In this paper, condensation of moisture in dwellings is described in detail and how it causes building damage, in more than 70% of the problems with the buildings the humidity is one of the major causes. Moisture reduces the thermal insulation ability of the material, long-lasting mois-ture causes building material degradation, corrosion damage of reinforcement concrete, wood material rupture, salt crystallization that causes plastering, barking of brick, stone, mortar or plaster and other causes and effects of moisture action also described. Condensation is the tran-sfer of water vapor into the liquid phase that is expressed as an aqueous film on a surface occurs when the surface temperature lower than the dew point of the surrounding air. After condensati-on on the walls and the appearance of the mold remain dark spots on the walls, the mold can be destroyed by a variety of biocidal means, however, the problem and the moisture source are not removed and the mildew occurs soon. Proper diagnostics moisture maintenance will not appear again, as explained in detail at the end of this work.