Renewable and Sustainable Energy Reviews 161 (2022) 112388 Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Factors and actions for the sustainability of the residential sector. The nexus of energy, materials, space, and time use Laura À. Pérez-Sánchez a, *, Raúl Velasco-Fernández a, Mario Giampietro a, b a Institute of Environmental Science and Technology (ICTA-UAB), Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain b ICREA, Passeig Lluís Companys 23, Barcelona, 08010, Spain A R T I C L E I N F O A B S T R A C T Keywords: Residential end-uses represent a significant share of final energy consumption and material stocks. However, Household metabolism approaching sustainability of the residential sector merely as an environmental technical problem is insufficient. Nexus Home is the center of daily life providing essential functions to people. Household metabolism is not a matter of Social innovation the sum of individual behaviors, typologies of buildings, or energy uses stripped out of context, but the system Sufficiency Energy efficiency that emerges from the historical combination of these elements and the functions it performs. The residential Construction sector sector comprises both families (units of organized individuals) and dwellings (within municipalities/urban forms). To analyze these dynamics, we draw upon practice theory and Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism (MuSIASEM) illustrating with data from Sweden and Spain in 2015. The objective is to establish an interdisciplinary framework for analyzing the sustainability of the residential sector. We also present a list of possible measures and their trade-offs in diverse dimensions: energy carrier consumption and greenhouse gas emissions, materials, floor area, human activity, social organization and institutions, finance and desirability. Even though the inclusion of all variables in a single model is not feasible, the holistic understanding of household metabolism can help build coherent anticipation scenarios by selecting plausible hypotheses. Ul­ timately, this allows making profound transformations to sustainability. 1. Introduction Plain technological assessments assume given standardized needs. In many cases, they reduce the problem to the thermal performance. They Dwellings are a central part of daily lives and where we spend most analyze the artifact, i.e., the envelope and heating devices, but not its of our time. They represent a big share of the in-use material stocks, whole diversity of functions and contexts. Even though in most northern greenhouse gas emissions, and final energy carrier consumption [1,2]. EU countries heating is the largest energy end-use in households, the These large impacts but at the same time essential function generate functions and use of appliances become essential when analyzing sus­ great policy interest in improving its sustainability. In the European tainability and wellbeing. Governments and companies have put sig­ Union, it has resulted in diverse directives and initiatives approaching nificant effort into decreasing energy use within the framework of mainly its technical side: the Renovation wave for Europe, the New technical energy efficiency. However, defining theoretically sound European Bauhaus, and the Energy Performance of Buildings Directive. operational definitions of energy efficiency is not possible [6–8]. One of This interest is also reflected in a large and growing literature. Many the most common definitions is spending less energy on the same ser­ methods, scopes, and dimensions to analyze the housing stock or vice. Generally, the definition of service is not questioned, overlooking buildings coexist, which can be divided in broad terms into social sci­ alternative solutions [9,10]. Yet existent technical solutions for sus­ ences and engineering. Swan and Ugursal [3] and Kavgic et al. [4] tainability are even acknowledged to be not enough [11–14]. Some reviewed and classified models for residential energy consumption and models assessing housing stock development in time do include some Langevin et al. [5] updated Swan and Ugursal’s classification. Even social factors like occupancy or area per inhabitant. When they are though each field irremediably includes aspects of the other, largely are included in models, these are generally more impactful changes than only briefly mentioned, and truly interdisciplinary approaches are energy retrofits [14–19], but the compatibility with social dynamics has lacking. not been fully assessed yet. Therefore, understanding what home is, its * Corresponding author. E-mail addresses: laura.perez.sanchez@uab.cat (L.À. Pérez-Sánchez), raul.velasco@uab.cat (R. Velasco-Fernández), mario.giampietro@uab.cat (M. Giampietro). https://doi.org/10.1016/j.rser.2022.112388 Received 25 July 2021; Received in revised form 24 February 2022; Accepted 16 March 2022 Available online 5 April 2022 1364-0321/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 functions, and its relation to technical issues becomes essential. to other contexts, but the analysis is centered in developed countries On the other side, econometric models are the most commonly used with a large amount of built environment and in this specific time in approach the sustainability of the residential sector [20]. Econometrical history. Homes have changed profoundly through the XXth century both or agent-based analyses are grounded on rationality, giving centrality to in terms of size and types. price signals and individual behavior. Yet the voluntaristic change of In section 2, we describe the theoretical frameworks where the rest of consumer choices is constrained by the option space framed by society. the paper is grounded: MuSIASEM and practice theory. Then, we define Daily life is neither made by a set of discretional individual actions nor the residential sector as the combination of families or household units determined solely by infrastructure. Therefore, it depends on the orga­ and dwellings. Afterwards, we explain the main dynamics of each of nizational and institutional systems and hardware of wires, pipes, and them in sections 4 and 5. Despite this organization in sections, it is power plants: practices are socially ordered [21]. This means that daily impossible to isolate completely the topics, since their dynamics are life can be carried out in a variety of possible patterns of actions [22]. entangled and co-evolve. In section 4, we analyze the members’ These must be coherent in their time use, family needs and duties, cul­ composition and functions of families and put the focus on their time use ture, existent infrastructure, and available external services. patterns. In section 5, we present the housing stock, the social and Even though a case-by-case analysis of each building to assess its technical issues affecting its use, performance, reproduction, and condition and possible refurbishment plays a key role, the mere sum of resource use. We also assess the economic role of the construction and individual solutions will not necessarily increase sustainability. Solu­ real estate sectors. Finally, we present the main conclusions. tions need to be scalable and coordinated in time and space. It is essential to have a broad overview of the combination of families (as 2. MuSIASEM and practice theory institutions of meaning and competences, and as bodies with different characteristics) and dwelling stocks (technologies conformed by mate­ MuSIASEM is a system of accounting to analyze societies and systems rial elements heir to preterit practices). These systems have large inertia in a multi-dimensional and multi-scalar way that is based on Georgescu- and thus changes are progressive. This large-scale perspective is useful Roegen’s fund-flow scheme [29,30]. Funds sustain the activities of the for a variety of issues: the activities carried out by households and their society and must be reproduced. They are considered to remain the same insertion in daily lives, what should society do with existing housing, the during the period of analysis and define the size of the system. In this need (or not) for its expansion, and how to maintain and build it. case, we consider human activity (in hours per year), floor area (in m2, It is not only the scale of analysis but also the multidimensional the space devoted to housing), and power capacity (in W, the power of character of the residential sector that is important. When addressing devices and appliances). sustainability issues and policy, it is unavoidable to face “wicked Human Activity is a central variable of the social side of the resi­ problems” [23], in which many relevant perspectives and dential sector: household units, who must manage their budget of time non-equivalent dimensions coexist. They should be considered simul­ to fulfill their needs and duties. On the other hand, the most techno­ taneously because there are incompatibilities between goals. This un­ logical side of the residential sector (dwellings) is defined by the Floor avoidable existence of conflicting criteria of performance makes that Area and the Power Capacity. As we will see in the next sections, these there is no optimal answer to social problems. Only when considering dimensions are in fact connected. both the large-scale and multidimensionality, transformative solutions When we talk of dwellings, we do not refer to a static monolithic can be proposed for a democratic discussion, acknowledging the structure. They consist of different parts or layers of different levels of possible trade-offs and uncertainties. flexibility and lifetimes (site, structure, skin, services, space plan, and Mata et al. [20] made a review of the most significant variables in stuff) [31,32]. Here we divide them into the two main funds, considering models for energy and CO2 emissions studied in the literature for the their broad functions and partaking artifacts: Floor Area and Power residential sector. Mata et al. [24] made a review on non-technological Capacity. The structure and envelope of buildings define Floor Area (in and behavioral options for decarbonizing buildings. Hertwich et al. [25] m2) and are built in the construction sector (section 5.5.). Floor Area is a also listed a set of strategies in the framework of material efficiency for key variable for desirability and resource uses (materials, land use, en­ buildings. However, a truly integrative perspective to the diversity and ergy, GHG emissions, etc.). Dwellings are full of an ever-increasing trade-offs of variables from both social and technological approaches in number and variety of appliances that carry out functions and/or the residential sector is lacking. reduce the required time and effort to perform them by metabolizing The objective of this paper is to unravel the tight entanglement be­ energy carriers, the Power Capacity (in W) [33]. The size, access, and tween social and technological issues in household metabolism and to use of these funds are key to understanding the performance of the explore possible actions for increasing sustainability of the residential residential sector. On the other hand, flows are those inputs and outputs sector. We analyze their trade-offs between a large variety of di­ that are metabolized or generated by the funds: GHG emissions, energy mensions, focusing on the relation of the use of time, space, energy, and carriers, materials, etc. materials. To do so, we build on concepts from practice theory [21,26] A characterization of the metabolic pattern in terms of flow-fund and Multi-Scale Integrated Assessment System of Accounting (MuSIA­ relations allows an integrated analysis of the use of human time, en­ SEM) [27]. Throughout the paper, we detail points to consider in the ergy, and materials inside the functional and structural elements oper­ analysis and possible actions to increase sustainability belonging to: (i) ating in the residential sector. An overview of the set of relations changes of social practices (adopted by the households, but only if an considered to integrate the different quantitative assessments of the appropriate context is available) and (ii) technological improvements residential sector is given in Fig. 1. There it is possible to see how the (applied to structural elements associated with the dwellings). They are concept of metabolism – i.e., forced relations over flows and fund ele­ summarized in Tables 1 and 2 (numbered for ease of reference in the ments within a metabolic pattern having the goal to reproduce the body of the paper), including their effects on energy, greenhouse gas whole metabolic system – can be used to integrate information and in­ emissions, space, materials, time