One-stop shops as leverage points for renovation sufficiency

3.1 OSS FOR BUILDING RENOVATIONS

OSS for building renovations have emerged as organisational responses to persistent barriers in the renovation market, including fragmented responsibilities, lack of coordination between actors, and limited technical and financial expertise among building owners (Boza-Kiss et al. 2021; Bagaini et al. 2022). By integrating multiple services into a single interface, OSS aim to simplify renovation processes and reduce uncertainty for building owners.

Across the literature, OSS are commonly described as service models that accompany building owners throughout the renovation process, from initial assessment to implementation and, in some cases, post-renovation follow-up (Bagaini et al. 2022; Bertoldi et al. 2021a; Biere-Arenas et al. 2025; Panakaduwa et al. 2025b; Pardalis 2021). Typologies in the literature distinguish OSS according to their scope of services, ranging from facilitation and coordination models to all-inclusive and energy-service company-type models, as well as according to governance structure, including public-driven, private-driven and hybrid forms (Pardalis et al. 2022). Despite these differences, most OSS are oriented toward increasing renovation uptake and delivering measurable energy performance improvements. Comparative analyses of integrated home renovation services (IHRS) and OSS business models further indicate that governance structure (e.g. public, private or hybrid) shapes value priorities and operational logics, thereby influencing how renovation ambition is defined, communicated and standardised within advisory practice (Elgendy et al. 2024).

Beyond reducing transaction costs and coordination barriers, OSS also play a decisive role in shaping renovation pathways by structuring early-stage assessments, defining renovation scope and framing performance expectations. This role is operational rather than merely supportive because it influences how renovation options are formulated and compared before technical design and implementation. In this sense, OSS contribute to structuring renovation decision-making processes, even though this function is rarely made explicit in the literature (Pardalis et al. 2025). Recent analyses also highlight the growing integration of OSS with renovation passports and digital tools such as building logbooks and building information modelling-based diagnostics, further reinforcing their role in sequencing interventions and structuring renovation pathways over time (Barbosa & Almeida 2025). Through these tools and advisory routines, performance-maximisation targets can become embedded as default renovation trajectories.

This orientation is reflected in how OSS performance is typically evaluated. Studies frequently assess OSS using indicators such as achieved energy performance improvements, renovation uptake, investment volumes and the number of completed renovation projects (Pardalis et al. 2022, 2025). These indicators serve not only as ex post evaluation metrics but also as operational reference points within policy programmes and OSS business models. They influence how renovation ambition is translated into service offerings, scenario development and advisory practices (Witherley et al. 2025; Pardalis et al. 2025). While such metrics are relevant for tracking progress, they tend to privilege comprehensive or policy-defined ‘deep’ renovation packages, i.e. renovation strategies aiming for large performance gains across multiple building components, and higher volumes of implemented measures (Pardalis et al. 2022; Panakaduwa et al. 2025b). This institutional embedding is reinforced in recent Energy Performance of Buildings Directive (EPBD) implementation guidance, which positions OSS within an enabling framework that explicitly links national renovation plans, renovation passports, financing mechanisms and performance standards such as minimum energy performance standards and zero-emission building targets (Efficient Buildings Europe 2024). By aligning OSS functions with regulatory performance trajectories, this architecture consolidates performance-based metrics as organising principles of renovation delivery.

As a result, OSS advisory and evaluation practices often align renovation success with the depth and extent of intervention rather than with proportionality, actual demand or avoidance of unnecessary measures. This mechanism helps explain how overestimated energy demand assumptions and comprehensive renovation scopes become standardised in practice, with downstream effects on system sizing and component replacement decisions. Empirical research on household retrofit preferences also shows that non-financial factors such as perceived disruption significantly shape renovation decisions (Curtis et al. 2024), underscoring that the way renovation pathways are framed within OSS advisory processes may influence uptake beyond purely technical or economic considerations. Questions of proportionality (understood here as the principle that renovation scope, system sizing and investment should be matched to actual need and demand rather than maximised against performance targets), necessity or diminishing returns are not absent by oversight but are structurally sidelined within prevailing OSS evaluation and delivery logics. It should be noted, however, that staged or phased renovation approaches are not exclusive to sufficiency-oriented strategies. Efficiency-oriented advisory practice, including renovation passports and individual renovation roadmaps, already sequences interventions over time with the explicit aim of ensuring technical compatibility between measures (European Commission 2025). What distinguishes sufficiency-oriented staging is not the sequencing of interventions per se, but the prior questioning of whether each intervention is necessary, proportionate and consistent with actual demand, a reframing that goes beyond performance-oriented optimisation toward adequacy. This distinction is developed further in the framework presented in Section 4.

