It is very important to make a research in external wall design due to increased requirements to energy efficiency. The objective of the research is determining of main principles of designing three-layer external walls. The article describes features of designing walls. Particular attention is paid to the design and installation errors of three-layer external walls. Recommendations are made to increase the maintenance-free life by performing specific design requirements. Article would be useful for engineers working with energy-efficient solutionsin civil and industrial designing.