use, social organization, and desir­ dicators calculated using different metrics – flows per hour of Human ability. Understanding these dynamics is essential to make plausible Activity and flows per square meter of Floor Area or watt of Power scenarios in models and effective policies. Capacity. We complement the explanations with data from Sweden and Spain Practice theory connects the use of time and daily patterns of people in 2015. Sweden and Spain are both European countries but have sig­ to the existent infrastructure and knowledge. Both societal patterns and nificant differences in types of dwelling, income, and the organization of technology are tightly linked. Practice theory defines the following el­ care [28], and thus in daily life patterns. Most of the included literature ements: material elements, competence, and meaning [21]. The time is referred to western countries. In this sense, ideas might be applicable uses require building competence (skill, know-how, technique) through 2 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Table 1 Actions to increase sustainability of the residential sector at the household unit dimension (social innovation) and effects on diverse variables. Families/household units Possible effects and trade-offs Action Examples Energy and GHG emissions Floor area, power Human activity Social organization and capacity and desirability Operational Production materials Shareability (1.1) Increase Families living Decrease with Decrease due to Fewer dwellings, Less overall time use if Social acceptance of and household together for longer, economies of scale. shared spaces larger but relatively activities are shared new family types and/ economies size: larger avoiding individual Shared activities (kitchen, smaller.Basic (cooking, household or living in a of scale. occupation. households, entail shared energy bathroom), services like kitchen maintenance, etc.) but community. transforming use. infrastructure, and bathroom and larger Requirement of household units to If people live and devices. many other devices synchronization and organization and larger multi-family together but still do are shared so less coordination. commitment (less units with common not commit to space per capita is individualism and spaces and common activities needed. loneliness, but activities. (e.g., cooking), the Compatibility with potentially more operational current dwelling conflicts). Purchasing resource use might stock must be power within the not decrease checked: number of market enables significantly. rooms, size, etc. individualization. . (1.2) Shifting Cooking in Less energy per unit Decrease (fewer Fewer but larger Increase time in Requirement of activities from community kitchens of service devices are devices are collective activities organization and the household or restaurants, (economies of needed). required. More and/or requirement commitment in to the organized childcare, scale). collective space is to give salaries if they communities, or community or product-service required at expense are considered paid significant changes in market. systems. of privative space work. Potential companies from (with economies of economies of scale product to service scale). This kind of and quality provision. space might lack in improvement by existent buildings. specialization of Cultural change on how work. needs are fulfilled. Requirement of density of demand for providing the service at scale, related to the type of municipality and urban form. (1.3) Sharing Carpooling, cooking Less energy in use Decrease (fewer Fewer devices are Time of the device use Tight organization: less the use/service for the whole per unit of service. devices are needed. is shared but it individual flexibility of power household unit. needed). requires strong time- and more commitment capacity. space synchronization to schedules. with others. (1.4) Share Carsharing,laundry Possibility to have Decrease, but Fewer devices are No immediate access Requirement of power rooms in apartment better or more devices may be required. to devices. Sometimes organization and rules capacity. buildings, tool diversity of devices used less Less space is devices are needed at (less flexibility) and libraries due to shared cost carefully, required at home the same time so their commitment to care for and to update their shortening their but alternative utilization factor common devices. characteristics more lifetime. common spaces to cannot increase (e.g., The social distinction often due to its more store those devices special or larger given by the ownership intensive use and must be found. cooking devices for of devices might thus shorter Christmas or car use disappear when lifetime. for commuting). sharing. Flexibility of (1.5) Decrease Lower indoor Decrease. Less devices might Decreasing time Acceptance of lower time and quantitative or temperature in be needed. pressure. standards or new daily level of qualitative winter and higher in routines (e.g., suits in services. expectations of summer, not offices in summer are activities. washing clothes not compatible with every time they are warm weather). used, simpler food, living closer to work. (1.6) Give Members of the Flexibility in the time use budget makes Less devices might The time pressure of If household units are flexibility to household without the use of technology (and energy) less be needed (e.g., car the household is larger, retired members the household strong scheduling necessary due to the decrease in time for matching relieved. Possibility could provide support time budget. and with time to pressure. multiple activities that some members to other members. If devote to household It could be useful to adapt to electricitiy with strong do not have access to household units keep needs (e.g., systems with demand response. scheduling such as sufficient own income the nuclear family childcare, elderly paid work and and therefore have an model, the model care): stay-at-home childcare). economic dependency would be a stay-at- parents, part-time on others. home parent. Other workers, retired. alternatives for Flexibilization of increasing flexibility paid working hours. could be found from paid work or public or private services. 3 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Table 2 Actions to increase sustainability of the residential sector at the dwellings dimension (technical) and effects on diverse variables. Dwellings Possible effects and trade-offs Action/strategy Examples Energy and GHG emissions Floor area, power Human activity Social organization capacity and and desirability Operational Production materials Amount of (2.1) Use less Bike instead of a Decrease. Decrease. Less materials and More time is Social structures power power capacity. car, manual devices. required for the should allow for capacity and chopping instead of Potential increase in same activity (‘Time flexibility and its control. a blender. shareability of investments in the changing devices if they are environment’) expectations of used only seldom. activities. (2.2) Smart Sensors, internet of Higher stand-by Increase. Increase of need of Automation allows Comfort might homes and things, baseline electricity electronics, internet services to delink increase with digitalization automatization. use. infrastructure. from presence of automatization (e. Use of appliances Electronic devices inhabitants (more g., turning on can be shifted are difficult to flexibility in time heating before given external recycle and have an use). More inhabitants get information on increasingly diverse possibility for home) but might be energy prices of scarce materials. multitasking. expensive, difficult allowing demand to accept or learn to response. use by certain parts of society. Its use can be associated with symbolical power, which increases its desirability. Maintenance and (2.3) Improve Refurbishment of With better Increase. More materials. Maintaining jobs in Business as usual of renovation thermal dwellings insulation, The distribution of construction sector. practices. (trade-off of characteristics increasing buildings need less emissions and Buildings with operational of buildings insulation, energy to provide energy use worse energy and construction of the same service. changes: a larger performance are manufacturing nZEB buildings. Expectations and peak of impacts in usually related to resource use) thus service might the construction lower income increase at a lower phase and lower households. The cost, increasing operational in high costs of overall energy time. refurbishment can demand (Jevons’ be a burden to them paradox). or generate Some processes of characteristics for renoviction. thermal performance are set in early design stage that are not changeable during refurbishment (e. g., orientation), so the improvement via refurbishment is limited. (2.4) Replacement of Less energy in use Increase. Larger amount and Maintaining jobs in Business as usual in Substitution of heating systems or but must be The balance rarer materials manufacturing, less daily life. appliances for appliances with a checked with between lifetime difficult to recycle jobs in reparation. decreasing better energy energy in and improvement (e.g., more operational certificate. manufacturing (a in operational electronics, and energy use shortened lifetime energy must be sensors). would increase considered. overall energy consumption) Possible rebound: e.g, a fridge that spends less energy by unit of food but that is larger and therefore ends up using more energy. (2.5) Extend life Repair, More energy in use Less energy in Less materials Less jobs in Acceptance higher of devices - refurbishment, (not updated manufacturing in required in the long manufacturing but risk of failure of ensure remanufacture, technology and the long term. term. Possibly more more in repair. devices. durability maintain, not wear). materials are needed Design for buying up-to-date for the same product durability and devices when old for sturdiness. repairability. ones still work. Materials stay in use longer (fewer recycling loops). (continued on next page) 4 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Table 2 (continued ) Dwellings Possible effects and trade-offs Action/strategy Examples Energy and GHG emissions Floor area, power Human activity Social organization capacity and and desirability Operational Production materials Devices must be designed for repair and maintainability. (2.6) Electrification of The important If the transition of Material use Acceptability of the Substitution of cooking and factor is the change power capacity depends on the replacement of old appliances for heating, biomass of energy carriers follows current recyclability of the devices if new ones changing for heating, electric and not so much renovation rates, it replaced devices. are considered energy carriers vehicles (in order the quantity of may not change. If expensive or old to decrease energy carriers, a the transition ones are in good operational GHG more traditional replaces devices condition. emissions or avoid definition of that could last depletion of fossil energy efficiency more time in use, it fuels). (which are not increases. comparable when considering two different energy carriers). Design/layout (2.7) Space Smaller rooms, Less energy for Decrease. Less materials in Less time for Acceptance of living (dwellings) reduction - smaller dwellings, heating. construction. household in smaller spaces. Downsizing kitchenless homes. If downsizing is maintenance (e.g., Reflection and related to adapting cleaning). definition of what to smaller household sufficient space is. size, this could Sharing spaces with overall increase the more people (larger number of household size) for dwellings, area, and economies of scale. number of appliances. Activitiesshifted to dwellings may require extra space (telework, etc.). (2.8) Give Urban planning Better heating Decrease also Reduction in land Density of Multi-dwelling preference to that concentrates performance in considering use. population given by buildings have apartments (vs new dwellings in multistorey infrastructure In turn, density of apartments allows shared spaces that houses) apartments in the buildings. (roads, pipes, etc.). demand of services proximity of require city instead of Less relative allows some services (less time organization (stairs, promoting houses capturing area for collective services for mobility, lift, gardens, etc.). in suburban sprawl. solar energy and more compact economies of scale). There are less generation in infrastructure (e.g., privacy and private relation to district heating, green areas. consumption. public