Basement Moisture

We’ve talked many times about how important it is to maintain the moisture levels in your home, especially the crawl space. (see (1) (2) & (3)). If you have a basement instead of a crawl space, you may think that you’re off the hook. Unfortunately, that is not the case. It is also crucial to maintain a proper humidity level in your basement. High humidity levels in the basement will not only make your home uncomfortable, but also affect the structural integrity of your home. Additionally, high humidity has the potential to cause health issues for the people living there. This is especially true, if the basement shares duct work with the rest of your home or if the basement is used as a living area.

There are a few signs to look out for that indicate moisture issues in the basement. Obvious signs would include standing water or air that feels damp and humid. In addition, you may notice a musty odor and signs of mold. Another indication of moisture problems would be rotting or decaying wood.

One of the issues with high moisture levels is the effect it can have on the structure of your home. The severity of the damage will depend on a few factors including amount of moisture and the time it is left untreated. Environmental factors such as indoor and outdoor temperature will also play a role. Examples of moisture damage would be wood decay, buckling of siding, mold, and peeling paint.

Structural damage caused by moisture has been examined in multiple studies. For instance, a Canadian Field Survey studied over 200 homes to see what the effects of moisture damage would be. The results included buckling of sheathing, window frame damage, warped siding, severe window condensation, and more. Another study completed by the Canadian Mortgage & Housing Corporation determined that high moisture levels in wall cavities led to many of the same effects listed above.

Another issue that occurs with excessive moisture levels in your basement is the accompanying health risk. High moisture increases the likelihood of problems, such as mold, fungi and pests, all of which can be harmful to a person’s health. In a study of 4,625 children across 6 American cities, 50% of homes showed signs of dampness. Living in a damp home increased the chance of a child showing respiratory symptoms. In a Netherlands study of 185 homes, the more dampness characteristics the home had, the higher the mold spore count which led to a higher incidence of respiratory symptoms.

Moisture can be quite the issue for your basement. The question is where does it come from? There are three main sources of moisture in your basement- rain or groundwater, indoor moisture sources, or outdoor, humid air. As you might imagine, rain water is a significant source of moisture. One inch of rain over a 2,000 square foot home yields 1,250 gallons of water. In addition, there are many indoor moisture sources that you may not consider such as bathrooms, humidifiers, or moisture from cooking. Furthermore, if the outside air is humid, you may be adding moisture to your home through sources like open windows, or gaps in doors.

Most sources of moisture are outside the home but there are several ways that moisture can enter the home. First, is obviously liquid water flow. Another source could be capillary suction. This occurs when moisture moves through a porous material, such as concrete. Capillary suction is what causes the ring of dampness on concrete walls. Water could also enter your home through vapor diffusion. Vapor diffusion occurs when moisture is in a vapor state and diffuses from wetter ground through porous walls or floors. Finally, moisture may enter your home through air movement. The main example of this would be the stack effect, where warm, moist air is drawn in the basement and rises throughout your home.

Moisture movement often occurs because of errors in the building process. For instance, if the yard isn’t properly graded, it may direct ground water into the base of the foundation. Furthermore, if the foundation is experiencing any cracking or settling, the water could easily enter the basement.

Basement moisture can lead to long term consequences. The best way to deal with it is try to prevent moisture issues from developing. This starts at the construction process when you need to ensure drainage systems are properly set up and shortcuts aren’t taken during construction. After that, it’s important to maintain the humidity in your basement and keep an eye out for signs of moisture. One simple way to maintain humidity levels in the basement would be to install a WatchDog dehumidifier. The WatchDog will automatically maintain the humidity in your basement and help prevent mold, pests, and other moisture issues.

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Carmody, Joe, and Brent Anderson. “Moisture in Basements: Causes and Solutions.” University of Minnesota Extension, University of Minnesota, 2014,
Cheple, Marilou, and Patrick H. Huelman. “Why We Need to Know More About Basement Moisture.” From Basements to the Roof, VIII, pp. 1–12., B8 papers/090_Cheple.pdf.