Odd Mildew

[Yankeesouth]

My cabin is on pilings ranging from 1foot to 5 feet.  The bottom of the cabin is not enclosed nor is the floor insulated.  It is pretty much a seasonal cabin with a weekend or two of use in the winter via a wood burner.  The cabin is insulated in the walls and ceiling.  The ceiling is vaulted.  This past year I noticed mildew on some wooden chairs and closets.  This happens when the cabin is unused for a month plus.  Doesn't happen in the summer more in the fall and spring when temps are in the 70's.  The cabin is in a valley near a stream and does not get much sunlight.  I have been told that my mildew could be from the insulated floor.  Any thoughts?   Suggestions for a cure?

[flyingvan]

 You started by saying the floor is uninsulated so I'm going with that. 

  Try this experiment---take a clean, dry clear drinkin glass outside.  Set it upside down on the ground and leave it for a few days.  Is it fogged with condensation now?  If so, that's exactly what your cabin's doing.   If moisture can get in through the floor but can't get out anywhere, humidity is bound to rise.   Is there a ventilated attic?

[John Raabe]

It would likely help if you could have some passive ventilation such as a partly open high window that can let air escape without letting in rain or snow. Best would be a screened and louvered vent that can be closed with an insulated door from the inside when you are heating the cabin.

[Don_P]

I'm guessing the temp and dew points are closer during those seasons. Venting may be the better option. If you can maintain a few degrees above the morning low temps you're in drying rather than condensing conditions, so heat would work. A conventional dry kiln is mostly just heat and vent. Insulating the floor might help decouple the floor from the cool beneath the cabin and buy you those few degrees. Or, it might not 

[flyingvan]

A vapor barrier under the place wouldn't hurt either

[Yankeesouth]

Flyman.....I like the idea about the glass.  I am going to give it a try.