transport, Urban form more waste collection, favorable to public sharing power transport and capacity). proximity of Depends also on the services and jobs existent housing: (less energy in existent buildings mobility). can generate lock-in. (2.9) Flexible Indeterminate Larger in relation Decrease, since This type of flexible housing. spaces for diverse to climatization. there is less spaces is related to possible uses functional larger floor area. In (avoiding obsolescence, and this case, the scripting). the space is used material benefits are more effectively in in the smaller the long run. obsolescence and thus longer use, and not in the sense of using less floor area. Flexible floor plans Potentially less Decrease, since The floor area can be Less time for The dwelling can with modular energy for heating space can be adapted to the cleaning and adapt to the rooms or walls, since spaces are adapted to the use. household size and maintenance. different foldable furniture, more effectively thus can avoid configurations of etc. used. overkill. However, family along time, this space must be to alternative well coordinated household units or with the to different uses. surrounding spaces However, (matching with the institutions and needs of all affected regulations should users). be able to manage Flexible wall the changes of (continued on next page) 5 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Table 2 (continued ) Dwellings Possible effects and trade-offs Action/strategy Examples Energy and GHG emissions Floor area, power Human activity Social organization capacity and and desirability Operational Production materials divisions might not layout (contracts, have good acoustic ownership, etc.). quality. Materials (2.10) Light- Choose carefully Check impact in Decrease due to Less raw material is More time in Adapt work weighting. structural elements thermal load and less energy for used. engineering design processes. not with a the thus thermal material Structural design (high salaries) and Business as usual in minimum number performance. production. with smaller safety also in construction daily life of users. of sections, but factor. (more carefully adapted to the management). specific load instead, increasing the variety of types of components. (2.11) Reuse of Demountable parts, – Less energy for Less raw materials Less work in Requires new parts. modular structures. material and are required in the construction in situ paradigm of design component long run. Quality (prefabricated for disassembly: production. control to ensure components). More reverse logistics, mechanical work in design, risk properties. deconstruction and assessment, etc. In Material use is less selective general, optimized: designs deconstruction. professionals do not must be adapted to Salaries are higher have experience in existent materials than current designing reusable and might use more material cost. This buildings and material than could change with manage required if higher deconstruction. optimized for environmental Logistics are more lightweighting. protections and complex (space for In global terms, increasing raw storing large Housing stocks are material scarcity. amounts of large growing, so more compnents, materials are transport of large required in new parts). construction than Business as usual in the ones demolished. daily life of users. Old buildings that are currently being demolished were not designed for reuse. (2.12) Recycling Recycled aggregate – Less energy for Housing stocks are More work in Maintenance of of construction concrete, material increasing (so more deconstruction and construction sector material. secondary steel. production, but materials are classification of activity (but with maybe it is required in new materials. higher costs). required for construction than Business as usual in sorting, collection that demolished). daily life of users. and recycling. Most buildings that Energy for are demolished were transport if it not designed for travels long recycling. Material distances. can mostly be downcycled or cascaded. Use of secondary materials requires also raw material and, in many cases, does not fulfill original characteristics. Recyclability is limited by tramp elements and a sufficient concentration of scrap that allows sorting and collection. The cost of recycled materials is higher than raw materials. (2.13) Change Steel production by – Change of energy – These changes do production hydrogen, carbon carriers, important not depend on the (continued on next page) 6 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Table 2 (continued ) Dwellings Possible effects and trade-offs Action/strategy Examples Energy and GHG emissions Floor area, power Human activity Social organization capacity and and desirability Operational Production materials processes of capture in cement changes in the Creation of new construction sector primary production. production infrastructure for itself. They must be materials. infrastructure. new processes. carried out by material production companies that may be even foreign, whose infrastructure is very large, and that have long investment periods. (2.14) Use of Timber as a Worse thermal Carbon Limited yearly Reduction of The largest end-use alternative substitute for steel performance. sequestration supply of renewable building time (due of concrete and biobased and concrete. depending on the material with to modular steel is materials. end-of-life and increasing prefabricated construction. management of competition of other parts). Decreasing demand the harvested end uses (energy, would decrease forestry land. chemicals, etc.). Not activity and jobs in all forestry products those sectors while are useful for increasing in building. Forestry and Wood Potential for industry. reusable modular Building codes construction. might still not be adapted to biobased materials. Professionals and companies do not have enough expertise. Fig. 1. The two parts of the residential sector (household units and dwellings) and simplified key flows from Paid Work and the Environment. time in education and culture, and the material elements make possible practice theory. and limit the allocation of time uses in different ways. Meanings are the cultural conventions and the expectations of people, therefore the 3. The residential sector desirability, which will also depend on the existent and expected ma­ terial base. Devices materialize the sociotechnical imaginaries coming The residential sector is a central part of societal dynamics and of the from society and at the same time affect the social organization option daily life of people. In modern societies, it could be concisely defined as space [34]. Here, material elements refer mainly to Power Capacity and the sector complementary to paid work and the market economy that is Floor Area, our funds. Therefore, there is not a single direction of cau­ responsible for the reproduction of society, as shown in Fig. 1. However, sality or determination, but a co-evolution of the three elements of this is a very simplified view. The residential sector is the combination of 7 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Fig. 2. The residential sector is formed by organized individuals in families that live in dwellings, which are located in and generate different types of municipality, affecting their access to services and paid work. families/household units (of organized individuals) and dwellings thus challenging and not universal. (within municipalities/urban forms), whose functions adapt with the In this sense, families rely on a large variety of out of home support surrounding informal and formal sectors in paid work. This continuous systems, which could be classified as: non-formal (work groups, church, adjustment makes the boundary definition and energy accounting more etc.), informal (extended family, neighbors, extended kin), and formal challenging. What happens in dwellings and home is variable and co­ (school, health agencies, protective agencies, welfare agencies) [40] evolves with the material arrangements and daily practices. It has (see Fig. 7). Although the dichotomy shown in Fig. 1 between paid work changed through history [35,36] and the concept is described differently and households may be too strict since there are other elements outside among disciplines [37,38]. In short, we can say that it is not only a place paid work, it is becoming a reality in countries like Sweden. There, the of rest and leisure but also of (mostly unpaid) work and a center of or­ loss of informal care networks is compensated by a large state formal ganization of daily life and social reproduction. In dwellings, people support within paid work [41], whereas Spain still relies largely on the carry out a large array of activities, including: extended family. The individualization of life and the loss of social interaction based on streets and neighborhoods broke down the balance - Sleeping and rest of family life and the collective [42–44]. - Cooking (food management and cooking, washing dishes) and eating In part, this can be explained by the hypermobile society [45], which - Personal care (showering, dressing up, etc.) delinks people from the area close to home by means of the universali­ - Clothing care (washing clothes, ironing, drying, etc.) zation of the private vehicle and other transport modes. The area and - Leisure (reading, TV, computer, hobbies, social interaction, etc.) social network of daily life can be larger at the expense of being weaker. - Caring for others (helping children with homework, helping with The set of dwellings plus other buildings form municipalities with spe­ personal care, etc.) cific urban forms and define accessibility to services, goods, and work - Telework and other kinds of work (workshops, agriculture, etc.) through daily mobility (from a short walk to a long car drive) (Fig. 2). Metropolitan cities allocate the largest amount and variety of services, The segmentation of “domestic” resource use does not adequately but rural areas are essential in their functions of the management of address modern life practices [39]. The residential sector is connected biomass and mineral flows and ecosystems. Compact urban forms that and interdependent to many other sectors to which can leak activities comprise multi-dwelling buildings generate higher densities of demand. and their concomitant resource use. For example, food can be provided In consequence, they make viable services such as retail and education by cooking at home with diverse levels of support of processed products and centralize water, energy, internet, transport, and waste infrastruc­ from the food industry, home delivery or by going to a restaurant. This ture. Proximity and vitality, among others, enableenable active mobility means that functions that could be found within families in a type of and thus potentially decrease energy use and GHG emissions in mobility society, can be collectivized or marketed partially or completely in [43,46,47]. Single-family houses allow a life a priori closer to green others. These are especially important in the domain of unpaid work: areas, but the generalization of this model in suburban sprawl occupies food provisioning, care centers for the elderly and children, laundry, etc. large extensions of Land Use, increasing the distance to services and For example, a couple with children could follow a male breadwinner work. This entails a dependency on the private car for the most basic model, where all reproduction tasks are carried out unpaid by the daily needs, overriding the initial individual benefits. Single family stay-at-home mother: cooking, cleaning, care, etc. On the other hand, a houses are thus private goods [48], that can provide benefits to a certain young professional may live on his own in a small flat. This professional limited amount of people, but lose their intrinsic characteristics when works long hours, always eats out, contracts a worker for housekeeping, they are extensively put into practice. Therefore, both the type of and even showers at the gym. In this case, all household services are dwelling and the emerging context play a role in time and energy use in marketed, and the dwelling is basically a place to store and sleep when transport [49–51]. he is in town. Much of the expected residential energy consumption is In general, each family or household unit lives in a dwelling, but shifted to service sectors. Setting the boundary of the household sector is there are other housing options (retirement homes, student dorms, jails, 8 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Fig. 3. Combination of types of household and