For decades, building codes and conventional wisdom prescribed ventilating crawl spaces with outside air as the primary means to control moisture in crawl space foundation homes. Because of this, many homes built on crawl space foundations in the Southeastern United States have suffered from poor moisture management within the structure and also the ailments caused by excessive moisture.

Some of the common symptoms of excessive crawl space moisture are:

  • Mold or moisture damage in the crawl space or living area
  • Musty odors in the living area
  • Condensation (“sweating”) on air conditioning ductwork or equipment
  • High humidity in the crawlspace and living area which can be seen as mold growth on surfaces
  • Condensation on insulation, water pipes or metal (rust) in the crawl space
  • Buckling hardwood floors
  • Doors and windows that stick due to swelling
  • Insect infestations such as termites and wood
  • Structural issues due to wood rot

Research and now actual usage has shown that closing the crawl space, so that the crawl space has NO ventilation to the outside, can provide greatly improved moisture control and results in significant energy savings when installed properly.

Conversion Process

The process of converting a vented crawl space to a closed crawl space involves sealing vents and installing a sealed moisture barrier on the crawl floor.


Outside air – warm, moisture-saturated air brought into the cooler crawl space from open vents can become a major source of excessive moisture in the crawl space. Why? When warm, moist air cools in the crawl space it no longer has the ability to hold as much moisture. When this very wet air touches a cooler surface the water vapor condenses (Dew Point) and water forms on those surfaces.

The ground – poor drainage in the crawl space can be the main source of moisture. This can be seen in some obvious cases as pooled water or poor drainage can just be adding to the crawl space moisture from the saturated soil caused by poor drainage.

The foundation – below grade foundations may not have properly designed drainage. This can be seen in moist cinder blocks or concrete foundation walls. The moisture from the saturated foundation adds to the crawl space moisture level.

Problems Created From Excessive Moisture

Excessive moisture can cause many structural issues to occur in your home and it can also lead to health issues caused by mold and fungi. These structural issues associated with excess moisture are reduced or eliminated by properly closing the crawl space:

  • Insect Damage
  • Air Quality Issues
  • Wood Rot
  • Swelling of Doors and Windows
  • Mold in Crawl Space