The article estimates the influence of external finishing coating characteristics on the humidity regime in the walls of aerated concrete blocks with the density of 350–600 kg/m3 (D350–D600 grades). The research is in demand due to the fact that condensation of excessive moisture in the enclosing structure is one of the most common reasons for the destruction of plaster coatings for walls of aerated concrete. To assess the humidity regime in the walls of aerated concrete, the temperature of the onset of moisture condensation tsk was determined. The temperature of the onset of condensation tsk is the temperature of the outside air: a temperature drops to this level causes formation of condensate in the enclosing structure. It was revealed that due to the use of the developed dry building mixture for D350–D600 concrete blocks finishing, moisture condensation begins at a significantly lower outdoor temperature. The moisture regime in the walls of D350–D600 aerated concrete blocks was studied for the conditions of various climatic zones on the example of three cities: Rostov-on-Don, Voronezh, Novosibirsk. A linear model is obtained that reflects the dependence of the temperature of the onset of condensation tsk in the walls of D350–D600 aerated concrete blocks on the thermal properties of the wall material and the finishing layer.