Most basement floors, even in new homes, are damp. Concrete is a porous substance and requires air circulation. As temperatures in the basement fluctuate, it creates the perfect environment for moisture to accumulate between the underpad and concrete. This is where mold can begin to germinate which can lead to poor indoor air quality. A subfloor ensures there is an air gap between the finished floor and the concrete to help protect against moisture, mold and mildew.