My ducks and chickens sleep in the same house the only thing separating them is a door with chicken wire on it, I have not seen any build up moisture in the coop at all. I don't keep water or feed inside the coop though because ducks are very messy and can really muck up the bedding splashing their water out. they also have wetter poop than chickens, actually I don't think my chickens would appreciate having to sleep in the same room with the ducks or vise aversa