Minimizing the Climate Impact of Slab-on-Grade Foundations Through Life Cycle Analysis: Considering energy performance and material use across different building types and material configurations

Abstract

While it is commonly perceived that increasing insulation thickness improves performance by reducing heat loss through the foundation, this also increases material use and environmental impact. In parallel, interest in alternative foundation materials has grown, driven by the need to reduce embodied carbon and enhance energy efficiency. This thesis investigates the thermal and climate performance of slab-ongrade foundations across three building types: warehouse, residential building, and school/preschool. Three foundation systems, concrete, cross-laminated timber, and the Koljern system, are evaluated under two heating scenarios: heat pump and district heating. The study combines energy simulations in IDA Indoor Climate and Energy with Life Cycle Assessment covering material use (A1–A3) and operational energy (B6). Thermal transmittance, zone-wise insulation configurations, and total climate impact measured as Global Warming Potential are determined for each combination of system and scenario. U-values are calculated in accordance with Sandin’s model, which accounts for the influence of thermal zones in slab-on-grade constructions. Results are presented through line diagrams, stacked bar charts, and supporting tables. The analysis highlights how varying insulation thickness across different thermal zones influences the balance between emissions from material use and emissions from operational energy. The results show that the cross-laminated timber system consistently achieves the lowest total climate impact across all buildings and heating scenarios. For the other two systems, the lowest climate impact varies depending on building type and heating system. Further, the results show that the most climate-efficient foundation design is not necessarily the one with the lowest U-value, but the one that effectively balances material use and operational energy. In summary, the study shows that strategic choices, such as selecting a different slab-on-grade system or aligning insulation strategy with the heating system, can lower a building’s overall climate impact. However, the results also indicate that in certain cases, such as buildings with a relatively small slab-on-grade area, the benefits of insulation optimization are limited. Keywords: slab-on-grade foundation, cross-laminated timber, concrete, Koljern, life cycle assessment, material use, operational energy, insulation optimization, thermal transmittance, global warming potential.