Prefabrication for housing retrofit: governance, innovation and resident experience

2.1 CLIMATE POLICY AND THE EUROPEAN RENOVATION WAVE

Buildings in the European Union account for around 40% of final energy use and 36% of energy-related GHG emissions. The existing stock decarbonisation represents the key target for Europe (European Commission 2020): an estimated 75% of buildings are energy-inefficient; around 80% to 90% of these will still be in use in 2050. The EU Renovation Wave (European Commission 2020) and the Energy Performance of Buildings Directive recast (European Commission 2024) frame deep retrofit as a strategic solution and invite Member States to increase the annual retrofit rates. However, it is now established that markets alone will not deliver the required scale of intervention, as observed average retrofit rates remain around 1% annually across Europe, far below the 2.5% to 5% needed to reach climate neutrality (Bertoldi et al. 2025; Lihtmaa et al. 2025).

This gap between retrofit policy ambition and delivery cannot be attributed to technology alone. It reflects the sociotechnical (technologies are embedded in social systems) (Sundling & Szentes 2021), distributive (costs, risks, benefits and decision power are allocated unevenly across actors and regions) (Lihtmaa et al. 2025) and governance (the architecting of rules, roles, intermediaries and coordination mechanisms) complexity of intervening in building stock retrofitting at scale. Consequently, the retrofit challenge is increasingly characterised as a wicked problem (Rittel & Webber 1973), stemming from a high degree of stakeholder interdependence and divergent value systems that require complex trade-offs. Furthermore, when coupled with uncertain economic or social payoffs, these frictions resist the simple, linear logic that dominates conventional renovation policy (Murto et al. 2019; Sundling & Szentes 2021).

2.2 ESTONIAN APARTMENT STOCK AND CURRENT GOVERNANCE MODEL

Estonia is good representative case for the CEE building stocks. Approximately 22,600 apartment buildings (totalling around 28 million m²), mostly standardised typologies, were constructed before the year 2000 (Iliste et al. 2023). After the Soviet occupation, approximately 95% of Estonian dwellings were privatised, resulting in a high proportion of owner-occupancy. Today, these buildings are managed by apartment associations, which function as non-professional, collective clients for renovation with limited technical and managerial capacity. Decisions to retrofit require majority approval, financial trust and perceptions of fairness rather than meeting energy-performance metrics alone (Ojamäe & Paadam 2015; Reindl 2020).

Since 2010, the Estonian government has implemented a retrofit grant programme administered by KredEx (now the EIS) (Lihtmaa et al. 2025). This national grant scheme integrates co-financing with mandatory technical standards, an accredited ‘technical consultant’ intermediary role and the compulsory use of the Estonian Public Procurement Register (Kuusk & Kalamees 2016). Later iterations introduced regional differentiation of financial support, indoor air quality requirements and, since 2021, a dedicated grant line for prefabricated industrial retrofit (Lihtmaa et al. 2025).

The 2021 prefabricated retrofit grant programme was established based on demonstration projects that renovated 1980s Soviet-era apartment buildings to meet nearly zero-energy (nZEB) standards (Hamburg et al. 2020; Nigumann et al. 2024). The project used prefabricated insulation elements, mechanical heat recovery ventilation and on-site renewables. A process analysis of this first pilot identified procurement, design, fabrication and construction integration, and technical skills as the main barriers to industrialised retrofit (Pikas et al. 2021). The study found that conventional design–bid–build (DBB) arrangements excluded manufacturers and contractors from the early design phases, where decisions with a high impact are made. Furthermore, at the time, the industrialised retrofit cost was between 400 and 450 €/m², while state-supported on-site renovations ranged between 300 and 350 €/m² (Pikas et al. 2021).

Despite a substantial public investment of €635 million between 2010 and 2024, outcomes remain uneven (Lihtmaa et al. 2025). Uptake is spatially skewed towards growing regions, while progress in demographically declining areas (like Ida-Virumaa) remains slow. The overall retrofit rate persists below the trajectory planned in the Estonian Long-Term Renovation Strategy (LTRS 2020).

