The paper analyzes the significance of quality of execution and ongoing controls affecting the final airtightness of building envelope. The realization of building with well airtight building envelope must be more consistent and rigorous than the realization of conventional building. There are two ways to realization of energy - efficient buildings. On the one hand, there is a realization using a professional construction companies. On the other hand, it is a realization of the building themselves (self-build). The aim of the paper is to verify the statistical dependence of the final airtightness building envelope between the realizations using by professional construction companies and self-build.