Most remaining historic buildings today are brick buildings, especially in the cities of the Baltic Sea region. Bricks in unprotected masonry are exposed to moisture and large temperature fluctuations during different seasons. Researchers have proven that moisture not only significantly reduces indoor comfort level but may cause significant deterioration of the construction materials leading to loss of mechanical resistance and stability. There is a lack of understanding of historical building performance in the industry and policy and a lack of connection between good research, standards, certification processes, guidance and practice. This work covers the theme of refurbishment measures in historical buildings – the specific measures like inside insulation and risks that can arise because of it. This is done by simulation using computer models that require appropriate input data for material properties gained by laboratory tests. Simulation models are validated by long term in situ measurements.