2.3 GOVERNANCE PERSPECTIVES

Research evidence from across Central and Eastern Europe contexts suggests that proactive intermediation by property managers, technical consultants and city-led demonstration programmes (rather than the initiative of individual households) determines whether public funding translates into retrofit activity (Cirman et al. 2013; Truu et al. 2024). Retrofit governance could be understood through three complementary views:

• From the multi-level perspective on sociotechnical transitions (Geels 2002), retrofit industrialisation has been framed as a niche innovation (Kivimaa & Martiskainen 2018; Lazarevic et al. 2020). The diffusion depends on the co-evolution of regime elements, including procurement arrangements and practices, building engineering guidelines, professional cultures, financing instruments and skills. Evidence from different initiatives (Bertoldi et al. 2025; Brown et al. 2019; Uyarra et al. 2020) demonstrates that prefabricated retrofit niches underperform when the identified regime elements are not deliberately and systematically reconfigured.

• Literature on intermediary actors, such as demand aggregators, knowledge brokers and network orchestrators, bridge the gap between fragmented supply chain members and dispersed, non-professional clients (Bird & Barnes 2014; Brown et al. 2019; Kivimaa & Martiskainen 2018; Talmar et al. 2022). Research suggests that residents and apartment associations adopt deep retrofit solutions when complexity is reduced, financial implications are translated into typical household terms (such as monthly utility bills before and after renovation) and trustworthy intermediaries endorse performance and quality (Naeyaert et al. 2026; Ricci et al. 2025; Straub & Meijer 2025).

• Transition design and mission-oriented frameworks utilise systemic interventions and coordination to mobilise innovation towards solving complex societal challenges within defined timeframes. By actively shaping markets and aligning regulatory measures, these frameworks enable to drive transformative change and generate measurable value (Irwin 2015; Mazzucato 2021).

This study treats governance as an important driver directly shaping innovation outcomes, rather than just a background setting.

2.4 GOVERNANCE AND PROCUREMENT

Current research on demand-side innovation policy positions the state beyond the mere grant distributor role (Edler & Georghiou 2007; Mazzucato 2021; Uyarra et al. 2020): it can act as a market-maker, problem-framer and rule-setter, intentionally shaping the change. Public innovation procurement, mission-oriented programmes and demonstration schemes support the niche spaces required to develop, certify and scale industrialised retrofit methods (Edler & Yeow 2016; Kivimaa & Martiskainen 2018).

Procurement is not a neutral administrative instrument but a means for promoting innovation. For example, by determining who is involved and when, how risk is allocated and how information flows, it enables or limits the early integration of designers, manufacturers and contractors that prefabrication of insulation elements requires (Lahdenperä 2012; Pikas et al. 2021; Salcedo Rahola & Straub 2016). Table 1 contrasts the impact of different procurement models on renovation industrialisation.

The reviewed literature suggests that scaling renovation industrialisation in owner-occupied apartment stock requires the co-development of three critical dimensions:

1. Policies: Mechanisms that provide demand certainty and reward systematic, joint/district-level interventions over single-building retrofits.

2. Intermediary capacities: Entities and mechanisms that translate complex technical solutions into actionable choices for non-expert collective clients (e.g. apartment associations and residents).

3. Procurement practices: Procurement models that integrate designers, contractors and fabricators early to exploit the specific prefabrication information requirements.

While existing studies have examined these dimensions in isolation, and mostly within Western European housing contexts, limited research documents the simultaneous reconfiguration of all three within the CEE contexts. This paper analyses the scaling of Estonian industrialised retrofit pilot as a unique case positioned within these three dimensions.

