Why is a cool basement damp, in terms of humidity?

Question

I know that when you increase temperature and relative humidity decreases but I don't get how this fits?
It's a closed environment so maybe there is condensation?

Answer 1

Yes, hot air holds more water.
Fog happens if air saturated with all the moisture it can hold cools down. Similarly if saturated air comes in contact with a cool surface like a basement wall that air cools and the water condenses out.

Interestingly by the way, hot water holds less air :) Cold water deep in the ocean tends to have a lot of dissolved air (and of course oxygen) in it. If that cold oxygen rich water rises into a shallow area, for example a fishing bank, it rises full of oxygen and grows lots of plants and fish, which is why it is called a fishing bank ;)