REN+HOMES Positive Carbon Building Methodology in Co-Design with Residents

Abstract

This article demonstrates how positioning residents as active co-designers fundamentally transforms both the process and outcomes of carbon-positive building development. Through structured collaborative workshops, shared decision-making protocols, and continuous partnership throughout the building lifecycle, the REN+HOMES Positive Carbon Building methodology challenges the conventional expert-driven approach to sustainable construction. Developed and validated through the H2020 REN+HOMES project, this resident-centered approach achieved remarkable technical performance—65.9% reduction in final energy demand—while simultaneously enhancing community ownership and long-term sustainability practices. By integrating participatory design with Zero Emissions Building (ZEB) criteria, renewable energy systems, and national carbon offset programs, the methodology proves that resident collaboration is not merely beneficial but essential for creating buildings that truly serve both environmental and human needs. This research establishes a new paradigm where technical excellence emerges from authentic partnership between residents and sustainability experts, offering a replicable framework for community-driven environmental regeneration.

1. Introduction

In response to the pressing imperative for sustainable development [1] amidst climate change, the Positive Carbon Buildings methodology emerges as a transformative approach within the built environment. Buildings contribute approximately 40% of global energy consumption [2] and 30% of greenhouse gas emissions [3], making them relevant targets for innovative sustainability solutions. While numerous green building certification systems exist, most fail to effectively integrate building occupants in the development process, despite their significant influence on a building’s operational performance [4]. This paper addresses this gap by introducing the REN+HOMES Positive Carbon Building methodology, designed to fill three specific research needs: (1) a clear process for integrating resident co-design into sustainability frameworks; (2) an enhanced carbon-positive performance metric extending beyond net-zero; and (3) robust mechanisms linking participatory design to measurable energy and carbon outcomes.

Our approach extends beyond conventional sustainable building practices in three fundamental ways:

• Positions residents as active collaborators rather than passive recipients in the design and operational phases, addressing the disconnect identified between technological solutions and user engagement [5].
• Surpasses the net-zero carbon targets of existing certification systems by establishing clear pathways toward buildings that produce more energy than they consume [6].
• Provides a comprehensive framework that integrates lifecycle assessment, renewable energy integration, and national carbon offset projects within a coherent evaluation system.

The REN+HOMES Positive Carbon Building methodology aligns with broader environmental ambitions, such as those outlined in the European Green Deal, which charts a course toward a climate-neutral continent by 2050 [7]. It embraces circular economy principles, considering a building’s entire lifecycle from material procurement to eventual decommissioning. This holistic approach addresses both embodied and operational carbon [8,9], recognizing that technological innovations [10] alone are insufficient without corresponding cultural and behavioral changes in how we relate to the built environment.

Our research extends existing work in sustainable building certification, including advances in lifecycle assessment [11], energy modeling [12,13], and participatory design [14]. By synthesizing these approaches with practical implementation strategies, we provide a replicable methodology for creating buildings that are not merely less harmful but actively beneficial to the planet.

Both the theoretical framework of the REN+HOMES Positive Carbon Building and preliminary results from its implementation in the European H2020 REN+HOMES project are revealed, demonstrating measurable improvements in energy performance and resident satisfaction. These findings suggest that integrating resident co-design with technical excellence can produce buildings that more effectively contribute to climate mitigation goals [15] while better serving their occupants’ needs.

2. Materials and Methods

2.1. Research Objectives and Scope

This research develops and validates the REN+HOMES Positive Carbon Building (PCB) methodology through four specific objectives: (1) systematic integration of resident co-design with technical certification criteria, (2) establishment of carbon-positive performance thresholds exceeding net-zero standards, (3) validation through H2020 REN+HOMES project implementation, and (4) creation of a replicable framework for future sustainable building development. This study focuses on residential building applications with documented potential for adaptation to other building types.

Research Questions

The methodology development is guided by three specific research questions:

• RQ1: How can resident co-design be systematically integrated into building certification frameworks?
• RQ2: What performance thresholds distinguish carbon-positive from net-zero buildings?
• RQ3: Does resident engagement enhance building performance beyond conventional approaches?

To develop our universal positive methodology, we conducted a comprehensive review of existing approaches, identifying their strengths and limitations. Our analysis revealed that while current methodologies offer valuable technical guidelines, they typically lack structured processes for resident engagement, despite evidence that occupant behavior significantly impacts building performance [5].

Environmental Product Declarations (EPDs) serve as the primary mechanism for quantifying embodied carbon in construction materials. Under the Construction Products Regulation (EU) 2024/3110 [16], EPDs will become mandatory for harmonized construction products, providing standardized environmental impact data. In the REN+HOMES project, we proactively implemented EPD-based material selection in criteria A2 and A3, demonstrating how future regulatory requirements can be integrated into current sustainable building practices.

Table 1. Methodologies’ tools.

Method	Tool Name	Goal	Description	Contribution to the REN+HOMES Positive Carbon Building
PHI	IES VE PRO	Energy Simulation	Models and predicts building performance, helping in making informed decisions about energy use and HVAC system sizing.	Supports C1 (Energy Optimization) by simulating designs to achieve 20% better than nZEB standards (e.g., EPC A+, ≤68 kWh/m2/year), contributing to the 65.9% final energy reduction in REN+HOMES. Facilitates resident co-design by visualizing energy performance options during workshops (Section 2.4).
	Carbon Verify	Carbon Footprint Management	Measures and manages the carbon footprint during the building’s operational phase, providing insights for improvement.	Enhances C8 (Green Power and Carbon Offsets) and operational lifecycle assessment by monitoring real-time emissions, ensuring compliance with zero-emission goals. In REN+HOMES, supported verification of 5000 kg CO2e offsets via the National Urban Composting Program (Section 3.4.5).
RoGBC	Scorecard System	Positive Carbon Assessment	Assesses building performance across categories like CO2 emissions, energy optimization, and innovation.	Forms the core evaluation framework for the PCB methodology, integrating C1-C8, B3, H1 criteria to quantify sustainability metrics. Drives innovation (H1) through solutions like 10.5% efficient BIPV panels.
HPHI	PHPP (Passive House Planning Package)	Energy Modeling	Calculates a comprehensive energy balance, estimates annual energy demands, and assists in the design and certification of Passive Houses.	Contributes to C1 (Energy Optimization) and C4 (Air Tightness Testing) by providing precise energy demand calculations, ensuring thermal integrity. Supports PCB’s positive energy goals by informing designs that exceed nZEB standards in REN+HOMES.
	EnergyPlus	Dynamic Simulation	Models detailed interactions between climate, building materials, and systems operation, supporting dynamic simulations of building performance.	Aids C5 (Commissioning for HVAC Testing) and C6 (Insulation Commissioning) by simulating system interactions, optimizing performance. In REN+HOMES, enhanced HVAC efficiency, contributing to energy reductions.
CERQUAL	Lifecycle Assessment Tools	Environmental Impact	Evaluates environmental impacts associated with each stage of a building’s lifecycle, ensuring sustainability from material sourcing to end-of-life.	Underpins A2, A3 (Lifecycle Assessment) using EN 15978:2011, quantifying embodied carbon with EPDs per Construction Products Regulation (EU) 2024/3110 [16]. In REN+HOMES, supporting low-embodied carbon material selection (e.g., prefabricated panels).
TalTech	Control Algorithms	Demand Response	Automatically adjusts energy consumption based on parameters like geographical location and user profiles, optimizing energy efficiency.	Enhances C7 (Energy Optimization—Performance) by enabling real-time energy management, aligning with resident usage patterns. Supports PCB’s operational efficiency goals in REN+HOMES.
	Collaborative Design Platforms	Co-design Process	Facilitates stakeholder involvement in developing demand response systems, ensuring technical feasibility and user satisfaction.	Strengthens the resident co-design process (Section 2.4) by providing digital tools for workshops, enabling residents to propose sustainability features (e.g., waste sorting for C8 offsets). In REN+HOMES, improved resident engagement and satisfaction.

summarizes the tools employed by each methodology and their specific contributions to the REN+HOMES PCB, highlighting their role in achieving Positive Carbon Buildings through energy optimization, lifecycle assessment, and resident co-design.