dwelling in Sweden 2015. Data: number of people [52] and households [53], employment [54], area per dwelling [55], rooms per person [56]. etc.). Households may have more than one residence for example for occupation. Akrich [59] coined the term “scripting”, the framework of specific periods of time (e.g., holidays) or might have problems afford­ action that technical objects define. In the case of dwellings, they ing even one. Here we only account for dwellings in use, but there is embody a type of family/household occupants and of expected func­ always a share of unused housing. tions. For example, an apartment with three bedrooms, one of a larger Fig. 3 and Fig. 4 show an overview of the organization of types of size, would be adapted to a family of a couple and two children. This household units in types of dwelling in 2015 in Sweden and Spain, hierarchy of bedrooms or a one-room apartment would not be fitted for a respectively. In Spain, the housing stock is mainly composed of apart­ household unit of three single adults [60]. These combinations would ments (67%), whereas in Sweden the percentage is smaller (48%). In surely not be desirable, but could still technically work out. Sweden, there is a strong distinction between the uses of apartments and Even though the area per capita is somewhat large in Sweden, the houses. There, most single people live in apartments, while houses are under occupation in terms of the number of rooms per capita is not occupied by couples and couples with children. In the case of Spain, all substantial. Rooms in Sweden are larger than in Spain (Figs. 3 and 4). types of households live more often in apartments, whose size is larger Apartments and houses are thus larger in terms per capita in Sweden, but (86m2/dwelling compared to 77m2/dwelling in Sweden). The Swedish they are designed for the number of people that occupies them nowa­ stock of apartments was designed more for one-person households, days in terms of the number of rooms. Therefore, occupancy cannot whereas apartments are common in Mediterranean countries for larger increase substantially without losing the privacy of a room per person or families. without construction work to change the layout. Two key questions to Both demographic structures and the built environment have large address in sustainability for the residential sector are the possibility to inertia and change only gradually. This generates a strong lock-in effect. transform these prevailing notions on types of household units and An incompatibility of dwellings and household units will require adap­ dwellings, or/and to transform the existent dwellings to match new tation of housing in terms of layouts or number, or of expectations and social realities. We are going to further examine them in the following practices. Otherwise, this could result in overcrowding or under- sections. Fig. 4. Combination of types of household and dwelling in Spain 2015. Data: number of people and households [57], employment [54], area per dwelling [58], rooms per person [56]. No data for "other" type of dwelling. 9 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Fig. 5. Demographic structure of the population of Sweden in 2015 by type of household and role (adults vs children). Data from Statistics Sweden [52]. 4. Families or household units type of family. In this case, the share of the population in the family type “cohabiting with children” is larger (50% in Spain vs 38% in Sweden), There are different types of families or household units: one-person mostly at expense of single and couple households (see Fig. 7). households, cohabiting couples, diverse types of families with children In Sweden, as in other developed countries, women live on average (single parents, nuclear family model, or more extended alternatives), longer than men and usually end up living by themselves. Few people and other types without family ties, for example, student flats. The latter live in retirement homes or with their adult children. The large shares of may not coordinate activities like cooking so much. The organization in elderly living alone and of early emancipation from parental home household units is dynamic in time throughout life, namely the family define a short time of nuclear family with a household size larger than 2 life cycle or life-course trajectories [61]. People play different roles in people. Half of people by 22 have left the parental home, a younger age different kinds of households along their lifetimes but also in commu­ than other EU countries. This translates into a large share of one-person nities and employment. These roles (carer, employee, friend, son, etc.) households (39%) compared to other EU countries, for example, Spain define the possible patterns of their daily lives and are reflected in their (25%). Changing these deeply rooted values of independence and au­ time use (section 4.1). Therefore, they are not mere individuals acting by tonomy is not an easy task, but these affect heavily resource consump­ their own interests and criteria. Their autonomy is limited. As family tion. Sweden is a telling example of families choosing their dwellings to members, they participate in the organization and duties and/or receive accommodate expected “peak household” moments [68]. The prevision care from others in different reciprocal ways [62,63]. Within the do­ of young couples of having children and the subsequent “empty nests” mestic sphere, unpaid work done by women still plays a central role years after results in an overkill: an under-occupancy of the nuclear [64–66]. This is important because it forces women to have a double family houses for long periods of time. In turn, there is a larger demand shift (increasing time pressures) or to renounce fully or partially to paid for housing for emancipated young people. employment, making them dependent on their partners. The combination of all these types of families makes that Sweden has The family distribution by age in Sweden in 2015 is shown in Fig. 5. an average household size of 2 persons, similar to Denmark or Germany, At least half of the Swedish population between 31 and 53 years old but a very low value compared to other countries such as Spain (2.5) lived with their children. The most frequent type of family with children [69,70], a value even higher than Sweden in 1980 (2.4) [71]. Both are are nuclear families with two parents, also with the largest average far away from Spain in 1958 (4.5) [72]. While in the last decades household size, almost 4. It only represents 21% of the households in household size has generally fallen all around the world, European and Sweden. In Fig. 6, there is the demographic structure of Spain in 2015 by North American households are still way smaller than those in Fig. 6. Demographic structure of the population of Spain in 2015 by type of household. Data from INE [57]. 10 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 Fig. 7. Household units and their relation to services in paid work and informal care networks. Human Activity is provided from household units to paid work through employment and a share returns in the form of services to households. Some human activity goes to informal care networks, where different household units (community, friends or extended family) provide services in a reciprocal mode/unpaid work. These relations generally require mobility to take place. Classification of paid work services to people from [67]. developing countries (e.g., Colombia 3.53 or Chad 5.78 in 2015) [73]. authority constraints [84]. In this sense, paid work and family care play This specific societal organization with small household units decreases key roles in the organization of daily life and generate great temporal internal coordination requirements within households but entails constraints. This shows the limited autonomy and choice of the external support for care needs of children, elderly, and disabled people individual. and larger material resources, both in area per person, energy, and There are some strategies that can be followed in order to save time power capacity (i.e., appliances and devices). In market economies and [85,86]. These go beyond the residential sector but are useful to un­ depending on the welfare state type, the external support depends derstand the trends. To make more of the day and ease the time burden, heavily on the purchasing power and the choices defined by the market. people (i) use Power Capacity and energy, (ii) decrease their expecta­ What is more, the individualization of life generates loneliness, tions on quality or quantity of activities, (iii) increase the household size, impacting health [74]. Considering all these drawbacks, we could make (iv) buy services in the market or use public services, (v) or collectivize a thought experiment: if all adult single people in Sweden would live activities outside the household. These strategies have impacts as well in with another person, Sweden would need 26% fewer apartments and the material dimensions, listed in Table 1. For decreasing GHG emissions 10% fewer houses. We could assume an equivalent reduction in energy and energy use, the first strategy, using Power Capacity for time consumption in heating and common appliances (e.g., fridges) and a compression, should be reversed considering always the impacts in time certain reduction in other types of energy consumption (cooking, use and daily patterns. Therefore, in order to improve the energy per­ lighting, etc.). Yet there is a crucial question: Would Swedish citizens formance and sustainability of the residential sector in a broader sense, consider that to be an acceptable solution? we could shift the usual framework of technological change to that of social innovation [87]. For this approach to succeed, desirability plays a significant role. Citizens must accept the social conditions of these 4.1. Human activity and social organization alternative arrangements to provide the subsequent benefits in terms of environmental feasibility and social viability [88,89]. In Georgescu-Roegen’s fund-flow scheme [29,30], where MuSIASEM is grounded, time is considered a fund: Human activity associated with 4.1.1. Decrease use of Power Capacity the physical existence of human beings [27]. Families reproduce human There is a trade-off or nexus between the fund Human Activity and activity physically by raising children and maintain it by means of care energy. Some Power Capacity allows to carry out activities with less activities. Although the residential sector is the central actor, there are time and effort by the use of energy, defined as time-saving technology also activities in services within paid work that take part in the repro­ [90]. In contrast, time-using technology would enhance the perceived duction of the fund Human Activity, for example, education and quality or allow different kinds of leisure, for example the TV. This healthcare (Fig. 7). generates an energy-time nexus, quantified in the MuSIASEM frame­ Human time is one of the key but rather overlooked variables in work with the Energy Metabolic Rate [MJ/h], which defines the amount sustainability, albeit it is required for all activities. Some residential of energy per human activity [27,91]. energy models have already recognized the role of time use and have The availability of technology makes that more activities can be made it the central variable [75–82]. People can already generally performed in the same time, potentially generating a time rebound. acknowledge the centrality of time. We feel the pressure and hurriedness Ecological changes in lifestyle such as moving by public transport of the 24 h/day in our daily life, even more on weekdays [83]. People instead of a private vehicle could be considered “time investments in the and families organize the allocation of their time considering all con­ environment” [92] (strategy 2.1 in Table 2). These investments are in straints and activities in and outside the home. In this sense, duration is many cases not individually possible without certain waivers, or not not the only important aspect, but also other many dimensions of time, universally possible, and therefore only generalizable through societal such as synchronization, sequence, and rate, among others [84]. The change. For example, living without a car in the many areas of the US is hourly and daily organization is defined by coupling with others and by 11 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 not possible due to the sprawl urbanism, the lack of public transport (about 3.5 inhabitants per dwelling). These household types different and/or services and jobs close to homes. Social and