Hygrothermal assessment of internally added thermal insulation on external brick walls in Swedish multifamily buildings

Proper and efficient renovation requires understanding the behavior of existing buildings and of different building materials. Analyzing hygrothermal measurements in two case studies, one with and the other without an internally added thermal insulation system, enabled us to identify factors of critical importance for further assessment through simulations, and to validate a hygrothermal simulation model of a solid brick masonry wall, a model used then to assess internally added thermal insulation systems of different types. A mold resistance design (MRD) model shows that, in connection with all internally added thermal insulation systems, the risk of mold growth is appreciable when brought on by solar driven vapor from the exterior. This, if biological material is present in either of two critical areas, those of the boundary between the thermal insulation and either 1) the existing masonry wall, or 2) the exterior surface of an internally added vapor barrier. Furthermore, assessments of corrosion risks are conducted for two critical placements of the bed-joint reinforcement. At a depth of 30 mm from the exterior surface, the corrosion risk was found to be less with use of capillary-active vapor-open systems than when no thermal insulation was employed, other systems increase the corrosion risk. At a depth of 90 mm, all thermal insulation systems increase the corrosion risk. Excluding precipitation uptake eliminates all risks, showing that this is the most crucial factor. Solutions that limit this uptake or increase the drying-out rate should thus be considered beneficial.