Is the moisture level too high inside my crawlspace? How do I know if its a problem or not? These are common questions that I hear from homeowners here in the Raleigh/Durham triangle area. Unfortunately the answers can be complicated. The two measurements most commonly used in determining moisture problems are the Relative Humidity of the air inside the crawlspace, and the Wood Moisture Content of the wood inside the crawlspace. Both of these measurements factor in to answering the question: “Does my crawlspace have a moisture problem?”.
The Relative Humidity in a crawlspace should be less than 70% to prevent mold and mildew. At 75% the wood may start to warp and deteriorate. At 85% and higher the wood may begin to rot. The Relative Humidity can be measured by a hygrometer that can be purchased at most hardware stores.
The Wood Moisture Content inside a crawlspace should be less than 20%.
This reading can be taken by a wood moisture meter which can be a little harder to find and usually cost over a hundred dollars. A reading less than 12% is very dry and represents a dry environment. Between 12% and 16% is considered ideal for wood members inside of a crawlspace. Between 16% and 20% is still good but maybe there is a simple way to improve it. Does water make its way into the crawlspace every time it rains? Is the a/c condensation line leaking? Is the clothes dryer venting into the crawlspace? Is the air circulation obstructed? Is there a vapor barrier covering the ground? All of these can make the difference between having a 16% or a 20% reading. If your reading is between 20% and 28% then your crawlspace is ideal for surface mold. There is a possibility of wood decay over time. At 28% or higher rot and decay is probably already present.
Other evidence of a moisture problem inside the crawlspace include visible surface mold, signs of where water flows across the surface of the soil, water stains on the foundation walls or support columns, and condensation on the air conditioner duct work.
You also need to consider that moisture levels are usually higher in the summer months than the winter due to the higher humidity levels of the outside air.
Click here for more info and tips (and great photos and videos) on moisture control inside your crawlspace.