Should we spray the crawl space under our house with a fungicide?


Should we spray the crawl space under our house with a fungicide?

Asked by Sharon Haislip

There is some evidence of mold on the floor studs, and our neighbor had this done to her house because she had mold on the floor studs.

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Danny Kelly's picture

Mold is a sign of a moisture problem and simply spraying a fungicide on the floor joists will not solve your moisture problem.

If you have a vented crawl space, the hot humid air from the outdoors in getting into your cool crawlspace and this can be your main moisture source.

A few things to do to correct the moisture issue first:

  • Inspect the exterior of your foundation - be sure you have positive drainage away from your foundation and all gutter downspouts are draining away from the house properly.
  • Install a minimum 6 mil vapor barrier over 100% of your crawl floor. Also wrap the vapor barrier up the foundation walls so it is above the exterior grade. For advanced options you can tape the seams and run the vapor barrier up the interior piers as well
  • Close off all the foundation vents and seal up all holes in your foundation walls.

Consult your local code to see what is required as far as ventilation goes in your area for a closed crawl. Your ventilation options are typically:

  • supply only,
  • exhaust only, or
  • dehumidifier.

We typically recommend the exhaust only approach on an existing home. Install a continuous running exhaust fan at 1 CFM for every 50 square feet of crawl area. This will bring down some of the dry air from your house into your crawl space.

  • Periodically measure the moisture content of the floor joists and the relative humidity in your crawl. If they seem high you can also install a dehumidifier to help out.
  • Other code requirements in your area may be to install a floor drain incase you ever have a water leak in your crawl.

Once the moisture is controlled you can then remove the mold with soap and detergent - all of the fancy chemicals are unnecessary. If moisture levels are controlled - no fungicide will be required either.

A good resource for closed crawl systems is for more information.

It is important to continue to monitor your crawl space on a regulat basis.

Good Luck!