Aya Elghandour

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.    

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).

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).