People ask me why crawlspaces seem so mold-prone these days, as opposed to the homes we lived in 35 years ago. There are a lot of little reasons why this is the case, but the simple answer is the tightness of our current construction. Windows are one reason.
I’ve attached two pictures that depict typical window sealing in modern construction, as evidence of this fact.
You will notice the vapor-taped windows and home-wrap seams, caulk sealants, and double-pane (energy efficiency) windows, as one example.
These are all great things for energy savings. But these technologies also serve to inhibit effective ventilation of the warm, moist air that rises from the crawlspace. This creates an environment where the space below the home cannot shed the moisture from below. It becomes trapped, soaking into the organic substrate beneath the home, which leads to elevating wood moisture content and, eventually, mold.
Doesn’t seem like much, but it really is the little things.