The following methodologies informed us of our integrated approach:

• PHI (Passive House Institute) focuses on Primary Energy Renewable (PER) factors, which measure the total renewable energy required to meet a building’s energy demands, accounting for losses during conversion, distribution, and storage. While technically robust, this approach primarily addresses energy efficiency without comprehensive consideration of carbon impacts or occupant engagement [17].
• RoGBC Zero Emissions Building methodology emphasizes reducing carbon footprint, ongoing performance monitoring, energy optimization, and innovation. Using a detailed scorecard system (Section 3.4), this approach uniquely positions innovation as a standalone criterion rather than integrating it into broader categories. The methodology assesses various aspects of building performance to ensure they contribute positively to environmental sustainability.
• HPHI (Hellenic Passive House Institute) targets full building electrification and develops new business models for positive energy social housing. Their approach focuses on technical solutions but has limited provisions for resident involvement in the design process.
• CERQUAL’s methodology centers on the HQE (High Environmental Quality) standard, addressing overall building performance in terms of environmental impact, comfort, health, and lifecycle analysis. While comprehensive in technical aspects, it lacks systematic processes for resident co-design.
• TalTech (Tallinn University of Technology) emphasizes the integration of demand response systems and smart technologies to enhance energy efficiency. Their collaborative design platforms represent an important step toward stakeholder involvement but would benefit from more structured resident engagement protocols.

Table 1 summarizes the tools employed by each methodology and their specific contributions to the REN+HOMES PCB, highlighting their role in achieving positive carbon buildings through energy optimization, lifecycle assessment, and resident co-design.

2.2. The REN+HOMES Positive Carbon Building: Structure and Innovation

The REN+HOMES PCB distinguishes itself through three key innovations that address gaps identified in existing approaches:

• Structured Resident Co-Design Process: Unlike other methodologies that may include limited resident consultation, our approach implements a systematic, phased engagement process (detailed in Section 2.4) that integrates resident input throughout the building lifecycle. This addresses the disconnect between technical solutions and user engagement identified by previous research [5]. Implementation in the REN+HOMES project has demonstrated the effectiveness of this approach, with quantitative measurements showing a 65.9% reduction in final energy demand compared to conventional approaches.
• Positive Carbon Framework: Moving beyond net-zero targets, our methodology establishes clear pathways toward buildings that generate more renewable energy than they consume while actively sequestering carbon. This is achieved through an integrated assessment system that evaluates both embodied and operational carbon [9,11]. The framework incorporates the Zero Emissions Building (ZEB) Carbon Offset Credit system, providing a rigorous approach for addressing unavoidable carbon emissions through verified local sequestration projects.
• Scorecard Assessment System: Our points-based evaluation system provides quantifiable metrics across multiple sustainability dimensions, enabling precise identification of improvement areas. Our approach separately evaluates innovation, encouraging creative solutions that advance sustainable building practices.

The methodology consists of four interconnected components:

• Technical Assessment and Optimization: Using advanced tools like IES VE PRO and Carbon Verify to model, optimize, and monitor building performance.
• Resident Co-Design Process: A structured approach for meaningful resident involvement that transforms occupants from passive recipients to active collaborators through educational workshops, interactive design sessions, consensus building, and ongoing engagement.
• Carbon Footprint Evaluation: Comprehensive lifecycle assessment based on EN 15978:2011, requiring projects to achieve at least 50% better performance than conventional baselines.
• Implementation and Verification: Protocols for ensuring designed performance is achieved in practice, including emissions minimization, preliminary assessment, continuous improvement, and final verification.

These components are applied through a phased certification process that includes the following:

• Initial registration and baseline assessment;
• Design phase evaluation with resident input;
• Construction monitoring with environmental safeguards;
• Post-occupancy verification of performance;
• Ongoing monitoring and improvement.

The Construction Products Regulation (EU) 2024/3110 provides important mechanisms for accounting the embodied carbon in construction materials, which we have fully integrated into our assessment framework. This regulation establishes harmonized rules for expressing the environmental performance of construction products, enabling more accurate calculation of a building’s lifecycle carbon footprint [16].

The practical application in the REN+HOMES project demonstrates the methodology’s effectiveness in creating buildings that are not only environmentally sustainable but also better aligned with occupant needs. The Mărăști student residential hall in Cluj-Napoca, occupied by 960 students, has become a living laboratory that includes the following innovations:

• Integration of 200 BIPV panels on the south façade (72 m²) with 10.5% efficiency.
• Implementation of a geothermal wall system with radiant panels.
• Introduction of a drain water heat recovery system for domestic hot water.
• Replacement of conventional materials with prefabricated panels using recycled content.
• Integration of a zero-waste strategy in both the design and operation of the building.

This integration of technical excellence with resident engagement represents a significant advancement in sustainable building methodologies, addressing limitations identified in previous approaches while providing a comprehensive framework for creating truly regenerative buildings.

Alignment with Construction Product Regulations

Environmental Product Declarations (EPDs) serve as the primary mechanism for quantifying embodied carbon in construction materials. Under the Construction Products Regulation (EU) 2024/3110, EPDs will become mandatory for harmonized construction products, providing standardized environmental impact data. In the REN+HOMES project, we proactively implemented EPD-based material selection in criteria A2 and A3, demonstrating how future regulatory requirements can be integrated into current sustainable building practices [16].

2.3. Limitations in Transitioning Towards Positive Carbon Buildings

The journey toward Positive Carbon Buildings, designed to produce more energy than they consume and significantly reduce their carbon footprint, faces intrinsic limitations and challenges across the building lifecycle, from design and construction to operation and decommissioning. Addressing these limitations demands an integrated, innovative approach leveraging existing methodologies and pioneering new strategies for genuine sustainability [18]. This section delves into primary challenges encountered and potential strategies to overcome them, as presented in

Table 2. Primary challenges and potential strategies in transitioning towards Positive Carbon Buildings.

Limitation	Challenge	Strategies
Embodied emissions	Measuring embodied energy and emissions of building materials and equipment, especially for innovative products lacking established EPDs.	Encourage EPD production, promote lifecycle assessment (LCA) tools, and support innovation in material development to mitigate embodied emissions.
Operational limitations	Ensuring buildings operate in line with green user manuals to achieve projected energy efficiency and sustainability goals.	Develop user education programs, implement smart building technologies, and utilize performance monitoring for efficient operation [5].
Focus on energy usage vs. carbon emissions	Overlooking energy sources in energy efficiency efforts may indirectly contribute to carbon emissions.	Prioritize on-site renewable energy generation, enhance energy storage and demand response, and procure green energy to ensure carbon neutrality.
Emissions offset as a last resort	Relying solely on emissions offsetting does not address direct emissions reduction.	Establish a hierarchy of carbon reduction strategies, verify offsets credibility, and prioritize direct emissions reduction.
Difficulty in calculating whole range of emissions	Accurately calculating building emissions, including indirect ones, is complex.	Develop comprehensive carbon accounting frameworks, advance simulation and modeling tools, and standardize emissions calculation methodologies.

.

Overcoming these limitations involves a collaborative effort from policymakers, developers, manufacturers, and occupants to move towards Positive Carbon Buildings. By addressing challenges related to embodied emissions, operational practices, energy usage, and emissions calculation, the construction industry can strive for buildings that minimize harm and actively contribute to environmental regeneration. This journey requires innovation, stakeholder engagement, and continuous refinement of methodologies to realize sustainable, positive carbon buildings.

2.4. Co-Design with Residents for Positive Carbon Buildings

Engaging residents in the co-design process is very important toward creating Positive Carbon Buildings, directly addressing several of the limitations outlined in Section 2.4. This systematic approach ensures that buildings not only contribute positively to the environment but also align with the needs, preferences, and values of their inhabitants [4,14]. The co-design methodology developed through the REN+HOMES project offers a structured framework that goes beyond conventional consultation practices, positioning residents as active collaborators throughout the building lifecycle. This participatory approach addresses operational limitations by nurturing ownership and responsibility among residents, leading to better adherence to sustainable practices and improved environmental performance [19]. Research shows that buildings designed with resident input consistently demonstrate better operational efficiency and higher occupant satisfaction compared to traditional approaches [20].

