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posted: 11/23/2013 1:00 AM

How much mold is too much?

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By Dwight Barnett

Q. My house sold recently, but an inspection turned up mold in the foundation. My house has a narrow crawl, and the heating ducts and plumbing are in the crawl. The inspector did not do any testing, but said he was sure that what he found was mold on the floors and that it should be treated. I have never had any trouble with mold in the 30 years I have lived here. The buyers decided to buy another home and now I don't know what I should do. Do you have any suggestions?

A. In the thousands of homes I have inspected, I would estimate that close to 80 percent have at least some mold in the dark and damp areas of the home. For mold to grow, three things must be present: moisture, warmth and a food source.

A crawl space is an ideal laboratory for growing mold. The very word "mold" in a real estate transaction often places undue fear in the buyers because of sensationalized evening news shows, trade magazines and newspaper articles expounding on the dangers of mold and the effects it could have on your health. While there are some extreme cases that can affect existing health problems, what you don't hear is that mold is all around you every day and that certain molds are essential to your health, as in penicillin, or in baking and brewing.

The mold in the crawl space is living on the cellulose in the wood floor joists and subflooring and is unlikely to travel from its dark, damp environment of the crawl to the clean living space of the home unless there are dark, damp areas inside the home.

How much mold is too much, and when should you treat the home for mold? Energy auditors have a rule of thumb: if they find more than 10 square feet total of mold, they will not test the home under a negative pressure.

The home must be treated for mold before testing. This is for energy audits only and there are no national standards for concentrations of mold in a home (

Since we all react differently to molds, the best recommendation when selling a home would be to either have the home treated for mold or eliminate the moisture that is feeding the mold. By drying out the crawl space, the mold will go dormant.

The relative humidity in the crawl needs to be below 55 percent.

If the moisture levels are between 55 and 70 percent, steps need to be taken to remove the moisture by adding a ground-cover vapor barrier and possibly using fans or a dehumidifier.

Molds will always be with us, but we can control our home's environment by performing annual inspections and correcting the sources of moisture that feed the molds.

• Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at

Scripps Howard News Service

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