There have historically been, and still are, problems with water intrusion into new external walls of prefabricated concrete sandwich elements in Sweden to a varying extent. However, it has been unclear exactly what the causes are. It appears as if there is an application of single line of defence in sealing of joints in walls, which are known to be problematic. The aim of this study was to obtain documented knowledge and data on driving rain resistance, to provide a basis for improvements and calculations in a common kind of concrete sandwich system with façade components and sealing products, and to grade the driving rain resistance of various sealing principles. The study included inspections of concrete sandwich walls in the field and driving rain resistance testing of experimental set-ups in a laboratory. By scaling down concrete elements in the experimental set-up, it was possible to study multi-storey façades and made by experienced producers and contractors. Intentional defects were also created in an extra experiment based on inspection results. Inspection results showed that, in all buildings, vertical joints between the concrete elements were often significantly too narrow and, at the same time, adhesion loosening of building mastic in these joints was common. In general, the joints were equipped with small openings of tubes for depressurization, drainage and ventilation. However, they were often incorrectly placed or had a bad incline. Lab results for intact concrete sandwich walls indicated inward leakage at window-wall interface, even without wind pressure, through the tubes despite a sharp incline, in element joints with a new kind of application of pre-compressed joint sealing tape. The largest leakage flows were of 0.4% of the vertical water flow cross a unit width of the façade at the given height. To our knowledge, there does not appear to be a performance report on the current solutions, which in itself is a major uncertainty, i.e. the right conditions did not exist to avoid inward leakage.