3.1 PILOT SELECTION AND RETROFIT SOLUTIONS

Approximately 14,000 buildings (with a total net area of around 18 million m²) require retrofitting; 78% were built between 1946 and 1990 with three main types of structures, including prefabricated concrete large panel, brick and lightweight large block (Iliste 2023). Because energy prices were low during the post-Second World War mass construction era, the thermal and energy performance of buildings were not a high priority.

The stock includes approximately 5,246 apartment buildings (containing 36,753 dwellings), with occupancy rates below 80%. These buildings represent a challenging segment for retrofit owing to demographic decline and financial incapability. From the perspective of economies of scale, medium-to-large apartment buildings are the main target for industrialised retrofit; these constitute 28% of the building stock by count but include 72% of all apartments (Lihtmaa & Kalamees 2025).

As mentioned in Section 2.2, the Estonian housing stock is characterised by a high rate of ownership. Apartment buildings are managed by building-specific apartment associations (Lihtmaa et al. 2025; Lihtmaa & Kalamees 2025). All residential and non-residential unit owners are members of the association. Decisions are authorised by a simple majority vote (minimum 51%) during the association’s general assembly.

The 19 apartment buildings analysed in this study were not selected by researchers but entered the pilot through a competitive public application process governed by EIS and eligibility criteria embedded in the national grant scheme (MTMm no. 51, 2020). The three most important criteria for this study were:

• Building type: Applicant buildings were required to belong to one of four standardised apartment typologies (see Appendix 1 in the supplemental data online) to ensure comparability. The four typologies together represent around 51% of the post-war Estonian apartment stock by share, ensuring representativeness of the most replicable segment.

• Number of storeys: To address the industry feedback on the learning curve, only buildings up to five storeys were eligible.

• Baseline performance: Buildings were ranked by baseline energy use and net floor area, prioritising the most energy-inefficient and to avoid selecting partially renovated buildings.

The selected 19 buildings represented the most replicable segment of the Estonian post-war building stock. Because pilot buildings complied with the same grant scheme and procedural requirements, the study allowed for a controlled comparison.

The technical intervention utilised prefabricated timber-framed insulation elements (see Figure 2). These elements are constructed with a centre-to-centre (c/c) stud spacing of 600 mm, utilising thermal batt or loose-fill insulation (mineral wool or cellulose), or rigid foam insulation.

Figure 2

3.2 DATA SOURCES AND ANALYSIS

For the final evaluation, three data sources were used and combined: stakeholder interviews, construction site diaries and project and grant documentation. In total, 18 semi-structured interviews were conducted with different stakeholder categories (see Table 2): 10 (53%) apartment associations, 2 (100%) design companies, 2 (100%) insulation element fabricators, 2 (100%) main contractors and 2 (100%) quality inspection/commissioning companies.

The interviewed apartment associations represented more than 50% of the participating buildings. Coding of interview results focused on the three research questions.

• The interviews with apartment associations focused on how the retrofit decision was made, how the procurement process was managed, how the association fulfilled its client role during the retrofit and how the outcomes and overall success were evaluated.

• The interviews with designers focused on data collection, assessing the load-bearing capacity, evaluating the hygrothermal performance, examining the condition and design principles of building service systems, and addressing considerations related to life-cycle assessment, circular construction.

• The interviews with fabricators focused on the input data required from building surveys and design documentation, the specification of installation methods and fabricator-specific innovations.

• The interviews with main contractors focused on collecting data, identifying the main challenges encountered during the installation and associated building service systems.

The document analysis involved the study of grant documentation (the grant regulation, EIS procurement announcements, consortia tender submissions and framework contracts), building-specific project documents from 15 of the 19 buildings (pre-design surveys, laser-scan reports, design models, drawings, specifications, change orders and as-built documentation) and daily construction site diaries for identifying activity durations, sequencing, resource flows, stoppages and delay reasons. Analysis results were compared to interview results.

