Contemporary tendencies of building constructions are mainly concentrate on saving energy and reducing greenhouse gas emissions in accordance with the rules of sustainable development. The significance of the airtightness of building envelope is demonstrably non-negligible for energy-efficient constructions. Uncontrolled flow of air through the building envelopes negatively influences the energy balance of the building. In some cases, it reduces the life of the structure and increases the risk of defects, such as condensation of water vapor and the occurrence of mold. High quality and airtight building envelope can reduce the demand for heating by up to 10 %. The paper deals with the determination of significant factors of building airtightness using the method of pairwise comparison (Fuller’s triangle). The method of Fuller’s triangle is based on select preferred factor of a pair of factors. The newly acquired results are compared with previously obtained information based on statistical methods (statistical Test of independence) and quality management tools (Cause and Effect Diagram and brainstorming). Implementation of new knowledge into the building practice can significantly affect the quality of envelope already in pre-production phase and design phase.