Reducing the energy consumption of buildings is a major challenge in building physics. Traditional methods like simulations often struggle to capture complex interdependencies. This study explores the use of Fault-Tree Analysis (FTA), originally developed in aerospace, to identify and evaluate energy-saving measures in buildings. FTA enables a hierarchical breakdown of influencing factors, revealing interconnections and vulnerabilities. This structured approach supports the identification of effective strategies and equivalent alternatives. A key focus is integrating FTA into the planning process, considering both effectiveness and costs. Given rising construction expenses due to interest rates, labor shortages, and material scarcity, this is especially relevant. Practical examples illustrate common weaknesses in building systems and their effects on energy efficiency. The results show that FTA complements conventional methods by providing a solid foundation for decision-making and improving communication among planners and stakeholders. FTA offers new perspectives for energy-efficient planning, especially in complex projects, promoting sustainable and economically viable building solutions.