4.1 GOVERNANCE FRAMEWORK AND PROJECT FINANCING

The Estonian state grant scheme, primarily for deep retrofits, is administered by the EIS, which establishes building-level targets for energy performance and indoor climate categories alongside component-level requirements for thermal transmittance and the mitigation of thermal bridges (Kuusk & Kalamees 2016). Between 2010 and 2020, around 1,400 buildings were renovated, representing a total investment of €650 million and €260 million in subsidies.

In 2020, the EIS launched a dedicated €18 million grant programme for industrialised retrofit, covering up to 50% of retrofitting investment. The main difference from previous renovation grants was the technical mandate of using prefabricated insulation elements, at least one storey in height, with pre-installed windows (MTMm no. 51, 2020). This eliminated the need for on-site scaffolding, significantly changing the traditional renovation workflow (Pikas et al. 2021).

However, given the retrofit market’s limited experience with industrialised retrofit, the EIS transformed from a passive financier to a proactive intermediary. The EIS assumed the role of an intermediary, preparing the grant programme, coordinating the joint design and construction procurement and serving as the primary contractual and communication interface between apartment associations and the industry consortia. During the procurement preparation and coordination, it became evident that there was a significant difference from conventional retrofit project delivery.

This shift necessitated changing typical financial flows. Traditional renovation costs accrue during on-site construction, but industrialised methods incur a large proportion of expenses during the factory production phase. To accommodate this, the payment schedule was adjusted to a four-stage model: an initial 5% upon design approval, 30% upon acceptance of the manufactured elements, 50% based on construction progress via bank loans, and a final 15% upon completion of all works.

4.2 INDUSTRY INVOLVEMENT AND PROJECT DELIVERY METHOD

Parallel to the development of the overall project governance framework, a technical working group of industry leaders was established and led by the Estonian Woodhouse Association to refine renovation solutions based on earlier demonstrators (Pihelo et al. 2017) and the specific characteristics of the building types involved in the project (see Appendix 1). The technical group was tasked to address the following research questions:

• What experiences have we gained so far, including the positive and negative aspects?

• What similar experiences exist in other countries regarding additional insulation with prefabricated insulation elements?

• What is the biggest challenge faced in industrial retrofit?

• How is our housing stock categorised by construction type?

Design documentation for typical buildings was obtained from the archive. Retrofit drawings were created for three types of apartment buildings, developed by different companies. The working group focused on standardising critical details and connections within the building envelope. The standard retrofit solutions were published in a guide: initially for buildings up to five storeys (Luht-Kallas et al. 2021) and later up to nine storeys (Pukk & Vogt 2023). Harmonising fire safety requirements was important, providing a common ground and understanding for building design engineers and evaluators, as the market players and fire safety officials lacked experience with new industrial renovation technologies, leading to inconsistent interpretations in different Rescue Services Agency regions.

The pilot marked a departure from the traditional DBB method (see Figure 3 above), which excludes contractors and manufacturers from the early design phases, where high-impact decisions are made. The pilot identified that the industrialised retrofit success requires the early integration of contractors’ and fabricators’ expertise. Accordingly, the pilot employed an integrated retrofit design and construction delivery (Figure 3 below), which was expected to improve relationships between consortium members (2016), such as client, contractor and fabricator. This allowed for a more accurate early-stage cost assessment but also demanded a thorough preliminary building survey and architectural brief. To assist non-professional apartment associations, the involvement of an independent technical consultant was introduced to advise the associations throughout the project delivery.

Figure 3

4.3 PUBLIC PROCUREMENT AND FINANCIAL IMPLICATIONS

Led by the EIS in late 2020, the procurement process involved simultaneous calls for apartment associations and retrofit consortia, including designers, contractors and fabricators. While building associations were the primary beneficiaries, funding design and construction through a mix of grants, savings and loans, the EIS served as a central intermediary (see Table 3). The EIS managed a competitive selection process where consortia bid on groups of buildings of the same typology (see Appendix 1). Selection was determined by the lowest total cost for the building group, after which individual associations entered into integrated renovation design and construction delivery contracts with the successful consortia.

