[Lada]

I use chtMultiRegionFoam to simulate heat transfer through building walls. What I need to include into the simulation is an extra transport equation to solve water vapour diffusion through the wall as well so I could evaluate where condensation happens within the wall.
I guess I need to rewrite the solver but I am afraid I am not so skilled yet to do so.
Could you give me a hint where to start and what to look for, or if rewriting is the way?