infrastructure from the strict nuclear family or one-person households could be changes to allow making these time investments and depend less on extended family or peer-shared types. This arrangement might not be energy-consuming power capacity, are the precondition for time wealth currently desired by citizens, but the only way compatible with their (Zeitwohlstand) [93]. This is considered key to a more sustainable life economic and/or care situation. To become a compelling alternative, it and includes sufficient time, plannability, synchronization, and sover­ requires the establishment of rituals, negotiation and conflict resolution, eignty [94,95]. This all-rounder outlook of time is important because the and a revision of power dynamics within families. operation of appliances is not always only directly related to duration. Taking a further step, there are examples in the whole reorganization For example, fridges and freezers work continuously to preserve food. of space and activities in larger units or with collective areas in the They affect food provisioning by reducing the frequency of trips to buy residential sector under different names: cohousing, collaborative groceries and allowing the consumption of otherwise perishable foods, housing, coliving, communal housing, or collective housing [105–108], for example dairy or cooked food. Through innovation, the technical also specific for older people including or not care and support services object might use less energy by volume of stored food. But this might [109,110], and historical examples such as the history of collective make people use larger freezers in order to reduce the number of trips to housing considering reproduction work [111] or apartments with col­ supermarkets or to avoid planning meals, backfiring the relative effi­ lective housekeeping services in New York at the end of the XIXth cen­ ciency per unit of food [96]. tury [112]. In this kind of larger collective organization, the coordination takes a higher level with external management and/or 4.1.2. Decrease quantity or quality of activities and provide flexibility regular meetings and working groups [108,113]. Yet energy or green­ The increasing energy use and power capacity ownership is the house gas emissions savings associated with these solutions have not current main strategy to overcome the daily personal and family budgets been studied enough [106]. The existent power capacity and infra­ of time. The availability of technology has raised the expectations of the structure does not match the needs of these alternative modes, which quality or quantity of activities carried out during the day and it the end would include shared or public spaces and larger and sturdier common normalized the ownership of certain Power Capacity and activities. This appliances. has accelerated the pace of life and compressed activities, reducing the Neighborhood organizations, the market or the government can pauses between activities or increasing multitasking [97]. For example, support specific functions which are traditionally associated with the existence of washing machines has not reduced the time in this ac­ households, such as public kitchens or canteens, daycare centers, laun­ tivity due to the increased frequency linked to the higher standards of dromats, or tool libraries (strategy 1.2). Some of these strategies are cleanliness. Some authors state instead that the time pressure in modern framed with the concepts of product-service systems, where the objec­ societies is closely related to a middle-class expectation of levels of lei­ tive of companies is not to sell products anymore but to enable ownerless sure [98]. consumption of goods, or to offer the services that those products pro­ Therefore, to ease the strain on the time budget, the number, time, vide [114–116]. However, these collectively provided services are only and quality of activities could decrease (strategy 1.5 in Table 1). For viable if people are willing to do them as unpaid work for the community example, due to the time in childcare, parents of young children opt for or if companies can sustain wages for their workers. The viability of more part-time jobs or staying at home (at expenses of income de­ waged employment is one of the main challenges raised by pendency), for a job closer to home so mobility is reduced, or could have product-service literature [114–116]. It also entails a complete trans­ fewer sleep hours, affecting their health and wellbeing. formation in the companies’ structure and functioning [114]. To some In the specific example of quitting a job in the family unit or relying extent for some sectors, this shifting to paid work has already been on extended family members without a job, this does not only entail a implemented. While in Sweden jobs in education, health and other care liberation of a quantity of time, but also it would give flexibility to the are common in the public sector, Spain does not have such broad public family time budget (strategy 1.6 in Table 1). Both childcare and paid support, and extended families play a great role in child and elderly care. work have generally strict scheduling which may be difficult to make Also, wage workers usually carry out more specialized tasks and can compatible. It must be taken into account that it is women that normally invest in their education and improve the quality of the service, whereas take this role nowadays and that we could find alternatives to address within households, adult members must carry out a large variety of this inequality while providing flexibility. activities. For example, in terms of food provisioning, professionaliza­ tion could improve logistics (e.g., reducing food waste and packaging), 4.1.3. Shareability and economies of scale and fulfill societal expectations of quality and healthy eating, instead of Furthermore, we could make further deeper structural changes in the laying the burden on individuals and families. Yet collectivization could mode of provision to yield economies of scale by decreasing the labour entail the loss of the cultural load and intimacy of house and care work and resources per person. These are increasing size and organization made by families (mostly women). within households, building communities, and providing services in These changes in social organization and the function of the house­ paid work. Most of these strategies run counter to the current individ­ hold can lead to radical changes in the layout of dwellings as we un­ ualization trend. These social innovations require a broader analysis of derstand them now, for example with kitchenless homes if they take the needs and how they are provisioned. For example, stay-at-home cooperative housekeeping to the maximum level [111,117,118]. The parents and kindergartens are two ways of coping with childcare, and changes in layouts and the existence of less privative space for the people can cook at home, or alternatively, they can enjoy the service in a benefit of communal spaces with economies of scale can be also in restaurant or canteen. relation to leisure and social interaction [119]. This transforms the Sharing a dwelling and its activities (strategy 1.1) requires negotia­ dwelling into a multi-scale space (privative and communal), opening the tion, coordination, and commitment with more people, but at expense of definition of the household and including the community. overall lower resource use and duration of tasks. Literature shows that The expected functions and form of dwellings can be adapted in larger household units use fewer resources per capita [99], for example, relation to the services provided by its context in paid work. For energy in Denmark [100], energy in Australia [101], water in 4 Euro­ example, what is considered a paradigmatic example of a minimum pean countries [102], and energy and carbon footprints in EU countries dwelling, Le Corbusier’s Cabanon de vacances (13.4 m2), does not include [103]. When sharing is not voluntary but by necessity and not built a shower and kitchen. This small size is possible due to its location, around a household organization of tasks, it may backfire the expected adjacent to a restaurant, and surrounded by a large natural area, savings (e.g. see Klocker et al. [104]). Nowadays, only 9% of the including a beach. households in Sweden and Spain (Figs. 3 and 4) are “other households” 12 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 4.1.4. Demand response conflicting criteria for diverse dimensions (e.g., smart home systems The electricity mix is a key variable regarding indirect impacts from may decrease operational energy carrier consumption by increasing electricity end uses in buildings [17,120]. The intermittency of the material use) [25,132]. Therefore, strategies to tackle a specific point ever-increasing share of renewables in the mix could make that the might be shifting important impacts outside the picture if we do not national or domestic electricity systems cannot adapt anymore to de­ address the issue in a holistic way. The incomparability of the diverse mand at all times as it does now in developed countries. This change for dimensions adds to the large uncertainty in the future: discount rates, sustainability forced by the energy system also affects daily practices. climate, availability of new technologies, future patterns of use, popu­ Demand response strategies aim to shift activities in the everyday ac­ lation, distribution in household units, etc. tivity context or via smart systems. On the one hand, daily practices might have to change actively by users, requiring flexibility from the rest This section starts with the current state of the housing stock, its of activities to adapt to the price signals (related to strategy 1.6) characteristics, its path dependence, and lock-in. Afterwards, we focus [121–125]. On the other hand, electronics and smart systems (strategy on the sufficiency framework, analyzing the economies of scale and 2.2) allow the disconnection between functioning of appliances and the levels of service that affect energy use. These measures might have a presence of users (for example with programmed laundry and heating), larger impact than technical changes. We also analyze the trade-off and the possibility to adapt demand to information from the network or between production and operational GHG emissions and energy. Then, aggregator companies (for example, charging electric cars at night when we address the growth of the fund floor area, its material requirements, electricity demand is lower). These systems are expected to cut down and impacts. Finally, we analyze the role of the construction and real energy consumption even with an rise in standby energy or to allow estate sectors. demand-side management by the electricity system operator. While they may decrease or shift energy use, they have impacts in other dimensions 5.1. The state of dwellings such as material depletion [126]. Electronics are hardly recyclable and use an increasing variety of scarce materials [127–129]. Moreover, these The existent housing sets the initial conditions. It consists basically of technologies are not necessarily inclusive due to the cost for lower in­ houses and apartments, but there are other types such as residential come households [130] and due to the complexity of their control [131]. housing for students or the elderly, prisons, etc. Within the set of dwellings, there may be parts that are not used for long-term residential 5. Housing uses, such as holiday homes or tourist accommodation. A great amount of built environment exists already. While some has Homes are places full of symbolism and meaning. Despite this strong been refurbished and will last long in the future, other is of poor quality cultural dimension, dwellings are a very material reality. Dwellings as a and expected to be short-lived. The renovation of the stock of buildings technical object are in fact the most common framework in sustain­ is slow due to the long lifespans and cultural values. This locks in ability analysis of the residential sector. In many cases, this even only practices and uses [133] and consequently might generate different includes heating, ventilation, and air conditioning (HVAC). The housing kinds of obsolescence: poor construction or design, weak market posi­ stock is made of physical realizations of structural types, where large tion, or location [134]. Changes in specifications and requirements for shares of the total final energy in society are transformed into end uses new buildings will take decades to have a deep effect on the performance providing services. Therefore, the analysis must be centered not