The crawlspace under my house is wet with sweat from condensation. I have insulation between the floor joists with plastic stapled underneath. The house has five vents, three on the west side and two on the east. What could be causing the moisture problem under my house? -Eve

Hi Eve,

From your description, I see several problems that could be causing excess moisture in the crawl space under your house:

• Not Enough Vent Space: You may need more ventilation in the crawl space. The rule of thumb is to have at least one square foot of vent area for every 150 square feet of crawl space.
• Inadequate Cross Ventilation: You also need to have adequate cross ventilation with vents on all sides of your house, not just two.
• No Plastic Ground Cover: The plastic sheeting should be covering the ground of the crawl space, to keep moisture from coming up through the soil, not stapled beneath the insulation.
• Leaky or Uninsulated Ductwork: If you have ductwork for your HVAC system under your house, have it inspected for any air leaks, and to make sure it has enough insulation to prevent condensation on the outside of the ducts when the air conditioner is running during the summer.
• Add Fan Venting: If you’re still having problems, have a small fan installed on one of the vents with a humidistat set to turn the fan on at 70% relative humidity to remove excess moisture from your crawl space.

Good luck with your project,

Further Information

• How to Solve Moisture Problems Under Your Home (article)
• How to Keep Wood Floors from Buckling and Cupping (article)
• How to Reduce Mold and Moisture Under Your Home (video)
• How to Insulate a Crawl Space Under Your Home (article)

Tags: , ac condensation, crawlspace, moisture, plastic, remove moisture, vent, ventilate