The article discusses the deviation that occurs when a non-destructive testing methods are used in the survey of buildings and structures. The errors in the calculation of the load-carrying ability of metal deck slabs, which is a consequence of this deviation are estimated, as well. Two types of slab are considered: plain and hollow. The paper surveyed the NDT methods such as: ultrasonic method, rebound hammer method, shock pulse method and surface hardness method. These methods are used to determine reinforced concrete parameters: concrete strength, steel strength, protective concrete layer, width reinforcement. The calculation was made according to the current set of rules and construction norms and regulations of Russian Federation.