Furthermore, OSS represent one model within a broader landscape of renovation advisory services. Other advisory contexts, including housing advice for elderly residents, social housing support schemes and community-based retrofit programmes, may also incorporate elements of sufficiency thinking, such as right-sizing, space adaptation or the avoidance of unnecessary intervention (Broers et al. 2022; Graham et al. 2024; Sahakian et al. 2024). The focus on OSS here reflects their policy prominence rather than implying they are the only relevant advisory model.

3.2 SUFFICIENCY IN BUILDING RENOVATIONS

Sufficiency has gained prominence in debates on the decarbonisation of the building sector as a response to the limitations of efficiency-oriented strategies (Ness 2023; Hock et al. 2022). While energy efficiency seeks to reduce energy use per unit of service or floor area, a ratio measure commonly expressed through area-normalised indicators such as kWh/m², energy performance refers to the modelled outcome of a building or renovation assessed against a regulatory or design standard, such as an EPC rating or a zero-emission building target. Both concepts are analytically distinct from sufficiency, which addresses absolute levels of demand by questioning how much space, comfort and building services provision are necessary to meet acceptable living conditions within ecological limits (Darby & Fawcett 2018; Kropfeld 2023). Rather than focusing on performance-oriented optimisation alone, sufficiency foregrounds demand assumptions and the scale of intervention. It is therefore increasingly discussed as a complement, and in some strands as a precondition, to efficiency and renewable energy strategies (Ness 2023; Hock et al. 2022). However, despite this growing recognition, sufficiency remains inconsistently applied and unevenly operationalised within building research and policy debates, particularly where performance-maximisation logics dominate renovation delivery frameworks.

In the context of buildings, sufficiency is commonly defined as the equitable provision of basic energy and housing services while remaining within ecological boundaries (Darby & Fawcett 2018). This framing positions sufficiency between a minimum threshold required to meet basic needs and an upper bound beyond which additional space or services generate disproportionate environmental impacts (Bierwirth & Thomas 2019). The equity dimension of this definition is analytically significant and directly relevant to renovation contexts. Sufficiency-oriented approaches, including low-intervention scenarios, proportional system sizing and avoided unnecessary component replacement, are not only environmentally preferable, but may also be more accessible and affordable for lower income households and vulnerable groups who face the greatest barriers to engaging with comprehensive deep renovation packages. Research on energy transition policy has highlighted that low-income households, elderly residents, tenants and other vulnerable groups face compounding structural barriers to participation in mainstream energy policies and programmes, and are systematically underserved by one-size-fits-all approaches (Sequeira et al. 2024). A sufficiency-oriented advisory framework, by foregrounding proportionality and necessity of intervention rather than maximisation of modelled performance, may therefore offer a more inclusive entry point for groups whose renovation needs and financial circumstances are not well served by conventional deep renovation pathways.

Empirical evidence from European contexts shows that efficiency gains have often been offset by increasing living space per capita and expanding material stocks (Bierwirth & Thomas 2019; Hock et al. 2022; BPIE & Ramboll 2024). As a result, absolute energy demand has in many instances stagnated or increased despite improvements in performance indicators (Darby & Fawcett 2018). This rebound at scale suggests that efficiency-oriented renovation strategies, even when technically successful, may be structurally insufficient to achieve absolute reductions. These scale effects are particularly relevant for renovation, where declining operational energy demand increases the relative contribution of embodied emissions and material use to life-cycle impacts (BPIE & Ramboll 2024; Ness 2023). This shift in the relative weight of embodied versus operational emissions has a direct implication for how renovation ambition should be evaluated. Low-intervention and ‘do less’ scenarios, which preserve the existing building fabric, avoid premature component replacement and reduce material flows, generate whole-life carbon savings relative to deep renovation precisely because they avoid the embodied carbon associated with new materials, systems and construction activity (Röck et al. 2020; Ramírez-Villegas et al. 2019). A balance therefore needs to be sought between reducing operational energy demand through efficiency measures and avoiding the embodied carbon costs of unnecessary intervention, a balance that current performance-maximisation frameworks, focused primarily on modelled operational energy savings, are structurally ill-equipped to strike.

