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posted: 12/26/2014 12:01 AM

Unexpected moisture problem under house

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Q. My house is built on a raised foundation and has a moisture problem under the floor. I first noticed this when the flooring began to warp and to change color. So I crawled under the house and discovered a plastic membrane that covers the underside of the floor framing. I removed a portion of it and found the insulation to be all wet. This surprised me because the subarea is well vented, and the ground is dry. I pulled out the wet insulation from the areas where the flooring was warped and stained and have installed fans under the house to dry out the framing. How could this problem be happening, and what should I do about it?

A. Whoever installed that plastic membrane made a major mistake. That membrane created unvented spaces where moisture condensation could occur. Even when the ground is dry and the subarea is well vented, the air under a home tends to be humid. When humid air is trapped in unvented places, condensation can do more damage than most people realize. Besides affecting the interior flooring, moisture can promote fungus that can rot an entire floor structure, requiring major reconstruction and repairs.

You should complete the removal of the plastic membrane and insulation. The entire floor structure should then be inspected by a licensed pest control operator to detect where fungus has begun to grow. It is almost certain that some fungus infection will be found. Hopefully, repairs will not be too costly.

Q. We bought our home about four years ago. At the time we noticed a small crack in the foundation and pointed this out to our home inspector. He said this was a typical stress crack and advised us not to be concerned. This year, the crack became larger and extended into the brick wall. Our neighbor said this is because of the drought, and he advised us to keep the ground wet around the building. We installed a soaker hose, and the cracks became small again in about a month. Do you think our home inspector missed a serious problem, or are we overly concerned?

A. The fact that the crack became large during a drought and returned to its original condition after wetting the soil indicates you have expansive soil. Some clay soils are like this, expanding when wet and shrinking when dry. Maintaining constant wetness around the house, as you have done, is a good way to avoid damage caused by expansive soil. However, it would be advisable to have the foundation evaluated by a licensed structural engineer to determine if there are any structural defects that warrant attention.

If the engineer determines there are no significant foundation issues, this information can be used for disclosure if you eventually sell the property. If structural problems are found, you can determine a course of corrective action based on the engineer's recommendations.

• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.

© 2014, Action Coast Publishing

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