In reinforced concrete structures, a key influence on the protection of reinforcement against corrosion is the properly designed and constructed concrete cover, the thickness of which should be adopted according to the exposure class in which the structure will be used. This article presents the standard guidelines for the design of concrete cover and the changes that have been made in this area in successive standards with a noticeable trend toward increasingly stringent regulations. Also summarized are results of tests performed for two elements of the structure of a residential building (made with W-70/MK large slab technology) designed for two different exposure classes, i.e. the exterior wall of the loggia and the interior wall of the kitchen, in which improperly executed concrete cover led to the development of corrosion of the reinforcement. Tests were performed by non-destructive methods using PS 200 ferroscan to determine the distribution of rebar and the thickness of the cover, and the polarized galvanostatic pulse method to assess the corrosion of the reinforcement.