Symptoms
- Damp or muddy dirt floor in the crawl space
- Musty smell noticeable from inside the house above
- Condensation on floor joists or ductwork visible in the crawl space
Likely causes
- CommonExposed dirt floor without a vapor barrierGround moisture evaporates continuously into the crawl space air without a barrier to block it.
- CommonPoor drainage or grading directing water into the crawl spaceWater pooling near the foundation can seep into an unsealed crawl space.
- PossibleExcess ventilation bringing in humid outside air in summerIn humid climates, older-style vented crawl spaces can actually pull in more moisture than they release.
What to do
- Put on protective clothing and a mask before entering, since crawl spaces can have dust, mold, or pests.
- Check for standing water, wet insulation, or visible mold on joists and address any active leak or drainage issue first.
- Fix exterior grading and downspouts to direct water away from the crawl space area.
- Lay a heavy-duty polyethylene vapor barrier over the dirt floor if one isn't already present, overlapping and taping seams.
- Insulate exposed water pipes and consider insulating the crawl space walls or floor above per local building recommendations.
- Consider closing vents and adding a dehumidifier in a humid climate (an 'encapsulated' crawl space) rather than relying on outdoor air ventilation.
- Have a crawl space specialist assess and install a full encapsulation or drainage system if moisture is severe or recurring.
Tools and parts
- Mask
- Flashlight
- Utility knife
Crawl space vapor barrierSearch: “crawl space vapor barrier plastic”
Crawl space dehumidifierSearch: “crawl space dehumidifier”
When to call a pro
Call a crawl space or waterproofing specialist for full encapsulation or persistent moisture problems.
Safety
Use caution
Wear a mask, gloves, and long sleeves in a crawl space, and watch for pests or unstable footing.