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By: Jasna Aleksandrova

Moisture problems

Crawlspace moisture can cause a lot of headaches for any homeowner. Moisture causes surface condensation, mildew, musty odors, fungi growth and it attracts insects. It also affects electrical systems and insulation beneath the flooring which increases heating and cooling costs. Keeping all of this in mind, anyone can see how important it is to prevent moisture from forming.

Preventing the problem

Measures to prevent moisture in a crawlspace should start with controlling of the amount of water that seeps into the ground around the base of the house. A homeowner should install a proper drainage system for the roof with downspouts that stretch at least 5 feet from the house and frequently check the gutters to ensure they are free of debris. Another way to keep water away from the house is to avoid excessive yard watering. Lastly, it is important to make sure that the soil around the home angled away from the house by at least 2 degrees which will allow water to drain away from the house, not under it.

Drainage systems

Excessive water in and around the crawlspace can be drawn away by installing a drainage system located beneath the lowest point of the foundation. These perimeter drainage systems can be installed on the outside or the inside of the foundation wall. Installing a drainage system on the inside wall of the crawlspace is cheaper because it is easier to access.

Moisture barriers

The next step to solving the problem is to prevent moisture from evaporating from the soil into the crawlspace. This is considered to be fairly easy and not very expensive because this is done by covering the entire area with a non-porous barrier. Usually this is accomplished by laying out polypropylene sheeting which blocks moisture and prevents it from entering the crawlspace. In order to properly install the sheeting, it is important to remember that the sheets need to overlap to prevent gaps in coverage.


Although polypropylene sheeting stops the moisture in the soil from evaporating into the crawlspace, temperature differences between the inside and the outside of the crawlspace will still create moisture. Installing vents is a good way to control these temperature changes. Simple vent openings covered with nets are not the best solution because in the winter cold air circulates underneath the floor which cools the interior of the house increasing the heating bills. Automatic vents are a much better solution. Depending on the outside temperature, these vents open and close automatically creating the right humidity level in the crawlspace. In the winter time the vents will remain closed to retain heat and they open in the summer to allow for proper air flow which helps prevent moisture from forming. Another option is alternative power vents. They function similar to automatic vents but they also pump air out of the crawlspace.

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