Ideal Relative Humidity for Crawlspaces & Basements
The ideal relative humidity for crawlspaces & basements is generally between 30% to 50%.
What happens if humidity is too high?
High humidity in basements (above 60%) provides the perfect damp environment for black mold, mildew, and wood rot, which can threaten the structural integrity of the floor joists above.
What happens if humidity is too low?
While basements are rarely 'too dry', extreme dryness combined with high heat can theoretically cause floorboards above to shrink and gap, though dampness is the primary concern for 99% of homeowners.
Frequently Asked Questions
- Do I need a dehumidifier in my crawlspace?
- Yes, if you live in a humid climate or notice a musty smell. Encapsulating the crawlspace and adding a commercial-grade dehumidifier is the best way to prevent structural rot.
- Why do basement walls sweat in the summer?
- Because the underground walls are cool. When warm, humid summer air enters the basement, it cools against the walls, reaches its dew point, and condenses into liquid water.