When embedded within advisory and assessment routines, such efficiency gains risk lending legitimacy to expanded ambitions for renovation scopes in advisory practice, rather than constraining overall resource use. Yet this dynamic does not straightforwardly translate into higher actual renovation rates: despite increasing renovation activity across member states, deep renovation rates remain limited and incremental interventions continue to dominate (CAN Europe 2025).

A central theme in the sufficiency literature concerns space per capita as a determinant of both operational and embodied energy demand (Bierwirth & Thomas 2019; Darby & Fawcett 2018; Graham et al. 2024). While proposed reference values for living space per person vary widely, the literature consistently emphasises that adequate space is context dependent and shaped by household composition, life-course dynamics and cultural norms (Jungell-Michelsson & Heikkurinen 2022; BPIE & Ramboll 2024). This temporal dimension is particularly relevant in renovation contexts, where decisions made today have long time horizons. Research on renovation decision-making shows that periods of transition in the household life-course, such as retirement, children leaving home or changes in household size, represent salient moments that shape how space is used and what is considered adequate (Wilson et al. 2015). Similarly, research on housing sufficiency documents how adjustments in living arrangements following changes in family composition are among the key practical motivations for reconsidering space needs (Lehner et al. 2024). A sufficiency-oriented OSS assessment should therefore consider not only current occupancy and use patterns but also plausible future trajectories, in order to avoid sizing systems or scoping interventions for conditions that may not persist over the renovation time horizon. Sufficiency therefore highlights the importance of questioning default assumptions about space use in renovation decision-making rather than prescribing universal thresholds. Research in high-income countries suggests that prevailing norms around home size may be subject to gradual shifts, as awareness of the environmental and financial costs of large dwellings grows among households, though such normative change remains slow and uneven (Cohen 2021). Yet in practice, dominant renovation assessment frameworks rarely interrogate spatial norms, treating conditioned floor area as a fixed input rather than a variable subject to deliberation, thereby narrowing the scope of what is considered a legitimate renovation option.

Beyond spatial considerations, the literature identifies additional sufficiency dimensions that directly influence renovation scope and system design. Material sufficiency emphasises preservation, repair, reuse and selective replacement over comprehensive renewal (Pauliuk et al. 2021; Pauliuk & Heeren 2021; BPIE & Ramboll 2024). In renovation contexts, material sufficiency is directly linked to embodied carbon savings: avoiding unnecessary replacement of building components that retain serviceable life reduces the material flows associated with renovation and lowers whole-life carbon relative to comprehensive deep renovation packages (Röck et al. 2020). This makes material sufficiency not merely a principle of resource conservation but an active strategy for minimising life-cycle environmental impact, particularly as operational emissions decline and embodied carbon becomes a proportionally larger share of a building’s total carbon footprint. Technical sufficiency promotes right-sized, robust and low-tech building service systems rather than highly optimised systems designed for overestimated demand assumptions (Hock et al. 2022). Performance sufficiency concerns targeting adequate rather than maximal comfort levels and explicitly questions norms embedded in standards and modelling conventions (Calvin et al. 2023; Hock et al. 2022). Across these dimensions, adequacy functions as a normative principle within sufficiency: it denotes the condition of meeting actual needs proportionately, without excess provision or unnecessary intervention, and within ecological limits. As such, adequacy is a component of sufficiency rather than a synonym for it; sufficiency additionally encompasses proportionality of intervention scope, avoidance of unnecessary measures and absolute demand reduction. Taken together, these dimensions frame sufficiency as a principle of proportionality between intervention, actual demand and long-term environmental impact. While some strands of the literature address the integrated application of sufficiency dimensions within buildings and advisory contexts (Fouiteh et al. 2024; Hock et al. 2022; Sahakian et al. 2024), these dimensions are more commonly discussed in isolation from one another, and their translation into institutionalised renovation advisory structures, such as OSS, remains limited and underexplored.

