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Homeowner’s Guide to Dew Point: What Does It Mean?


The dew point temperature is the temperature at which condensation (moisture) forms as the air is cooled. At the dew point temperature, the air is saturated and any further cooling will result in condensation. Both 70 degrees Fahrenheit and 100% Relative Humidity crawl space air and 85 degrees Fahrenheit and 60% Relative Humidity outside air have the same dew point temperature, which is 70 degrees Fahrenheit.

The picture shows condensation on a surface due to the dew point temperature.

In the Carolinas, we routinely see temperatures and humidity levels rise far above 85 degrees Fahrenheit and 60% Relative Humidity. If we vent any crawl space with this air, we are allowing higher dew point temperature air to enter the crawl space. In fact, we are adding more moisture to the crawl space. Thus, making our problems worse. Mechanical fans often exacerbate the problem on an exponential level.

Vented crawl spaces will cause condensation problems. Floors rot, mold or cup because of excess moisture. Ductwork sweats and becomes saturated with water. Duct energy losses increase because the insulation doesn’t work properly when it is wet.

Mortgage, pest control, and home inspection industries flag crawl space wood moisture contents above 20% as a potential problem. At this wood moisture content percentage, mold can grow. Sometimes, our experts see problem-free crawl spaces with wood moisture contents of 16% or less, but not very often. Truly dry crawl spaces in homes are very rare in the Carolinas.

Many homeowners have their crawl spaces tested for moisture year-round; however, this can be misleading. What time of year are you testing? Most crawl spaces will test low for moisture in dry weather periods. But, visual inspections for signs of moisture such as mold, fallen insulation, wet foundation walls, and sweating ducts are indicators of high moisture levels, whether it is winter or summer time.

If you see any of these moisture issues with your home, please call Dry Pro today for a free crawl space inspection. Dry Pro services the Lawndale, NC, area and its surrounding cities.

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