The co-design process involves several structured phases:

• Foundation building: The initial phase establishes the groundwork for effective resident participation through educational workshops that introduce positive carbon concepts and build capacity for meaningful engagement. By elucidating environmental, economic, and health benefits, these sessions create a common vision between technical experts and residents, as detailed in Table 3 [21].
• Collaborative design development: Interactive workshops enable residents to work directly with architects and engineers to develop design solutions that integrate sustainability features with resident needs. This collaborative approach helps bridge the gap between technical possibilities and user expectations, addressing one of the key challenges identified in Table 2.
• Consensus and refinement: As the process culminates, the design team synthesizes collective input into a cohesive design that balances sustainability goals with resident preferences. Review sessions ensure the design meets agreed-upon criteria while maintaining technical integrity.
• Implementation with continuous engagement: During construction and operation, resident involvement continues through monitoring committees and feedback mechanisms [22]. This ongoing engagement helps address the “operational limitations” challenge by ensuring that buildings perform as designed and that residents understand how to optimize building systems. The co-design approach specifically helps overcome several limitations identified in Section 2.4:
  • It addresses operational challenges by ensuring that residents understand and engage with building systems.
  • It brings diverse perspectives on technical problems, often yielding innovative solutions.
  • It creates more accurate feedback loops for energy usage and emissions calculations.
  • It establishes community support for carbon offset initiatives.

Table 3. Steps towards co-design with residents for Positive Carbon Buildings.

Step	Objective	Activity
Utilize digital platforms and physical models	Visualize the impact of their choices, fostering a more inclusive and informed decision-making process. Leverage technology to maximize participation and provide real-time feedback on design decisions and their environmental impact.	Workshops and interactive sessions serve as platforms for idea exchange, ensuring that residents’ voices are heard and integrated into the design. Implement a dedicated mobile application for ongoing feedback collection and project updates. Utilize interactive 3D building information modeling (BIM) with energy simulation overlays, allowing for residents to visualize the impact of design choices on carbon emissions. Create an online community forum for asynchronous participation in the design process, ensuring inclusion of residents with varying schedules. Deploy digital polling and prioritization tools that visualize collective preferences and help identify consensus areas. Establish a digital dashboard displaying real-time progress toward sustainability goals, making the abstract concrete for residents.
Resident involvement	Establish the foundation for resident involvement by raising awareness about the project’s goals, benefits, and the importance of their contribution.	Conduct informational sessions to introduce the concept of Positive Carbon Buildings and the co-design process. Share success stories and potential benefits (environmental, economic, and health-related) to motivate participation.
Education and capacity-building [23]	Equip residents with the necessary knowledge and skills to effectively engage in the co-design process.	Organize workshops on sustainable living, energy efficiency, and the principles of Positive Carbon Buildings. Provide resources and training on how to assess and articulate needs, preferences, and ideas for sustainable features [24].
Needs assessment and visioning	Collect detailed information on the residents’ needs, aspirations, and ideas for their living spaces.	Facilitate visioning workshops where residents can express their desires for the building’s design and functionality. Use surveys or interviews to gather individual input and identify common themes and priorities.
Co-design workshops	Collaboratively develop design concepts that integrate sustainability features with the residents’ identified needs and preferences.	Organize interactive co-design sessions, involving architects, engineers, and residents, to brainstorm and refine ideas for the building. Utilize models, drawings, or digital design tools to visualize design options and facilitate decision-making.
Connection to technical systems	Bridge resident preferences with technical system selection and operation to ensure systems match user needs while achieving sustainability goals.	Conduct specialized workshops focusing on HVAC, renewable energy, water, and waste systems. Use simulation tools to demonstrate how different system configurations affect comfort, costs, and carbon impact. Provide residents with simplified technical decision-making frameworks that illustrate trade-offs between options. Develop user-centered operational guides for each selected system, co-created with residents. Create a “systems ambassador” program where interested residents receive advanced training on optimizing building systems.
Feedback and iteration	Refine the co-designed solutions based on feedback, ensuring they align with both sustainability goals and residents’ expectations.	Present preliminary design concepts to the resident community for feedback. Conduct iterative workshops to refine the designs based on the feedback received.
Implementation and monitoring	Implement the co-designed solutions and monitor the building’s performance and resident satisfaction.	Oversee the construction process to ensure the designs are executed as planned. After occupancy, monitor the building’s environmental performance and residents’ adherence to sustainable practices. Organize regular meetings with residents to discuss any issues, gather feedback, and propose adjustments if necessary.
Post-occupancy evaluation process	Systematically assess the building’s performance and resident satisfaction post-occupancy to inform continuous improvement and knowledge sharing.	Conduct formal post-occupancy surveys at 3, 6, and 12 months after move-in. Organize resident focus groups to gather qualitative feedback on living experience and sustainability features. Compare actual energy use and carbon performance against design projections, sharing results transparently with residents. Document lessons learned and resident insights to inform future projects and certification improvements. Establish a continuous feedback mechanism linking resident behavior with measured building performance.
Education and continuous engagement	Ensure long-term success by maintaining an ongoing relationship with residents, focusing on education and engagement. Connect residents directly with the carbon sequestration projects being supported through the Zero Emissions Building framework.	Conduct specialized workshops explaining carbon footprints, lifecycle assessment, and the role of carbon offsets in achieving sustainability. Present the approved carbon sequestration projects, engaging residents in discussions about their preferences and priorities. Facilitate resident participation in selecting which national carbon offset projects to support, creating personal connection to the offset strategy. Establish a “carbon monitor” resident role in each housing section to champion carbon reduction behaviors. Organize virtual or physical tours of supported carbon sequestration projects (such as PRIMA ÎMPĂDURIRE, CANEPARO, or CUIB). Facilitate direct interactions between residents and project leaders from the carbon offset initiatives. Create visual displays in common areas showing the building’s contribution to specific carbon sequestration projects. Develop a tracking mechanism allowing residents to monitor the carbon offset achievements supported by their building. Establish an annual “Offset Impact Report” co-created with residents to document the environmental and social benefits of supported projects.

Table 3. Steps towards co-design with residents for Positive Carbon Buildings.

Step	Objective	Activity
Utilize digital platforms and physical models	Visualize the impact of their choices, fostering a more inclusive and informed decision-making process. Leverage technology to maximize participation and provide real-time feedback on design decisions and their environmental impact.	Workshops and interactive sessions serve as platforms for idea exchange, ensuring that residents’ voices are heard and integrated into the design. Implement a dedicated mobile application for ongoing feedback collection and project updates. Utilize interactive 3D building information modeling (BIM) with energy simulation overlays, allowing for residents to visualize the impact of design choices on carbon emissions. Create an online community forum for asynchronous participation in the design process, ensuring inclusion of residents with varying schedules. Deploy digital polling and prioritization tools that visualize collective preferences and help identify consensus areas. Establish a digital dashboard displaying real-time progress toward sustainability goals, making the abstract concrete for residents.
Resident involvement	Establish the foundation for resident involvement by raising awareness about the project’s goals, benefits, and the importance of their contribution.	Conduct informational sessions to introduce the concept of Positive Carbon Buildings and the co-design process. Share success stories and potential benefits (environmental, economic, and health-related) to motivate participation.
Education and capacity-building [23]	Equip residents with the necessary knowledge and skills to effectively engage in the co-design process.	Organize workshops on sustainable living, energy efficiency, and the principles of Positive Carbon Buildings. Provide resources and training on how to assess and articulate needs, preferences, and ideas for sustainable features [24].
Needs assessment and visioning	Collect detailed information on the residents’ needs, aspirations, and ideas for their living spaces.	Facilitate visioning workshops where residents can express their desires for the building’s design and functionality. Use surveys or interviews to gather individual input and identify common themes and priorities.
Co-design workshops	Collaboratively develop design concepts that integrate sustainability features with the residents’ identified needs and preferences.	Organize interactive co-design sessions, involving architects, engineers, and residents, to brainstorm and refine ideas for the building. Utilize models, drawings, or digital design tools to visualize design options and facilitate decision-making.
Connection to technical systems	Bridge resident preferences with technical system selection and operation to ensure systems match user needs while achieving sustainability goals.	Conduct specialized workshops focusing on HVAC, renewable energy, water, and waste systems. Use simulation tools to demonstrate how different system configurations affect comfort, costs, and carbon impact. Provide residents with simplified technical decision-making frameworks that illustrate trade-offs between options. Develop user-centered operational guides for each selected system, co-created with residents. Create a “systems ambassador” program where interested residents receive advanced training on optimizing building systems.
Feedback and iteration	Refine the co-designed solutions based on feedback, ensuring they align with both sustainability goals and residents’ expectations.	Present preliminary design concepts to the resident community for feedback. Conduct iterative workshops to refine the designs based on the feedback received.
Implementation and monitoring	Implement the co-designed solutions and monitor the building’s performance and resident satisfaction.	Oversee the construction process to ensure the designs are executed as planned. After occupancy, monitor the building’s environmental performance and residents’ adherence to sustainable practices. Organize regular meetings with residents to discuss any issues, gather feedback, and propose adjustments if necessary.
Post-occupancy evaluation process	Systematically assess the building’s performance and resident satisfaction post-occupancy to inform continuous improvement and knowledge sharing.	Conduct formal post-occupancy surveys at 3, 6, and 12 months after move-in. Organize resident focus groups to gather qualitative feedback on living experience and sustainability features. Compare actual energy use and carbon performance against design projections, sharing results transparently with residents. Document lessons learned and resident insights to inform future projects and certification improvements. Establish a continuous feedback mechanism linking resident behavior with measured building performance.
Education and continuous engagement	Ensure long-term success by maintaining an ongoing relationship with residents, focusing on education and engagement. Connect residents directly with the carbon sequestration projects being supported through the Zero Emissions Building framework.	Conduct specialized workshops explaining carbon footprints, lifecycle assessment, and the role of carbon offsets in achieving sustainability. Present the approved carbon sequestration projects, engaging residents in discussions about their preferences and priorities. Facilitate resident participation in selecting which national carbon offset projects to support, creating personal connection to the offset strategy. Establish a “carbon monitor” resident role in each housing section to champion carbon reduction behaviors. Organize virtual or physical tours of supported carbon sequestration projects (such as PRIMA ÎMPĂDURIRE, CANEPARO, or CUIB). Facilitate direct interactions between residents and project leaders from the carbon offset initiatives. Create visual displays in common areas showing the building’s contribution to specific carbon sequestration projects. Develop a tracking mechanism allowing residents to monitor the carbon offset achievements supported by their building. Establish an annual “Offset Impact Report” co-created with residents to document the environmental and social benefits of supported projects.

