Heat, Air and Moisture (HAM) modelling of building performance is a quite young research subject but the experimental determination of material properties is often based on classical methods. One should review the manner in which we define characteristic material parameters and there is a need to develop an approximation used to generate the required material functions for input to HAM-transport simulations. The paper presents such an approach, called an engineering model for hygrothermal material characterisation. The paper poses the question, how to arrive at input data that can be used for a model based on thermodynamically defined potentials (Only such a model allows introduction of new potential components (freezing depression, osmotic pressure, air pressure, overburden envelope pressure)) (e.g., Grunewald, J. (1997) and Grunewald, J. (1999)) and yet the respective functions used to describe changes in the material response as a function of the variables of state. Such functions should have a reasonable precision and goodness of fit while the number of measured points must be reduced to a minimum. Those measurements should be relatively easy to perform (i.e., they would not require determination of temporal and spatial profiles of moisture). This discussion paper highlights steps already taken (Part 1), and lists issues that need to be resolved before reaching this goal (Part 2).