Comparing the environmental impacts of building materials at the building level can be biased because a building design is optimized for a primary structural material. To achieve objective comparisons, this study compares the environmental impact of reinforced concrete (RC), cross-laminated timber (CLT), and timber-concrete composite (TCC) at the component level with equivalent structural performance. A slab was selected as the target structure member because its design does not consider lateral forces. Equivalent structural performance was defined as the minimum quantity of slab materials for comparable span and live load conditions. The functional unit for this study was defined as a 1 m2 slab. The system boundary covered the cradle-to-gate perspective, including raw material extraction, transportation, and manufacturing. The structural design method and material design values followed the Korean building code and standards. Environmental product declaration data developed in Korea were used to evaluate the carbon footprint. The CLT emitted 75 % less carbon dioxide, the primary greenhouse gases responsible for anthropogenic climate change, compared with RC regardless of conditions, while the TCC emitted 65 % less CO2, and its environmental impact improved as the span lengthened. The results also indicated that timber slabs are thinner than concrete slabs and can be structurally rational.