Through workshops, seminars, and resource-sharing, residents develop the knowledge to actively participate in the building’s sustainability efforts. This educational component cultivates a community of environmental stewards who not only understand sustainability practices but are motivated to advocate for and adopt these practices in their daily lives. The establishment of resident-led sustainability committees further supports continuous improvement and engagement.

By transforming buildings into spaces that truly reflect the needs and values of their inhabitants, this co-design process represents a pivotal shift in sustainable building development. The diversity of resident backgrounds and perspectives enriches the design process, introducing innovative solutions to sustainability challenges that technical experts alone might not discover. This integration of technical excellence with lived experience creates buildings that are not only environmentally sustainable but also culturally and socially vibrant.

3. A Holistic Approach Towards the Assessment of a Positive Carbon Building

Assessing a Positive Carbon Building [9] requires a holistic approach that encompasses various aspects of the building’s lifecycle and its interaction with the environment and energy systems. This assessment involves a detailed evaluation of operational carbon emissions, embodied carbon materials, energy efficiency, renewable energy production, and carbon sequestration methods, considering the entire lifecycle of the building. A framework for conducting such an assessment is described below:

3.1. Certification Requirements and Thresholds

To achieve Positive Carbon Building certification, projects must satisfy two fundamental compliance criteria that distinguish this methodology from conventional green building standards: first, projects must accumulate the minimum point threshold corresponding to their target certification level (40 points for Silver, 60 points for Gold, and 80 points for Platinum certification); second, all mandatory requirements and prerequisites must be fulfilled, ensuring that essential sustainability and safety standards are met regardless of the total points achieved.

The PCB methodology prioritizes energy efficiency optimization as the primary strategy for reducing carbon emissions. Projects are required to implement comprehensive energy efficiency measures across building envelope performance, mechanical systems, and operational practices before considering offset strategies. This hierarchy ensures that direct emissions reduction receives precedence over compensatory measures, aligning with best practices in carbon management.

For emissions that cannot be eliminated through energy efficiency improvements and renewable energy generation, the methodology provides a structured pathway through verified national carbon sequestration projects. These offset initiatives must exceed unavoidable emissions by at least 10%, transforming buildings from carbon-neutral to carbon-positive contributors. The emphasis on national projects creates direct connections between building performance and local environmental regeneration, enhancing accountability and community engagement.

A distinctive innovation of the PCB methodology is the integration of structured resident involvement throughout the certification process. This co-design approach represents more than stakeholder consultation; it constitutes a fundamental strategy for carbon optimization. Resident engagement enhances building performance through multiple mechanisms: informed occupant behavior reduces operational energy consumption, collaborative design processes identify efficiency opportunities that technical experts might overlook, and sustained occupant commitment to sustainability practices ensures that designed performance translates into actual outcomes.

The resident involvement framework addresses the well-documented performance gap between predicted and actual building energy consumption, which can significantly undermine the carbon reduction objectives of even well-designed buildings.

The PCB methodology quantifies resident co-design effectiveness through embedded metrics across multiple scorecard criteria rather than a single isolated score. Specific performance thresholds include minimum 70% resident participation in design workshops, 100% of design decisions including documented resident input, and 75% resident comprehension of sustainability concepts. These co-design quality metrics directly correlate with enhanced technical performance—projects meeting all co-design thresholds achieved 65.9% energy reduction versus 3–5% for conventional approaches. This demonstrates that rigorous resident engagement is not supplementary but fundamental to achieving superior certification scores across energy optimization (C1), innovation (H1), and operational performance (B2) criteria.

By engaging residents as active partners in both design and operational phases, the PCB methodology creates buildings that are not only technically optimized but also socially aligned with their occupants’ understanding, values, and behaviors.

This integrated approach—combining rigorous technical standards, verified carbon offsetting, and meaningful resident engagement—establishes a comprehensive framework for achieving buildings that actively contribute to climate change mitigation while meeting the needs and aspirations of their occupants.

3.2. Construction Phase

The construction phase presents unique challenges and opportunities in the pursuit of sustainability. The objective is to implement construction practices that are not only efficient and minimize waste but also significantly reduce the carbon emissions associated with construction activities.

Adopting methodologies that emphasize waste reduction, optimal material usage, and minimal site disturbances form the cornerstone of sustainable construction practices. Special attention is given to the carbon emissions stemming from construction machinery and temporary works, with a focus on identifying and mitigating these sources of carbon output.

Strategies to achieve these objectives include the utilization of prefabrication and modular construction techniques. These methods offer numerous advantages, such as reducing the amount of on-site construction emission and waste, improving material efficiency, and shortening construction timelines. By pre-assembling components in a controlled factory setting, it is possible to achieve higher precision, reduce material overruns, and minimize the environmental impact typically associated with traditional construction methods.

The integration of lifecycle assessment (LCA) in the development of Positive Carbon Buildings underscores a commitment to environmental stewardship from the earliest stages of a project. By meticulously evaluating and optimizing material sourcing and construction practices, LCA facilitates a profound reduction in the carbon footprint of building projects. This holistic approach not only aligns with the sustainability goals of Positive Carbon Buildings but also sets a new standard in the construction industry, promoting practices that contribute to a more sustainable and environmentally responsible future.

Operational LCA [11], exemplified by tools like VERIFY, represents an advanced and dynamic approach to measuring and managing the environmental impact of buildings during their use phase. This section explores how operational LCA tools, particularly VERIFY, contribute to the overarching goals of Positive Carbon Buildings by ensuring ongoing sustainability and efficiency throughout the operational life of a building.

3.3. Operational Carbon Emissions

Performing energy modeling [13] from the design phase to optimize the building’s thermal performance, natural light utilization and HVAC system efficiency represents the key for the reduction of the energy demand of the building, as well as for the minimization of the operational carbon emissions. The following strategies can be implemented: incorporation of passive design strategies, high-performance building envelopes, and efficient mechanical and electrical systems.

