The construction industry is among the largest consumers of energy and natural resources worldwide and is responsible for a significant share of greenhouse gas emissions, environmental degradation, and waste generation. Rapid urbanization, population growth, increasing demand for buildings, and the impacts of climate change have intensified the need for more sustainable approaches in the built environment. As a result, improving the environmental performance of buildings has become a major objective in contemporary architectural and construction research. Life Cycle Assessment (LCA) is widely recognized as one of the most comprehensive methods for evaluating environmental impacts throughout a building’s life cycle, from raw material extraction and manufacturing to operation, demolition, and end-of-life treatment. Despite its extensive application, conventional LCA approaches are generally based on linear models that emphasize resource extraction, consumption, and disposal. Such approaches often overlook circular material flows, resource recovery opportunities, and the environmental benefits associated with bio-based construction materials.
In recent years, the concepts of circular economy and regenerative design have emerged as promising strategies for reducing environmental impacts and improving resource efficiency. Simultaneously, bio-based materials have gained increasing attention due to their renewable origin, lower embodied energy, carbon storage capacity, and reduced environmental footprint. However, existing assessment frameworks rarely integrate environmental performance, material circularity, and bio-based resource management within a single analytical structure. Consequently, there is a growing need for enhanced evaluation methods capable of addressing these interconnected dimensions of sustainability.
The present study aims to develop an enhanced bio-circular model for building life cycle assessment by integrating conventional environmental assessment with circular economy principles. The proposed framework extends the scope of traditional LCA by incorporating material circularity considerations, biogenic carbon storage, resource recovery potential, and end-of-life material flows. The objective is to provide a more comprehensive assessment methodology capable of evaluating both environmental impacts and circular performance within a unified framework. Furthermore, the study investigates the effectiveness of the proposed model through its application to the external wall assembly of a residential building.
The research adopts a numerical and simulation-based methodology that combines building energy modeling, life cycle assessment, and material circularity analysis. The framework was developed in accordance with established LCA principles while introducing additional dimensions related to circular resource management. To validate the model, a residential building located in Lahijan, Iran, within moderate -humid climatic region, was selected as a case study. Two scenarios were examined: a conventional wall assembly representing common construction practices and an alternative assembly incorporating bio-based materials. The external wall was selected because of its substantial influence on thermal performance, operational energy demand, embodied environmental impacts, and overall building sustainability.
Environmental impacts were assessed across the building life cycle, while energy performance was evaluated through simulation. In addition, material circularity was quantified using the Material Circularity Indicator (MCI), which measures the extent to which materials remain within productive cycles through reuse, recycling, and recovery processes. The integration of MCI with conventional LCA indicators represents one of the principal innovations of the proposed framework, enabling a broader understanding of sustainability beyond environmental burden assessment alone.
A key limitation of conventional building life cycle assessment frameworks is their inability to adequately represent the long-term value retention of materials beyond the end-of-life stage. In many existing assessments, materials are considered waste once their initial service life is completed, while the potential for reuse, refurbishment, recycling, and energy recovery is only partially addressed. This limitation can lead to an underestimation of the environmental benefits associated with circular construction strategies. The proposed bio-circular framework addresses this challenge by extending the analytical perspective from a linear life cycle approach toward a regenerative system in which material flows are continuously evaluated in relation to their future recovery and utilization potential.
Furthermore, the developed model enhances the interpretation of environmental performance by establishing a stronger connection between resource efficiency and life cycle impacts. Rather than evaluating environmental indicators in isolation, the framework considers the interactions between embodied carbon, operational performance, and material circularity. This integrated perspective enables a more comprehensive understanding of how design decisions influence environmental outcomes throughout the entire building life cycle. Such an approach is particularly relevant for contemporary architectural practice, where reducing carbon emissions, improving resource productivity, and supporting circular economy objectives have become central priorities in sustainable building design.
The results demonstrate that the proposed bio-circular framework provides a more comprehensive evaluation of building performance than conventional life cycle assessment approaches. The incorporation of bio-based materials in the external wall assembly led to a significant improvement in environmental performance. Compared with the reference scenario, annual operational energy consumption was reduced by approximately 16%, indicating the positive contribution of bio-based materials to thermal efficiency and energy conservation. Improved insulation characteristics and reduced heat transfer through the building envelope contributed to lower energy demand during the operational phase.
The embodied carbon assessment revealed additional environmental benefits. The bio-based wall assembly achieved a reduction of approximately 31% in embodied carbon emissions compared with the conventional alternative. This reduction was associated with lower manufacturing-related emissions and the capacity of bio-based materials to store atmospheric carbon during their life cycle. These findings highlight the importance of material selection in reducing the overall carbon footprint of buildings and support the growing adoption of renewable construction materials as part of climate-responsive design strategies.
The circularity assessment further confirmed the advantages of the proposed model. The Material Circularity Indicator increased by approximately 36% in the bio-based scenario, demonstrating enhanced resource efficiency and improved opportunities for material recovery and recirculation. The results suggest that bio-based materials can contribute not only to environmental impact reduction but also to the development of more circular construction systems. By considering resource recovery pathways and material retention within biological and technical cycles, the proposed framework provides insights that are not typically captured by conventional LCA methodologies. Furthermore, the analysis demonstrated that external wall assemblies play a critical role in determining the environmental performance of residential buildings. Although representing only one component of the building envelope, wall systems significantly influence energy consumption, embodied impacts, and resource efficiency throughout the building life cycle.
The proposed framework contributes to the advancement of life cycle assessment methodologies by introducing circularity as an additional dimension of evaluation. Unlike conventional approaches that focus primarily on environmental burdens, the developed model enables a more holistic assessment of sustainability through the integration of environmental performance, carbon storage, resource recovery potential, and material circularity. This broader perspective supports informed decision-making during the design and specification of building materials and provides architects, engineers, and policymakers with a practical tool for evaluating sustainable construction alternatives.
In conclusion, this study developed and validated an enhanced bio-circular model for building life cycle assessment and demonstrated its applicability through a residential building case study. The findings indicate that integrating bio-based materials and circularity-oriented indicators into conventional life cycle assessment can substantially improve building sustainability performance. The proposed framework achieved reductions in operational energy consumption and embodied carbon emissions while significantly enhancing material circularity. By extending traditional LCA boundaries to include circular economy principles, resource recovery strategies, and biogenic carbon considerations, the model offers a more comprehensive approach for assessing sustainable buildings. The framework can therefore support the transition toward low-carbon, resource-efficient, and environmentally responsible construction practices while providing a foundation for future research on the integration of circular economy concepts into building assessment methodologies