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)

Life Cycle Costing (LCC) is a method used to estimate the overall cost of a building during its different life cycle stages, whether from cradle to grave or within a predetermined timeframe (Nucci et al., 2016; Wouterszoon Jansen et al., 2020). The Standardised Method of Life Cycle Costing (SMLCC) identifies LCC in line with the International Standard ISO 15686-5:2008 as "Methodology for the systematic economic evaluation of life cycle costs over a period of analysis, as defined in the agreed scope." (RICS, 2016). This evaluation can provide a useful breakdown of all costs associated with designing, constructing, operating, maintaining and disposing of this building (Dwaikat & Ali, 2018). Life cycle costs of an asset can be divided into two categories: (1) Initial costs, which are all the costs incurred before the occupation of the house, such as capital investment costs, purchase costs, and construction and installation costs (Goh & Sun, 2016; Kubba, 2010); (2) Future costs, which are those that occur after the occupancy phase of the dwelling. The future costs may involve operational costs, maintenance, occupancy and capital replacement (RICS, 2016). They may also include financing, resale, salvage, and end-of-life costs (Karatas & El-Rayes, 2014; Kubba, 2010; Rad et al., 2021). The costs to be included in a LCC analysis vary depending on its objective, scope and time period. Both the LCC objective and scope also determine whether the assessment will be conducted for the whole building, or for a certain building component or equipment (Liu & Qian, 2019; RICS, 2016). When LCC combines initial and future costs, it needs to consider the time value of money (Islam et al., 2015; Korpi & Ala-Risku, 2008). To do so, future costs need to be discounted to present value using what is known as "Discount Rate" (Islam et al., 2015; Korpi & Ala-Risku, 2008). LCC responds to the needs of the Architectural Engineering Construction (AEC) industry to recognise that value on the long term, as opposed to initial price, should be the focus of project financial assessments (Higham et al., 2015). LCC can be seen as a suitable management method to assess costs and available resources for housing projects, regardless of whether they are new or already exist. LCC looks beyond initial capital investment as it takes future operating and maintenance costs into account (Goh & Sun, 2016). Operating an asset over a 30-year lifespan could cost up to four times as much as the initial design and construction costs (Zanni et al., 2019). The costs associated with energy consumption often represent a large proportion of a building’s life cycle costs. For instance, the cumulative value of utility bills is almost half of the cost of a total building life cycle over a 50-year period in some countries (Ahmad & Thaheem, 2018; Inchauste et al., 2018). Prioritising initial cost reduction when selecting a design alternative, regardless of future costs, may not lead to an economically efficient building in the long run (Rad et al., 2021). LCC is a valuable appraising technique for an existing building to predict and assess "whether a project meets the client's performance requirements" (ISO, 2008). Similarly, during the design stages, LCC analysis can be applied to predict the long-term cost performance of a new building or a refurbishing project (Islam et al., 2015; RICS, 2016). Conducting LCC supports the decision-making in the design development stages has a number of benefits (Kubba, 2010). Decisions on building programme requirements, specifications, and systems can affect up to 80% of its environmental performance and operating costs (Bogenstätter, 2000; Goh & Sun, 2016). The absence of comprehensive information about the building's operational performance may result in uninformed decision-making that impacts its life cycle costs and future performance (Alsaadani & Bleil De Souza, 2018; Zanni et al., 2019). LCC can improve the selection of materials in order to reduce negative environmental impact and positively contribute to resourcing efficiency (Rad et al., 2021; Wouterszoon Jansen et al., 2020), in particular when combined with Life Cycle Assessment (LCA). LCA is concerned with the environmental aspects and impacts and the use of resources throughout a product's life cycle (ISO, 2006). Together, LCC and LCA contribute to adopt more comprehensive decisions to promote the sustainability of buildings (Kim, 2014). Therefore, both are part of the requirements of some green building certificates, such as LEED (Hajare & Elwakil, 2020).     LCC can be used to compare design, material, and/or equipment alternatives to find economically compelling solutions that respond to building performance goals, such as maximising human comfort and enhancing energy efficiency (Karatas & El-Rayes, 2014; Rad et al., 2021). Such solutions may have high initial costs but would decrease recurring future cost obligations by selecting the alternative that maximises net savings (Atmaca, 2016; Kubba, 2010; Zanni et al., 2019). LCC is particularly relevant for decisions on energy efficiency measures investments for both new buildings and building retrofitting. Such investments have been argued to be a dominant factor in lowering a building's life cycle cost (Fantozzi et al., 2019; Kazem et al., 2021). The financial effectiveness of such measures on decreasing energy-related operating costs, can be investigated using LCC analysis to compare air-condition systems, glazing options, etc. (Aktacir et al., 2006; Rad et al., 2021). Thus, LCC can be seen as a risk mitigation strategy for owners and occupants to overcome challenges associated with increasing energy prices (Kubba, 2010). The price of investing in energy-efficient measures increase over time. Therefore, LCC has the potential to significantly contribute to tackling housing affordability issues by not only making design decisions based on the building's initial costs but also its impact on future costs – for example energy bills - that will be paid by occupants (Cambier et al., 2021). The input data for a LCC analysis are useful for stakeholders involved in procurement and tendering processes as well as the long-term management of built assets (Korpi & Ala-Risku, 2008). Depending on the LCC scope, these data are extracted from information on installation, operating and maintenance costs and schedules as well as the life cycle performance and the quantity of materials, components and systems, (Goh & Sun, 2016) These information is then translated into cost data along with each element life expectancy in a typical life cycle cost plan (ISO, 2008). Such a process assists the procurement decisions whether for buildings, materials, or systems and/or hiring contractors and labour, in addition to supporting future decisions when needed (RICS, 2016). All this information can be organised using Building Information Modelling (BIM) technology (Kim, 2014; RICS, 2016). BIM is used to organise and structure building information in a digital model. In some countries, it has become mandatory that any procured project by a public sector be delivered in a BIM model to make informed decisions about that project (Government, 2012). Thus, conducting LCC aligns with the adoption purposes of BIM to facilitate the communication and  transfer of building information and data among various stakeholders (Juan & Hsing, 2017; Marzouk et al., 2018). However, conducting LCC is still challenging and not widely adopted in practice. The reliability and various formats of building related-data are some of the main barriers hindering the adoption of LCCs (Goh & Sun, 2016; Islam et al., 2015; Kehily & Underwood, 2017; Zanni et al., 2019).

