From the three pillars of sustainable development, economic, environmental and social, the latter  involving social equity and the sustainability of communities, has  been especially neglected. Ongoing problems caused by conflicting economic, environmental and social goals with regard to the processes of urbanisation continue. underpinning economic growth that contradict principles of environmental and social justice (Boström, 2012; Cuthill, 2010; Winston, 2009). Research on sustainable development highlights the need for further investigation of social sustainability (Murphy, 2012; Vallance et al., 2011). Social sustainability has been interpreted as an umbrella term encompassing many other related concepts; “social equity and justice, social capital, social cohesion, social exclusion, environmental justice, quality of life, and urban liveability” (Shirazi & Keivani, 2019, p. 4). A vast number of studies have been dedicated to defining social sustainability by developing theoretical frameworks and indicators particularly relevant to urban development and housing discourse (Cuthill, 2010; Dempsey et al., 2011; Murphy, 2012; Woodcraft, 2012). However, with a lack of consensus on the way of utilising these frameworks in a practical way, especially when applied to planning, social sustainability has remained difficult to evaluate or measure. Consequently, planning experts, housing providers and inhabitants alike understand social sustainability as a normative concept, according to established social norms, and less as an opportunity to critically examine existing institutions. Vallance et al (2011) provide three categories to analyse social sustainability, development, bridge and maintenance sustainability: (a) social development improves conditions of poverty and inequity, from the provision of basic needs to the redistribution of power to influence existing development paradigms; (b) the conditions necessary to bridge social with ecological sustainability, overcoming currently disconnected social and ecological concerns; and (c) the social practices, cultural preferences as well as the environments which are maintained over time. Maintenance social sustainability particularly deals with how people interpret what is to be maintained and includes “new housing developments, the layout of streets, open spaces, residential densities, the location of services, an awareness of habitual movements in place, and how they connect with housing cultures, preferences, practices and values, particularly those for low-density, suburban lifestyles” (Vallance et al., 2011, p. 345). Therefore, the notion of maintenance is especially important in defining social sustainability by directly investigating the established institutions, or “sets of norms” that constitute the social practices and rules, that in turn, affect responsibilities for planning urban spaces. A conceptual framework that appears frequently in social sustainability literature is that of Dempsey et al. (2011)⁠ following Bramley et al. (2009), defining social sustainability according to the variables of social equity and sustainability of community and their relationship to urban form, significantly at the local scale of the neighbourhood. In terms of the built environment, social equity (used interchangeably with social justice) is understood as the accessibility and equal opportunities to frequently used services, facilities, decent and affordable housing, and good public transport. In this description of local, as opposed to regional services, proximity and accessibility are important. Equitable access to such local services effectively connects housing to key aspects of everyday life and to the wider urban infrastructures that support it. Sustainability of community is associated with the abilities of society to develop networks of collective organisation and action and is dependent on social interaction. The associated term social capital has also been used extensively to describe social norms and networks that can be witnessed particularly at the community level to facilitate collective action (Woolcock, 2001, p. 70). They might include a diversity of issues such as resident interaction, reciprocity, cooperation and trust expressed by common exchanges between residents, civic engagement, lower crime rates and other positive neighbourhood qualities that are dependent on sharing a commitment to place (Foster, 2006; Putnam, 1995; Temkin & Rohe, 1998). In fact, “the heightened sense of ownership and belonging to a locale” is considered to encourage the development of social relations (Hamiduddin & Adelfio, 2019, p. 188). However, the gap between theoretical discussions about social sustainability and their practical application has continued. For example, the emphasis of social sustainability as a target outcome rather than as a process has been prioritised in technocratic approaches to planning new housing developments and to measuring their success by factors which are tangible and easier to count and audit. Private housing developers that deal with urban regeneration make bold claims to social sustainability yet profound questions are raised regarding the effects of gentrification (Dixon, 2019). Accordingly, the attempted methods of public participation as planning tools for integrating the ‘social’ have been found to be less effective - their potential being undercut due to the reality that decision-making power has remained at the top (Eizenberg & Jabareen, 2017). Therefore, social sustainability is not a fixed concept, it is contingent on the interdependence of the procedural aspects (how to achieve social sustainability) and substantive aspects (what are the outcomes of social sustainability goals) (Boström, 2012). From this point of view, social sustainability reveals its process-oriented nature and the need to establish processes of practicing social sustainability that begin with the participation of citizens in decision-making processes in producing equitable (i.e. socially sustainable) development. As a dimension of sustainable development that is harder to quantify than the economic or environmental aspects, the operationalisation of social sustainability goals into spatial, actionable principles has remained a burgeoning area of research. In such research, methods for enhancing citizen participation are a particularly important concern in order to engage and empower people with “non-expert” knowledge to collaborate with academic researchers.

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).

