We had an addition put onto our house approximately 5 years ago. This addition included a second story bathroom which we rarely use for any reason. In the past 6 months, we have noticed a mold, mildew or musty smell in this bathroom and cannot find the source. We have smelled all of the drains and nothing. We have removed the trim and cut a hole in the wall to see if mold was growing, but nothing was found. We do have a bathroom on the first floor directly before this bathroom, which is not vented. Could the steam rising from the shower on the first floor be causing this smell in the second floor bathroom? Any ideas or suggestions before we rip the entire bathroom apart? Thanks.

Hi! Porta1, welcome to AMHD :)

That's possible. By not vented, do you mean no exhaust fan in the lower bathroom?

Was the upper bathroom professionally done or was it a DIY?

In either case there could be leaky drains, improper soldering or gluing of connections.
Have you pulled the toilet to see if there were any leaks under that? Look for water stains before you pull it.

Can you remember anything in the last year that may have caused you to start smelling this "in the past 6 months".

Is the upper bathroom against an exterior wall? You may need to look for leaks where the exterior house siding matches up with the old.
Check Roof vents, flashing.

Might even be a small dead animal, :eek: but I kind of doubt it.

This is just my "short list", it's hard to tell without actually being there.

K