Here you can see mold on the wooden subfloor joists. These joists are often thr first place you see mold growth because the air from outside is being drawn up through the rest of the house due to air pressure. The phenomenon is called "the stack effect" and it tells us that the air you breathe in your home is drawn up from your lowest level -- in this case, the crawl space. You can find out more about creating healthy crawl spaces by contacting us for your free inspection.