Introduction
The construction sector is responsible for approximately 37% of global carbon dioxide emissions and 36% of final energy consumption, establishing it as a critical driver of climate change. While recent decades have seen significant advancements in reducing operational carbon through energy efficiency and renewable energy integration, the role of embodied carbon—emissions associated with material extraction, manufacturing, transportation, construction, and end-of-life phases—has emerged as a pivotal concern. For new buildings, embodied carbon can constitute 67% to 76% of total life cycle emissions. Despite the growing body of literature on sustainable construction, there remains a notable gap in comprehensive, probabilistic assessments that simultaneously evaluate multiple novel material families within a hybrid structural framework. This study addresses this gap by conducting a life cycle assessment (LCA) of high sulfate calcium silicate cement (HSCSC), engineered wood products/cross-laminated timber (EWP/CLT), mycelium-based composites (MBC), and hemp concrete (HC), focusing on embodied energy and carbon footprint indicators across the complete building lifecycle.

Methodology
The assessment was conducted in accordance with ISO 14040/14044 standards and the EN 15978 framework, utilizing a cradle-to-grave system boundary (modules A1–C4). A hybrid LCA (H-LCA) approach was adopted, integrating process-based inventory data from the Ecoinvent 3.9.1, ICE, and ÖKOBAUDAT databases with input-output tables to capture indirect supply chain effects. Four structural scenarios were evaluated for a five-story residential building in Tehran, Iran: S1 (conventional reinforced concrete as the baseline), S2 (HSCSC-based concrete), S3 (all-CLT timber construction), and S4 (a hybrid system combining HSCSC, CLT, MBC, and HC). To account for data variability and parameter uncertainty, a Monte Carlo simulation with 10,000 iterations was employed, utilizing normal distributions for material coefficients (15% standard deviation) and quantities (10% standard deviation), alongside a uniform distribution for building service life (40–60 years). Sensitivity analysis was performed using Pearson correlation coefficients across eight input parameters to identify the dominant contributors to the total carbon footprint. Model validation was achieved through internal, external, and cross-database comparisons.

Results and discussion
The baseline LCA results for the hybrid scenario (S4) demonstrated an embodied energy of 1.33 GJ/m2 and a carbon footprint of 116.41 kgCO2eq/m2, representing reductions of 68% and 69%, respectively, compared to the conventional reinforced concrete scenario. Disaggregated analysis revealed that the production phase (A1–A3) contributed 83% of total emissions. The bio-based materials (CLT, MBC, and HC) collectively sequestered 41.5 kgCO2eq/m2 during production, effectively offsetting 30% of the positive emissions generated by cementitious materials. Monte Carlo simulation estimated a mean carbon footprint of 96.52 kgCO2eq/m2 with a 95% confidence interval of [60.71, 135.54] and a coefficient of variation (CoV) of approximately 19.8%, confirming that the deterministic value (116.41) falls within this range and underscoring the necessity of probabilistic approaches. The scatter plot revealed a strong positive correlation between embodied energy and carbon, though the dispersion suggests that reducing embodied energy does not guarantee a proportional reduction in carbon. Sensitivity analysis identified material type (34.53%), embodied energy coefficient (24.64%), and carbon emission coefficient (15.51%) as the most influential parameters, collectively explaining 74.68% of the variance, while transport distance (1.17%) and ambient temperature (1.54%) exhibited negligible impact. A critical finding emerged in the end-of-life (EoL) phase: while cement-based materials showed negative EoL emissions (benefiting from recycling credits), bio-based materials exhibited positive EoL emissions due to the reversal of recycling benefits in materials with negative emission factors.

Conclusion
This study provides robust quantitative evidence that a hybrid structural strategy combining low-carbon cement, engineered timber, and bio-based composites can achieve substantial reductions in embodied carbon (69%) and embodied energy (68%) without compromising structural feasibility for mid-rise buildings. The findings establish material selection at the early design stage as the most effective lever for decarbonization, followed by production process improvements and material optimization. However, the positive end-of-life emissions of bio-based materials highlight a critical trade-off: carbon sequestration benefits are partially reversed without proper end-of-life management. Therefore, achieving a truly carbon-negative life cycle requires the integration of circular economy strategies, such as design for disassembly and advanced recycling infrastructure. The validated MATLAB-based framework, which operates without external statistical toolboxes, provides an accessible decision-support tool for designers and policymakers. Future research should focus on developing localized life cycle inventory databases for Iran, integrating LCA with Building Information Modeling (BIM) for automated assessments, and conducting dynamic LCA to account for future energy grid decarbonization.