This node adds an initial value for the relative humidity that can serve as an initial condition for a transient simulation or as an initial guess for a nonlinear solver. In addition to the default Initial Values node always present in the interface, you can add more Initial Values nodes if needed.

For User defined, enter a value or expression for the initial value of the Relative humidity φ. The default value is 0.5. Else, select an Ambient relative humidity defined in the Ambient Settings section of a Heat Transfer or Heat Transfer in Shells interface.

Physics Tab with interface as Moisture Transport in Air or Moisture Transport in Building Materials selected:
Domains>Initial Values