To ensure technical and financial reliability, bidding consortia were required to meet the following qualification criteria:

• Financial and legal: A minimum €4 million annual turnover (with €2 million specifically from prefabrication) and recognised legal status with ETAG 007 certification for wood-based construction.

• Capacity: Experience in at least five projects with more than 3,000 m² of prefabricated external wall or roof elements.

• Technical team members: A multidisciplinary team including qualified architects, structural engineers and HVAC specialists.

Six consortia applied, with five proposing timber- and concrete-based elements. Simultaneously, 37 apartment associations applied for the grant. These buildings were grouped by typology and ranked by energy intensity and net floor area to prioritise the most inefficient structures. For the same energy use, a building with a larger net surface area was preferred. A specific grant budget was allocated to each building type group (around €4 million). Based on an initial estimate of 400 €/m² (Nigumann et al. 2024) and given the overall grant programme budget, 29 buildings were originally identified for retrofit.

Following the tender evaluation, 19 apartment associations decided to proceed. The projects were awarded to two consortia, including well-established retrofit market companies (with long-term experience and holding 10–20% of market share). The buildings were divided roughly equally between the two main contractors and the two manufacturers. One designer provided services for both consortia. The division of buildings between the two consortia and the retrofit cost per building and building type series are presented in Appendix 2 in the supplemental data online.

The actual retrofit cost reached 660 €/m² (see Figure 4, left). This surge was driven by a 30% rise in global construction costs during 2021 (due to COVID-19) and higher unit costs for buildings smaller than 2,500 m² (see Figure 4, right side). This cost increase was not specific to Estonia; shortages and rising prices of labour and materials also occurred in other countries (Ling et al. 2022; Salami et al. 2023).

Figure 4

The results showed that, while apartment associations had the right to withdraw from the pilot project after the procurement process, bidders faced demand uncertainty that prevented the realisation of volume-based cost reductions. For example, in the 1-464 typology group (1-464 refers to a standardised precast concrete apartment building system developed in the late 1950s in the USSR for rapid, low-cost mass housing; the building system was made from factory-produced reinforced concrete wall and floor panels), only an eligible association signed a contract (see Appendix 1).

This risk appears more manageable in smaller clusters, as evidenced by recent successful four-building procurements in the same region (Truu et al. 2024). To address volatile economic conditions and risks during these multi-year projects, the grant framework included a 10% flexibility margin; this allowed for an increase in funding if the national construction cost index (published by Statistics Estonia) rose by more than 2% quarterly or 6% annually.

4.4 PILOT RENOVATION IMPLEMENTATION AND FEEDBACK

Pre-design involved detailed surveys, 3D laser scanning and a scan-to-BIM workflow. Prefabricated timber-frame units (250–350 mm thick; 0.11–0.24 W/(m²·K)) were manufactured off site, installed in units up to size 2.7×9 m, and three windows embedded. On average, renovating 16 m² of floor area took one day (ranging from 6 to 36 m²/day), though progress was not linear. While panels were installed swiftly (two to six weeks compared to three to six months for traditional methods), total project durations varied from 95 to 309 days (see Figure 5). That is, despite the swift installation, the entire renovation remained lengthy. Industrial renovation will not achieve its full effectiveness without accelerated preparatory work, including removal of existing facade elements (porch and loggia railings, eaves boards and so on), logistics-related activities and the organisation of cranes and assembly equipment and, after installation, sealing joints and finishing the connection of different building envelope parts.

Figure 5

The most significant delays and work stoppages arose from both engineering design aspects, such as inaccurate structural data on existing conditions necessitating redesigns, and management issues, like human and communication errors and poor subcontractor coordination. Figure 5 shows many building renovations were performed simultaneously or in close succession. Concurrent projects overloaded design firms, which have limited availability of resources, extending lead times.