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)

A universal definition of social housing is difficult, as it is a country-specific and locally contextualised topic (Braga & Palvarini, 2013). This review of the concept focuses on social housing in the context of the UK from the late 1980s, which Malpass (2005) refers to as the phase of ‘restructuring the housing and welfare state’, to the early 2000s, known as the phase of the ‘new organisation of social housing’. In response to previous demands for housing, such as those arising during the Industrial Revolution, and recognising the persistent need to address the substandard quality of housing provided by private landlords in the UK (Scanlon et al., 2015), the primary objective of social housing has historically been to enhance the overall health conditions of workers and low-income populations (Malpass, 2014; Scanlon et al., 2015). However, this philanthropic approach to social housing changed after the Second World War when it became a key instrument to address the housing demand crisis. Private initiatives, housing associations, cooperatives and local governments then became responsible for providing social housing (Carswell, 2012; Scanlon et al., 2015). Social housing in the UK can be viewed from two perspectives: the legal and the academic (Granath Hansson & Lundgren, 2019). Along these two perspectives, social housing is often analysed based on four main criteria: the legal status of the landlord or provider, the tenancy system or tenure, the funding mechanism or subsidies, and the target group or beneficiaries (Braga & Palvarini, 2013; Carswell, 2012; Granath Hansson & Lundgren, 2019). From a legal perspective, social housing maintained its original goals of affordability and accessibility during the restructuring period in the late 1980s. However, citing the economic crisis, the responsibility for developing social housing shifted from local authorities to non-municipal providers with highly regulated practices aligned with the managerialist approach of the welfare state (Granath Hansson & Lundgren, 2019; Malpass, 2005; Malpass & Victory, 2010). Despite the several housing policy reviews and government changes, current definitions of social housing have maintained the same approach as during the restructuring period. Section 68 of the Housing and Regeneration Act 2008, updated in 2017, defines social housing as low-cost accommodation provided to people whose rental or ownership needs are not met by the commercial market (HoC, 2008; 2017, pp. 50-51). The Regulator of Social Housing, formerly the Homes and Communities Agency, has adopted the earlier definition of social housing and clarified which organisations provide it across the UK. These organisations include local authorities, not-for-profit housing associations, cooperatives, and for-profit organisations (RSH, 2021). In contrast, the National Housing Federation emphasises the affordability of social housing regardless of the type of tenure or provider (NHF, 2021). From an academic perspective, Malpass (2005) explains that during the restructuring phase, social housing was defined as a welfare-supported service – although it did have limitations, which meant that funding principles shifted from general subsidy to means-tested support for housing costs only, which later formed the basis for the Right to Buy Act introduced by the Thatcher government in the early 1980s (Malpass, 2005, 2008). The restructuring phase, however, came as a response to the housing 'bifurcation' process that began in the mid-1970s and accelerated sharply from the 1980s to 1990s (Kleinman et al., 1998; Malpass, 2005). During this phase, the role of social housing in the housing system was predominantly residual, with greater emphasis placed on market-based solutions, and social housing ownership concerned both local authorities and housing associations (Malpass & Victory, 2010). This mix has influenced the perception of social housing in the 'new organisation' phase as a framework that regulates public housing intervention for specific groups and focuses on enabling non-municipal providers (Malpass, 2005, 2008; Malpass & Victory, 2010). Currently, as Carswell (2012) explains, social housing plays an important role in nurturing a variety of initiatives aimed at providing ‘good-quality’ and ‘affordable’ housing for vulnerable and low-income groups (Carswell, 2012). Oyebanji (2014) sees social housing as any form of government-regulated housing provided by public institutions, including non-profit organisations (Oyebanji, 2014). Additionally, Bengtsson (2017) describes social housing as a system that aims to provide households with limited means, but only after their need has been confirmed through testing (Bengtsson, B, 2017 as cited in Granath Hansson & Lundgren, 2019). To a great extent, social housing in the UK can be seen as a service system that is intricately linked to the welfare state and influenced by political, economic, and social components. Despite being somehow determined by common factors and actors,  the relationship between social housing and the welfare state can sometimes be complex and subject to fluctuations (Malpass, 2008). In this context, the government plays a vital role in shaping and implementing the mechanisms and practices of social housing. While the pre-restructuring phase focused on meeting the needs of the people by increasing subsidies and introducing the right to buy (Stamsø, 2010), the aim of the restructuring phase was to meet the needs of the market by promoting economic growth (privatisation, market-oriented policies and reducing the role of local authorities) (Stamsø, 2010; Malpass, 2005) . The new organisational phase, on the other hand, works to meet and balance the needs of all, with people, politics and the economy becoming more intertwined. Welfare reform legislation passed in 2010 aims to enable people to meet their needs, but through 'responsible' subsidies, leading to a new policy stance that has been described as 'neoliberal' thinking (Hickman et al., 2018). However, there are still no strict legal requirements for the organisation and development of social housing as an independent service system, and most of the barriers to development are closely related to the political orientation of the government, rapid changes in housing policy and challenges arising from providers' perceptions of existing housing policy structures (Stasiak et al., 2021).