Heart Pine Floors & a Foggy Crawl Space

From the comments I have received, my webinar on wood floors and summer moisture went over well last week. One of the items I covered was the relationship between temperature and relative humidity, and how the RH goes up when air is cooled. In the summer, this means that when warm air leaks into a cool building, the RH of the air goes up.

I visited one house after the webinar last week that I wish I had seen earlier. It would have made a terrific example. I have been in literally thousands of crawl spaces over the years and this it the first one I have been in where it was foggy. Outside was pushing 90 degrees, but the crawl space was about 73 degrees. Usually, crawl spaces are dusty, so it took a little time to realize that the stuff in the air in front of my flashlight was fog, not dust.

This house has a very low crawl space, with barely enough room for ductwork.  Mr. Homeowner is digging a ditch from one end of the crawl to the other, a 5-gallon bucket at a time. You can see the buckets in one of the photos. That's me in the ditch as well.

The thing that really caught me off guard in this house was that the homeowners are not running AC, and it was 80 degrees inside. The soil is cool, and digging a ditch exposed more cool soil. Basements work the same way: Cool walls and floors make the RH go up, so you Northerners who don't have crawl spaces aren't immune from this effect.

This 1920-vintage house has heart pine flooring with no problems, even though the crawl space was wet enough to grow mold on the shovel handle.  So the question of the week is: Why is the floor not affected?