only on of the whole system. In Fig. 9 and Fig. 10, there are the demographic the amount of energy carriers but on the services that they are providing. structures of the housing stock in Sweden and Spain divided into houses Following the central idea presented in section 3, there must be a and apartments. The decade where most of the Swedish dwellings were match between families and dwellings. This connects what could be built was the 60s. This is a consequence of the million homes program considered “purely technical” with the inherent social side of housing. (Miljonprogrammet), which was made by the Swedish Parliament in However, only considering the technical side there are important 1965. Following the oil crisis of the 70s and the referendum to replace Fig. 8. Housing stock characterization and reproduction of funds floor area and power capacity. Flows in operation, and production and end-of-life. 13 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 social configuration around it. Both the household size (economies of scale) and the different types of families, their incomes, and practices affect energy use and emissions. We could even say that a fridge used by 4 people is 4 times as efficient as one used by a single person. These and other issues touched upon in the introduction make essential a frame­ work widening from efficiency to sufficiency, aiming to decrease total consumption in absolute terms by assessing the needs [137–139]. This means not only considering the energy quantity or a specific relative improvement but also characterizing the functions and qualitative as­ pects (space, temperature, shareability, cleanliness, etc.) associated with energy uses. For that matter, the social dynamics explained in section 4 regarding time pressure and its nexus to energy must be understood. The amount and type of appliances and dwellings will depend on social organization (types of household units and size) and the existence of systems of shareability of devices at the community level, which affect time use and daily patterns, on the shift of activities to paid work, which requires the viability of wages, on the ability of states to levy taxes and develop welfare state and the desirability of society to support them, and other changes in daily patterns regarding the expectations on quantitative and Fig. 9. Demographic structure of housing in Sweden (2015) [136]. qualitative aspects of the activities (e.g., choice, leisure types, space, room temperature and cleanliness). Structural domestic services are subject to economies of scale in terms both of Power Capacity and Floor Area. Any dwelling customarily has at least a bathroom and a kitchen, with its subsequent equipment, irrespective of size and number of occupants, and these coevolve with legal, infrastructural and cultural conventions [140]. If a dwelling is occupied by one or more people, it will affect mainly their size and the size of the devices, only at substantially larger occupations, the number of bathrooms and appliances will increase. Shareability of devices within or between households (washing machine, laundry room or laundromat, fridge, TV, or those used less often such as tools) also re­ duces the number of appliances that must be manufactured. The case of the washing machine is paradigmatic. In some countries such as Sweden, it already represents an appliance that is commonly shared between households of the same apartment building, requiring organization and rules. Klint and Peters [141] estimate that the GHG emission savings of a shared laundry room can be 26% in comparison to having washing machines in every apartment. Collective power capacity can be of better quality or performance due to shared costs. This is also true for district heating systems, which operate at a larger scale and increase efficiency compared to individual devices but require a certain level of density of demand. Fig. 10. Demographic structure of housing in Spain (2015) [57]. Some household devices are even used very seldom, i.e., they have small utilization factors (e.g., printers, tools, or specific cooking de­ nuclear power, a Building norm was introduced in 1980, SBN 1980, vices). Consequently, their largest impact lies in their embodied energy which tightened the rules for insulation of buildings [135]. Of the and materials, within the manufacturing and material extraction sectors. existent buildings today in Sweden, most were built before this building Ownerless consumption of these items could exist in the form of col­ norm. Therefore, the different regulations and building codes are re­ lective ownership or rental, increasing the utilization factor and flected in their contemporary cohorts and qualitative changes in the reducing the embodied impacts per unit of service. However, the whole stock take decades to take place. widespread penetration of devices [142] and thus immediate avail­ In Spain, the largest cohort existent today was built in the 70s, where ability allows patterns of daily routines that require less planning. the average family was of almost 4 members [72], but the customs in Ownership in many cases represents a tool of social distinction and space were lower. To some extent, the construction in a given year symbolic power [116,143,144]. matches current or expected types of household units. The only possible Moreover, the energy, GHG emissions, and time use can also be low-cost flexibility in the current building stock leans towards individ­ divided if tasks are shared so more than one person enjoys its outcomes ualization (more space per person in a dwelling) instead of towards (cooking, washing clothes, etc.). This means that fewer resources per larger household units, which would require larger refurbishments or capita are required for the same function when, for example, cooking for the acceptance of downward changes in space per capita. 1 or for 3 people [105,145]. Therefore, we can work with fewer devices and/or space (and their embedded resources) (strategy 1.4), or even 5.2. Economies of scale and level of service with fewer devices and time in use if tasks are shared (strategy 1.3). However, this affects current lifestyles, expectations of choices and au­ Knowing the characteristics of the dwelling and the power capacity, tonomy, or typologies of families and communities, explained in section we could make assumptions on energy throughput and direct emissions 4. This depends thus on desirability. in use (operational). A specific performance rate for a building or a Another key aspect of operational energy use is to understand the device can lead to a large variety of end uses per capita depending on the level of service that is expected and to understand what the end use or 14 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 need to fulfill is. Here, we are going to use the example of heating to (strategy 2.6) or improvements in energy efficiency or lowering emis­ illustrate it. sions (strategy 2.4). In this case, there are trade-offs affecting the two The difference between calculated theoretical energy and GHG main variables (energy/GHG emissions and materials) and phases emissions from an expected level of service and the actual monitored (manufacturing in diverse sectors/operational in the residential sector/ one defines a performance gap [146]. For example, in a sample of 410 end-of-life), which at the same time involves different actors (com­ homes in the UK, Palmer [147] found a large discrepancy between the panies, public services, and households). There are two different types of real measurements and their energy performance certificate. The soci­ resource uses which are allocated in different societal sectors and etal availability of cheaper energy services when technical improve­ depicted in Fig. 8: (i) the flows metabolized by the funds – i.e., opera­ ments are put in place might ultimately increase overall energy tional resource uses (residential end uses); and (ii) the flows needed to consumption due to the Jevons’ paradox [148,149]. This difference produce and maintain the funds – i.e., production of power capacity and between expected and effective energy use can be also in terms of lower construction and maintenance of floor area (in the construction and energy consumption, then called the prebound effect [150]. The ex­ upstream sectors). For example, energy efficiency strategies such as pected energy performance of a building will not be fulfilled if users buying a fridge with new technology might shift impacts to cannot afford the price, which is common for heating in poorly insulated manufacturing and upstream sectors in terms of both materials and buildings. energy. In practical terms, the end-user, the household, might be Indoor temperature is a key parameter for calculating heating and perceiving a lower energy consumption, but in overall terms, this might cooling loads and thus HVAC energy consumption, one of the largest not be true if we consider the embodied resources in production of both end-uses in many countries. People expect to live in comfortable envi­ the new and the substituted fridge. The construction and manufacturing ronments no matter the external climate. This has generated a conver­ of new updated products may not always pay back the potential future gence of inner temperatures among countries and seasons [151]. Even savings if the substituted product is still new. If the substitution is though the maintenance of an adequate temperature is normally framed required at a higher rate for phasing out of energy carriers due to as a technical problem that must be approached with technology and scarcity, the overall energy and GHG emissions balance might be chal­ innovation, it is heavily affected by the conventions on comfort, which lenging to evaluate. Also, models exploring payback times or building are not universal. ‘Adequate’ has a different meaning for different service times involve making assumptions of very uncertain variables people. Temperature comfort is socially and technically constructed such as future uses and innovation in technological upgrades. [152] and has changed over time [153]. Technical systems are designed In terms of thermal performance, buildings with conventional energy according to pre-established and not contested conventions of average standards generate most of the GHG emissions in their use phase [49]. temperature defined in building codes, for example, those listed in Although Nearly Zero Emission Buildings (nZEB) or other low-energy Guillén-Lambea et al. [154]. The questioning of these conventions on building standards decrease energy in use for thermal end-uses, there temperature is another example of strategy 1.5: decrease quantitative or is a larger initial investment [159,160]. Vilches et al. [161] indicate that qualitative expectations of activities (Table 1). Mata et al. [155] have the share of operational energy in the life cycle of a building is modelled a set of measures for the housing sector in Sweden. According decreasing from 80 to 60%. The timing of the transition becomes to this paper, decreasing the indoor air temperature to 20 ◦ C provides important due to the large peak of emissions and other resource uses in the greatest energy savings. The rest of the measures require physical construction. Also, the reduction in technical energy carrier consump­ changes with energy and material investments in buildings, and only tion clashes frequently with the material efficiency and circularity, for give marginal returns in part because the thermal technical specifica­ example, with smart homes and the concomitant deployment of tions of Swedish building sector are already high. Guillén-Lambea et al. hard-to-recycle electronics. [154] modelled the energy consumption for heating and cooling of The thermal performance of a building is defined at different levels conventional and nZEB buildings in diverse cities in Spain and found and is more or less changeable depending on the layer of the building. significant differences in energy demand even within a small range of Some of the characteristics of the outer layers are considered to be room temperatures (for example, savings from 13 to 23% for conven­ especially relevant: orientation, shape, and building aspect ratio [162], tional dwellings when decreasing heating temperature from 20 ◦ C to 19 which are set in the design phase and therefore not changeable with a ◦ C). Sahakian et al. [156] organized a living lab “heating challenge” in 8 retrofit. This includes the distinction between houses and apartments European countries where the participants ended up acknowledging that (strategy 2.8), where houses tend to have larger operational energy