Despite the relative conceptual maturity of sufficiency as a theoretical framework, the integration of it into renovation practice remains limited. A key reason identified in the literature is the dominance of assessment and modelling conventions that rely on area-normalised indicators such as kWh/m² or kg CO2/m² (Hock et al. 2022; Kost et al. 2021). These indicators privilege relative efficiency improvements and obscure absolute demand reductions achieved through space reallocation or avoided intervention, thereby reinforcing the very performance-maximisation logic that sufficiency seeks to question. As a result, sufficiency measures often remain undervalued in renovation decision-support tools and performance benchmarks and are rarely positioned as primary pathways within structured renovation scenarios.

Research on sufficiency adoption further shows that decision-making is shaped by both personal and contextual factors (Wyss et al. 2022; Malik & Hong 2024). In renovation contexts, intermediaries such as architects, advisors and OSS play a central role in framing renovation problems and shaping which solutions are presented as reasonable (Nielsen et al. 2016; Farsäter 2022; Sula et al. 2025). Yet the literature has rarely examined how these intermediaries translate, filter or potentially neutralise sufficiency principles within structured advisory processes, even though such processes determine which renovation pathways are presented as standard, ambitious or feasible.

Taken together, sufficiency in renovation operates at the level of demand assumptions and decision framing. While its principles are well established, far less attention has been given to how they might be embedded in the organisational processes through which renovation decisions are actually structured and delivered. This gap is particularly significant given that early-stage advisory and assessment practices may pre-emptively exclude sufficiency-oriented options before performance-oriented optimisation even begins, thereby reproducing performance-maximisation trajectories within renovation delivery systems.

3.3 OSS AS DECISION FRAMEWORKS

In building renovations, OSS are typically involved at early stages of the renovation process, when fundamental decisions are made regarding renovation objectives, energy demand assumptions and technical solutions. These decisions establish boundary conditions for energy performance assessment and strongly influence both system sizing and renovation scope. Building on the preceding analysis, this section synthesises how OSS structure renovation decision-making and conceptualises them as decision frameworks that institutionalise specific renovation logics at early stages of the renovation process. Table 1 illustrates how OSS intervene at key decision stages and different framings influence energy demand and system design.

To further clarify how these framings unfold sequentially across renovation processes, Figure 2 compares performance- and sufficiency-oriented decision logics at each stage of OSS intervention. While Table 1 analytically maps the implications of different framings for energy demand and system design, Figure 2 illustrates how early-stage assumptions structure downstream modelling, system sizing and financial decisions.

Figure 2

Importantly, Figure 2 emphasises the path-dependent character of renovation decision-making within OSS processes. Assumptions established during initial assessment, renovation scope definition and scenario development (Stages 1–3) tend to persist throughout subsequent modelling, system sizing and financial evaluation. Once baseline demand levels, performance ambitions and renovation scope are framed within a performance-maximisation logic, these assumptions become embedded in modelling conventions, system capacity calculations and subsidy structures. Later decisions therefore reinforce rather than question earlier framings. Sufficiency-oriented reframing is consequently most effective when introduced at the earliest advisory stages, before performance-maximisation logics become stabilised and translated into technical specifications and financial commitments.

Table 1 highlights that OSS influence renovation outcomes primarily through early-stage decision-making. These stages function as institutionalised points of path formation, where performance benchmarks, baseline demand assumptions and definitions of ambition become stabilised. Once established, these assumptions tend to persist throughout the renovation process, shaping subsequent system selection and sizing. As a result, performance-maximisation framings introduced at these stages can propagate through modelling, system design and financial structuring, narrowing the range of renovation pathways considered feasible.

5.1 INTERPRETING THE FRAMEWORK

This section discusses the implications of positioning renovation OSS as decision frameworks and of introducing sufficiency as an alternative decision logic within renovation processes.

