C030 -- Assessment of the Impact of Interior Insulation on Exterior Walls in Three Swedish Buildings

Among thermal improvements of external walls in heritage buildings, interior insulation of external walls might be the only option. However, interior insulation is associated with several risks of damage due to the diminishment of the hygrothermal performance of the existing wall. This project aims to assess the impact of available solutions for interior insulation through field measurements and hygrothermal simulations on external walls in three Swedish buildings. Temperature and relative humidity were measured indoors, outdoors, and on the exterior and interior surfaces of the external walls. Measurements were used to validate models of the walls in WUFI Pro. The models were used to determine the impact of 13 different solutions for interior insulation. The solutions are either vapor-tight or open, and some are capillary active. The results were analyzed regarding risks for microbial growth using the Viitanen model. The validation regards the temperatures and relative humidity on the interior surfaces of the included walls and shows that the models can be accepted for an assessment. The validation also shows that the measured indoor climate can be replaced with an indoor climate standard yielding reliable results. The results show that the risk for damage relies on the design of the existing external wall. If the wall is already hydrophobically treated, the risks are reduced significantly. Furthermore, suppose the wall is poorly insulated. In that case, a larger relative reduction of the transmission losses might be achieved with a lower amount (thickness) of additional insulation, which also results in lower risks for moisture damage. Nonetheless, results show that all included external walls can be insulated from the interior without considerable risks of moisture damage, but that one of them should also be hydrophobically treated.