and an inferior temperature than usual could be considered enough. That GHG emissions due to heating. This shows that the renovation wave can said, the whole paradigm of space heating for temperature comfort can have a limited effect and that existing building stock has a lock-in in be challenged as well. Further alternatives to heating spaces can also be terms of both function and performance. a solution, for example, clothing and personal heating devices [157]. Coming back to the thermal performance, the level of insulation is Verhaart et al. [158] reviewed literature on personalized comfort sys­ calculated with the transmittance (U values) of walls, floor, and roof. In tems and their combination with common HVAC systems have an the Swedish case, the U values of windows are equal no matter the age of energy-saving potential of up to 34% and an increase in occupant the building [163], because the change requires minor work, whereas satisfaction. changing the insulation of the walls and roof represents a deeper retrofit. However, in comparison to other EU countries, overall Swedish U values 5.3. Energy retrofits and the trade-off of production and operational are relatively low [58]. Deep refurbishment with an upgrade in thermal energy characteristics is still not put into practice at the pace that would be expected. While 12.3% of the residential buildings in the EU28 were For the improvement of the energy and emissions performance of the renovated in 2012–2016, only 0.2% of the residential buildings in EU28 residential sector, we must always consider the social innovation stra­ were deeply renovated in energy terms (more than 60% energy savings), tegies and preanalytical framework explained before related to share­ 0.1% in the case of Sweden and 0.3% for Spain [164]. ability and economies of scale, and the conceptualization of services. However, the technical improvement of dwellings and power capacity 5.4. Expansion of the fund floor area and the substitution of devices with updated technology also play important roles. Housing is currently expanding, with still low rates of demolition in The construction of new dwellings or production of power capacity is relation to construction. The expansion of the fund Floor Area, provided in part related to the substitution of old appliances to phase-out of that monetary dynamics are favorable, is driven by population growth, certain energy carriers (e.g., electrification of kitchen appliances) expectations of space per capita and functions, the increase of one- 15 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 person households, change of preferred location or type of dwelling construction paradigm is that of building rationalization, which uses ((peri-)urbanization/ruralization) and the demand for other uses (e.g., standardized beams with a limited number of cross-section sizes [182]. second homes and tourist accommodation). This expansion is a key This entails the use of oversized beams and defensive design strategies driver of materials, energy, and land use. It also determines the func­ used by engineers and required by codes [183]. Therefore, they use tioning of the construction sector and its supplier industries and locks in more material than would be required in order to ensure stability and the demand for resources in the subsequent use of buildings. Therefore, load-bearing. If the objective of minimizing overall cost would shift to it requires a deep analysis of the existing stock and future needs. This that of optimizing loads at all points, steel and other material use could will be large in developing countries such as China, with intense ur­ be minimized at expenses of higher costs and complexity in design. banization and expansion of the floor area [165]. Alternatively, lightweighting could be done by changing materials with The construction of new dwellings generates impacts, but most of a higher strength ratio per weight, for example, composites. However, them are induced in upstream sectors related to material production [2, the initial savings in material quantities entails a future difficulty to 166–168]. The production of construction materials represents about recycle them. 11% of the global energy and GHG emissions, and more than half are related to steel and cement manufacturing [159]. The bulk of materials 5.4.3. Changing production processes of primary materials for buildings in weight corresponds to those most consumed overall: Emissions from primary material production of steel and cement are concrete, steel, other non-metallic minerals, and timber. However, there process emissions challenging to decarbonize [184,185]. The produc­ is increasing diversity and amounts of rarer materials, both in power tion processes of these materials could be transformed (strategy 2.13). capacity and parts of the building (e.g., insulation). The transformation of production chains involves a large number of If it is considered that new buildings are required, some strategies strategies depending on the material that we are not going to detail here could decrease the impact of materials and construction. These must be but are available in the literature [185–187]. These include direct a central criterion in the design phase and are difficult or impossible to reduction with hydrogen instead of coke for steel or increasing use of implement in later stages in the life cycle of buildings. These include: (i) cement clinker substitutes and include carbon capture and storage sys­ reduction of floor area or downsizing, (ii) lightweighting, (iii) new or tems for cement production. The transformation of the supply chains of improved production technologies of primary materials, (iv) substitu­ primary steel and cement depends on large investments that are made in tion of materials, (v) recycling of materials, (vi) reuse of parts, (vii) in­ long investment cycles [188] and are out of the direct control of the crease durability and (vii) increase flexibility. construction sector. 5.4.1. Reduction of Floor Area or downsizing 5.4.4. Material substitution Reducing the available space (strategy 2.7) reduces the quantity of Another way to avoid the emissions of primary material production materials (embodied resources) and also thermal operational energy. is to find substitutes to those materials. biobased materials play a special However, it must come with a reflection on what is sufficient space. This role (strategy 2.14). Timber is gaining traction as a carbon-capturing can be related also to larger household sizes and economies of scale and low material intensity alternative to the emission-intensive mate­ explained in Sections 4.1.3 and 5.2. Zhong et al. [18] define space rials concrete and steel [189]. Increasing wood use in construction is the reduction as the most powerful measure to reduce emissions in material most impacting material efficiency strategy for reducing GHG emissions production for buildings. It is also relevant for thermal energy uses, for considered in the global model of Pauliuk et al. [190]. However, timber example as shown by Cordroch et al. [169] in a model for the German has worse thermal performance than concrete due to its lower heat ca­ housing heating demand. Pauliuk et al. [14] define increasing household pacity (less thermal mass and more overheating) [120,191]. It must be size by 15% and decreasing floor area per capita as the combined also protected from humidity and plagues and parts must be sized for measures that can cut down GHG emissions by 53% in the Norwegian adequate fire resistance [189,191]. dwelling stock by 2050. Very high thermal performance standards could Sawnwood and wood-based panels come from renewable resources, be backfired by the increase in the size of dwellings [170–173]. There­ but their availability is determined by the maintenance of the fund land fore, assessments of energy efficiency using only intensive variables such use (quality of the soil, use of fertilizers, irrigation, etc.), forestry har­ as energy per area may be misleading [172]. Moreover, larger floor area vest, the increasing competition of other uses (materials, energy, and per capita and lower energy per area are usually related to higher in­ chemicals) and the conservation of natural areas for biodiversity. In the comes [174]. model of Churkina et al. [189], only the lower timber content (10 and While the fund Floor Area is growing due to both population and 50% timber) building scenarios could be satisfied with current harvest household increase, also floor area per capita is increasing. Space rates plus re-directing a part of other end uses such as fuelwood. How­ standards have evolved through history concomitantly to the expecta­ ever, not all forestry products can be used for construction. tions of privacy and the number of rooms required by families In Sweden, wood is used largely for frames in detached houses [175–177]. Moreover, new realities may require duplicate spaces, like in (around 80–90% [192], very large compared with other countries such the cases of joint custody of children, and telework. A larger dwelling as Germany: 2% [193]) but still minor in multi-dwellings (around 8.8% also defines more work to maintain it clean and working. While there is a in 2014 (TMF 2016)). This shows that it is already conventional practice trend of downsizing due to the decreasing household size and the in some countries for some building types. However, in many cases shortage of land in cities, data indicate that dwellings are getting rela­ bio-based are still to be introduced in regulations to make possible its tively larger per person overall [178]. This is due to the fact that, for generalized use in structures other than low-rise buildings. example, two apartments for one person are generally larger than one apartment for 2 people. The average housing standards in Europe define 5.4.5. Recycling minimal aggregate living space (living and dining rooms, and kitchen) of Existent buildings and their parts are hardly reusable or recyclable. 21,9 m2 for 2 inhabitants and 19.6 m2 for 1 inhabitant [179]. Moreover, Most of the construction waste is currently deposited in landfills, or downsizing, as performed nowadays, is not framed within sufficiency downcycled (e.g., backfilling). This cascading of materials can also in­ but driven by rising land prices in cities. This reduction is not compatible crease the secondary inputs to construction. Currently, old scrap is with prevailing perceptions of sufficient space [180,181]. mostly recycled into construction steel, which has lower specifications in comparison to other steels [194]. We will face a challenge in the 5.4.2. Lightweighting future management of the end-of-life of current building stock, which Another approach is to reduce the quantity of materials and their has been mostly built in the last decades without consideration of embodied impacts: lightweighting (strategy 2.10). Nowadays, the reusability or recyclability and it could become obsolete simultaneously. 