Polymer flexible roll waterproofing materials (membranes) are widely used in the construction of flat and low-slope roofs of buildings and structures. Their projected service life is atleast 20 years, but sometimes it comes much earlier. The results of the analysis of the most probable causes that caused the violation of the continuity of the PVC membrane and theformation of leaks of the soft roof of an industrial building after 1.5 years since its installation are presented. As the most likely factors that caused coating defects (cracks of differenttypes and sizes) and, ultimately, roof leaks, are considered: non-compliance with the requirements for the conditions of transportation, storage and installation of PVC membranes atnegative temperatures, as well as a biological external influencing factor (the corrosive effect of synanthropic bird droppings).