By linking sufficiency dimensions to specific renovation decision stages and, within those stages, to the framing assumptions that determine which measures are considered necessary, proportionate and appropriate, the framework advances existing understandings of both sufficiency and OSS models. In the sufficiency literature, demand reduction is often discussed at the level of lifestyles, behaviour or high-level policy targets (Darby & Fawcett 2018; Lorek & Spangenberg 2019; Sahakian et al. 2024). In contrast, the OSS literature focuses on improving coordination, uptake and delivery efficiency, typically without questioning underlying assumptions about renovation ambition or scope (Bertoldi et al. 2021a; Boza-Kiss et al. 2021; Pardalis et al. 2022). The proposed framework brings these strands together by showing where and how sufficiency considerations can be operationalised within existing renovation delivery processes, thereby connecting demand-reduction theory to institutionalised decision-making structures. It should be noted, however, that the framework operates at the level of decision logics and framing assumptions rather than prescribing how specific efficiency and sufficiency measures should be combined within individual renovation projects. How such combinations can be optimally designed and evaluated at the measure level represents an important direction for future empirical and methodological research.

5.2 IMPLICATIONS

The framework contributes to the literature in three main ways. First, it reframes OSS as active intermediaries that shape renovation pathways, rather than neutral conduits for predefined renovation goals. While previous studies have acknowledged the coordinating role of OSS (Bagaini et al. 2022; Panakaduwa et al. 2025a, 2025b), the present paper makes explicit how OSS practices embed particular framings of ambition, demand and performance into renovation decision-making. This perspective aligns with broader insights from research on intermediaries and early-stage decision support in building renovation (Nielsen et al. 2016; Farsäter 2022), but extends them by explicitly linking these mechanisms to sufficiency, thereby introducing a normative dimension to the analysis of intermediation.

Second, the framework advances sufficiency research by moving beyond behavioural or normative accounts and situating sufficiency within organisational decision processes. Rather than treating sufficiency as an outcome of individual preferences or values alone (Wyss et al. 2022; März 2018), the framework highlights how institutionalised practices, such as energy modelling conventions, scenario comparison criteria and performance benchmarks, condition what is perceived as reasonable or desirable renovation action. This helps address a recognised gap in sufficiency research concerning how demand-reduction principles can be embedded in everyday decision-making contexts (Hock et al. 2022; Jungell-Michelsson & Heikkurinen 2022) and shifts the analytical focus from individual choice to structural framing.

Third, the framework challenges the implicit assumption that higher renovation ambition, deeper intervention or greater investment necessarily lead to better climate outcomes. By foregrounding proportionality, sufficiency-oriented adequacy and avoided intervention, it complements existing critiques of performance-dominated approaches that overlook scale effects, rebound dynamics and embodied emissions (Röck et al. 2020; Scott et al. 2018; BPIE & Ramboll 2024). In doing so, it offers a conceptual basis for evaluating renovation success in terms of absolute demand reduction and life-cycle impacts, rather than performance indicators alone, thereby redefining what counts as ‘ambition’ within the renovation discourse.

5.3 RENOVATION PRACTICE AND POLICY DESIGN

From a practical perspective, the framework suggests that integrating sufficiency into renovation practice does not require entirely new delivery models but rather shifts in how existing OSS processes are designed and evaluated. In particular, it points to the importance of early-stage advisory practices, where renovation objectives, demand assumptions and performance targets are still negotiable, and where optimisation-oriented defaults can either be reproduced or critically reassessed.

For OSS practitioners, this implies expanding advisory services to include explicit discussion of space use, comfort expectations, synergetic sufficiency measures that can be implemented alongside efficiency interventions, and the necessity of intervention, alongside conventional energy assessments. The inclusion of low-intervention or staged renovation scenarios, as highlighted in the framework, can make sufficiency-oriented options visible and comparable within decision-support processes that currently prioritise maximum energy savings or investment volumes, thus broadening the perceived solution space available to building owners. Here it is important to distinguish sufficiency-oriented staging from the phased renovation sequences already embedded in efficiency-oriented tools such as renovation passports, tools that OSS already routinely support. In the latter, staging is primarily a technical strategy to ensure measure compatibility over time. In a sufficiency-oriented framing, staging is additionally informed by a prior assessment of demand adequacy and intervention necessity, asking not only how to sequence measures efficiently but also whether and to what extent each measure is warranted. OSS practitioners are well placed to make this distinction explicit in their advisory processes.