16 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 The recycling of materials (strategy 2.12) could still be possible to a making sturdier and long-lasting products pays off when the initial in­ certain extent, but it would require dismantling buildings carefully vestment is large [209,210] (strategy 2.5). This also requires good separating the different materials instead of demolishing and disposing maintenance during the lifetime. of them (more labor and planning). Logistics, cost, lack of regulation, Durability is not only a matter of sturdy structures but also of an and time are considered the main barriers to recycling [195]. On the one adaptable function and/or form (strategy 2.9). In fact, in many cases, the hand, the large amounts of materials that are in a building facilitate their demolition of a building is not due to the degradation of the structure or recycling (potential higher collection rate), but, on the other hand, the components, but due to functional or locational obsolescence. The lack fact that they were constructed with wet joints and composite materials of flexibility does not only affect the materials and their future uses in difficult to detach (e.g. reinforced concrete) hinders it. new buildings, but also the possibility of adapting the use of existing The production process of secondary materials can be 10% or 50% of buildings by changing their layouts [211]. For example, the evolu­ the primary production for aluminium and steel [13], respectively. In tionary change in size and number of rooms could accommodate a some cases, the incentive to recycle does not come from the reduction in family throughout its different phases over time. In this sense, there is resources in secondary material production since it might not be as the paradigm of flexible buildings [211–214] (strategy 2.9), which could beneficial considering sorting, collection and transport, but from the rely on indeterminate spaces (soft vs hard use [212]: multi-functional scarcity of raw materials [196]. The overview of the system puts into rooms) or the modularity and changing partitioning of buildings (soft question circularity. The building stock is expanding and therefore vs hard technologies [212]: e.g., flexible wall divisions, switchable accumulating more materials. Therefore, the system requires continuous rooms joinable with adjacent apartments, folding components). Inde­ inputs of raw materials. Buildings designed now for recyclability will terminate spaces use to be linked to a provision of more space [212], take decades to be actually recycled. Demolition does not play a suffi­ thus potentially backfiring in the short term the resource use improve­ ciently large role in providing secondary materials yet. And even in a ments in the long run. The invested resources might be useful for a steady-state context, there are always a limited maximum recycled longer time but are larger in the first place. In any case, flexibility must content potential, losses due to dissipation and low concentration, and be projected as a core objective from the design phase, which implies a the inclusion of tramp elements limit recyclability [129,194,196–198]. cost that developers may not be willing to take [215]. The structure and services (e.g., wiring, and electrical outlets) and types of construction, 5.4.6. Design for disassembly which are not currently flexible, may lock the possibilities of rearranging Another strategy is to implement design for disassembly in new floor plans. Therefore, most existent buildings cannot accommodate construction (strategy 2.11). This way, the structure and envelope of a large changes over time. This flexibility of function and form is expected building are not a monolithic unit with a clear lifetime anymore. to be required in a society in permanent change and innovation but Instead, the life cycle of components is expected to be longer than the might not be as much in a steady-state economy. buildings in which they take part. Parts are kept within the technosphere and must be useful in the future for further uses in new buildings. 5.5. Construction and real estate sectors The new projects with modular buildings with reusabe parts would The functions of the construction sector are refurbishment, mainte­ affect a very small share of the current housing stock. Now, these nance, demolition, and new construction not only of housing but also of reusable parts are in fact newly manufactured, but a system (regulations, other types of buildings and infrastructure. In other words, it adapts the market, etc.) must be created to manage their future reuse. The design fund Land Use for different functions and multiplies it into Floor Area. objective is not to calculate an optimum with standardized new parts Moreover, it is a key economic sector. The construction sector rep­ anymore, but adapting the design to the available parts from decon­ resented directly in 2015 6% of the gross value added and 7% of the structed buildings or standardized parts [199]. This entails potentially working time in paid work for both Sweden and Spain [216,217]. The extending the life of parts but decreasing material efficiency and limiting sector needs a continued expansion of the stock or an important in­ lightweighting at the level of the building [200,201]. Also, not all types vestment in refurbishment. It is not only the sector devoted to building of materials and parts can be reused at the same level [202]. Reusable houses to fulfill societal demands, but it requires a continuous demand parts require more work, special transport, storage space, and infra­ for housing to maintain production and therefore the existence of the structure to maintain and guarantee their functionality [203], while sector. In Spain, during the years previous to the housing bubble burst in business as usual depletes the available materials by simply throwing 2008, the vertically integrated construction employment represented them away into landfills [204]. This represents a whole new paradigm 19.7% in 2004 of the Spanish economy [218], with 12% directly that requires new logistics, design methods and tests to ensure the me­ devoted to the construction sector. chanical performance and geometric tolerances of reused materials [32, For the sake of the immediate revenue of construction activities, the 199,205]. This includes creating reverse logistics and reused component additions to the built environment are designed according to current or markets, defining disassembly plans in the design phase, and more near-future expected most profitable demand instead of having a stra­ specific technical aspects such as using dry or reversible mechanical tegic long-term perspective. Therefore, the existent housing stock is a instead of wet connections. On the other hand, it has other potential stockpiling of dwellings designed according to needs at the time of advantages: industrialization of processes, standardization, and pre­ construction as perceived by developers within the limits of regulation. fabrication of parts. This multidimensionality is shown in Küpfer et al. The future needs of the users, the municipality or the country are not [206], which proposes a multi-criteria decision framework for diverse necessarily included if governments do not enforce them. levels of reuse of structures and dimensions: environment, risk, costs, In consequence, homes are not only the place where people live but and construction complexity. also an economic asset. We cannot conclude the paper without Both recycling and disassembly require more working time than mentioning this aspect, which is crucial because people spend a signif­ demolition, challenging the financial viability of deconstruction and icant share of their income to access housing by means of rent or reuse. The current low cost by volume or mass of primary construction mortgage. Rents represented 11% in Sweden and 3% in Spain of the materials in comparison to wages does not enable their reuse or recy­ monthly expenses in 2015 [219]. In Spain, ownership of housing is more cling. Transport distances also play a key role in the economic and common than in Sweden, and it represents 8% of the value added (L68A environmental gains and if very long could even overtake avoided im­ – imputed rents of owner-occupied dwellings). This is important when pacts of primary materials and components [207,208]. assessing the capability of households to access a dwelling and the further large investments in maintenance and refurbishment. The lower 5.4.7. Durability and flexibility income population tends to live in buildings with worse thermal per­ Buildings could be designed to be long-lasting. Studies point out that formance and landlord-led retrofits might entail processes of renoviction 17 L.À. Pérez-Sánchez et al. Renewable and Sustainable Energy Reviews 161 (2022) 112388 [220]. operation and production), monetary cost, recyclability, flexibility, and The economic character of dwellings is most clear in the real estate modularity can be mutually exclusive. The emerging combination of sector, its financial manager. In the case of the EU28, it represented in long-lasting housing and other infrastructure in types of urbanism and 2015 11% of the value added (including L68A – imputed rents of owner- municipalities generates strong lock-in in their uses and related dy­ occupied dwellings) and 1.1% of the HA in paid work [216,217]. In this namics such as mobility. Therefore, new construction concepts may only context, dwellings are not only the places where people live but an tackle new buildings, which take decades to take over the whole system economic asset. This has led to financialization and housing bubbles due to the large life of buildings. Moreover, it requires a new culture of [221–224]. The ratio of household mortgage debt to GDP in 2009 was work for architects, engineers, town planners, and other construction 64% in Spain and 82% in Sweden [221]. The material dynamics are workers. Finally, we must consider that many of these technical strate­ more tightly driven by financial cycles rather than by the needs of the gies may entail higher up-front costs that might not be acceptable for population. developers, which do not have a high interest in the future uses of Several dynamics and trade-offs described in the paper are influ­ buildings. The longevity of buildings sets a challenge for future uses and enced by access and other property rights over dwellings. For example, potential lock-in of functions and resource use, and also in regard to the distributing dwellings not through the current logic based on private accountability for maintenance and end-of-life. property (purchasing capacity and inheritance rights), but to other so­ The current centrality of the narrow definition of energy efficiency cioeconomic characteristics (e.g., distance to work and social network, does not provide a robust enough framework to improve the residential household size, age, etc.) would help improve the relations between sector. Sustainability oriented to artifacts and individual behavior people and buildings and sustainability. Also, the property or access should be shifted towards functions and systems. This would make it format affects the form. Property or access types enable or limit the possible to contextualize local efforts, generate truly innovative pro­ flexibility in distribution of space and rooms between adjacent apart­ cesses and provisioning of services and evaluate trade-offs across scales ments. In a similar way, the provisioning of services generates technical and dimensions. In this paper, we have reviewed and discussed a set of requirements. For example, the payment of electricity defines the way actions to improve the sustainability of the residential sector. Beyond meters and wiring are installed. The institutions involved in dwelling this review, we have proposed an interdisciplinary framework to ownership or access and the provisioning of services also affect the analyze the sustainability of the residential sector as the integration of possibility of investments (e.g., retrofits) and the policies that govern­ families/households units and dwellings, identifying key entanglements ments can implement. between them, with paid work sectors, and with the environment. We expect this work to help in the holistic interdisciplinary understanding 6. Conclusions of household metabolism that will ultimately set the foundation for transformative changes and policy for social, economic, and environ­ Interdisciplinarity is key for sustainability. Technical solutions are mental sustainability. insufficient and should be adequately contextualized. We must really understand social dynamics and their entanglements with technology to Declaration of competing interest propose coherent and transformative practices. In this paper, we have provided an overview of factors for the sustainability of the residential The authors declare that they have no known competing financial sector and assessed qualitatively trade-offs and impacts in energy, ma­ interests or personal relationships that could have appeared to influence terials, time use, and social organization of possible measures ranging the work reported in this paper. from social innovation to construction methods. To this effect, we have framed biophysical flows and funds using MuSIASEM, as well as around Acknowledgements current cultural and institutional settings using practice theory. Some important variables are left out of the analysis, such as health, water, Laura Pérez-Sánchez gratefully acknowledges financial support of and contamination. the Catalan administration/AGAUR (Grant number: 2019FI_B01317). The residential sector is the center of daily life. Homes have changed The authors also acknowledge financial support by the government of throughout history, both in functions and form. Household units of Catalonia (AGAUR), through the support for research groups (2017- organized individuals live in diverse typologies of dwellings (houses, SGR-230), and the Spanish Ministry of Science and Innovation apartments, and others, with different layouts) and these configurations (MICINN), through the “María de Maeztu” program for Units of Excel­ have shaped the diverse dwelling cohorts. A clear definition of the lence (CEX2019-000940-M). 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