From the perspective of reducing Whole Life Cycle (WLC) carbon, selecting construction methods with low Upfront Carbon (UC) and natural materials is essential in interior design for buildings. Overseas studies indicate that earth-based building materials require less energy input, and that combining recycled materials with locally sourced natural materials is most effective for reducing WLC. While Japan has a long history of utilizing soil and wood as building materials, research on construction methods for modern buildings that prioritize the post-demolition reuse of soil and wood is scarce. The authors focused on "soil," a natural material capable of carbon sequestration at relatively low cost, and investigated how differences in material selection and construction methods affect UC emissions. This report examines the relationship between UC emissions and the moisture-regulating and thermal insulation properties of "soil" through parametric analysis. The results indicate a trade-off relationship between moisture regulation, thermal insulation, and UC emissions, highlighting the need to carefully balance these factors.