Introduction

The recast Energy Performance of Buildings Directive (EPBD) marks a decisive evolution in European building policy. By formally introducing Zero-Emission Buildings (ZEBs) as the benchmark for new construction and major renovation, the Directive establishes buildings as a central pillar of the European Union’s pathway to climate neutrality by 2050. Under the revised framework, buildings are no longer assessed solely on their operational energy efficiency but increasingly on their contribution to greenhouse gas emissions across the entire life cycle.

Articles 7 and 9 of the recast EPBD require that all new buildings achieve zero operational emissions, while Annex I introduces life-cycle global warming potential as a core performance indicator. This represents a fundamental shift from the nearly zero-energy building (NZEB) paradigm towards a broader, more systemic understanding of sustainability in the built environment (European Commission, 2024). Yet despite the clarity of this policy's ambition, its implementation poses substantial challenges.

Delivering ZEBs requires coordinated action across design, construction, operation, and governance. Designers must integrate life-cycle thinking from the earliest project stages. Material producers and contractors must adapt to circular construction principles. Public authorities must translate European targets into coherent national regulations and incentive schemes. At the same time, buildings must remain affordable, comfortable, and socially accepted.

In this complex landscape, research and innovation projects play a bridging role between policy ambition and built reality. Among them, the Horizon Europe project GreeNest provides a comprehensive response to the EPBD challenge. Rather than focusing on individual technologies, GreeNest develops and validates an integrated ecosystem for ZEBs, combining circular materials, energy-efficient systems, digital tools, and innovative design methodologies. These solutions are tested and monitored in real buildings across different European regions, generating evidence that directly supports EPBD implementation.

EPBD zero-emission requirements and GreeNest performance targets

The recast EPBD defines ZEBs through a combination of operational, technical, and life-cycle criteria. Article 11 establishes the elimination of on-site emissions from fossil fuels as a core requirement, while Article 15 strengthens the role of building automation and control systems. Annex I introduces mandatory consideration of life-cycle global warming potential, signalling the increasing regulatory importance of embodied carbon.

GreeNest demonstration buildings are explicitly designed to comply with, and in several areas exceed, these requirements. All buildings eliminate on-site fossil fuel use and rely exclusively on high-efficiency electric heat pumps, combined with on-site renewable energy generation. Operational energy demand is minimised through advanced envelope systems and integrated design, achieving at least a 10% reduction in final energy consumption than national NZEB benchmarks.

Depending on national regulatory contexts, remaining grid interaction is either fully offset or reduced to a very low level, ensuring compliance with Article 9 requirements for zero operational emissions. Beyond operational performance, GreeNest explicitly addresses embodied carbon. Through the use of bio-based, earth-based, and recycled materials, as well as digitally optimised construction processes, the project targets a 50% reduction in embodied carbon compared with NZEB reference buildings. Recent scientific studies confirm that substantial reductions in life-cycle greenhouse gas emissions are achievable when life-cycle assessment is integrated at early design stages, enabling informed decisions on materials, systems, and building form (Asdrubali and Grazieschi, 2020).

The GreeNest ecosystem: a systemic response to EPBD implementation

One of the key insights underlying the recast EPBD is that building performance cannot be improved through isolated measures alone. Articles 7, 15 and 18 increasingly emphasise integrated approaches that link envelope performance, technical systems, automation, indoor environmental quality, and long-term adaptability.

GreeNest responds to this challenge through a building ecosystem approach structured around three interdependent pillars. The first pillar focuses on circular and bio-based materials, selected to minimise embodied carbon and enable reuse and recycling. The second pillar addresses energy-efficient envelopes and renewable technical systems, ensuring that operational energy demand is both minimised and fully decarbonised. The third pillar consists of digital tools and data-driven processes, supporting informed decision-making throughout the building life cycle.

_{Figure 1: GreeNest ecosystem concept. Source:  GreeNest Project.}
 

This ecosystem approach ensures that design decisions remain aligned with performance targets from concept to operation. It also reflects the EPBD’s growing emphasis on building quality, performance transparency, and user-centred design. Comfort, indoor air quality, and occupant interaction are treated as integral components of Zero-Emission performance, rather than secondary considerations.

Designing ZEBs and integrated methodologies from the outset

Conventional design workflows often address sustainability late in the process, leading to costly redesigns or suboptimal outcomes. GreeNest addresses this limitation by embedding life-cycle thinking from the earliest design stages through two complementary methodologies.

The design-by-inventory methodology uses locally available and reclaimed materials as a starting point for architectural and structural design. Rather than treating material availability as a constraint, it becomes a design driver. This approach directly supports Article 7 objectives related to resource efficiency and waste reduction and aligns with the EU Circular Economy Action Plan (European Commission, 2020).

In parallel, the DeltaSmart methodology focuses on upgrading conventional building typologies to Zero-Emission standards. Instead of requiring radical departures from established construction practices, DeltaSmart incrementally improves envelopes, systems, and layouts. Recent research indicates that incremental and scenario-based design approaches, particularly in renovation projects, can limit cost premiums while improving life-cycle environmental performance, thereby supporting broader market uptake (Cusenza et al., 2021). Together, these methodologies ensure that Zero-Emission performance is not an afterthought but a core design principle.

