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Why the Dew Point Matters in a Home Inspection


For those who frequently check weather reports, the dew point is likely a well-recognized but poorly-understood figure. When the water vapor reaches its saturation point, it’s known as dew point. The vapors get condensed and convert into water. This leads to moisture in surrounding areas, which can cause mold growth.

What is Dew Point?

According to the National Oceanic and Atmospheric Administration's National Weather Service, the dew point is "[a] measure of atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant). A higher dew point indicates more moisture present in the air. It is sometimes referred to as Dew Point Temperature, and sometimes written as one word."

How Does Dew Point Affect Home Inspection?

Just like any other weather phenomenon, the dew point has implications for the proper functioning and maintenance of many systems throughout a home. Real estate professional publication WorkingRE went in-depth on how these effects impact a home inspection.

The effects of dew point can be observed on window panes during the winter. Some condensation often forms on windows when the outdoor temperature is significantly different than the indoor temperature. When it's cold outside but warm inside, condensation tends to form on the lower edges of a window pane. Since cold air tends to fall relative to warmer air, the coldest air at the bottom of the window may freeze during periods of extreme cold. This can cause problems with the area surrounding windows including warped frames and mold growth.

A home inspector can find signs of moisture and conclude that it is resulting from condensation. When they attribute moisture and mold growth to dew point, they can recommend one of two fixes for the issue. For one, the temperature of the window itself could be raised. This may require a fan or the application of more direct sunlight to the window. The other solution is to reduce the humidity of the interior air. This might be the less practical solution, since dehumidifiers require high amounts of electricity and may make the inside space uncomfortable.

How Dew Point Can Help Determine Mold Growth

Understanding dew point, condensation and humidity is central to fixing issues related to mold growth. Mold likes to grow in warm, damp areas. However, some homeowners may be confused to find moisture, and thus mold, growing where there are seemingly no holes where rain could enter. This is a common reason for mold growth on a roof deck. Very small leaks allow warm, moist air to enter a space in a roof or attic. This air is then cooled below the dew point, causing moisture to form. Voila, a mold problem has begun. 

To stop this mold from forming, it is recommended to find and seal these air leaks. This may be accomplished by installing air seals between the window and the frame. using this simple fix, many common mold problems may be alleviated.

The Role of Dew Point in Identifying Mold Growth

Understanding what dew point means and how it can lead to unexplained condensation can help to quickly identify the source of the problem. Ultimately, home inspectors can utilize dew point to determine mold growth in the surrounding area, which poses health risks and degrade the home’s structure.

Getting a Mold Inspection by WIN can allow homeowners to protect their investment and ensure the health and safety of their family. Click here to schedule a Mold inspection today!