For building owners and occupants, the framework has direct implications for how renovation conversations are initiated and structured. A sufficiency-oriented advisory process would engage building owners not only as recipients of technical recommendations but also as active participants in defining what constitutes adequate comfort, appropriate space use and necessary intervention (Sula et al. 2025; Wilson et al. 2015). This includes explicit discussion of current and anticipated occupancy patterns, comfort expectations, and the trade-offs between intervention scope and life-cycle cost. For occupants, sufficiency-oriented renovation outcomes, such as right-sized heating systems, a preserved building fabric or avoided unnecessary component replacement, can translate into lower maintenance burdens, reduced disruption during renovation and more stable long-term energy costs (Curtis et al. 2024). These outcomes are often more immediately tangible to occupants than modelled energy performance improvements, and their visibility within advisory processes may support broader acceptance of proportional renovation approaches.

For policymakers, the framework highlights potential misalignments between policy objectives and delivery mechanisms. Current subsidy schemes, performance benchmarks, and evaluation criteria often reward comprehensive renovation packages and high modelled energy savings (Pardalis et al. 2022; Castellazzi et al. 2022). While effective for driving renovation activity, such incentives may unintentionally discourage proportional or demand-oriented approaches. They may also inadvertently disadvantage lower income households and vulnerable groups, including elderly residents, tenants and those with health conditions, for whom comprehensive deep-renovation packages may be financially inaccessible, structurally disruptive or simply disproportionate to actual need (Sequeira et al. 2024). Sufficiency-oriented approaches, by contrast, open up lower cost and lower disruption renovation pathways that may be more accessible to these groups, and better aligned with their actual comfort needs and life circumstances. Aligning subsidy design and advisory criteria with sufficiency principles could therefore contribute not only to environmental objectives but also to equity goals within renovation policy. Recent implementation guidance for the EPBD further emphasises alignment between national renovation planning, performance thresholds and financing instruments, reinforcing deep renovation and zero-emission trajectories as default reference points for policy evaluation (Efficient Buildings Europe 2024). This would require complementing area-normalised indicators with metrics that capture avoided demand, reduced intervention and life-cycle impacts, as suggested in recent policy-oriented sufficiency research (BPIE & Ramboll 2024; Saheb 2021), thereby reducing structural bias toward volume-based renovation metrics.

More broadly, the framework suggests that OSS could serve as strategic leverage points for translating high-level sufficiency goals, such as limiting absolute energy demand, avoiding unnecessary increases in conditioned floor area or material use, into concrete renovation decisions. This role is particularly relevant in the context of long-term renovation strategies under the EPBD, where implementation depends on regulatory targets and how renovation pathways are structured in practice (European Commission 2020; Castellazzi et al. 2022), and where advisory intermediaries mediate between abstract policy ambition and situated decision-making.

5.4 LIMITATIONS

As a conceptual paper, this study has several limitations that should be acknowledged. The framework is derived from a selective synthesis of the existing literature and has not been empirically validated. As such, it does not assess how sufficiency-oriented OSS practices perform in specific national, institutional or market contexts, nor does it capture the diversity of existing OSS business models and governance arrangements. Furthermore, the literature reviewed draws predominantly on European contexts, which reflects the concentration of OSS development and sufficiency policy within EU frameworks. The applicability of specific findings, such as those relating to EPBD implementation or national renovation passports, may therefore vary in non-European settings. The conceptual framework itself, however, operates at the level of decision logics, framing mechanisms and intermediary roles, and is not inherently EU specific. It is intended to be transferable to any national context where renovation advisory intermediaries play a structuring role in building upgrade decisions.

In addition, the framework assumes a degree of flexibility in OSS advisory practices that may not exist in all settings. Regulatory requirements, standardised energy modelling procedures and funding conditions can all constrain the extent to which sufficiency-oriented reframing is feasible in practice. The framework also does not explicitly address potential tensions between sufficiency-oriented advice and business models that rely on transaction volume or investment size, an issue highlighted in previous research on OSS sustainability and scaling (Witherley et al. 2025; Pardalis et al. 2025), and which may create structural resistance to proportional renovation strategies.

