Known methods of defining the condition of plumbing systems with high level of wear do not fully take into consideration the uncertainty at the buildings and their networks operation. In these methods the value of objects residual resource is considered as a random value, and tolerance zone borders – as a determinate value. The urgency of the approach consists in the account of possibility of tolerance range limits fuzzy value. The purpose of the work was increasing the efficiency of decision-making at justification of actions for ensuring durability of building plumbing systems. The purpose was reached by use of the tools of fuzzy sets in the joint analysis of retrospective, current and expert information on change of plumbing system object technical condition and variable limits of its tolerance range. It is offered to carry out the calculation of residual resource by means of fuzzy values of time and probability of crossing the tolerance range limits by the object parameter. The computational testing of the proposed approach showed its effectiveness. On the basis of these results the conclusions about the area and conditions of application of the developed algorithms and model were drawn.