Why Vented Crawlspaces Can Make Humidity Worse

Vented crawlspaces introduce excessive moisture, through unsealed vents, and improperly installed liners which contributes to wood rot, mold growth, increased indoor allergens, and increased pest activity. Moisture in crawlspaces migrate to the upper levels of the home through “stack effect” which can account for more than 50% of air inside the home. Stack Effect is a natural occurrence in every home, the warm air rises and escapes out the top through all the tiny seams and holes created during construction, as warm air rises and escapes through the upper levels of the home, new air finds its way into the home to replace what’s been lost. The air that comes in at the lower levels is through the damp unsealed crawlspaces. This leads to costly problems such as wood rot of floor joist, mold growth, increased air conditioner loads, damage to duct work, and cupping of hardwood floors. Air infiltration from the crawlspace often carries odors and contributes to poor indoor air quality and uncomfortable humidity levels.

The excessive moisture in crawlspaces is also associated with increased energy consumption. During the wintertime the cool air enters the crawlspace through small crack and openings even while the vents are closed contributing to heat loss from the home and could cause frozen plumbing lines. In the summer, warm outside air under the home contributes to high humidity, increasing cooling loads. The high humidity condensates on duct work and any HVAC equipment in the crawlspace causing additional system load and premature failure. Ventilation of a crawlspace to control relative humidity was common under older building code but has been changed because it was found to actually cause more issues and add significant quantities of moisture.


The Eastern Shore Maryland and Delaware have no shortage of vented crawlspaces and with the high humidity during the summer it’s no surprise to find extremely high humidity in crawlspaces with condensation forming on duct work and insulation. When air handlers are located in these crawlspaces rust becomes a major issue causing the equipment to fail prematurely but during the time of operation the system has to worker to remove all the excessive moisture that leaks into the small holes in the duct work and the air handler. The system also removes all the excess humidity that enters the home from the crawlspace through stack effect, adding to the load.

Dr. Energy Saver Delmarva is your local total home performance professionals offering Energy Audits, Weatherization Services, Crawl Space Repair.

We proudly offer air sealing, insulation, and ductwork in Easton, Centreville, Chestertown, Berlin, Ocean Pines, Salisbury, St Michaels, Bethany Beach, Lewes, and more!