Problems after sealing a crawlspace
To dry out my crawlspace, I recently laid a plastic vapor barrier over its dirt floor. However, last winter, the 1920s-vintage house developed gaps in the hardwood floors and warped doors, which I believe are a result of the decreased humidity. How can I fix this situation?
Scott D. McClure, Sanford, NC
Larry Janesky, author of Sealing a Crawlspace and owner of Basement Systems in Seymour, Connecticut, replies: Even those of us who don’t have crawlspaces are used to the phenomenon of gaps in hardwood floors opening in dry winter months and closing in humid summer months. That’s part of living in a wooden house in a variable climate. But a dirt crawlspace contributes an endless invisible stream of moisture from the earth into the house, so the wood in your house probably never had a chance to dry out completely.
If you just installed the vapor barrier in your decades-old house and you’re suddenly experiencing these problems, my guess is that the wood in your house is shrinking as it’s drying out. While the gaps in the floors and the warped doors are a pain, the condition should not be entirely unexpected, especially given the length of time the wood has had a high moisture content. Rest assured that the benefits of drying out the house—minimizing mold, mildew, and rot—outweigh any inconvenience of gaps in the floorboards.
My suggestion is to leave the crawlspace vapor barrier in place and to make sure the crawlspace vents are kept closed. To combat the extreme swings in relative humidity between winter and summer, use humidifiers to add moisture when and where you need it. If portable humidifiers are used, be careful not to introduce too much moisture because micro-environments can form that support mold growth. One indication of too much moisture in a room is condensation forming on the windows.