Weakened floor joists and girders due to moisture and wood rot or moisture and brick decay. Because crawlspaces are often unsealed from the earth, excess moisture and humidity is a problem. Naturally, wood begins to rot, get moldy, and become weak. The weakened girders and floor joists are unable to continue supporting the weight above, and the floor above the crawlspace becomes bouncy, soft, and saggy. The combination of moist air and a cool crawlspace equals condensation and increased mold, rot, and other issues.