How does poor site drainage affect crawlspaces?

Poor site drainage can significantly increase humidity levels in crawlspaces. When water does not effectively drain away from the foundation, it can accumulate around the perimeter or beneath the structure. This stagnant water can evaporate into the crawlspace, raising the humidity levels. High humidity creates an environment conducive to mold growth, wood rot, and pest infestations, which can compromise the integrity of the building and negatively impact indoor air quality.

Though other choices mention important consequences of poor drainage, the direct relationship between excess moisture and increased humidity in the crawlspace makes the first option the most relevant. Acceleration of foundation settling, reduction in air quality, and increased energy usage are all potential issues that arise from high humidity, but they are indirect consequences rather than the immediate effect of poor drainage itself.