The framework additionally assumes a sequential and open-ended advisory process, beginning with an initial assessment and progressing through renovation scope definition, scenario development and system design. In practice, building owners frequently approach OSS with a narrower brief, seeking advice on a specific component, a single measure already under consideration or a particular step in the process such as financing. In such cases, the early stage leverage points identified in the framework may not be accessible, as key framing decisions will already have been made before OSS engagement. The framework’s applicability is therefore strongest where clients engage at an early and open-ended stage of renovation planning, and its relevance diminishes as the entry point moves further along the decision sequence. Furthermore, while the framework introduces future occupancy and life-course dynamics as a relevant dimension of sufficiency-oriented initial assessment, it does not fully operationalise how such assessments should be conducted in practice. Translating anticipated household trajectories into concrete renovation scenarios and system-sizing decisions raises methodological questions—about the time horizons considered, the uncertainty of life-course projections and the appropriate tools for integrating dynamic occupancy assumptions into energy modelling—that go beyond the scope of a conceptual framework and require dedicated empirical and methodological development.

Finally, the paper focuses primarily on decision-framing and organisational processes and does not examine how sufficiency-oriented renovation pathways are received by building owners, contractors or financiers. These actor perspectives are likely to shape the practical viability of the proposed framework and may either reinforce or challenge sufficiency-oriented reframing efforts. The paper also does not systematically review advisory programmes beyond OSS that already incorporate sufficiency principles in practice, such as housing advice services for elderly residents, social housing support schemes or community-based retrofit programmes. Such programmes may offer valuable lessons for sufficiency-oriented OSS design that the present framework does not capture. The framework also does not address the equity dimensions of sufficiency-oriented renovation in depth, including how low-intervention approaches could be designed and targeted to better serve lower income households, energy-poor groups and other vulnerable populations whose renovation needs are poorly served by conventional performance-maximisation approaches. Given that equity and fairness lie at the heart of sufficiency’s definitional foundations, this dimension warrants dedicated attention in future empirical research.

5.5 FUTURE RESEARCH

The framework developed in this paper opens several avenues for future research. A first priority is empirical testing of the framework through case studies of existing OSS, examining how renovation objectives, demand assumptions and scenario comparisons are currently structured, and whether sufficiency-oriented alternatives are considered or excluded.

Second, future research could investigate how different policy and funding environments influence the ability of OSS to adopt sufficiency-oriented practices. Comparative studies across countries or regions, including non-European contexts where analogous renovation intermediary models operate under different institutional and regulatory conditions, could help identify enabling and constraining conditions, including regulatory requirements, subsidy design and performance evaluation criteria.

Third, there is scope for developing and testing decision-support tools and indicators that make sufficiency outcomes visible within renovation processes. This includes metrics for avoided intervention, reduced system capacity or life-cycle material savings, which could complement existing energy performance indicators and counterbalance the dominance of area-normalised performance metrics.

Fourth, future research could examine how sufficiency principles are integrated across different advisory models beyond OSS, including services targeting specific population groups such as elderly residents, social housing tenants or community-based retrofit programmes. Comparative analysis across these advisory contexts could help identify where sufficiency-oriented approaches are already embedded in practice, and what lessons might be transferable to OSS design and evaluation.

Fifth, the decision logic developed in this paper, questioning the necessity, proportionality and scope of intervention before committing to a renovation pathway, is in principle applicable beyond renovation to earlier and more fundamental building decisions, including whether to renovate, retrofit, adapt for a new use or avoid new construction altogether. The sufficiency principle of questioning how much intervention is warranted, and at what scale, is directly relevant to decisions about new build, demolition and rebuild, or adaptive reuse, where embodied carbon implications may be even more significant than in renovation alone (Ness 2023; BPIE & Ramboll 2024). Extending the decision framework to these upstream decisions represents a promising direction for future research, though it would require engagement with a broader body of literature beyond the scope of this paper.

Finally, research is needed on the social and organisational dynamics of sufficiency-oriented renovation advice, including how building owners perceive proportional renovation options, how advisors negotiate comfort expectations and how sufficiency-oriented recommendations interact with prevailing norms of renovation ambition. Addressing these questions would help bridge the gap between conceptual sufficiency frameworks and their implementation in everyday renovation practice, thereby advancing both sufficiency research and the study of renovation intermediaries.