Because I’ve written so much about moisture in buildings, I get a lot of questions on the topic. Some are about walls. Some are about the attic. Some are about windows. Some are about the crawl space (which generates the most questions on this topic).
The key to answering a lot of those questions boils down to an understanding of how water vapor interacts with materials. Once you know that, it’s easy to see the two rules for preventing damage from humidity.