Condensation Covering dirt floor of crawl space

Published on April 6th, 2016 | by Henri

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Condensation drips in crawl space of log house

Q.  I have a log home built from a kit, with 6-inch-thick walls, and floor beams  made of 2x10s, 16” on center. The plywood floor has foam insulation and wall-to-wall carpet. The foundation walls are poured concrete and there are two air vents, one on each end.

The foundation is a crawl space about 5 feet high. The crawl-space floor is dirt with nothing on top of it. I get water seeping in, and I have a small pump to get it out.

My problem is this: the floor beams have the insulation in between them and are dripping water. This water is not coming from any water leaks from above, I think it is condensation. When I write “dripping,” I mean all of the floor beams have water droplets coming off them. Mold is also there and I will have to address that problem as well. Any suggestions  would be appreciated.

A. You should first check the grade around the home. The moisture seeping indicates that the grade may be too flat or slope toward the foundation. Correct any deficiencies by adding loam with some clay (no sandy or gravely soil), so the grade slope away from the house.

Thoroughly cover the soil under the crawl space with 6-mil plastic, bringing it up the foundation walls to a point above the outside-grade level in order to control the moisture emanating from the soil, which is also responsible for the condensation wetting the insulation between the floor joists.

Be sure that you install the plastic along the walls, which will extend on the floor of the crawl space, first, and then lay the center plastic over it. If there is any further leakage from outside, the water will not pool over the plastic if so installed. Tape the joints in the plastic as added precaution.

Your biggest problem will be to dry all the wood members. To do that, you will have to remove the insulation, lay it on the floor and hope that it will eventually dry. If it quite wet, you may have to replace it. You may also have to use a heavy-duty dehumidifier, and perhaps fans.

Once the crawl space is dry and smells sweet, and the floor joists thoroughly dry, reinstall the existing insulation if it has also completely dried, or install new insulation.

Regarding the mold, you may want to wipe it off, or wash it off, with a solution of one part bleach to three parts water. Make sure that the treated areas dry up before proceeding to the next step.

An easier alternative is let the mold die on its own once the relative humidity in the crawl space is below 20 percent.

Then, close the two vents; they only bring in damp air from outside.

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