The paper focuses on the necessity of using ventilation slots in plinth areas of buildings. The main purpose of these slots is to reduce the amount of the capillary rising of water. At the same time it is important to draw attention to the lack of knowledge in the area of basic physics among construction companies; building renovations conducted by them, not only of historical buildings, but also of new ones, lead to serious failures. The moist air discharge through the cracks in the plinth areas presented in this article is one of the methods allowing for proper moisture reduction and for making renovations in damp underground parts of historic buildings. Additionally, this method allows to create a proper plinth area in the modern building industry.