The development of probabilistic methods of computation for building structures has mainly been aimed at improving the computation methodology. The attention was given to the accumulation of actual data as well to the research of statistical properties of influence and parameters of strength. However, it is necessary to mention that hardly ever new investigations have been done in the sphere of probabilistic evaluation. The priority attention was paid to the first ultimate state. The problems of structure reliability should not be restricted to the structure durability and stability estimation, and not all possible structure failures can be analyzed with probabilistic methods. It is reasonable to develop some original approaches to probabilistic reliability estimation. One important fact should be taken into account; it is the risk of structure vulnerability and a lack of statistical data for its estimation. It is sensible to evaluate both durability and longevity to prevent outer-boundary vulnerability all along the structure. In order to solve this problem, a new characteristic (mobilization of structure) and its definition are given. The paper presents some considerations and common examples to justify this method. The authors consider this issue to be polemic and ready to cause further professional discussion.