Achieving Greenhouse Gas (GHG) emission goals in the construction and real estate industry requires early integration of environmental considerations during design stages. Life Cycle Assessment (LCA) is key for this goal, yet technical installations are often underestimated. This paper presents – through a comparative study – an Early-Stage Parametric Based Life-cycle Analysis (ESPB-LCA) method developed at EPFL to evaluate building-related environmental impacts at early design stages, with special attention to HVAC and sanitary systems. It compares the ESPB-LCA approach with KBOB Swiss database averages, Lesosai software outputs, and real project data. Results highlight the need for detailed technical system assessment to avoid significant underestimation of environmental impacts, supporting better-informed sustainable design.