moisture flow in wall assembly
 

Hello, I am trying to study heat and moisture flow in a wall assembly with an insulated cavity. I'm using the species model, and setting the mixture as air and H2O. I know I have to provide a moisture mass fraction for the inlet, but I don't know how to do that. I don't have an inlet. My boundary conditions are an exterior and an interior surfaces with set temperature (set as walls). The only place where I can set the mass fraction is in the insulation cavity, but I want to see how the moisture coming in distributes in the insulation cavity, so it doesn't make sense to give initial conditions there. Any help with this is appreciated...

Thanks Saba