Life cycle assessment and life cycle cost analysis of different walling materials with an environmental approach
Introduction
Environmental approaches to walling materials represent a critical pathway for sustainable construction in emerging economies facing climate pressures and housing shortages.
This comprehensive analysis examines a peer-reviewed life cycle assessment (LCA) and life cycle cost (LCC) study conducted in Iran that systematically compares earth-based and conventional load-bearing wall systems for affordable housing in arid climates. The research provides actionable data for architects, policymakers, and housing developers seeking to balance affordability, durability, and environmental responsibility.
Research Scope and Methodology: Cradle-to-Site Assessment Framework
The study, published in The International Journal of Life Cycle Assessment (2024), evaluates 22 distinct load-bearing wall configurations for a single-family affordable housing unit in Ardakan City, Yazd Province, Iran—a region characterized by hot, dry summers and cold winters. The functional unit is standardized at 1 m² of wall assembly, enabling direct comparison across diverse construction techniques.
System Boundary and Life Cycle Stages
The analysis adopts a cradle-to-site perspective, encompassing four life cycle stages defined by environmental product declaration standards:
- A1: Raw material supply
- A2: Transport to manufacturing
- A3: Manufacturing and production
- A4: Transport to construction site
Operational energy use (B1–B7) and end-of-life stages (C1–C4) were intentionally excluded due to data variability and uncertainty in the Iranian context. This focused boundary allows for precise comparison of embodied carbon and upfront costs, which are increasingly significant as operational efficiency policies reduce in-use energy consumption.
Wall Systems Analyzed
The research compares two broad categories:
- Conventional techniques (4 systems): Fired brick (FB), autoclaved aerated concrete block (AAC), ceramic hollow block (CB), and concrete masonry unit (CMU)—all widely used in Iranian low-cost housing.
- Earth-based techniques (18 systems): Including unsterilized and stabilized variants of adobe, rammed earth (RE), and compressed earth block (CEB). Stabilizers evaluated include straw, cement, lime, and alkali-activated binders (fly ash, ground granulated blast slag, sodium silicate, sodium hydroxide, calcium hydroxide).
All configurations include appropriate interior and exterior plaster layers per Iran's National Building Regulations, ensuring functional comparability beyond the primary structural material.
Environmental Performance of walling materials with an environmental approach
Embodied Carbon Results: Unsterilized Earth Leads
The life cycle impact assessment reveals that unsterilized earthen walling alternatives demonstrate substantially lower greenhouse gas emissions than conventional or stabilized systems.
The unsterilized compressed earth block (UCEB) emerged as the top performer, generating only 270.3 kg CO₂eq per functional unit. In contrast, stabilized adobe using straw (SA) recorded the highest impact at 3,043.6 kg CO₂eq—approximately 11 times greater—primarily due to long-distance transportation of straw from outside the province.
Key environmental findings include:
- Unsterilized systems (UCEB, URE) consistently outperformed stabilized and conventional alternatives.
- Cement and lime stabilization, even at low percentages (4–6%), significantly increased embodied carbon due to calcination processes.
- Alkali-activated binders showed promise for reducing cement dependency but incurred high transportation impacts when sourced remotely.
- Conventional materials (FB, AAC, CB, CMU) exhibited moderate-to-high emissions, driven by kiln firing and clinker production.
Transportation Dominates Environmental Impact
A critical insight from the study is that module A4 (transport to site) accounted for 70–95% of total embodied carbon across most wall systems. This finding underscores that walling materials with an environmental approach must prioritize local sourcing to achieve meaningful emission reductions. For instance:
- Straw transportation for stabilized adobe contributed over 600 kg CO₂eq alone.
- Alkali-activated stabilizers sourced from Tehran or other distant industrial centers amplified transportation impacts despite lower production emissions.
- Unsterilized systems using on-site subsoil minimized transport burdens, reinforcing the value of hyper-local material strategies.
Sensitivity analysis modeling direct versus indirect transport routes confirmed that reducing travel distances—especially beyond 50–100 km radii—dramatically lowers both carbon footprint and costs.
Economic Analysis: Cost Efficiency of Sustainable Walling
Life Cycle Cost Breakdown
The LCC assessment, limited to production and transportation costs within the cradle-to-site boundary, reveals that economic feasibility aligns closely with environmental performance when local materials are prioritized. The unsterilized compressed earth block (UCEB) achieved the lowest total cost at $4.43 per m², while stabilized adobe (SA) was the most expensive at $29.41 per m².
Cost drivers identified include:
- Material production: Labor-intensive processes (e.g., adobe brick molding) and imported stabilizers increased costs.
- Transportation: Heavy materials like rammed earth incurred higher freight expenses; lightweight alkali-activators had disproportionate cost impacts due to long-haul logistics.
- Stabilizer selection: Cement and lime showed moderate cost increases with percentage; alkali-activated alternatives were significantly more expensive in the Iranian market.
Conventional systems (FB, CB) demonstrated moderate costs, while cement-based options (AAC, CMU) were comparatively higher due to industrial processing requirements.
Affordability and Scalability Considerations
For affordable housing programs, the study emphasizes that walling materials with an environmental approach can be both low-carbon and low-cost—but only when supply chains leverage local resources.
Unsterilized earth techniques require minimal processing, utilize excavated subsoil, and avoid expensive chemical additives. However, successful adoption depends on:
- Technical training for local labor forces
- Quality control protocols for soil selection and compaction
- Regulatory frameworks that recognize earthen construction performance
Strategic Recommendations for Policy and Practice
Prioritize Local Material Sourcing
The sensitivity analysis conclusively demonstrates that transportation distance is the dominant variable influencing both environmental impact and cost. Policymakers and developers should:
- Map regional material availability before selecting wall systems
- Incentivize on-site soil testing and processing infrastructure
- Establish regional hubs for stabilizer production to reduce haul distances
Integrate LCA Data into Building Codes
Iran's current building regulations focus primarily on operational energy efficiency, overlooking embodied carbon. The study advocates for updating codes to:
- Require environmental product declarations (EPDs) for major walling materials
- Include embodied carbon thresholds in affordable housing procurement criteria
- Support pilot projects demonstrating the durability of unsterilized earthen walls in desert climates
Advance Research on Alkali-Activated Binders
While alkali-activated stabilizers showed technical promise for replacing cement, their current cost and logistical barriers limit scalability in Iran. Future research should:
- Develop local production pathways for industrial byproducts (fly ash, slag)
- Optimize binder formulations for arid-region soil types
- Assess long-term durability under thermal cycling and moisture exposure
Conclusion: Enduring Value of walling materials with an environmental approach
This rigorous life cycle assessment provides a replicable framework for evaluating construction materials in resource-constrained, climate-vulnerable regions. By demonstrating that unsterilized earthen walling materials with an environmental approach can achieve superior environmental and economic performance, the study challenges assumptions that sustainable construction requires premium costs or complex technologies.
The findings reinforce that hyper-local material strategies—prioritizing on-site soil, minimizing transport, and avoiding energy-intensive stabilizers—offer the most viable pathway to affordable, low-carbon housing.
As global housing demand intensifies, especially in arid and semi-arid regions, the methodological clarity and empirical evidence presented in this research will remain an essential reference for advancing regenerative building practices worldwide.
Walling materials with an environmental approach are not merely an alternative—they represent a scalable, dignified, and climate-resilient foundation for the future of affordable housing.
Also read: Matrix of Affordable Housing Assessment