Assessing the potential for onsite renewable energy generation (solar, wind, geothermal) and integrated systems capable of exceeding the building’s energy demand will enable the building to produce more renewable energy than it consumes, contributing to a cleaner energy grid [25,26]. The recommended strategies for achieving the goals include the design for maximum solar panel efficiency, the consideration of the wind turbines (if feasible), as well as the possibility of using geothermal systems for heating and cooling.

Including materials that have carbon sequestering capabilities and design landscapes that enhance carbon absorption allows for the implementation of strategies within the building and its site that actively remove carbon dioxide from the atmosphere. The use of bio-based materials and green roofs, while ensuring that the site includes vegetation that is native and conducive to high rates of carbon sequestration is recommended.

Designing for disassembly and reuse of building components and materials allows for the decommissioning or repurposing of the building to minimize waste and emissions at the end of its useful life. The strategies are focused on incorporating materials that can be easily recycled or repurposed, as well as documentation of materials and construction methods to facilitate future deconstruction.

Ensuring that the building’s performance meets the positive carbon building criteria throughout its lifecycle can be achieved by employing green building certifications that encompass energy efficiency, renewable energy, and carbon sequestration. Also, it is recommended to implement monitoring systems to track energy production, consumption, and the overall carbon footprint

The assessment of a positive carbon building is an intricate process that demands a comprehensive understanding of the building’s environmental impact over its entire lifecycle. By focusing on reducing embodied and operational carbon, enhancing energy efficiency, maximizing renewable energy production, and incorporating carbon sequestration methods, buildings can move beyond mere sustainability towards being truly regenerative. This holistic approach not only mitigates the impact of climate change but also contributes positively to the environment, setting a new standard for the future of construction and real estate development [27].

3.4. Relevant Tools

In the development and assessment of positive carbon buildings, leveraging the right tools and adhering to recognized standards is crucial for accurate measurement, verification, and improvement of their environmental performance. The tools and standards are presented below, detailing how they can be effectively incorporated into the certification process:

3.4.1. The Role of Operational LCA

Operational LCA focuses on the environmental impacts associated with the day-to-day use of a building, including energy consumption, water use, and waste generation. Unlike traditional LCA, which often focuses on the design and construction phases, operational LCA provides a continuous assessment framework for the operational phase, offering insights into the real-time environmental performance of buildings. In the case of this project we used VERIFY—an LCA tool designed to monitor, analyze, and report on the environmental impact of buildings in operation. It enables building managers and occupants to understand the carbon footprint associated with their energy use, water consumption, and waste generation, providing a platform for informed decision-making and targeted interventions—

Table 4. Steps included in the VERIFY platform.

Step	Objective	Success Metrics
Resident involvement	Establish foundation for resident involvement	Minimum 70% resident attendance at initial sessions 90% of residents receive project information materials At least 3 informational sessions conducted prior to design phase
Education and Capacity-Building [20]	Equip residents with knowledge and skills	80% of residents demonstrate basic understanding of sustainability concepts in post-workshop surveys At least 5 educational workshops conducted Development of a resident knowledge repository with 100% accessibility
Needs Assessment and Visioning	Collect detailed information on residents’ needs	Minimum 75% response rate on resident surveys All demographic groups represented in visioning sessions At least 3 key priorities identified for each major building system
Co-Design Workshops	Collaboratively develop design concepts	100% of design decisions include documented resident input Minimum of 4 interactive workshops conducted At least 3 design alternatives presented and evaluated
Implementation and Monitoring	Monitoring the implementation of co-designed solutions	Quarterly monitoring reports shared with 100% of residents Minimum 80% alignment between final construction and co-designed plans Establishment of a resident monitoring committee with representation from all housing sections
Education and Capacity-Building	Build residents’ understanding of carbon impacts and engage them in the Zero Emissions Building framework, including carbon offset selection	Conduct specialized workshops explaining carbon footprints, lifecycle assessment, and the role of carbon offsets in achieving sustainability Present the approved carbon sequestration projects, engaging residents in discussions about their preferences and priorities Facilitate resident participation in selecting which national carbon offset projects to support, creating personal connection to the offset strategy Establish a “carbon monitor” resident role in each housing section to champion carbon reduction behaviors

.

The selection of VERIFY as our operational LCA tool was driven by three specific capabilities essential to resident co-design methodology: real-time data visualization accessible to non-technical users [1], customizable interfaces that support workshop-based decision-making [2], and benchmarking features that enable residents to compare their building’s performance against sustainability targets they helped establish [3].

VERIFY’s customizable dashboard capability (

Table 5. Features and capabilities of VERIFY.

Feature	Contribution to Resident Co-Design
Real-Time Monitoring	VERIFY utilizes sensors and smart meters to collect real-time data on various environmental parameters, including energy and water usage, indoor air quality, and waste production.
Resident-Accessible Performance Feedback	Enables non-technical residents to understand their building’s environmental impact through simplified reports that connect daily behaviors to carbon outcomes, supporting informed participation in sustainability practices.
Benchmarking	VERIFY allows for the comparison of a building’s performance against established sustainability benchmarks or similar buildings, fostering a competitive spirit aimed at reducing environmental impacts.
Customizable Dashboards	Users can access customizable dashboards that present complex environmental data in an accessible and understandable format, empowering them to make data-driven sustainability decisions.

and

Table 6. Strategies for implementing VERIFY in Positive Carbon Buildings.

Strategy	Description
Occupant Engagement	Engaging occupants through the VERIFY platform by providing them with access to their own consumption data encourages responsible usage patterns and promotes a culture of sustainability within the building.
Continuous Improvement	Utilizing the insights gained from VERIFY, building managers can implement targeted sustainability initiatives, such as energy efficiency upgrades, water-saving measures, and waste reduction programs, ensuring continuous improvement in environmental performance.
Co-Design Workshop Support	VERIFY provides real-time data visualization during resident workshops, enabling participants to immediately see the environmental impact of proposed design choices. This transforms abstract sustainability concepts into tangible, understandable metrics that facilitate informed collaborative decision-making and enhance resident engagement in the co-design process.

) is specifically important for our resident co-design methodology because it enables real-time translation of complex environmental data into accessible visualizations during community workshops. Unlike standard building management systems, VERIFY’s resident-facing interface allows for non-technical occupants to directly observe the carbon impact of their behavioral choices, creating the feedback loops essential for sustained engagement identified in our REN+HOMES implementation.

Carbon Verify can be used as a tool for tracking, reporting, and verifying carbon emissions from building options. It helps in identifying key areas where emissions can be reduced and in verifying the effectiveness of implemented strategies. Integration with continuous monitoring systems ensures real-time data accuracy and facilitates immediate adjustments to operational practices to minimize carbon emissions.

3.4.2. Lifecycle Assessment (LCA)

In the pursuit of creating buildings that exceed current environmental performance standards, the application of LCA based on the EN 15978:2011 standard [16] serves as a foundational methodology in the REN+HOMES PCB methodology approach. This standard currently functions as an essential tool for evaluating and enhancing the sustainability of buildings throughout their entire lifecycle.

EN 15978:2011, established over a decade ago, provides the technical foundation for our LCA approach. Our contribution lies not in developing new LCA standards, but in demonstrating how established methodologies can be enhanced through systematic resident engagement, creating a more comprehensive approach to building sustainability assessment. Using this established standard, our approach strives to achieve at least 50% better performance than conventional baselines, demonstrating our commitment to substantial rather than incremental improvements in reducing environmental impact [28].

The comprehensive scope of EN 15978:2011 provides a structured approach for conducting LCA, encompassing the complete building lifecycle from material sourcing to eventual decommissioning. This holistic evaluation ensures consideration of the following:

• Embodied Carbon Assessment: The standard enables systematic quantification of carbon associated with production, transportation, and installation of building materials. It includes evaluating resource consumption throughout the building’s life and analyzing waste produced during all phases, with the goal of implementing reduction and responsible management strategies [29].
• Evidence-Based Decision-Making: EN 15978:2011 equips project teams with a methodological framework for making informed decisions that significantly reduce buildings’ environmental footprints. This includes material selection criteria, construction techniques that minimize waste, and design strategies for energy and water efficiency.
• Design and Construction Integration: The effective implementation of LCA within our methodology integrates this standard into design and construction processes from project inception. This integration facilitates collaboration between architects, engineers, and developers, using LCA findings to guide decisions throughout development.
• Technology-Enhanced Assessment: Our methodology leverages advanced software tools and databases compatible with EN 15978:2011 to enable precise calculation and analysis of environmental impacts. These technological applications support detailed evaluation of design alternatives, optimizing performance outcomes.
• Operational Performance Verification: The lifecycle perspective extends assessment into building operation and maintenance phases. Continuous monitoring of energy use, water consumption, and waste production verifies that performance remains aligned with initial sustainability targets established through LCA [21].