Furthermore, the efficiency of industrial renovation was hampered by on-site bottlenecks:

• The manual removal of old facade elements and the labour-intensive finishing of internal window reveals and sills (averaging 0.9 and ranging from 0.3 to 1.8 days per apartment). This required entering the apartment several times, which is disruptive to residents and prolongs the renovation process.

• Flat roof renovations proved more time-efficient than pitched roofs owing to simpler geometry and work, including tasks related to load-bearing structures, eaves, safety barriers and weather-related downtime.

• Retrofit of building services typically required three to six months. The companies renovating building service systems were, on average, involved for six months in the retrofit of heating and ventilation systems and three months in the renovation of water and sewerage systems (first and last entries in the construction diary).

Overall, the project duration was affected by both the complexity of the renovation and the coordination and integration of works. Employing specialised finishing teams and partial mechanisation of work sections would help reduce both time and costs.

5.1 SCALING RENOVATION INDUSTRIALISATION AS A MULTI-LEVEL TRANSITION

Findings highlight that industrialised retrofit cannot be scaled by improving the technical aspects of prefabricated elements alone (Geels 2002). Implementation required the reconfiguration of different regime elements: grant regulation, procurement practices (competitions and integrated contracts), building engineering guidelines, financing instruments and skills (technical consultant and designer training). This is aligned with international evidence from IEA ECBCS Annex 50 (Zimmermann 2011) and Energiesprong (Brown et al. 2019), showing the significance of the funding and procurment regime on retrofit; without it, technically successful demonstrators fail to scale (Kivimaa & Martiskainen 2018).

The Estonian pilot contributes to the literature currently dominated by single-site demonstrators and Western European social-housing portfolios (Brown et al. 2019; Rose et al. 2021; Straub & Meijer 2025) with one important aspect: client/ownership structure. While Energiesprong and the Dutch social-housing projects were operated by professional landlords, the Estonian cases were operated by non-professional apartment associations, which had the right to withdraw from the pilot after procurement results. This difference introduced several governance-related challenges (such as lack of knowledge and understanding, additional explanation of technological and financial implications to non-professional building associations, window replacements) described in Section 4. The pilot itself covered the most replicable segment (the four selected building types represent around 51%) of the Estonian post-war building stock, making the learning on governance, procurement and resident engagement transferable to many other similar buildings.

5.2 GOVERNMENT AS A SYSTEMIC TRANSITION INTERMEDIARY

In this pilot, the EIS acted as a systemic transition intermediary, streamlining the demand (from 37 applicants to 19 contracted) and supply diversity (two out of six consortia were selected). Strict qualification requirements (≥€4 million turnover (€2 million prefabrication), at least five projects and ≥3,000 m² volume) limited the potential pilot suppliers to those holding 10–20% of the national market. This highlights how high entry barriers mitigate early execution risk but potentially reduce the supply base, limiting long-term competition.

Financially, the EIS changed and introduced a four-stage payment schedule (mentioned in Section 4.1) to synchronise public grants with industrialised renovation cashflows. This supported the integrated design and construction procurement and contracting and succeeded because of close collaboration between the rule-setting ministry and the EIS.

At the project level, accredited technical consultants served as intermediaries translating complex parameters for non-professional building associations. Without them, the administrative burden of change orders and design iterations would have exceeded building associations’ capacity (Naeyaert et al. 2026; Reindl 2020; Ricci et al. 2025). Expanding this capacity regionally, especially in demographically declining areas (Lihtmaa et al. 2025), still remains a structural precondition for scaling industrialised renovation.

5.3 PROCUREMENT FOR STEERING INNOVATION

Findings of this pilot demonstrate that public procurement can drive innovation rather than function as neutral administration (Edler & Georghiou 2007; Edler & Yeow 2016; Uyarra et al. 2020). The shift from DBB to integrated retrofit design and construction delivery (Hall et al. 2014; Lahdenperä 2012) helped to address the weaknesses identified in the predecessor pilot (Pikas et al. 2021): the late involvement of fabricators and a lack of the front-loaded geometric and structural information that prefabrication requires.

