Due to climatechange, an increasein extreme weather events, including heavy rainfall and flooding, is predicted for Central Europe, with an increase in moisture problems within buildings. The building materials most susceptible to failure due to moisture are bio-based materials and highly porous materials such as cellular concrete. This paper presents a model situation of a single-family house with damp walls made of cellular concrete blocks. A simulation in WUFI Plus software was used to monitor the drying process of the damp masonry, which was insulated from the outside with polystyrene foam, mainly towards the inside. The simulation program allows a holistic approach, taking into account the effect of ventilation, internal heat and moisture gains, solar radiation and thermostat settings in calculating the indoor environment conditions. The investigation resulted in a realistic pattern of higher indoor relative humidity, exceeding the unhealthy level of 60% for several months. A direct comparison with the drywall scenario demonstrates that insulated buildings with damp masonry cannot be considered equivalent to buildings with dry masonry. This conclusion indicates that it is erroneous and illegal to hold such a view.