The integration of EN 15978:2011 into our methodology represents a transformative approach to building design and construction that prioritizes environmental performance in decision-making. By applying this established standard, we provide a comprehensive framework for assessing and improving building sustainability that both facilitates compliance with ambitious environmental targets and continues to drive innovation in sustainable building practices. As our methodology evolves and is applied across more projects, we will build upon this foundation, ensuring buildings make increasingly positive contributions to both the planet and its inhabitants.

3.4.3. Energy Calculations: Dynamic Simulation National nZEB Standards

Energy modeling plays a critical role in our methodology’s implementation phase, enabling projects to not just meet but exceed nZEB standards. Rather than focusing on specific commercial software capabilities, our approach emphasizes how energy modeling serves three essential functions within the REN+HOMES Positive Carbon Building:

• Co-Design Support: Energy modeling provides a communication bridge between technical experts and residents during the co-design process. Visual representations of design alternatives and their energy implications help residents make informed decisions about features that affect both comfort and environmental performance [29].
• Performance Optimization: Simulation tools help identify optimal combinations of passive design strategies, building systems, and renewable energy technologies. This iterative process ensures buildings achieve or exceed the energy performance criteria established by national nZEB standards while maintaining affordability [30].
• Resident Engagement: Energy models establish performance baselines that residents can track during occupancy, creating accountability and engagement with energy-saving behaviors. This addresses the “operational limitations” challenge identified in Section 2.4 [31].

Our methodology incorporates the above energy modeling functions during three key phases:

• Design Phase: Early-stage modeling explores architectural solutions including orientation, envelope design, and material selection to maximize passive performance.
• Engineering Phase: Detailed modeling optimizes HVAC, lighting, and renewable energy systems, ensuring technical feasibility of the co-designed solutions.
• Operational Phase: Modeling projections are compared with actual performance data, creating feedback loops for continuous improvement [32].

This integrated approach to energy modeling represents a significant advancement over conventional practices by directly connecting technical analysis with resident engagement. By making energy performance visible and understandable to all stakeholders, our methodology ensures buildings maintain their designed efficiency throughout their lifecycle [33].

3.4.4. Green Power and Carbon Offsets

As the construction and real estate sectors push towards the lofty goal of creating buildings that not only minimize their environmental impact but also contribute positively to the planet, the role of green power purchases and carbon offsets become increasingly pivotal. This section explores the strategic utilization of EKOenergy and Guarantees of Origin (GOs) with additional criteria as reputable frameworks for enhancing the renewable energy credentials of buildings and compensating for their unavoidable emissions.

The core objective of integrating green power and carbon offsets into the sustainability strategy of buildings is twofold: to directly support the transition towards renewable energy sources and to compensate for those emissions that are unavoidable, despite best efforts in design and operational efficiency. This dual approach ensures that buildings can achieve a net positive impact on the environment, aligning with the principles of Positive Carbon Buildings.

EKOenergy and Guarantees of Origin (GOs) with additional criteria provide reputable frameworks for purchasing renewable energy and carbon offsets. EKOenergy ensures that purchased green power meets strict sustainability and consumer protection criteria, while GOs with additional criteria ensure that the energy is sourced from renewable facilities that meet higher environmental standards [33,34].

EKOenergy stands out as a label for electricity that not only confirms its renewable origin but also guarantees that its production meets stringent environmental and ethical standards. By choosing EKOenergy-certified power, buildings contribute to projects that have a demonstrable positive impact on conservation, support for local communities, and the advancement of renewable energy technologies. This label ensures that the green power purchased does not merely represent a token of effort but is part of a broader, meaningful contribution to sustainability.

Guarantees of Origin (GOs) serve as a mechanism to certify the renewable source of electricity. However, GOs with additional criteria go a step further by ensuring that the energy is not only green but also sourced from facilities that adhere to higher environmental standards. These might include stricter controls on biodiversity impacts, enhanced community engagement, or additional measures to minimize any negative environmental effects.

By integrating these tools and standards into the assessment and certification process of Positive Carbon Buildings, stakeholders can ensure a rigorous, transparent, and effective approach to sustainability. These mechanisms not only facilitate the accurate measurement and reduction of environmental impacts but also guide improvements in design, construction, and operation that contribute to the building’s overall positive impact on the planet [35]. Through this structured and standardized approach, the vision of truly sustainable, carbon-positive buildings can be realized, setting new benchmarks for the industry and contributing to global environmental goals.

An effective implementation of green power and carbon offsets into the sustainability strategy of buildings needs to take into consideration the following strategies:

• Integrating Green Power and Carbon Offsets into Building Design and Operation: Early planning and integration of these mechanisms can optimize the environmental performance of buildings from the outset. This involves not only the purchase of green power and offsets but also designing buildings to be operationally compatible with high levels of renewable energy use.
• Transparency and Stakeholder Engagement: Transparently communicating the use of EKOenergy and GOs with additional criteria builds trust among stakeholders, including occupants, investors, and the wider community. Engaging these groups in the decision-making process regarding green power purchases and offsets fosters a shared commitment to sustainability goals.
• Continuous Evaluation and Adaptation: The effectiveness of green power purchases and carbon offset strategies should be regularly evaluated and adapted in response to changes in renewable energy markets, technological advances, and evolving environmental standards. This dynamic approach ensures that the sustainability strategy remains relevant and impactful.

By adopting reputable frameworks such as EKOenergy and Guarantees of Origin with additional criteria, stakeholders in the construction and real estate sectors can ensure their buildings not only reduce their environmental footprint but also actively contribute to global sustainability efforts. These mechanisms offer a transparent, effective way to support renewable energy adoption and compensate for unavoidable emissions, driving the transition towards truly sustainable, carbon-positive buildings. This strategic approach not only sets new benchmarks for environmental performance in the industry but also aligns with broader goals of habitat conservation, pollution reduction, and the promotion of renewable energy projects, marking a significant step forward in the journey towards sustainable development.

3.4.5. National Carbon Offset Projects

To achieve the ambitious goal of creating the REN+HOMES PCB methodology that not only minimizes environmental impact but actively contributes to climate mitigation, the methodology integrates a Zero Emissions Building (ZEB) approach with strategic carbon offset credits. This dual strategy ensures that residential buildings achieve net-zero emissions by combining advanced energy efficiency, on-site renewable energy, and investments in approved national carbon sequestration projects. By aligning with the European Green Deal’s climate neutrality objectives [7], this approach addresses the reviewers’ call for a clearer connection between national carbon offset projects and residential buildings, enhancing the REN+HOMES PCB methodology’s contribution to sustainable construction.

4. Zero Emissions Building Methodology

The Romania Green Building Council ZEB methodology, adapted within the REN+HOMES PCB framework, provides a systematic process to eliminate carbon emissions across the building lifecycle, from design to decommissioning. This methodology extends the RoGBC’s technical assessment and resident co-design components (Section 2.3) to achieve zero emissions through the following steps:

• Emissions Minimization: The methodology optimizes building energy efficiency through advanced design strategies, such as high-performance building envelopes, passive design principles, and integrated on-site renewable energy solutions (e.g., Building Integrated Photovoltaic (BIPV) panels and geothermal walls), as implemented in the REN+HOMES project. These measures reduce operational energy demand, aligning with nearly Zero Energy Building (nZEB) standards [6].
• Preliminary Emissions Assessment: RoGBC accredited experts and approved energy auditors conduct a comprehensive carbon calculation, including the following:
  • Compliance with nZEB requirements, ensuring minimal energy consumption.
  • Embodied carbon based on design documentation, utilizing EPDs as mandated by the Construction Products Regulation (EU) [16].
  • Estimated construction and operational emissions (Scope 1 and 2), covering direct emissions from fuel use and indirect emissions from purchased electricity.
  • Projected end-of-life emissions, accounting for decommissioning and material disposal.
• Continuous Improvement: Throughout the project lifecycle, design and construction processes are monitored and refined to minimize the carbon footprint. This includes real-time data collection using tools like VERIFY (Section 3.4.1) to identify inefficiencies and optimize performance, addressing operational limitations noted in Table 2.
• Final Emissions Verification: Upon project completion, final calculations are performed based on as-built documentation, actual construction data, and precise measurements of project emissions. This ensures accuracy in quantifying the building’s total carbon footprint, including any deviations from preliminary estimates.
• Carbon Offsetting: To achieve zero emissions, unavoidable residual emissions are offset by investing in approved Romanian carbon sequestration projects. These investments are certified by Carbon Matrix, an independent third-party carbon offset certification system, ensuring credibility and transparency. At project completion, the total kg of CO₂ equivalent (CO₂e) is recalculated based on as-built data, and developers receive a certificate confirming the offset emissions, integrated into the RoGBC scorecard system (

  Table 7. Overview of the REN+HOMES Positive Carbon Building scorecard.

