Thank you very much for your advise. I will get a hydrometer

HI, Does The bathroom mirror fog up after a shower? Do you have a bathroom fan?If you have a fan and turn it on and say it can move a Hundred cubic feet a minute but you have the door closed and the space under the door only allows ten cubic feet per minute that is good as it gets, the room will fog up and moister will get on the walls and mirror, sounds like the problem you have. To test next time, you shower leave the door open some to let the air in<.and see what happens.

Good Luck Woodbutcher

i'm not an expert andthis may be more serious than what a fan can solve. But I always try to make sure my bathroom fan runs for at least a half hour after my shower. You can use a timer in your wall switch if you have to run out the door immediately after showering. I also squeegee the walls completely in my shower. Finally in my last place which was an I had a dehumidifier running concurrently with my bathroom fan. Sometimes longer. But that was a much older home than yours. If these things do not solve this issue it may be more serious.

Hi woodbutcher. This is a upstairs bathroom that gets minimal use. Only when guest are over so maybe the shower is used 2-3 times a month at most. We have continued to replace the damp rid bags every week. We have a box fan blowing in attic. The bathroom vanity back is to the attic and we thought maybe it would help circulate air and push some of the heat out roof vents. I will run the shower and see if mirror fogs up. We continue to be at a lost to what to do.

If the bathroom gets only minimal use, and the high relative humidity is an ongoing issue, the root cause isn't likely to be poor ventilation during or after a shower. A couple of things to consider:

1. Moist air is more buoyant than dry air so it's typical to have higher relative humidity on the upper floors of a home. Get a hygrometer and check the relative humidity in the bathroom so you know the baseline.

2. Check to ensure proper performance of the 2nd floor HVAC system. If the 2nd floor is normally unoccupied, you still need to operate the HVAC to dehumidify the space. 60% is the top end. I like to maintain relative humidity at 50% or less to limit the potential for mold/mildew growth.

3 Keep the bathroom door open when the bathroom is not in use. There aren't HVAC returns in bathrooms (returns are prohibited by code) so return air flow relies on the undercut in the door which is usually inadequate.

4. Ditch the fan(s) in that attic. Operating them can change the pressure balance in the home and pull moisture into the home from crawl spaces, stud cavities, etc.

5. Check for moisture sources like a damp crawl space or basement. Seal any sources of air leakage into the bathroom from the attic.

6. Make sure to operate bath vent fans when showering and a range vent hood fan when the range is in use to vent moisture from those sources to the outdoors.

Thank you Charles we will get a hygrometer and try your recommendations. We keep ac on 71 upstairs (we are in Texas).

Maintaining the temperature at 71F doesn't guarantee you won't have relative humidity issues. In fact, it could result in elevated relative humidity if your air conditioner is oversized and it cools the space quickly and without adequate dehumidification.

HI, Make sure the fan vents through the roof not into the attic.

Good Luck Woodbutcher