Is it really that big of a deal not to install a fan? Nobody wants to open a window summer or winter. Sometimes in the winter you cannot even open a window in an unvented bathroom. I know why people don't want to use fans...noise, chilly air, whatever the reason people need the fans and should get used to using them or risk moisture building in your insulation and having your ceiling fall through- then what will the cost be?? It is code in many places regardless of the age of the home- the fact that it is a rental dictates the code. In your own "home" do what you like. I am a renter. can't open window during winter, and it's just as muggy outside during summer. If they keep the bathroom door open, and you can't open doors or windows due to weather then you will have moisture throughout the apartment or house. common sense. Sure they could use bleach or cleaning solutions... then you have residue and moisture filled bleach and steam filled with cleaning solution to make it's way into peoples lungs.