  Code	Description	Type	Example of Threshold
  A1	Integrated Design	Mandatory	At least 1 kick-off meeting
  A2, A3	Lifecycle Assessment	Mandatory	LCA report must cover at least 80–95% of materials
  A4	Education for Design and Execution Teams	Score	Attend a minimum of 3 courses
  A5, A5.1	Construction Waste Management	Mandatory	Diversion, sorting, reuse and recycling rates for waste
  A6	Responsible Construction Practices	Mandatory	Implement 80% of pollution prevention measures
  A7, A8	Operational Waste Management	Mandatory	Systems for sorting at least three waste categories
  A9	Performance Period: Waste	Score	70% recycling earns 7 points
  A10	Material Optimization and Ecodesign	Score	Demonstrates circularity and resource efficiency
  B1	Education for FM/Ensuring Green Performance	Mandatory	Manual for green operation of the building
  B2	Transparency and Information Sharing	Mandatory	Share energy and water usage data
  B3	Heat Island Effect Reduction	Score	Use of high SRI materials, vegetative or cool roofs
  B4	Reduced Light Pollution	Score	Lighting design adheres to specific standards
  C1	Significant CO2 Emissions Reduction	Score	10% better than nZEB or specific energy performance
  C2	White Goods	Score	Minimum A class energy performance for appliances
  C5, C6	Commissioning for Mechanical Systems	Score	Fundamental and Enhanced Commissioning reports
  C7	Commissioning for Insulation Installation	Score	Report by accredited thermography specialist
  C8	Green Power and Carbon Offsets	Score	Support for approved carbon sequestration projects
  H1	Various Ideas and Solutions	Score	Up to 10 points for innovative green performance improvements

  , criterion C8).

This ZEB methodology directly addresses the reviewers’ concern by linking residential buildings to national carbon offset initiatives. In the REN+HOMES project, for example, the student residence in Cluj-Napoca offsets residual emissions by supporting Romania’s National Urban Composting Program, ensuring that the building’s lifecycle emissions were fully neutralized. Residents were engaged in this process through co-design workshops, where they learned about carbon offsets and contributed to waste management strategies, fostering community-driven sustainability.

4.1. Carbon Offset Credits

Carbon offsets are tradable certificates that fund projects reducing or sequestering CO₂ in the atmosphere, allowing for developers to compensate for emissions they cannot eliminate through design or operations. Within the REN+HOMES PCB methodology, carbon offset credits are a critical component of achieving zero emissions, particularly for embodied carbon from construction materials and residual operational emissions. These credits are integrated into the scorecard (Table 7, criterion C8: Green Power and Carbon Offsets), where projects earn points for supporting certified carbon sequestration initiatives. Unlike global offset schemes used in certifications like LEED, the REN+HOMES PCB methodology prioritizes national projects to maximize local environmental and social benefits, aligning with the circular economy principles of the European Green Deal [7]. The process is transparent and resident-inclusive:

• Selection: Projects are selected from a list of approved carbon sequestration initiatives, certified by Carbon Matrix and evaluated by an independent committee.
• Funding: Developers allocate funds proportional to the project’s calculated CO2e emissions, ensuring 100% offset of unavoidable emissions.
• Resident Engagement: During co-design workshops (Section 2.4), residents are educated about offset projects and encouraged to participate in related initiatives (e.g., waste sorting for composting programs), enhancing community ownership.
• Certification: Upon offset completion, developers receive a Carbon Matrix certificate, which is documented in the PCB certification process, reinforcing accountability.

This approach not only neutralizes emissions but also fosters resident awareness and participation, addressing the reviewers’ request for a stronger connection between offsets and residential buildings.

The REN+HOMES Positive Carbon Buildings Scorecard (Table 7) represents a comprehensive assessment framework that distinguishes our methodology from other certification systems. This innovative scoring approach enables precise evaluation across multiple sustainability dimensions while incentivizing excellence beyond minimum requirements. Below is a detailed analysis of its structure, key components, and unique contributions to sustainable building certification.

4.2. Structure and Innovation of the Scorecard System

The scorecard is organized into four major categories that holistically address a building’s environmental impact:

• Leadership for Embodied CO₂ (Codes A1–A10): This category evaluates the embodied carbon aspects of a building, focusing on material selection, construction practices, and waste management. Unlike other certification systems that may treat embodied carbon as a secondary consideration, our scorecard places it as a primary assessment area, reflecting the growing understanding that embodied carbon can represent 40–70% of a building’s lifetime carbon emissions.
  Key Innovation: The inclusion of mandatory lifecycle assessment (A2, A3) as a requirement rather than an optional credit ensures all certified buildings undergo rigorous embodied carbon evaluation. This is further strengthened by criteria A10 (Material Optimization and Ecodesign), which rewards circular economy principles and adaptable design.

2.

Ongoing Performance (Codes B1–B5): This category focuses on the operational aspects that ensure buildings maintain their performance over time. It includes education for facility managers, transparency in reporting, and measures to reduce environmental impacts during operation.

Key Innovation: Unlike systems that focus primarily on design and construction, our scorecard emphasizes long-term performance through criteria like B2 (Transparency and Information Sharing), which requires continued reporting of energy and water usage data. This creates accountability and enables continuous improvement throughout the building’s lifecycle.

3.

Energy Optimization (Codes C1–C8): This category evaluates energy efficiency, renewable energy integration, and carbon reduction strategies. It includes both technical requirements and verification processes to ensure performance matches design intent.

Key Innovation: The scorecard’s approach to energy goes beyond efficiency to emphasize carbon impact through criteria like C8 (Green Power and Carbon Offsets), which connects to national carbon sequestration projects. This creates a direct link between building operations and environmental regeneration activities.

4.

Innovation (Code H1): By creating a separate category for innovation, the scorecard explicitly rewards creative solutions that advance sustainable building practices beyond established norms.

Key Innovation: Unlike systems that integrate innovation points within standard categories, our dedicated innovation section encourages breakthrough approaches that might otherwise be overlooked. This structure has proven effective in the REN+HOMES project, where it led to the adoption of novel solutions such as Building Integrated Photovoltaic (BIPV) panels and drain water heat recovery systems.

4.3. Unique Aspects

4.3.1. Balanced Point Distribution

The scorecard allocates points strategically across categories to reflect their environmental impact. For example, Energy Optimization (C1) carries 50 points, recognizing its critical importance, while innovative solutions can earn up to 10 points, encouraging experimentation while maintaining focus on core performance metrics.

4.3.2. Integration of Mandatory and Optional Criteria

The scorecard balances mandatory requirements (denoted as “Required”) with points-based criteria. This ensures all certified buildings meet essential sustainability thresholds while incentivizing higher achievement through additional points. This approach has proven more effective than purely prescriptive or purely performance-based systems.

4.3.3. Clear Performance Thresholds

For each criterion, the scorecard establishes specific, measurable thresholds. For example, C1 (Energy Optimization) requires buildings to be at least 10% better than nZEB standards or achieve EPC A+ classification with 68 kWh/m²/year (20% better than nZEB) for EU taxonomy compliance. These clear metrics eliminate ambiguity and set high performance expectations.

4.3.4. Scalability Across Building Types

The scorecard’s structure allows for application across diverse building types while maintaining consistent environmental standards. This flexibility has enabled successful implementation in both new construction and renovation projects, as demonstrated in the REN+HOMES student residential hall renovation.

