What is the purpose to know the composite wall U-value? If this is for energy demand evalualuation, it must be done manually in ArchiCAD. The tools are not working correct in case of composites, especially in case of ventilated facades and frame walls. The best solution is: to make calculation manually or with special software and then use the U-values applying them to non-composite walls. In addition thermal bridges should be considered. For openings it is quite simple, U-values can be defined in the object properties.
By the way, the tool for thermal bridges is quite simple to use, calculates proper values, but not the actual thermal bridge PSI value. The real value can be found by isolating parts of structures involved in thermal bridge and finding their PSI values.