Material and system innovation aligned with life-cycle performance

Material innovation is central to GreeNest’s contribution to climate-neutral construction. The project develops a portfolio of standardised, modular building components, including bio-based insulation materials, earth-based elements, reversible façade systems, and integrated renewable energy solutions.

_{Figure 2: Portfolio of standardised, modular building components developed in GreeNest.  
Source: GreeNest Project.}

Recent life-cycle assessment studies show that many bio-based building materials achieve approximately a 20–50% reduction in embodied greenhouse gas emissions compared with mineral-based alternatives under comparable conditions, while also providing beneficial thermal performance and moisture-buffering (hygroscopic) properties (Liu et al., 2025). Earth-based materials further contribute to thermal mass and indoor comfort, supporting energy efficiency and occupant well-being.

Reversible connections and modular assemblies enable design for disassembly, allowing components to be reused or adapted during future renovation cycles. This approach anticipates future regulatory developments related to material passports and circularity indicators, which are increasingly discussed at EU level.

Digitalisation, BIM, and smart readiness

Digital tools are essential enablers of EPBD implementation, particularly under Article 15 on building automation and control systems. In GreeNest, Building Information Modelling (BIM) functions as a common data environment linking design decisions to energy, carbon, and comfort indicators.

Beyond design, digital twins extend BIM into the operational phase. Sensors monitor energy use, indoor environmental quality, and system performance, enabling continuous feedback and optimisation. Empirical studies demonstrate that such monitoring can reduce the energy performance gap between predicted and actual consumption by up to 30% (van Dronkelaar et al., 2016).

This data-driven approach supports performance verification, transparent reporting, and adaptive control strategies. It also aligns with the EPBD’s increasing focus on smart readiness and performance transparency as prerequisites for ZEBs.

Demonstration buildings: living laboratories for EPBD compliance

A defining strength of GreeNest is its portfolio of demonstration buildings across diverse climatic, regulatory, and socio-economic contexts in Europe. These buildings, many of them public or community-oriented, function as living laboratories.

Public buildings play a strategic role in EPBD implementation. Article 7 explicitly highlights the exemplary role of public authorities, and research shows that public demonstration projects significantly accelerate innovation diffusion and market confidence (IEA, 2023). By testing Zero-Emission solutions under real construction and operational conditions, GreeNest provides tangible evidence that regulatory targets can be met in practice.

Practical applications supported by scientific and policy evidence

The technical strategies implemented in GreeNest are strongly supported by scientific and policy literature. Envelope-first strategies are consistently identified as the most robust pathway to reducing operational energy demand, with deep renovation studies reporting heating demand reductions of 40–70% (IEA, 2023).

The exclusive use of high-efficiency heat pumps reflects extensive empirical evidence demonstrating seasonal performance factors above 3.5, even in colder climates, when integrated with low-temperature distribution systems (EHPA, 2022). From a policy perspective, electrification of heating is recognised as a cornerstone of building decarbonisation in EU climate scenarios.

Embodied carbon research further confirms that life-cycle emissions can account for up to 50% of total building emissions in highly energy-efficient buildings, underscoring the importance of material choices. Circular construction strategies, including design for disassembly, enable reuse rates exceeding 70% for selected building components (Durmisevic, 2009).

Regional value chain readiness: insights from the GreeNest survey

Beyond technical performance, effective EPBD implementation depends on the maturity of regional value chains. An internal GreeNest survey assessed material availability, regulatory frameworks, financial incentives, and workforce readiness across partner regions.

Information collected in a survey of Germany, Greece, and Spain reveals clear patterns. Wood is widely available across all regions, confirming its role as a cornerstone material for low-carbon construction. However, recycled wood is far less accessible or not yet exploited for construction applications, indicating untapped circular potential. Other nature-based and recycled materials used in GreeNest, including hemp, straw, coffee-ground-based products, earth-based materials, and recycled insulation, are not considered widely integrated into mainstream construction markets. A key action point emerging from the survey is the need to actively develop regional access to these materials, in close cooperation with suppliers, processors, and local authorities.

All surveyed regions report the existence of regulations supporting sustainable construction, as well as financial incentive schemes. However, the availability and attractiveness of these incentives vary significantly, influencing investment decisions and project feasibility. Across all regions, a lack of qualified workforce with experience in sustainable construction materials emerges as a critical bottleneck, affecting planners, designers, and on-site workers alike.

_{Figure 3: Know-how, qualified experts and players on natural building elements. Source: GreeNest Project.}
 

From demonstration to market uptake and policy learning

GreeNest addresses these challenges through standardised solution packages, training activities, and engagement with regional value chains. These actions respond directly to non-technical barriers identified in EPBD impact assessments, including skills gaps and market fragmentation.

By generating monitored performance data and replicable solutions, GreeNest contributes to policy learning at national and European levels. The project provides practical insights that can inform EPBD transposition, long-term renovation strategies, and future regulatory development.

_{Table 1. GreeNest contribution to the EPBD.}
 

Conclusion

GreeNest demonstrates that ZEBs are achievable today when addressed through integrated ecosystems rather than isolated technological fixes. By aligning scientific evidence, EPBD policy requirements, and real-world demonstration, the project offers a practical blueprint for climate-neutral construction.

As Member States advance towards full EPBD implementation, ecosystem-based approaches such as GreeNest will be essential for translating regulatory ambition into durable, high-quality buildings that support Europe’s long-term climate objectives.