The beginning of our mold tour starts near the entrance to the crawlspace in this home. Just to the side of the crawlspace entrance, we found an area where the wooden support beam of the subfloor had completely rotted through due to mold and moisture and then had to be replaced with a new joist. This sort of aggressive rot isn't usual--instead, most homeowners start to notice creaking, squeaking, and spongy floors over crawlspaces. This means that the wood has absorbed some moisture and is becoming flexible, bowed, and unstable. It's a good idea to get squeaking, spongy floors checked out promptly! The sooner an issue is addressed, the cheaper it is to fix the problem.