This research addresses the environmental impact of foundations in lightweight housing units, focusing on BAM's timber house concept, FLOW. While the engineered timber superstructure is environmentally conscious, the foundation's contribution is often overlooked. The study aims to minimise the Environmental Cost Indicator (ECI) of FLOW houses by investigating three foundation variants through a Life Cycle Assessment (LCA). The LCA compares three foundation variants: prestressed prefab concrete piles, timber foundation piles with concrete caps, and shallow concrete strip foundations, considering soil profiles in Zwolle and Delft. Results show that the timber foundation has the lowest ECI, driven by CO2 storage in the spruce timber part. Sustainable options, such as Blast Furnace Slag cement, a reduced concrete strength, and optimised processes, significantly reduce ECIs. Timber foundation piles with concrete caps emerge as the most environmentally promising. Further technical implications and feasibility research are recommended for integrating timber foundations into lightweight structures like FLOW.