Hey I have a client who is in the middle of a renovation. Old 1940's house second storey knee wall - and they want to put a cold air return in the second storey - but they want to just extend the first floor cold air return - straight up. Doing so will put the cold air chase into the bathroom wall. They don't want to install any tin - and wanted to use the stud wall cavity as the plenum/chase. My concern is that this wall is a shower wall and that this wall may get a lot of moisture which may condense with the cold air return causing moisture issues. Thoughts on this? Should they put in tin and seal it?

Thanks.
Troy

I deal with mold issues every day. Sheetrock in a shower is the perfect place for microbials to grow. I see it all the time. Putting a cold air return in a wall that is subject to that much moisture is insane. If that is the only place to locate the return then I wouldn't do it unless it were ducted AND wrapped. That will, at least, reduce the chance of mold migration throughout the HVAC system and the rest of the house.