Is your Wood Floor Cupping due to Crawlspace Moisture?

wet_crawlspaceThere are basically three types of venting techniques used today in crawlspaces around America and all three are used in all regions of the country. Yet, we all know that there are climate differences in the various regions of the United States and these differences could affect the efficiency and usefulness of a particular type of vent during cold, warm or hot periods.

Typical requirements for a wood floor installation call for a moisture barrier covering the dirt or sand crawlspace floor and open vents.  The North Carolina Study found more moisture damage in vented crawlspaces in areas with high relative humidity. Elevated humidity in a crawlspace results in elevated moisture in the floor joists and sub-floors- which can result in cupped or buckled wood floors. Visit our pages for Moisture Control DIY Products for Moisture Barriers, Crawlspace Power Vents and Crawlspace/Basement Dehumidifiers

The type of Vents are:

Good: A Passive Manual Vent  –  Must be manually opened or closed
Better: A Temperature Vent (Temp Vent) – A sensor opens the vent at a set temperature and closes it at a set temperature. Generally, the vents close at 40 degrees and will gradually start to open above that until completely open at 70 degrees.
Best: An Automatic, Humastatically Controlled Vent – A vent that reads and monitors both temperature and humidity levels inside the crawlspace and at the exterior of the home. The vents will only open when the relative humidity levels are less than the interior humidity levels and low enough to avoid the risk of actually adding humidity to your crawlspace and creating additional moisture conditions and an unhealthy crawlspace environment.


For example:  In New Jersey (on average), we will experience 209 days during which outdoor relative humidity will be higher then 65% for the majority of the day. Mold growth is promoted anytime relative humidity rises above 55% in your crawlspace. Thus, if you replace the air in your crawlspace (through passive or traditional temp vents) with outdoor air that is above the 65% relative humidity level you are creating a bigger problem than if you had no venting at all. You could actually be raising the relative humidity levels in your crawlspace to unhealthy levels.


The North Carolina Study  –  Commencing in 2005 a study was conducted in North Carolina under the supervision of the US Environmental Protection Agency. This study involved 12 homes constructed for the Homes For Humanity program. Four of the homes had traditional temp vents and the other eight homes had their vents completely sealed off. All of the homes were built the same and placed over the same type of crawlspaces.

After several years of observations, they discovered homes with traditional vents actually had consistently higher relative humidity levels and potentially destructive levels, in their crawlspaces than did the homes that had the vents closed off.  What was concluded was that to vent just for the sake of venting is not a sound or advisable building technique. While venting is still useful and, for the most part, recommended by environmental experts, venting should be scientifically controlled based upon relative humidity levels and not just temperature.

While some professionals in the building industry promote the theory that no venting is better than poor venting, we believe that the correct science supports venting at the proper time and under the proper conditions.


  • Have Your Vents Inspected To Insure Proper Operation.
  • If you have temp vents, make sure they are tightly closed during any periods of high relative humidity.
  • Consider replacing old temporary vents with a humidistat (An electronic device analogous to a thermostat but which responds to relative humidity not temperature).
  •  If the dirt in your crawlspace is already covered with a vapor barrier, have it checked to make sure it is not torn dislodged in places or no longer properly secured.
  • If you don’t already have a vapor barrier covering the dirt floor of you crawlspace, a strong 12 Mil vapor barrier installed to protect your home and act as the first defense against unwanted moisture build-up and the subsequent unhealthy environmental conditions it creates.