However, bundling buildings of the same typology did not deliver the expected economies of scale. Building associations had the right to withdraw after procurement, which introduced considerable risk for potential suppliers. Also, the distribution was not uniform across typologies: only a single 1-464 building proceeded to contract, effectively limiting the expected benefits from bundling buildings. Multi-year strategic partnering arrangements with professional landlords, as in the Dutch social-housing sector (Straub & Meijer 2025), appears to outperform the single-cycle bundled procurement of this pilot.

The 65% cost escalation from an estimated 400 €/m² to a realised 660 €/m² was mainly driven by a sector-wide construction inflation shock of around 30% in 2021 (Ling et al. 2022; Salami et al. 2023). Rather than grant schema failure, this cost increase highlights the structural resilience of the programme. To absorb macroeconomic volatility over multi-year project life cycle, the framework utilised a 10% flexibility margin operationalised via construction-cost indexation (triggered when national indices rose by more than 2% quarterly or more than 6% annually). This adaptive adjustment capability serves as a transferable governance feature in high-volatility periods, contrasting sharply with conventional fixed-budget grant schemes that typically stall or require extensive post-award renegotiation under identical market shocks.

5.4 RESIDENT INVOLVEMENT AND LIMITS OF STANDARDISATION

Residents in owner-occupied housing prioritise trust, equity and financial implications over technical performance metrics alone (Naeyaert et al. 2026; Ojamäe & Paadam 2015; Truu et al. 2024). Consequently, industrialised retrofit initiatives must explicitly generate ‘trust evidence’ to secure collective buy-in within apartment associations (Bird & Barnes 2014). This sociotechnical dynamic often constitutes the upstream cause of the procurement uncertainty described above: the statutory 51% majority voting rule, combined with an association’s right to withdraw after procurement, generated the demand uncertainty that neutralised the economies of scale expected from bundling buildings of same type.

Furthermore, window-replacement disputes occurred in all pilot cases, highlighting that highly sensitive components require dedicated negotiation and process transparency. On site, the manual finishing of internal window reveals and sills averaged 0.9 days per apartment (range: 0.3–1.8 days), marking a disruptive, labour-intensive bottleneck where industrialised retrofit collides with individual household consent.

Finally, the significant difference between total project duration (95–309 days) and off-site panel installation (two to six weeks) indicates that, while the envelope’s technical core is industrialised, the surrounding administrative and trade interfaces remain unintegrated (Murto et al. 2019; Pikas et al. 2021). Conventional timelines for building services modernisation, averaging six months for HVAC and three months for plumbing, do not benefit from prefabrication and continue to dominate the project’s critical path.

5.5 IMPLICATIONS, TRANSFERABILITY AND LIMITATIONS

Industrialised retrofit should be designed as multi-year, demand-certain pipelines rather than single-cycle competitive grants, with rule-setting and disbursal authority vested in a single intermediary. Integrated renovation design and construction delivery (Lahdenperä 2012; Salcedo Rahola & Straub 2016) should be preferred for prefabricated renovation, supported by harmonised standards. Associations need intermediary support, such as technical consultants and decision-support tools, translating technical and financial aspects into household terms (Viik et al. 2026).

Findings are largely transferable to other CEE contexts, where high owner-occupancy is common (Cirman et al. 2013) but differs from Western social-housing contexts. The small state and construction sector permit a single national intermediary. Trust accumulated through pre-2021 demonstrators is not replicable on short timescales. Within these boundaries, central findings are likely generalisable to comparable owner-occupied apartment stocks in CEE and possibly Northern European settings. There are also limitations: the participatory research design carries subjectivity risk; the post-renovation observation window is short; and duration and unit-cost findings may vary across other typologies.