4.4. Implementation in the REN+HOMES Project

Implementation of the ZEB criteria in the REN+HOMES project has validated its effectiveness. The student residential hall in Cluj-Napoca achieved significant improvements across multiple criteria:

• Energy Optimization (C1): 65.9% reduction in final energy demand.
• Renewable Energy Integration: 200 BIPV panels (72 m²) with 10.5% efficiency, producing 7119 kWh annually and geothermal wall system.
• Material Optimization (A10): Use of prefabricated panels with recycled content, reducing embodied carbon.
• Innovative Systems (H1): Implementation of geothermal wall and drain water heat recovery systems.
• Implementation of a zero-waste strategy (

  Table 8. Approved carbon sequestration projects in Romania.

  Project	Description	Annual Carbon Offset (kg CO2e)
  CUIB (Centrul Urban de Initiative Bune)	An eco-social restaurant and community hub in Iași, promoting zero-waste practices and local food systems. As Romania’s first zero-waste certified restaurant, CUIB reduces food waste and fosters environmental education.	56,353
  Școala de Puieți	An initiative establishing organic orchards (7 hectares) using no-till cultivation, cover cropping, and composting to enhance soil carbon storage. It preserves local fruit tree varieties and offers educational workshops.	88,060 (63,560 tree sequestration, 24,500 soil sequestration)
  Prima Împădurire	A digital platform facilitating afforestation on degraded lands, planting over 1 million trees since 2021. It connects stakeholders for reforestation and monitors impact transparently.	5,731,667
  Caneparo	A hemp farming and processing initiative using regenerative agriculture to sequester carbon and produce carbon-negative construction materials (e.g., hempcrete).	3,703,500
  Repair Network	A network of over 200 repair hubs (e.g., tailoring, electronics) promoting circular economy practices, preventing waste, and extending product lifespans.	3,788,343

  ).

5. Discussion and Further Directions

The REN+HOMES Positive Carbon Building for Positive Carbon Buildings represents a significant advancement in sustainable building development through its innovative integration of resident co-design with technical excellence. Our implementation in the REN+HOMES project demonstrates both the feasibility and effectiveness of this approach, with measurable improvements in both environmental performance and resident satisfaction.

5.1. Comparison with Existing Methodologies

When compared with other approaches in the field (

Table 9. Comparison of REN+HOMES PCB with other certifications.

Metric	REN+HOMES Positive Carbon Building	LEED	BREEAM	Living Building Challenge
Energy Performance	Minimum 50% of final energy reduction	Min 5–7% reduction	Min 5–10% reduction	Net-positive energy required
Co-Design Integration	Structured resident workshops	Limited occupant input	Stakeholder consultation	Community engagement
Innovation Focus	Standalone H1 criterion (10 points)	Innovation credits (≤6 points)	Innovation category (≤10 points)	Imperatives encourage innovation

), the REN+HOMES Positive Carbon Building demonstrates distinctive advantages in several key areas. Unlike the PHI methodology [17], which focuses primarily on energy efficiency without substantial resident engagement, our approach actively incorporates occupant input throughout the building lifecycle. This integration of technical and social aspects yields measurable benefits—the 65.9% reduction in final energy demand achieved in the REN+HOMES project exceeds the typical 3% improvement for conventional retrofits.

Similarly, while HPHI and CERQUAL methodologies offer comprehensive technical frameworks, they lack structured processes for resident involvement. The participatory approach developed in our methodology aligns more closely with the engagement principles advocated by García et al. [35] but extends these concepts through a more systematic implementation structure and clearer integration with technical assessment tools.

The REN+HOMES PCB methodology outperforms market recognized existing certification standards in terms of final energy reduction mandatory requirements (50% vs. 5–7%) and uniquely prioritizes resident co-design.

The REN+HOMES Positive Carbon Building integrates tools like IES VE PRO and Carbon Verify (Table 1), outperforming PHI’s focus on energy efficiency by incorporating resident co-design and carbon offsets, as evidenced by a 65.9% final energy reduction in REN+HOMES.

5.2. Addressing Implementation Challenges

The practical implementation of our methodology revealed several challenges that required innovative solutions. The integration of LCA based on EN 15978:2011 with resident co-design initially presented communication barriers, as technical concepts needed translation into accessible language. Our development of visual communication tools and interactive workshops successfully bridged this gap, achieving 73% resident comprehension of key sustainability concepts compared to the 45% baseline measured before intervention.

The Construction Products Regulation (EU) 2024/3110 provided essential mechanisms for accounting for embodied carbon, enabling more accurate calculation of lifecycle impacts [16]. This regulatory framework was particularly valuable in communicating material choices to residents during co-design workshops, making abstract concepts like embodied carbon more tangible through comparative examples.

5.3. Future Research Directions

Based on our findings, several promising avenues for future research emerge:

• Long-term performance monitoring: Extended study of buildings designed using this methodology would provide valuable data on operational performance stability over time, particularly regarding the durability of resident engagement in sustainable practices.
• Methodology adaptation for different building types: While our initial implementation focused on residential buildings, the principles could be extended to commercial, educational, and mixed-use developments with appropriate modifications.
• Quantification of co-benefits: Further research should investigate how to quantify additional benefits beyond energy and carbon metrics, including health outcomes, social cohesion, and economic resilience.
• Digital tools for resident engagement: Development of more sophisticated digital platforms could enhance the co-design process, making technical information more accessible to diverse resident groups and facilitating ongoing interaction during the operational phase.

The REN+HOMES Positive Carbon Building demonstrates that meaningful integration of resident engagement with technical excellence is not only possible but essential for achieving truly sustainable buildings. By recognizing both the technical and social dimensions of sustainability, this approach offers a promising path toward buildings that are not only less harmful but actively beneficial to both people and planet.

6. Conclusions

This research has demonstrated that the REN+HOMES Positive Carbon Building framework offers a significant contribution to sustainable building practices through its novel integration of resident co-design with technical carbon reduction strategies. Our implementation in the European REN+HOMES project yielded quantifiable improvements in building performance, specifically achieving a 65.9% reduction in final energy demand compared to baseline measurements. REN+HOMES Positive Carbon Building distinguishes itself from other approaches through three key innovations:

First, our structured co-design process transforms residents from passive occupants to active collaborators, addressing the operational challenges identified in traditional sustainable building approaches. By systematically engaging residents through workshops, feedback loops, and monitoring committees, we observed higher rates of compliance with sustainable operational practices and greater resident satisfaction with building features.

Second, the methodology’s separate evaluation of innovation as a standalone criterion represents a significant departure from existing frameworks. Unlike systems that subsume innovation within broader categories, this approach directly incentivizes creative problem-solving and technological advancement. During the REN+HOMES implementation, this led to the adoption of novel solutions such as the integration of Building Integrated Photovoltaic (BIPV) panels and drain water heat recovery systems, which might otherwise have been overlooked.

Third, our comprehensive scorecard system with its transparent, points-based evaluation framework provides immediate actionable feedback to project teams. The tabular format with distinct categories enables precise identification of improvement areas and facilitates targeted interventions. This granularity proved particularly valuable during the design refinement phase of the REN+HOMES project, where specific adjustments to thermal bridging details resulted in measurable performance improvements.

The practical application of this methodology revealed that the integration of technical excellence with resident engagement is not merely theoretical but demonstrably effective. Buildings designed with resident input showed better alignment with occupant needs while achieving superior environmental performance metrics. Furthermore, the methodology’s flexibility allows for its adaptation across different building types and regional contexts while maintaining core sustainability principles.

Future work will focus on longitudinal studies of buildings developed using this methodology to assess long-term performance stability and resident engagement patterns. Additionally, we aim to develop enhanced digital tools to facilitate the co-design process across diverse resident populations and to further quantify the socioeconomic benefits of this approach.

By advancing beyond conventional sustainability frameworks to create truly regenerative buildings through structured resident participation, the REN+HOMES Positive Carbon Building approach offers a replicable model for addressing both the technical and human dimensions of the built environment. This integrated approach represents a necessary evolution in sustainable building practice if we are to meet the ambitious climate goals set forth in the European Green Deal and create buildings that genuinely contribute to environmental regeneration.