Moisture accumulation in renovated external walls

Multifamily apartment houses build up until 1993 have to be renovated in order to reduce energy consumption. After renovation, air tightness of buildings is increased, however, in most cases heating-ventilation systems are not changed, so they are unable to perform their functions in the sealed buildings. If adequate ventilation is not ensured, indoor environment in apartments might decrease, i.e. relative humidity might increase. If water vapour diffusion through the walls takes place during the cold season, water vapor condenses inside the envelope. The aim of this work is to determine the changes of moisture behavior of the external walls of the renovated buildings, to identify the possibility of accumulation of condensation under certain environmental conditions, to assess the risk of moisture condensation for the external envelope durability.