Industrialised Construction, also referred to as Modern Methods of Construction in the UK (Ministry of Housing, 2019) and Conceptueel Bouwen (Conceptual Building) in the Netherlands (NCB, n.d.), is a broad and dynamic term encompassing innovative techniques and processes that are transforming the construction industry (Lessing, 2006; Smith & Quale, 2017). It is a product-based approach that reinforces continuous improvement, rather than a project-based one, and emphasises the use of standardised components and systems to improve build quality and achieve sustainability goals (Kieran & Timberlake, 2004).  Industrialised Construction can be based on using a kit-of parts and is often likened to a LEGO set, as well as the automotive industry's assembly line and lean production. Industrialisation in the construction sector presents a paradigm shift, driven by advancements in technology (Bock & Linner, 2015). It involves both off-site and on-site processes, with a significant portion occurring in factory-controlled conditions (Andersson & Lessing, 2017). Off-site construction entails the prefabrication of building components manufactured using a combination of two-dimensional (2D), three-dimensional (3D), and hybrid methods, where traditional construction techniques meet cutting-edge technologies such as robotic automation. Industrialised construction is not limited to off-site production, it also encompasses on-site production, including the emerging use of 3D printing or the deployment of temporary or mobile factories. Industrialised Construction increasingly leverages digital and industry 4.0 technologies, such as Building Information Modelling (BIM), Internet of Things, big data, and predictive analysis (Qi et al., 2021). These processes and digital tools enable accurate planning, simulation, and optimisation of construction processes, resulting in enhanced productivity, quality, and resource management. It is important to stress that Industrialised Construction is not only about the physical construction methods, but also the intangible processes involved in the design and delivery of buildings. Industrialised construction offers several benefits across economic, social, and environmental dimensions. From an economic perspective, it reduces construction time and costs in comparison to traditional methods, while providing safer working conditions and eliminates delays due to adverse weather. By employing standardisation and efficient manufacturing processes, it enables affordable and social housing projects to be delivered in a shorter timeframe through economies of scale (Frandsen, 2017). On the social front, Industrialised Construction can enable mass customisation and customer-centric approaches, to provide more flexible solutions while maintaining economic feasibility (Piller, 2004). From an environmental standpoint, industrialised construction minimises waste generation during production by optimising material usage and facilitates the incorporation of Design for Disassembly (Crowther, 2005) and the potential reusability of building elements, promoting both flexibility and a Circular Economy (EC, 2020). This capability aligns with the principles of cradle-to-cradle design, wherein materials and components are continuously repurposed to reduce resource depletion and waste accumulation. Challenges remain in terms of overcoming misconceptions and gaining social acceptance, the slow digital transformation of the construction industry, high factory set-up costs, the lack of interdisciplinary integration of stakeholders from the initial stages, and adapting to unconventional workflows. However, Industrialised Construction will undoubtedly shape the future of the built environment, providing solutions for the increasing demand for sustainable and affordable housing (Bertram et al., 2019).

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).