Answer:
If you want to use a user-defined material in the design modules, make sure that it has the same properties as the standard-specific material.
Example
You want to design a user-defined material in RF‑/CONCRETE according to the standard EN‑1992‑1‑1. To create the material, proceed as follows: Select the material from the standard series EN‑1992‑1‑1 in the Material Library and select "Create New Material ..." Here, you can change all specified values. All these values are required for design in the add-on module.
