria to assess affordability and thus overlooking quality and sustainability may not prove sufficient. A poor-quality house can impose hardships on its residents, and an unsustainable dwelling can strain the environment. Mitigating this issue may involve complementing affordability measurements with indicators reflecting housing quality and sustainability to expand the purely economic view (Ezennia & Hoskara, 2019; Haffner & Heylen, 2011; Mulliner et al., 2013; Salama, 2011). Various indicators can be used to assess housing quality beyond just its cost. These indicators could be seen as serving three primary purposes: (1) to measure the quality of a housing scheme and compare it to others within a country (Homes and Communities Agency, 2011), (2) to measure the quality of housing in one country and compare it to other countries (OECD, 2021b), and (3) to measure housing satisfaction across groups (OECD, 2021a; Riazi & Emami, 2018). An example of the first purpose is England's Housing Quality Indicators (HQIs) system (Homes and Communities Agency, 2011), which is currently withdrawn. HQIs served  as “ measurement and assessment tool to evaluate housing schemes on the basis of quality rather than just cost” design standards mandated for affordable housing providers funded through the National Affordable Housing Programme from 2008 to 2011 and the Affordable Homes Programme from 2011 to 2015. The system comprised ten indicators, which can be categorized into four groups. The first category focused on the location and proximity to amenities and services. The second dealt with site-related aspects such as landscaping, open spaces, and pathways. The third pertained to the housing unit itself, encompassing factors like noise, lighting, accessibility, and sustainability. Lastly, the fourth category addressed the external environment (Homes and Communities Agency, 2011). To enable meaningful cross-country comparisons, it is crucial that the data used for measuring and assessing these indicators are both available and up-to-date. However, it is important to acknowledge that this may not be the case in all countries, as pointed out by the OECD in 2021 (OECD, 2021b). Consequently, to accurately determine what residents are paying for in terms of quality and to facilitate meaningful comparisons, the OECD 2021 Policy Brief on Affordable Housing has emphasized the necessity of two additional housing quality indicators to complement affordability measurements. The first proposed indicator is the "Overcrowding Rate," which evaluates whether a dwelling provides sufficient space for household members based on their composition. This metric assesses whether residents have adequate living space according to the size and structure of their household. The second indicator is the "Housing Deprivation Rates," which gauge inadequate housing conditions. This encompasses issues related to maintenance, such as roofs, walls, floors, foundations, and deteriorating window frames. Moreover, these rates consider the absence of essential amenities, including sanitary facilities. By taking all these factors into account, this indicator offers a comprehensive perspective on the overall quality and habitability of housing in a specific area. Considering subjective measures of housing affordability can be advantageous when assessing housing affordability and quality based on household perceptions. These measures aim to capture housing satisfaction, reflecting the quality of the dwelling as accommodation (OECD, 2021a). In a broader context, housing satisfaction might be termed residential satisfaction, encompassing not just the dwelling but also its surroundings, including places and people. Residential satisfaction assesses how well the current residence and surrounding environment align with the household's desired living conditions (Riazi & Emami, 2018). Therefore, incorporating subjective measures is valuable in assessing housing affordability, helping to identify the determinants of housing satisfaction. Indicators such as satisfaction with the availability of good and affordable housing are crucial aspects to consider in this context (OECD, 2021a). When it comes to sustainability indicators, incorporating them into the measurement of housing affordability remains a wicked  problem. Finding a single comprehensive measure that encompasses the multifaceted aspects of sustainability related to housing affordability is challenging. The technical complexity stems from the necessity to integrate assessments of household characteristics, environmental impacts, financing, and financial aspects, along with housing stress factors. This challenge is exacerbated by the persistent fluctuations in housing prices and recurring expenses like water and energy bills (AHC, 2019). Hence, easily calculable methods such as the Income-to-Rent Ratio (IRM) and Residual Income Model (RIM) continue to be widely used for assessing housing affordability from a top-down perspective at a macro level. Although imperfect, these methods still provide valuable support for policy decision-making to a certain extent (AHC, 2019; Haffner & Heylen, 2011; OECD, 2021a).   

Life Cycle Assessment (LCA) is a standardised method to comprehensively quantify environmental impacts caused by the production of goods and services, which can be used to inform decision-making in building design. Measurable indicators include Global Warming Potential (GWP), acidification, eutrophication, and water use to name a few (European Commission, 2010). LCA can be used to account for all input and output flows related to the entire building life cycle, from raw material acquisition, manufacture, use and maintenance (e.g. while the building is occupied), to the deconstruction and beyond End-of-Life phase (Sartori et al., 2021). Calculating an LCA requires information for building products and processes usually found in the Bill of Quantities, which includes the type of material and its density combined with the amount of material, measured in either volume or area. The European standard EN 15978 (2011) provides guidance for the calculation method, which breaks down the life cycle into phases A to D, these are: A Production and Construction, B Use, C End-of-Life, and D Beyond End-of-Life. It should be noted however, that it is difficult to compare different buildings using LCA, as methodologies and assumptions vary, impacting results (Ramboll, 2023). An LCA that includes stage D is known as a ‘cradle-to-cradle’ assessment, this supports a circular approach and considers scenarios relating to the building after its ‘useful service life’. It is crucial for stakeholders to consider the beyond End-of-Life impacts when planning and designing housing to support the circular economy transition, primarily through promoting future material reuse. LCA is an increasingly relevant component of sustainability assessments for buildings following demand for transparency from the construction industry and trends in performance-based design (Sartori et al., 2021). The LCA method has been incorporated into the European Level(s) framework (Dodd & Donatello, 2020), and BREEAM and LEED assessments. The European Commission advocates for LCA, describing it as the "best framework for assessing the potential environmental impacts of products" (European Commission, n.d.). LCA therefore plays an increasingly prominent role in supporting EU policy and meeting the ambitions of the European Green Deal and related initiatives, such as the Circular Economy Action Plan (European Commission, 2020). At the national level, several European countries utilise LCA to regulate embodied carbon, with other countries expected to follow suit in the coming years (Röck et al., 2022).

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.